Cell Division and Cycle Overview

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Questions and Answers

What type of cells undergo mitosis?

Sperm cells

Egg cells

Somatic cells (correct)

Germ cells

Which phase of the cell cycle is primarily associated with DNA replication?

G2 phase

Mitosis

S phase (correct)

G1 phase

What is produced as a result of meiosis?

Haploid cells (correct)

Diploid cells

Somatic cells

Genetic clones

During which phase does a cell rest before division occurs?

G2 phase Signup and view all the answers

Which of the following terms best describes an organism that has two identical alleles for a trait?

Homozygote Signup and view all the answers

What is the result of one round of mitosis in terms of chromosome numbers in daughter cells?

Each cell receives 46 chromosomes. Signup and view all the answers

What is the main role of the centromere during cell division?

To attach chromosomes to the spindle. Signup and view all the answers

How many haploid cells are produced at the end of meiosis?

Four haploid cells. Signup and view all the answers

During which phase of mitosis are sister chromatids separated?

Anaphase. Signup and view all the answers

What is the chromosomal composition of human gametes after meiosis?

23 chromosomes. Signup and view all the answers

What does recombination involve during meiosis?

Exchange between maternal and paternal chromosomes Signup and view all the answers

What structure forms when homologous chromosomes pair during meiosis?

Bivalent or Tetrad Signup and view all the answers

What is the main purpose of independent assortment during meiosis?

To generate genetic diversity Signup and view all the answers

What happens to primary oocytes in fetal ovaries during meiosis?

They are arrested in prophase of meiosis I. Signup and view all the answers

How does the process of meiosis differ from mitosis?

Meiosis produces four non-identical gametes. Signup and view all the answers

How many different alignments can three pairs of homologous chromosomes produce during meiosis?

Eight Signup and view all the answers

What initiates the continuous formation of human sperm?

Puberty Signup and view all the answers

What is a key result of crossing over during meiosis?

Modification of genetic material between homologous chromosomes Signup and view all the answers

What is the genotype ratio resulting from a cross between two heterozygous pea plants (Rr x Rr)?

1:2:1 Signup and view all the answers

Which type of genetic defects follows simple Mendelian inheritance patterns?

Single-gene defects Signup and view all the answers

Which of the following patterns is NOT a category of Mendelian inheritance?

Environmental inheritance Signup and view all the answers

What can be identified within families to study genetic traits and diseases?

Pedigree analysis Signup and view all the answers

Which of the following statements is true regarding disease genotype and phenotype?

A specific genotype can lead to a phenotype of a disease. Signup and view all the answers

What does recombination involve during meiosis?

Exchange of DNA sequences between chromatids Signup and view all the answers

What is a key characteristic of haploid gametes?

They arise from diploid precursors Signup and view all the answers

What defines an allele in genetic terms?

A variant form of a gene Signup and view all the answers

Which genotype represents a heterozygote?

Aa Signup and view all the answers

Which term describes the physical appearance of an organism?

Phenotype Signup and view all the answers

During what phase of meiosis does recombination occur?

Pachytene Signup and view all the answers

What occurs if mistakes happen during recombination or mitosis?

DNA sequences can be lost or gained Signup and view all the answers

What happens during fertilization?

Diploid zygote is formed from sperm and egg chromosomes Signup and view all the answers

What is the outcome of mitosis in somatic cells?

Diploid cells produce diploid cells Signup and view all the answers

During which phase of the cell cycle does the cell prepare for division?

G1 phase Signup and view all the answers

Which of the following best describes meiosis?

A specialized division creating haploid cells for reproduction Signup and view all the answers

What happens during the synthesis phase of the cell cycle?

DNA replication occurs Signup and view all the answers

Which of the following statements about the G0 phase is true?

It can vary in length and involves non-replication Signup and view all the answers

What is the genotype ratio of the progeny resulting from a cross between two heterozygous pea plants (Rr x Rr)?

1:2:1 Signup and view all the answers

Which category of genetic defects involves interactions of several genes and follows a complex inheritance pattern?

Polygenic defects Signup and view all the answers

Which pattern of inheritance includes both autosomal and X-linked forms?

Mendelian inheritance Signup and view all the answers

What is the primary method used to identify inherited diseases in families?

Pedigree analysis Signup and view all the answers

In the context of inherited diseases, what does the term 'disease phenotype' refer to?

The observable traits associated with the disease Signup and view all the answers

What is the ploidy level of the resulting daughter cells after one round of mitosis?

Diploid Signup and view all the answers

What happens to chromosomes that lack a centromere during mitosis?

They are not attached to the spindle. Signup and view all the answers

What characterizes the result of DNA replication in preparation for mitosis?

Two DNA molecules each with one old and one new strand. Signup and view all the answers

During meiosis, how many haploid cells are produced from one diploid cell?

Four Signup and view all the answers

Which of the following statements about sister chromatids is correct?

They are identical copies created during the cell cycle. Signup and view all the answers

What is the structure formed when homologous chromosomes pair during meiosis?

Bivalent Signup and view all the answers

Which of the following processes contributes to genetic diversity in meiosis?

Independent assortment Signup and view all the answers

What is the outcome of random segregation during meiosis?

Genetic variation Signup and view all the answers

How many different ways can 23 pairs of chromosomes align during meiosis?

8 million Signup and view all the answers

What phase may primary oocytes remain in after fetal development?

Prophase I Signup and view all the answers

What is a key difference in the formation of eggs and sperm in humans?

Sperm are produced in larger quantities than eggs. Signup and view all the answers

During meiosis, what is the primary role of the mitotic spindle?

To pull chromatids towards the poles Signup and view all the answers

What happens during recombination in meiosis?

DNA sequences are exchanged between chromatids without loss or gain. Signup and view all the answers

What are the possible combinations of paternal homologs based on the formula $2^{23}$?

8.4 x 10^6 Signup and view all the answers

Which term describes an organism's genetic constitution?

Genotype Signup and view all the answers

In which cell division process does recombination normally not occur?

Mitosis Signup and view all the answers

What characterizes alleles within a gene in a population?

Alleles can vary slightly in their DNA sequences. Signup and view all the answers

What defines a recessive trait in genetics?

It is only expressed in the phenotype when paired with another recessive allele. Signup and view all the answers

What is the outcome if non-disjunction occurs during meiosis?

Some gametes will have an extra chromosome or be missing one. Signup and view all the answers

What primarily determines an organism's phenotype?

Genotype primarily, but not exclusively. Signup and view all the answers

Which of the following statements about the cell cycle phases is accurate?

S phase requires more time than mitosis within the cell cycle. Signup and view all the answers

What is the primary consequence of meiosis in terms of genetic material?

It results in haploid cells with increased genetic variability. Signup and view all the answers

In which way do meiotic division and cellular differentiation differ fundamentally?

Meiotic division involves homologous chromosomes, while differentiation does not. Signup and view all the answers

Which term correctly describes the state of a cell in the G0 phase?

The cell is in a quiescent state and not actively dividing. Signup and view all the answers

Which of the following statements about genetic terms is true?

Alleles can be both dominant and recessive properties of a gene. Signup and view all the answers

What is the expected phenotype ratio of progeny from a cross between two heterozygous pea plants (Rr x Rr)?

3:1 Signup and view all the answers

Which type of genetic defect follows complex (non-Mendelian) inheritance patterns?

Multi-gene defect Signup and view all the answers

Which method is primarily used to trace inheritance patterns of diseases within families?

Pedigree analysis Signup and view all the answers

What defines a monogenic defect in terms of inheritance?

Controlled by a single allele, dominant or recessive Signup and view all the answers

Which of the following is true for autosomal dominant inheritance?

Affected individuals have at least one affected parent Signup and view all the answers

What is the primary reason chromosomes lacking a centromere fail to segregate properly during cell division?

They cannot attach to the mitotic spindle. Signup and view all the answers

Which of the following statements accurately describes the outcome of a single round of DNA replication followed by mitosis?

It generates two diploid cells with identical genetic material. Signup and view all the answers

During which specific phase of the cell cycle are sister chromatids separated from each other?

Anaphase Signup and view all the answers

In the context of genetic organization, how are chromosomes structured before cell division?

As replicated linear DNA forming sister chromatids. Signup and view all the answers

Which process specifically reduces the number of chromosome sets from diploid to haploid during gamete formation?

Meiosis Signup and view all the answers

What is a key process contributing to genetic diversity during meiosis I?

Crossing over Signup and view all the answers

Which statement accurately describes the formation of primary oocytes?

They are arrested in prophase of meiosis I during fetal development. Signup and view all the answers

What structural feature describes a bivalent during meiosis?

A four-stranded structure comprising two homologous chromosomes Signup and view all the answers

In terms of genetic alignment, how many different configurations can 23 pairs of homologous chromosomes produce during meiosis?

8,388,608 Signup and view all the answers

Which outcome occurs in the meiotic divisions of spermatogenesis?

More than one viable sperm is produced from each primary spermatocyte. Signup and view all the answers

What is the primary outcome of recombination during meiosis?

Maternal and paternal DNA sequences are exchanged. Signup and view all the answers

What is the significance of independent assortment in meiosis?

It allows for the random distribution of maternal and paternal chromosomes. Signup and view all the answers

Which statement accurately describes a heterozygote?

An organism with one dominant and one recessive allele. Signup and view all the answers

During which phase does genetic recombination primarily occur in meiosis?

Prophase I Signup and view all the answers

How are chromatids separated during meiosis compared to mitosis?

Chromatids are separated in both processes during anaphase. Signup and view all the answers

What phase of meiosis is characterized by the alignment of bivalents at the metaphase plate?

Metaphase I Signup and view all the answers

What role do alleles play in genetic variation within a population?

They are different forms of a gene resulting in genetic diversity. Signup and view all the answers

How does the phenotype of an organism relate to its genotype?

Phenotype is predominantly determined by genotype. Signup and view all the answers

What are the possible outcomes if non-disjunction occurs during meiosis?

Individuals may inherit an abnormal number of chromosomes. Signup and view all the answers

What is a key difference between genetic recombination during meiosis and during mitosis?

Only meiosis allows for the exchange of genetic material without loss. Signup and view all the answers

Which of the following accurately describes the concept of polymorphism in genetics?

The existence of multiple alleles for a gene across a population. Signup and view all the answers

Study Notes

Cell division

Vital for development and growth.
Occurs through mitosis in somatic cells, producing two identical daughter cells.
Involves duplication of DNA, resulting in diploid cells.
Meiosis occurs in germ cells, producing gametes (sperm and egg cells).
Meiosis reduces the chromosome number from diploid to haploid.

Cell cycle phases

G1 (Gap 1): Cell growth and preparation for DNA replication. Occurs prior to cell division.
S (Synthesis): DNA replication phase.
G2 (Gap 2): Short resting phase prior to mitosis, preparing the cell for division.
M (Mitosis): Cell division process, dividing the replicated genome into two daughter cells.
G0 (Gap zero): Non-replicative phase. Many differentiated cells remain in G0.

Humans

Have 23 pairs of chromosomes, including 22 autosomes plus sex chromosomes.
Sex chromosomes:
- XX: female
- XY: male

Mitosis

Duplicates the genome accurately and divides it between daughter cells.
DNA is copied once, followed by one cell division, resulting in two diploid daughter cells.
Involves sister chromatids: identical copies of DNA held together by a centromere.
Each sister chromatid contains one original and one newly synthesized DNA strand.

Stages of mitosis

Prophase: Chromosomes condense and become visible; spindle fibers form.
Metaphase: Chromosomes align at the metaphase plate, attached to spindle fibers.
Anaphase: Sister chromatids separate and move towards opposite poles of the cell.
Telophase: Chromosomes reach the poles, nuclear envelope reforms, and cytokinesis (cell division) starts.

Meiosis

Reduces the chromosome number from diploid to haploid.
Involves two successive divisions, meiosis I and meiosis II.
Prophase I:
- Leptotene: Chromosomes start to condense.
- Zygotene: Homologous chromosomes pair up (synapsis).
- Pachytene: Crossing over occurs between homologous chromosomes.
- Diplotene: Homologous chromosomes start to separate but remain attached at chiasmata where crossing over occurred.
- Diakinesis: Chromosomes condense further and the nuclear envelope breaks down.
Metaphase I: Homologous pairs line up at the metaphase plate.
Anaphase I: Homologous chromosomes separate and move to opposite poles of the cell.
Telophase I: Chromosomes reach the poles, nuclear envelope reforms, and cytokinesis occurs.
Meiosis II: Similar to mitosis, but starts with haploid cells. Sister chromatids separate, resulting in four haploid daughter cells.

Genetic variation

Independent assortment: Random alignment of homologous chromosomes at metaphase I.
Recombination (crossing over): Exchange of genetic material between homologous chromosomes during prophase I, resulting in chromosomes with new combinations of alleles.

Basic terminology

Diploid (2n): Two copies of each chromosome (one from each parent).
Haploid (n): Only one copy of each chromosome.
Allele: Different versions of a gene, which determine a specific trait.
Genotype: The genetic makeup of an individual, represented by the combination of alleles.
Phenotype: The observable physical characteristics of an individual, determined by their genotype.
Homozygote: Two identical alleles for a gene.
Heterozygote: Two different alleles for a gene.
Dominant: An allele that masks the effect of a recessive allele.
Recessive: An allele whose effect is masked by a dominant allele.

Mendelian inheritance

Describes the inheritance of traits controlled by single genes with dominant and recessive alleles.
Example: Round (R) versus wrinkled (r) peas.
Cross Rr x Rr leads to a phenotype ratio of 3:1 (3 round, 1 wrinkled).

Human inherited diseases

Can be caused by genetic defects, either single-gene or multi-gene.
Single-gene (monogenic): Due to a single defective allele, inherited in a simple Mendelian pattern.
Multi-gene (polygenic): Resulting from interactions of multiple genes, having complex inheritance patterns.
Pedigree analysis: Used to track the inheritance of traits and diseases in families, helping to identify disease patterns and modes of inheritance.

Cell Division

Cell division is essential for development & generating new cells in adults
Somatic cells divide through mitosis.
Mitosis occurs as part of the cell cycle.
Diploid cells result in diploid cells.
Diploid cells have 2 sets of chromosomes; One set from the mother and one set from the father.
Meiosis is a specialized form of cell division for sperm & egg cell production.
Diploid cells result in haploid cells.
Haploid cells are gametes (sperm & egg), they have one set of chromosomes.

Phases of the Cell Cycle

The cell cycle consists of: G1, S, G2, and M phases (mitosis).
G1 (Growth 1): This is a period of cell growth and preparation for cell division.
S (Synthesis): DNA replication
G2 (Growth 2): A short resting phase before cell division.
M (Mitosis): Cell division occurs.
G0: Non-replicative phase, a resting state that can be entered by differentiated cells, for example, hepatocytes.

Human Chromosomes

Humans have 23 pairs of chromosomes, 22 autosomes + 1 pair of sex chromosomes.
Sex-determining chromosomes: XX = female, XY = male

Mitosis

Essential for cell division & growth.
Mitosis is one sector of the cell cycle; describes the process of duplicated genomes getting segregated.
Chromosomal DNA is copied once within the cell.
The cell then divides once to produce two daughter cells.
All daughter cells are diploid (2n).

Mitotic Spindle

Spindle fibers form during cell division, pulling chromosomes to opposite poles.
The centromere is crucial for proper chromosome segregation.
Acentric fragments (lacking centromere) don't attach to the spindle which results in their loss during daughter cell formation.

DNA Replication in Mitosis

End result of DNA replication: two identical DNA molecules, each containing one old and one new strand.
Both new DNA molecules have the same sequence on each strand.
Individual DNA molecules form sister chromatids (identical chromosomes).
These sister chromatids are separated during anaphase, ensuring each daughter cell gets a complete copy of the DNA.
After separation, each chromatid is referred to as a chromosome.
Each daughter cell inherits a full copy of the genetic information from the parent cell.

Meiosis

A specialized form of cell division responsible for the production of gametes (sperm & egg).
Meiosis reduces diploid (2n) cells to haploid (n) cells.
Two meiotic divisions occur, resulting in four haploid cells.
Recombination: Exchange between maternal and paternal chromosomes (homologs) occurs.
Bivalent/Tetrad formation: 4 stranded structure (2 chromatids x 2 homologous chromosomes)

Meiosis I

During Prophase I, pairing of homologous chromosomes occurs: Bivalent/Tetrad formation.
Bivalents align at the metaphase plate in Meiosis I.
Spindle fibers pull one complete chromosome (2 chromatids) to either pole.
Random segregation of maternal and paternal chromosomes contributes to independent assortment.

Division without Replication

Meiosis II is essentially a mitotic division that follows Meiosis I.
Unlike Mitosis, DNA replication does NOT occur before Meiosis II.
The result is four haploid cells, each with a single set of chromosomes.

Egg and Sperm Formation

Egg formation: Starts in the fetal ovaries, arrests during prophase of Meiosis I.
Oocytes remain arrested in diplotene of Meiosis I until ovulation.
Only one of the four daughter cells becomes a functional egg (ovum).
Sperm formation: Occurs continuously in the testes after puberty.
Primary spermatocytes undergo meiotic divisions, creating sperm cells.

Comparing Mitosis & Meiosis

Feature	Mitosis	Meiosis
Number of Divisions	1	2
Daughter Cells	2	4
Ploidy	Diploid (2n)	Haploid (n)
Chromosome Duplication	1 before division	1 before Meiosis I
Recombination	Does NOT occur	Occurs during Prophase I

Mechanisms of Variation

Two main processes contribute to genetic diversity:
- Independent assortment: During Meiosis I, homologous chromosomes are randomly divided.
- Recombination: Crossing over (physical exchange of genetic material) between non-sister chromatids occurs during Prophase I.

Genetic Terminology

Diploid cells: Two homologous copies of each chromosome (one maternal + one paternal)
Allele: Each gene copy within a chromosome.
Genotype: Genetic makeup (AA, aa, Aa)
Phenotype: Physical appearance (healthy or disease)
Homozygote: Two identical alleles for a particular gene (AA or aa)
Heterozygote: Two different alleles for a particular gene (Aa)
Dominant allele: Determines the phenotype even when present with the recessive version.
Recessive allele: Only determines the phenotype when paired with another recessive allele.

Mendelian Inheritance

Single-gene defects: Affect a single gene, with either dominant or recessive inheritance patterns.
Multi-gene (polygenic) defects: Result from interactions of multiple genes, with complex inheritance patterns different from Mendelian.

Human Inherited Diseases

Diseases can be caused by genetic defects within DNA.
They can be categorized as either:
- Single-gene (monogenic) defects: Follow Mendelian inheritance patterns.
- Multi-gene (polygenic) defects: Involve interactions of several genes.
Pedigree analysis: Can help identify the inheritance pattern of traits in families.

Cell Division

Cell division is essential for growth and development.
In somatic cells, division occurs by mitosis, resulting in two diploid cells.
Meiosis is a specialized form of cell division that produces sperm and egg cells, resulting in haploid cells.

Cell Cycle Phases

G1 Phase: A period of cell growth and preparation for cell division.
S Phase: The "synthesis" phase where DNA replication occurs.
G2 Phase: A short resting phase before cell division.
Mitosis: The process of cell division.
G0 Phase: A non-replicative phase where cells may remain, such as hepatocytes.

Human Chromosomes

Humans have 23 pairs of chromosomes: 22 autosomes and 1 pair of sex chromosomes.
XX chromosomes determine female sex.
XY chromosomes determine male sex.

Mitosis

Mitosis is a process of cell division that ensures each daughter cell receives a full copy of the parental cell's genetic information.
DNA is copied once during mitosis, resulting in 92 chromosomes.
The cell then divides once, resulting in two cells each with 46 chromosomes.
The mitotic spindle is essential for chromosome segregation.
Centromeres are crucial for attaching chromosomes to the spindle.
Acentric fragments (lacking centromeres) are not passed to daughter cells.

Meiosis

Meiosis reduces diploid cells to haploid cells.
Meiosis involves two rounds of division: Meiosis I and Meiosis II.
Prophase I of meiosis I includes recombination, where maternal and paternal chromosomes exchange genetic material.
Bivalents, or tetrads, are formed in Prophase I, consisting of four chromatids from two homologous chromosomes.
During Metaphase I, bivalents line up at the metaphase plate.
Spindle fibers pull complete chromosomes (2 chromatids) to opposite poles, resulting in independent assortment of maternal and paternal chromosomes.
Division without replication occurs in Meiosis II.
Meiosis in females begins in the fetal ovaries and is arrested in prophase I.
Only one of the four cells produced by meiosis serves as the functional gamete (ovum).
Meiosis in males occurs continuously after puberty.

Comparison of Mitosis and Meiosis

Mitosis produces two identical daughter cells with the same number of chromosomes as the parent cell.
Meiosis produces four genetically distinct daughter cells with half the number of chromosomes as the parent cell.
Mitosis is involved in growth and repair.
Meiosis is involved in sexual reproduction.

Mechanisms of Variation

Independent assortment: The random segregation of homologous chromosomes during meiosis I.
Recombination by crossing over: The exchange of genetic material between homologous chromosomes during prophase I of meiosis I.

Basic Terminology

Diploid: Having two sets of chromosomes.
Haploid: Having one set of chromosomes.
Allele: A variant form of a gene.
Genotype: The genetic makeup of an individual.
Phenotype: The observable characteristics of an individual.
Homozygote: Having two identical alleles of a gene.
Heterozygote: Having two different alleles of a gene.
Dominant: An allele that masks the expression of the recessive allele.
Recessive: An allele that is masked by the dominant allele.

Mendelian Inheritance

Simple Mendelian inheritance involves single genes.
Recessive traits are often masked by dominant alleles.
The phenotype ratio for a cross between two heterozygotes is typically 3:1.

Human Inherited Diseases

Some diseases are caused by genetic defects.
Single-gene (monogenic) defects follow simple Mendelian inheritance patterns.
Multi-gene (polygenic) defects involve interactions of multiple genes and have complex inheritance patterns.
Pedigree analysis is used to identify patterns of inheritance in families.
Some diseases are autosomal dominant, autosomal recessive, X-linked dominant, or X-linked recessive.

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Description

Explore the critical processes of cell division and the cell cycle, including mitosis and meiosis. Understand how these processes contribute to growth, development, and genetic variation in humans. This quiz covers key phases and chromosome details pertinent to both somatic and germ cells.