Bio 6 Lecture Final Practice Test

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Questions and Answers

What are homologous chromosomes?

  • Chromosomes that are always identical in size and shape
  • Chromosomes that have different genetic makeup only
  • Chromosomes that are identical from the same parent
  • Chromosomes from different parents that have the same genes (correct)

During interphase, chromosomes are visible under a microscope.

False (B)

What is the primary function of the centrosomes during mitosis?

To generate spindle fibers.

The process of DNA replication occurs during the ______ phase of the cell cycle.

<p>Synthesis (S)</p> Signup and view all the answers

Match the following stages of the cell cycle with their descriptions:

<p>G1 = Cell growth and organelle duplication S = DNA replication G2 = Preparation for mitosis Mitosis = Division of the nucleus and cytoplasm</p> Signup and view all the answers

In what phase do chromatids attach to centromeres?

<p>Synthesis (S) (B)</p> Signup and view all the answers

What type of cells are produced through meiosis?

<p>Gametes</p> Signup and view all the answers

Sister chromatids are formed during the G1 phase of the cell cycle.

<p>False (B)</p> Signup and view all the answers

What is the primary purpose of meiosis?

<p>To produce four non-identical haploid cells (A)</p> Signup and view all the answers

Crossing over occurs during Anaphase I.

<p>False (B)</p> Signup and view all the answers

What is the role of spindle fibers during cell division?

<p>Spindle fibers help separate and pull chromatids or chromosomes apart during cell division.</p> Signup and view all the answers

Somatic cells are any cells in the body that are not involved in __________.

<p>reproduction</p> Signup and view all the answers

Match the following types of animal reproduction with their descriptions:

<p>Budding = Used by sponges, hydra, corals Fission = Used by flatworms, amoeba Fragmentation = Used by annelid worms, starfish Parthenogenesis = Unfertilized egg develops into offspring</p> Signup and view all the answers

During which phase of mitosis do sister chromatids split and move towards opposite poles?

<p>Anaphase (B)</p> Signup and view all the answers

The metaphase plate is where chromosomes line up during telophase.

<p>False (B)</p> Signup and view all the answers

What characterizes telophase in cell division?

<p>Distinct nuclei form at opposite poles, and the chromosomes become chromatin again.</p> Signup and view all the answers

The __________ is the central part of a chromosome that holds sister chromatids together.

<p>centromere</p> Signup and view all the answers

Match the phase of meiosis with its description:

<p>Metaphase I = Chromosomes line up in tetrads at the metaphase plate Anaphase II = Sister chromatids are pulled to opposite poles Prophase II = Nuclear envelope breaks down again Telophase I = Results in 2 non-identical haploid cells</p> Signup and view all the answers

What is the term for the process where homologous chromosomes pair up during meiosis?

<p>Synapsis (A)</p> Signup and view all the answers

All gametes are diploid cells.

<p>False (B)</p> Signup and view all the answers

What is the function of centrosomes during cell division?

<p>Centrosomes organize microtubules and help pull chromatids apart during division.</p> Signup and view all the answers

During __________, two identical cells are produced from one parent cell.

<p>mitosis</p> Signup and view all the answers

Match the following terms with their definitions:

<p>Haploid = Cells with one set of chromosomes Diploid = Cells with two sets of chromosomes Meiosis = Cell division for gamete production Mitosis = Cell division for growth and repair</p> Signup and view all the answers

What is the result of sperm entering a secondary oocyte during ovulation?

<p>Fusion of genetic material (A)</p> Signup and view all the answers

The phenotype is the genetic makeup of an organism.

<p>False (B)</p> Signup and view all the answers

What process turns a zygote into a blastula?

<p>Cleavage</p> Signup and view all the answers

In Mendel's experiments, the F2 generation showed a phenotypic ratio of _____ purple to white flowers.

<p>3:1</p> Signup and view all the answers

What is the term for the protective envelope created during the cortical reaction?

<p>Fertilization envelope (B)</p> Signup and view all the answers

Dominant alleles do not influence an organism's appearance if present with a recessive allele.

<p>False (B)</p> Signup and view all the answers

What does Mendel's law of segregation state?

<p>The two alleles for a trait segregate during gamete formation.</p> Signup and view all the answers

A gene that has multiple phenotypic effects is an example of _____ inheritance.

<p>pleiotropy</p> Signup and view all the answers

What is the main purpose of a Punnett square?

<p>To predict the possible genotypes of offspring (B)</p> Signup and view all the answers

Incomplete dominance results in phenotypes that are simply a mix of parental traits.

<p>True (A)</p> Signup and view all the answers

What are polygenic traits?

<p>Traits influenced by multiple genes.</p> Signup and view all the answers

The _____ refers to the location of a gene on a chromosome.

<p>gene locus</p> Signup and view all the answers

What is the effect of the addition rule in genetics?

<p>To calculate probabilities of separate events (C)</p> Signup and view all the answers

Match the following processes with their descriptions:

<p>Gastrulation = Process of forming the gut Cleavage = Rapid cell division of the zygote Organogenesis = Formation of organ systems Fertilization = Fusion of sperm and egg</p> Signup and view all the answers

Which sex chromosomes are typically present in females?

<p>XX (D)</p> Signup and view all the answers

Males only need two copies of a recessive trait to express it.

<p>False (B)</p> Signup and view all the answers

What is the primary cause of Down syndrome?

<p>Trisomy 21</p> Signup and view all the answers

The condition where an organism has an abnormal number of chromosomes is known as ______.

<p>aneuploidy</p> Signup and view all the answers

Match the following chromosomal abnormalities with their descriptions:

<p>Turner Syndrome = Monosomy X Klinefelter Syndrome = XXY Trisomy X = XXX XYY Syndrome = XYY males</p> Signup and view all the answers

What role did Thomas Morgan play in genetics?

<p>He studied inheritance using fruit flies. (D)</p> Signup and view all the answers

Linked genes are less likely to be inherited together compared to genes that are far apart on the same chromosome.

<p>False (B)</p> Signup and view all the answers

What is hemizygous?

<p>Having only one copy of a gene or chromosome segment instead of the usual two.</p> Signup and view all the answers

A person who carries a genetic mutation but does not express the associated condition is known as a ______.

<p>carrier</p> Signup and view all the answers

Match the following scientists with their contributions to genetics:

<p>Fredrick Griffith = Discovery of transformation in bacteria Avery, McCarty &amp; MacLeod = Identified DNA as the transforming agent Hershey &amp; Chase = Demonstrated DNA as genetic material using bacteriophages Watson and Crick = Discovered the double helix structure of DNA</p> Signup and view all the answers

What is a common symptom of Turner Syndrome?

<p>Short stature (D)</p> Signup and view all the answers

What is the role of DNA polymerase in DNA replication?

<p>To make new daughter strands (B)</p> Signup and view all the answers

Chromosomal alterations can include deletions and duplications.

<p>True (A)</p> Signup and view all the answers

The leading strand is synthesized in pieces known as Okazaki fragments.

<p>False (B)</p> Signup and view all the answers

What is trisomy?

<p>Having one too many chromosomes in a pair.</p> Signup and view all the answers

The wild type notation for red eyes in fruit flies is ______.

<p>w+</p> Signup and view all the answers

What are the three main components involved in protein synthesis?

<p>mRNA, tRNA, ribosomes</p> Signup and view all the answers

During transcription, RNA polymerase synthesizes RNA from a _____ template.

<p>DNA</p> Signup and view all the answers

Match the following enzymes with their functions:

<p>Helicase = Unwinds the DNA strands Primase = Creates RNA primers Topoisomerase = Prevents supercoiling Ligase = Seals gaps in DNA</p> Signup and view all the answers

What is the start codon for protein synthesis?

<p>AUG (D)</p> Signup and view all the answers

In eukaryotes, transcription and translation occur simultaneously in the nucleus.

<p>False (B)</p> Signup and view all the answers

What type of RNA carries genetic information from DNA to the ribosomes?

<p>mRNA</p> Signup and view all the answers

Okazaki fragments are characteristic of the _____ strand during DNA replication.

<p>lagging</p> Signup and view all the answers

Match the following processes with their respective definitions:

<p>Transcription = Copying DNA to RNA Translation = Synthesizing proteins from RNA Post-transcriptional modification = Editing mRNA before translation Mutation = Change in an organism's DNA</p> Signup and view all the answers

Which of the following statements about mRNA is correct?

<p>mRNA is a copy of a single gene. (C)</p> Signup and view all the answers

DNA mutations can have large impacts on an organism's traits.

<p>True (A)</p> Signup and view all the answers

Name one type of mutation and describe it briefly.

<p>Substitution - swapping one nucleotide for another.</p> Signup and view all the answers

The half-life of human mRNA is approximately _____ hours.

<p>10</p> Signup and view all the answers

Which of the following correctly describes homologous chromosomes?

<p>They are of the same size and shape but may have different alleles. (D)</p> Signup and view all the answers

What is the role of centromeres during mitosis?

<p>They hold sister chromatids together until they are separated.</p> Signup and view all the answers

In __________, a single cell divides to produce two genetically identical daughter cells.

<p>mitosis</p> Signup and view all the answers

Match the following phases of the cell cycle with their primary purposes:

<p>G1 = Cell growth and organelle duplication S = DNA replication G2 = Preparation for mitosis Mitosis = Division of the cell into two daughter cells</p> Signup and view all the answers

Sister chromatids are different from homologous chromosomes.

<p>True (A)</p> Signup and view all the answers

What are gametes and how do they differ from somatic cells?

<p>Gametes are reproductive cells produced through meiosis and are haploid, while somatic cells are diploid and make up most of the body.</p> Signup and view all the answers

What is produced at the end of meiosis?

<p>4 non-identical haploid cells (C)</p> Signup and view all the answers

Sister chromatids are separated during anaphase I of meiosis.

<p>False (B)</p> Signup and view all the answers

What type of cell division do somatic cells primarily undergo?

<p>mitosis</p> Signup and view all the answers

The process of homologous chromosomes pairing up is known as __________.

<p>synapsis</p> Signup and view all the answers

What are the sex chromosomes for typical females?

<p>XX (C)</p> Signup and view all the answers

Match the following stages of mitosis with their descriptions:

<p>Prophase = Chromatin condenses into chromosomes Metaphase = Chromosomes align at the metaphase plate Anaphase = Sister chromatids are pulled to opposite poles Telophase = Nuclear envelope reforms around separated chromosomes</p> Signup and view all the answers

All genes are located on the X and Y chromosomes.

<p>False (B)</p> Signup and view all the answers

Which of the following describes crossing over?

<p>Homologs exchange genetic material (A)</p> Signup and view all the answers

Which term describes the failure of homologous chromosomes to separate during meiosis?

<p>nondisjunction</p> Signup and view all the answers

Meiosis results in identical daughter cells.

<p>False (B)</p> Signup and view all the answers

Klinefelter syndrome is characterized by the presence of an extra ______ chromosome in males.

<p>X</p> Signup and view all the answers

Match the chromosomal alterations with their definitions:

<p>deletion = removal of a segment duplication = repeating a segment inversion = reversing a segment translocation = nonhomologous chromosomes swap sections</p> Signup and view all the answers

What is the role of the centrosome during cell division?

<p>Organizes microtubules and helps pull chromatids apart</p> Signup and view all the answers

During _________________, chromosomes line up double stacked in homologous pairs.

<p>metaphase I</p> Signup and view all the answers

Which syndrome is characterized by a person with one X chromosome?

<p>Turner Syndrome (C)</p> Signup and view all the answers

What occurs after the sperm enters the secondary oocyte?

<p>All of the above (D)</p> Signup and view all the answers

Individuals with Turner Syndrome are typically male.

<p>False (B)</p> Signup and view all the answers

The acrosomal reaction occurs after the fertilization envelope is formed.

<p>False (B)</p> Signup and view all the answers

What is the primary genetic material that transmits traits between bacteria?

<p>DNA</p> Signup and view all the answers

What is an example of asexual reproduction?

<p>Budding (B)</p> Signup and view all the answers

Independent assortment refers to the random distribution of chromosomes during gamete formation.

<p>True (A)</p> Signup and view all the answers

What is the term for the hollow sphere of cells formed during embryonic development?

<p>blastula</p> Signup and view all the answers

The wild type for fruit fly eye color is _____ eyes.

<p>red</p> Signup and view all the answers

In Mendel's experiments, the P generation consisted of _____ plants.

<p>true breeding</p> Signup and view all the answers

What is a common outcome of trisomy 21?

<p>Down Syndrome (A)</p> Signup and view all the answers

What is the result of spermatogenesis?

<p>Four haploid sperm cells</p> Signup and view all the answers

The X chromosome can contain dominant or recessive genes.

<p>True (A)</p> Signup and view all the answers

During telophase II, we end up with __________ cells.

<p>4 haploid non-identical</p> Signup and view all the answers

Which type of fertilization involves the male depositing sperm inside the female's reproductive tract?

<p>Internal fertilization (A)</p> Signup and view all the answers

Who was the scientist that studied Drosophila melanogaster to understand inheritance patterns?

<p>Thomas Morgan</p> Signup and view all the answers

What does Mendel's law of independent assortment state?

<p>Each pair of alleles segregates independently (B)</p> Signup and view all the answers

An individual requires one copy of a recessive allele for it to be expressed.

<p>False (B)</p> Signup and view all the answers

The ______ is the genetic condition resulting from deletion on chromosome 5.

<p>cri du chat syndrome</p> Signup and view all the answers

Match the following syndromes with their genetic characteristics:

<p>Klinefelter Syndrome = XXY Turner's Syndrome = X0 Trisomy X = XXX XYY Syndrome = XYY</p> Signup and view all the answers

What is the common phenotypic ratio observed in Mendel's F2 generation for single-trait crosses?

<p>3:1</p> Signup and view all the answers

The process where one gene affects the expression of another gene is called ______.

<p>epistasis</p> Signup and view all the answers

Match the following types of dominance with their definitions:

<p>incomplete dominance = When the phenotype is a mix of parental traits codominance = When both alleles are expressed equally pleiotropy = One gene affects multiple traits polygenic inheritance = Multiple genes influence one trait</p> Signup and view all the answers

What is the outcome of the sperm acrosomal reaction?

<p>Breakdown of the egg's protective coat (A)</p> Signup and view all the answers

Polygenic inheritance means that multiple genes influence multiple traits.

<p>False (B)</p> Signup and view all the answers

What type of alleles are represented by uppercase letters?

<p>dominant alleles</p> Signup and view all the answers

The central part of a chromosome that holds sister chromatids together is called the ______.

<p>centromere</p> Signup and view all the answers

What term describes the observable expression of genes in an individual?

<p>Phenotype (A)</p> Signup and view all the answers

What is the first enzyme involved in DNA replication that unwinds the DNA strands?

<p>Helicase (B)</p> Signup and view all the answers

The leading strand of DNA is formed continuously.

<p>True (A)</p> Signup and view all the answers

What is the role of RNA polymerase in transcription?

<p>To make a copy of DNA in the form of RNA.</p> Signup and view all the answers

The ______ are the sequences in mRNA that actually code for proteins.

<p>exons</p> Signup and view all the answers

Which of the following sequences signals the start of protein synthesis?

<p>AUG (D)</p> Signup and view all the answers

Mutations can have no impact or a significant impact on an organism's DNA.

<p>True (A)</p> Signup and view all the answers

What is unique about the process of transcription in prokaryotes compared to eukaryotes?

<p>Transcription and translation occur simultaneously in prokaryotes.</p> Signup and view all the answers

The enzyme that seals gaps between Okazaki fragments on the lagging strand is called ______.

<p>ligase</p> Signup and view all the answers

Match the enzyme to its function in the DNA replication process.

<p>Helicase = Unwinds the DNA strands Topoisomerase = Prevents supercoiling Primase = Lays down RNA primers DNA Polymerase = Synthesizes the new DNA strands</p> Signup and view all the answers

What structure begins the process of replication?

<p>Ori (C)</p> Signup and view all the answers

The codon sequence in RNA is made up of three nucleotides that correspond to an amino acid.

<p>True (A)</p> Signup and view all the answers

What are the stop codons in the genetic code?

<p>UAA, UAG, UGA</p> Signup and view all the answers

Which type of mutation involves swapping one nucleotide for another?

<p>Substitution (A)</p> Signup and view all the answers

During the elongation phase of translation, ______ brings in amino acids to the ribosome.

<p>tRNA</p> Signup and view all the answers

What is the term for the editing step that occurs between transcription and translation in eukaryotes?

<p>Post-transcriptional modification (C)</p> Signup and view all the answers

Flashcards

Sister Chromatids

Two identical copies of a chromosome created during DNA replication, joined at the centromere.

Homologous Chromosomes

Chromosome pairs (one from each parent) that are the same size, shape, and carry the same genes but potentially different alleles.

Interphase

The phase of the cell cycle where the cell grows, replicates its DNA, and prepares for cell division.

Mitosis

The process of cell division that produces two genetically identical daughter cells from a single parent cell.

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Haploid

Having a single set of chromosomes (e.g., gametes)

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Diploid

Having two sets of chromosomes (e.g., most body cells).

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Cell Cycle

The series of events that take place in a cell leading to its duplication (replication).

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Centromere

The region of a chromosome where sister chromatids are joined.

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Diploid (2n)

Having two complete sets of chromosomes from each parent, one from each parent.

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Prophase (Mitosis)

First stage of mitosis: chromosomes condense, spindle fibers form, and centrosomes move apart.

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Prometaphase (Mitosis)

Stage of mitosis where spindle fibers attach to chromosomes, further condensing them.

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Metaphase (Mitosis)

Stage where chromosomes line up in the middle of the cell (metaphase plate).

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Anaphase (Mitosis)

Stage where sister chromatids separate and move towards opposite ends of the cell.

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Telophase (Mitosis)

Stage where chromosomes reach the poles, nuclear envelopes reform, and the cell prepares to split.

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Cytokinesis (Mitosis)

Division of the cytoplasm to form two separate daughter cells.

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Haploid (1n)

Having only one complete set of chromosomes.

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Gametes

Reproductive cells (sperm and egg) produced through meiosis; they are haploid.

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Somatic Cell

Any cell in the body that is not involved in reproduction, and divides by mitosis.

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Prophase I (Meiosis)

Chromosomes condense, nuclear envelope breaks down, homologous chromosomes pair up, and crossing over occurs.

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Fertilization

The fusion of a sperm and egg to form a zygote.

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Zygote

A fertilized egg; a single cell resulting from the union of sperm and egg.

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Blastula

Hollow ball of cells formed by cleavage divisions of a zygote.

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Cleavage

Rapid cell division of the zygote that produces a blastula

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Gastrulation

Process of cell rearrangement that turns the blastula into a gastrula.

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Gastrula

Embryonic stage after blastula; characterized by the formation of germ layers.

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Gene

Segment of DNA that codes for a protein.

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Allele

Alternative version of a gene.

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Homozygous

Having two identical alleles for a gene.

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Heterozygous

Having two different alleles for a gene.

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Dominant Allele

Allele that expresses its phenotype even when paired with a recessive allele.

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Recessive Allele

Allele whose phenotype is not expressed if a dominant allele is present.

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Punnett Square

Grid used to predict possible gene combinations in offspring.

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Law of Segregation

Separation of alleles during gamete formation.

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Law of Independent Assortment

Different genes are sorted independently of each other.

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Bimodal Sex

Sex is categorized into distinct groups based on shared anatomical and physiological traits, not simply a spectrum.

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Sex Chromosomes

X and Y chromosomes determine an individual's sex. Females have two X chromosomes (XX), while males have one X and one Y chromosome (XY).

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Y Chromosome

A small chromosome containing about 78 genes, many of which are only expressed in the testes, playing a crucial role in male development.

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X Chromosome

A larger chromosome carrying many genes, some of which can be dominant or recessive. Females need two copies of a recessive gene to express it, while males only need one.

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Carrier

An individual who carries a genetic difference in one copy of a gene but doesn't express the associated trait or disease.

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Wild Type

The most common character observed in a natural population; can be either dominant or recessive.

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Linked Genes

Genes that are located close together on the same chromosome are more likely to be inherited together.

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Nondisjunction

The failure of homologous chromosomes or sister chromatids to separate properly during meiosis, resulting in an abnormal number of chromosomes.

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Aneuploidy

A condition where an organism has an abnormal number of chromosomes.

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Trisomy 21

Down syndrome, a condition caused by having an extra copy of chromosome 21, affecting facial features, stature, heart health, etc.

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Klinefelter Syndrome (XXY)

A condition affecting males with an extra X chromosome (XXY), resulting in male testes, no sperm production, and enlarged breasts.

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Swyer Syndrome

A condition affecting individuals with a normal number of chromosomes but mutations on the Y chromosome, resulting in a female phenotype.

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Cri du Chat Syndrome

A disorder caused by a specific chromosomal deletion on chromosome 5, characterized by a distinctive cat-like cry, small head, and intellectual disabilities.

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DNA Replication

The process of copying a DNA molecule to produce two identical DNA molecules. This process consists of unwinding the parent strand, creating a replication bubble, and building two new daughter strands by pairing complementary nucleotides to the parent strands.

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Replication Origin (ori)

A specific sequence of nucleotides on a DNA molecule where DNA replication begins.

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Replication Fork

The Y-shaped region where the two parental strands of DNA are separated during DNA replication.

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Leading Strand

The new DNA strand that is synthesized continuously during DNA replication.

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Lagging Strand

The new DNA strand that is synthesized discontinuously during DNA replication, in short fragments called Okazaki fragments

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Okazaki Fragments

Short segments of DNA synthesized on the lagging strand during DNA replication.

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DNA Polymerase

The enzyme responsible for synthesizing new DNA strands during DNA replication. It reads the parent strand and adds complementary nucleotides to build the daughter strand.

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Helicase

The enzyme that unwinds the double helix of DNA during replication. It breaks the hydrogen bonds holding the two strands together.

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Topoisomerase

The enzyme that prevents supercoiling of DNA during replication. It cuts and rejoins the DNA strands to relieve tension.

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Primase

The enzyme that synthesizes short RNA primers, which provide a starting point for DNA polymerase to begin synthesis.

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Ligase

The enzyme that joins the Okazaki fragments together on the lagging strand to create a continuous strand of DNA.

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Transcription

The process of copying a gene's DNA sequence into a messenger RNA (mRNA) molecule.

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RNA Polymerase

The enzyme that synthesizes RNA from a DNA template during transcription.

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Translation

The process of using the genetic code carried by mRNA to assemble amino acids into a protein.

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Chromatin

The complex of DNA and proteins (histones) that makes up chromosomes.

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Histones

Proteins that DNA wraps around to condense and organize genetic material.

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Haploid vs. Diploid

Haploid cells have one complete set of chromosomes (n), while diploid cells have two (2n). Gametes are haploid, while most somatic cells are diploid.

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What happens during Interphase?

The cell grows, copies its DNA, and prepares for cell division. It includes three stages: G1, S, and G2.

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Centrioles/Centrosomes

Structures involved in cell division. Centrosomes duplicate during S phase and give rise to spindle fibers during mitosis.

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Mitosis Phases

The four stages of mitosis: prophase, metaphase, anaphase, and telophase.

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Prometaphase

The stage of mitosis where spindle fibers attach to chromosomes, further condensing them.

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Metaphase

The stage of mitosis where chromosomes align at the center of the cell, forming the metaphase plate.

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Anaphase

The stage of mitosis where sister chromatids separate and move toward opposite ends of the cell.

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Telophase

The final stage of mitosis, where chromosomes reach the poles, nuclear envelopes reform, and the cell prepares to divide.

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Cytokinesis

The division of the cytoplasm that follows mitosis, resulting in two separate daughter cells.

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Nuclear Envelope

The double membrane structure that encloses the nucleus in eukaryotic cells, separating the genetic material from the cytoplasm.

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Synapsis

The pairing of homologous chromosomes in prophase I of meiosis.

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Transformation

The process by which bacterial cells take up genetic material from their environment, often in the form of DNA fragments.

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Semi-Conservative Replication

Each new DNA molecule contains one original strand and one newly synthesized strand.

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Secondary Oocyte

A haploid (1n) egg cell that is arrested in metaphase II of meiosis and awaits fertilization. It contains a nucleus and a first polar body.

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Fertilization Envelope

A protective barrier formed by the fusion of cortical granules with the egg's plasma membrane after sperm entry, preventing polyspermy (multiple sperm fertilizing one egg).

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Acrosomal Reaction

The release of enzymes from the sperm's acrosome, breaking down the egg's protective outer layer (zona pellucida) allowing the sperm to penetrate.

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Blastopore

The opening in the gastrula that will eventually form the anus in most species, forming the first opening of the digestive tract.

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Organogenesis

The process where the germ layers in the gastrula differentiate into organs, forming a complex organism.

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Gene Locus

The specific location of a gene on a chromosome. Alleles for the same gene occupy the same locus on homologous chromosomes.

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Trait

A specific characteristic of an organism, resulting from the combination of alleles.

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Codon

A sequence of three nucleotides in DNA or RNA that codes for a specific amino acid.

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Study Notes

Cell Cycle & Mitosis

  • Chromatin: DNA wrapped around histone proteins
  • Sister chromatids: Two identical copies of a chromosome in a dividing cell
  • Homologous chromosomes (homologs): Chromosomes of the same size and shape from different parents, carrying the same genes but potentially different alleles
  • Haploid (1n): Half the number of chromosomes (gametes)
  • Diploid (2n): Full number of chromosomes (somatic cells)

Interphase

  • Centrosomes/centrioles: Present, produce spindle fibers
  • Chromatin: Loose, not visible
  • Nuclear envelope: Intact
  • G1 (Gap 1): Cell growth, organelle duplication, chromosome building blocks, centromere production, energy storage
  • S (Synthesis): DNA replication (2 sister chromatids), attached to centromeres, centrosome duplication
  • G2 (Gap 2): Energy storage, organelle duplication, protein synthesis for chromosome manipulation, cytoskeleton disassembly
  • Result of interphase: 2 copies of DNA, organelles, stored energy, ready proteins

Mitosis

  • Purpose: Cell division in embryos, fetuses, juveniles, and to replace cells in adults
  • Daughter cells: Genetically identical to the parent cell
  • External control: Hormones or growth factors stimulate cell division, binding to receptors, relaying signals
  • Centromere: Bond holding sister chromatids
  • Gametes: Reproductive cells (haploid), created via meiosis.
  • Zygote: Single fused cell (diploid)
  • Cleavage: Cell division in animal cells

Mitosis Phases

  • Prophase: Centrosome duplication and movement, spindle fiber formation, chromatin condensation
  • Prometaphase: Spindle fibers attach to centromeres, chromosome shortening and thickening
  • Metaphase: Metaphase plate formation, chromosomes line up at metaphase plate, attached to spindle fibers
  • Anaphase: Sister chromatids split and move to opposite poles, becoming daughter chromosomes
  • Telophase: Chromosomes arrive at poles, become chromatin again, spindle disappears, two daughter nuclei form
  • Cytokinesis: Cytoplasm division, creating 2 daughter cells

Meiosis

  • Purpose: Produce 4 non-identical haploid cells (gametes)
  • Occurs: After G2 phase and before M phase
  • Genetic mixing/recombination: Increases DNA variety in future offspring
  • Somatic cells: Non-reproductive cells, divide only by mitosis
  • Gametes: Reproductive cells (haploid)
  • Nuclear envelope: Double membrane enclosing the nucleus, separating genetic material from cytoplasm
  • Centrosome: Organelle organizing microtubules, involved in chromosome separation
  • Centrioles: Tiny structures within the centrosome
  • Spindle fibers: Protein structures separating genetic material during cell division
  • Synapsis: Pairing of homologous chromosomes
  • Tetrad: Set of 4 chromatids
  • Crossing over: Genetic recombination
  • Metaphase plate: Imaginary line where chromosomes align during metaphase I and II
  • Centromere: Central section binding sister chromatids
  • Kinetochore: Proteins within centromere holding chromosomes together

Meiosis I

  • Prophase I: Chromatin condenses; nuclear envelope, homologous chromosomes synapse (tetrads), crossing over
  • Metaphase I: Tetrads align at metaphase plate, spindle microtubules attach, independent assortment
  • Anaphase I: Homologous chromosomes separated to opposite sides
  • Telophase I: Chromosomes move towards poles, cell begins to divide, 2 non-identical haploid cells
  • Prophase II: Nuclear envelope dissolves, new spindle fibers form, centrosomes move to poles
  • Metaphase II: Chromosomes (single file) align at metaphase plate, spindle fibers attach
  • Anaphase II: Sister chromatids separate, pulled to opposite poles
  • Telophase II: Distinct nuclei form, 4 haploid non-identical cells

Animal Reproduction

  • Asexual: No fusion of gametes, usually mitosis, e.g., budding, fission, fragmentation, parthenogenesis
  • Sexual: Fusion of sperm and egg, involves fertilization (sperm + egg → zygote), meiosis & fertilization, traditional (1F, 1M), sex reversal, hermaphroditism
  • Internal fertilization: Male deposits sperm inside/near female reproductive tract
  • External fertilization: Female & male deposit gametes into water
  • Chemical signals: Hormones (communicate within individual), pheromones (communicate between individuals).

Gametogenesis

  • Male: Spermatogonial stem cell (2n) → Spermatogonium (2n)→ Primary spermatocyte(2n) → Secondary spermatocyte(1n) → Early spermatid(1n) → Sperm cell(1n)
  • Female: Oogonium (2n) → Primary oocyte (2n) (arrested in meiosis I)→ Secondary oocyte (1n) plus polar body(1n) →Fertilized egg (zygote) (2n)- arrested in metaphase II until fertilization

Embryonic Development

  • Fertilization: Forms zygote
  • Cleavage: Zygote → Blastula (hollow sphere)
  • Gastrulation: Blastula → Gastrula (blastopore, digestive tract formation)
  • Organogenesis: Organs begin to form

Mendel & Genetics

  • Gene: Segment of DNA coding for a protein
  • Genome: All an organisms genes
  • Allele: Alternative versions of a gene
  • Gene locus: Particular gene location on a chromosome
  • Trait: Variant of a character (e.g., blue eyes)
  • Character: Heritable feature varying among individuals
  • Phenotype: Observable trait determined by gene combinations
  • Gregor Mendel: Father of genetics, studied pea plants
  • True-breeding plants: Bred only for one trait, P generation.
  • F1 generation: Offspring of P generation cross, dominant expressed
  • F2 generation: Offspring from F1 cross, 3:1 ratio (dominant: recessive)
  • Mendel's Model: Alleles, homologous chromosomes, dominance/recessiveness, law of segregation (alleles separate), and independent assortment (different genes independent).

Punnett Squares

  • Diagram predicting offspring genotypes
  • Used with more than one trait, calculate probabilities (addition/multiplication rules), determine heterozygous likelihood

Incomplete Dominance & Codominance

  • Incomplete dominance: Phenotype intermediate between dominant alleles.
  • Codominance: Both dominant alleles expressed.

Pleiotropy & Polygenic Inheritance

  • Pleiotropy: One gene → multiple traits.
  • Polygenic inheritance: Multiple genes → one trait.

Epistasis

  • Epistasis: One gene effects expression of another gene

Sex-linked Traits & Sex Chromosomes

  • Sex chromosomes: X and Y
  • XX: Female; XY: Male
  • X-linked genes: Dominant/recessive
  • Hemizygous: Having only one copy of a gene (common for males & Y chromosome genes)
  • Carrier: Person carrying a genetic difference without expressing it
  • Thomas Morgan: Studied Drosophila melanogaster (fruit flies) to understand inheritance
  • Wild type: Most common trait observed in nature

Chromosome Theory of Inheritance

  • Genes on chromosomes, their behavior during meiosis explains inheritance
  • Linked genes: Genes closer on same chromosome more likely to be inherited together.
  • Gene distance related to recombination rates

Chromosomal Abnormalities

  • Nondisjunction: Failure of chromosome separation during meiosis
  • Aneuploidy: Abnormal number of chromosomes, e.g., monosomic, trisomic
  • Trisomy 21 (Down syndrome): Trisomic condition affecting chromosome 21
  • Sex-linked abnormalities: Klinefelter (XXY), XYY, trisomy X, Turner (XO), Swyer syndrome

Alterations to Chromosomal Structure

  • Deletion: Removal
  • Duplication: Repeating
  • Inversion: Reversing
  • Translocation: Non-homologous chromosome swapping.

Disorders from Chromosomal Alterations:

  • Cri du chat syndrome: Chromosome 5 deletion (distinct symptoms & outcomes)
  • Chronic myelogenous leukemia (CML): Reciprocal translocation causing uncontrollable cell division

Molecular Basis of Inheritance

  • DNA as genetic material: Identified through experiments (Griffith, Avery-MacLeod-McCarty, Hershey-Chase)
  • Watson & Crick: Double helix structure.
  • DNA replication: Semi-conservative, using existing strands as templates, specific enzymes involved (helicase, topoisomerase, primase, DNA polymerase, ligase)
  • Steps: unwinding, preventing supercoiling, priming, copying, gluing.
  • Leading/Lagging strands: Continuous & discontinuous strands, Okazaki fragments

Transcription and Translation

  • Transcription: Copying DNA to RNA (RNA polymerase)
  • Post-transcriptional modification (eukaryotes): Introns removed, exons joined
  • Translation: RNA to protein (using ribosomes, tRNA, codons)
  • mRNA: Messenger RNA, carries genetic code to ribosomes
  • tRNA: Transfer RNA, carries amino acids to ribosomes
  • Codons: Three nucleotide sequences coding for amino acids
  • Start/stop codons: Indicate beginning/end of protein synthesis,
  • Ribosomes made of rRNA, crucial to translation process
  • Initiation: mRNA attachment to small subunit, start codon search & large subunit binding
  • Elongation: tRNA brings amino acid, polypeptide chain growth
  • Termination: Stop codon reached, polypeptide release
  • Prokaryotes: Transcription & translation simultaneous in cytoplasm

Mutations

  • Mutation types: Insertion, deletion, substitution, point mutations, frameshift
  • Effects of mutations: Silent, missense, nonsense, impact polypeptide sequence, may lead to different traits
  • Causes: UV radiation, replication errors, chemicals
  • Mutation correction: Proofreading, mismatch repair, nucleotide excision repair.

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