Biology Chapter on Genetics
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Questions and Answers

What is the primary purpose of meiosis?

  • To produce gametes (correct)
  • To produce identical daughter cells
  • To replicate somatic cells
  • To increase genetic variation in somatic cells

    • What are genes primarily made up of?

  • Lipid molecules
  • Segments of RNA
  • Proteins
  • Segments of DNA (correct)

    • How many chromosomes do human somatic cells have?

  • 46 pairs
  • 23 single chromosomes
  • 23 pairs (correct)
  • 92 single chromosomes

    • What term describes the specific position of a gene along a chromosome?

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

    What is heredity primarily concerned with?

    <p>Transmission of traits between generations</p> Signup and view all the answers

    What is a karyotype?

    <p>An ordered display of chromosome pairs</p> Signup and view all the answers

    What does genetic variation reflect in offspring?

    <p>Differences in appearance from parents and siblings</p> Signup and view all the answers

    What type of cells are responsible for passing genes to the next generation?

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

    What primarily drives the cell cycle?

    <p>Chemical signals in the cytoplasm</p> Signup and view all the answers

    What happens at the checkpoints during the cell cycle?

    <p>Cells stop until they receive a go-ahead signal</p> Signup and view all the answers

    What is a key characteristic of cancer cells in relation to the cell cycle?

    <p>They can become immortal and continuously divide.</p> Signup and view all the answers

    At which phase does a cell enter the G0 phase?

    <p>If it does not receive a go-ahead signal at a checkpoint</p> Signup and view all the answers

    Which of the following statements about different cell types is true?

    <p>Some cells like intestinal cells divide frequently.</p> Signup and view all the answers

    What is indicated by the term 'molecular clocks' in the context of cell regulation?

    <p>A systematic control of the cell cycle by chemical signals</p> Signup and view all the answers

    What unique characteristic is associated with HeLa cells?

    <p>They were harvested from Henrietta Lacks in 1951.</p> Signup and view all the answers

    How do changes in regulatory protein concentrations affect the cell cycle?

    <p>They dictate the timing of the cell cycle progression.</p> Signup and view all the answers

    What is the primary outcome of mitosis in most organisms?

    <p>Formation of genetically identical daughter cells</p> Signup and view all the answers

    What occurs during meiosis that increases genetic diversity?

    <p>Crossing over between homologous chromosomes</p> Signup and view all the answers

    What is the role of checkpoints in the cell cycle?

    <p>To prevent cells from progressing through the cycle when conditions are unfavorable</p> Signup and view all the answers

    What are haploid cells in humans?

    <p>Sperm and egg cells containing half the chromosome number</p> Signup and view all the answers

    How do plant and animal cells differ during cytokinesis?

    <p>Animal cells use a cleavage furrow, while plant cells form a cell plate</p> Signup and view all the answers

    What happens during the cell cycle that leads to the production of non-identical daughter cells?

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

    Which statement about chromosomes in eukaryotic cells is accurate?

    <p>Eukaryotic chromosomes consist of chromatin that condenses during cell division</p> Signup and view all the answers

    What are somatic cells in multicellular eukaryotes primarily responsible for?

    <p>Repair and growth of tissues</p> Signup and view all the answers

    What is the basic definition of the cell cycle?

    <p>The series of events that take place in a cell leading to its division</p> Signup and view all the answers

    Which statement correctly distinguishes asexual from sexual reproduction?

    <p>Asexual reproduction produces identical offspring, while sexual reproduction leads to genetic variation</p> Signup and view all the answers

    What is the primary difference between asexual and sexual reproduction?

    <p>Sexual reproduction involves the fusion of gametes.</p> Signup and view all the answers

    What type of cells are gametes?

    <p>Haploid cells with half the number of chromosomes.</p> Signup and view all the answers

    What is the diploid number of chromosomes in human somatic cells?

    <p>46</p> Signup and view all the answers

    What occurs during meiosis II?

    <p>Sister chromatids are separated.</p> Signup and view all the answers

    Which of the following describes homologous chromosomes?

    <p>They are similar in length and shape.</p> Signup and view all the answers

    What is a zygote?

    <p>A fertilized egg with one set of chromosomes from each parent.</p> Signup and view all the answers

    What biological process results in genetic variation during sexual reproduction?

    <p>Crossover during meiosis</p> Signup and view all the answers

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

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

    Which statement is true regarding the differences between mitosis and meiosis?

    <p>Meiosis results in cells that differ genetically from the parent.</p> Signup and view all the answers

    At what point in cellular division does crossing over occur?

    <p>In prophase I</p> Signup and view all the answers

    Which cell type undergoes meiosis to produce gametes?

    <p>Diploid cells</p> Signup and view all the answers

    What is the role of mitosis in the human life cycle?

    <p>To create somatic cells from the zygote.</p> Signup and view all the answers

    Which chromosomes determine the sex of a human?

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

    What role do cohesins play during cell division?

    <p>They attach sister chromatids along their lengths.</p> Signup and view all the answers

    What is the primary event during the S phase of interphase?

    <p>DNA replication occurs.</p> Signup and view all the answers

    Where are centromeres located on a duplicated chromosome?

    <p>At the narrow waist of the chromosome.</p> Signup and view all the answers

    During which phase of mitosis do cohesins get cleaved, allowing sister chromatids to separate?

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

    What is the function of the mitotic spindle?

    <p>To control chromosome movement during mitosis.</p> Signup and view all the answers

    In what cellular structure do microtubules assemble in animal cells during mitosis?

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

    What best describes the metaphase stage of mitosis?

    <p>Chromosomes are aligned at the metaphase plate.</p> Signup and view all the answers

    What is formed during cytokinesis in plant cells?

    <p>Cell plate</p> Signup and view all the answers

    What happens during the G2 phase of interphase?

    <p>Cell continues to grow and prepares for mitosis.</p> Signup and view all the answers

    Which structure is responsible for jerking chromosomes back and forth during prometaphase?

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

    What occurs during telophase?

    <p>Nuclear envelope reappears and chromosomes decondense.</p> Signup and view all the answers

    Which phase marks the beginning of the mitotic phase in the cell cycle?

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

    Which of the following is an event that occurs in anaphase?

    <p>Sister chromatids are pulled toward opposite poles.</p> Signup and view all the answers

    How does cytokinesis differ between animal and plant cells?

    <p>Plant cells form cell plates; animal cells form cleavage furrows.</p> Signup and view all the answers

    Study Notes

    Learning Objectives

    • Understand the functions of cellular division and the organization of genetic material in chromatin/chromosomes
    • Define key chromosome/genetic material terminology
    • Understand the major phases and processes occurring in the cell cycle during mitosis
    • Explain how the mitotic spindle contributes to chromosomal movement in all phases of mitosis
    • Understand the difference between animal and plant cell cytokinesis
    • Understand why cellular checkpoints are important and what happens when they malfunction
    • Explain how genetic material is passed through generations
    • Understand chromosomal numbers in humans, haploid vs diploid cells, and examples in the body, including the human life cycle
    • Describe the differences between asexual and sexual reproduction
    • Explain the major outcomes of meiosis, major phases of meiosis I and meiosis II, and how genetic diversity occurs
    • Compare and contrast mitosis and meiosis

    Cellular Division

    • Organisms reproduce through cell division
    • Cell division is the basis of the continuity of life

    Functions of Cellular Division

    • In unicellular organisms, cell division reproduces the entire organism
    • In multicellular organisms, cell division is responsible for: -Development from a fertilized egg -Growth -Repair

    Introducing the Cell Cycle

    • Cell division is an integral part of the cell cycle
    • The cell cycle describes the life of a cell from its formation to its own division
    • Most cell division results in two daughter cells with identical genetic information
    • The exception is meiosis, which creates non-identical daughter cells, including sperm and egg cells

    Cellular Organization of the Genetic Material

    • Genome: all the DNA in a cell
    • A genome can consist of:
      • A single DNA molecule (common in prokaryotic cells)
      • A number of DNA molecules (common in eukaryotic cells)
    • DNA molecules are packaged into chromosomes

    Cellular Organization of the Genetic Material (Eukaryotic Chromosomes)

    • Chromatin: a complex of DNA and protein (histones) that condenses during cell division
    • Every eukaryotic species has a characteristic number of chromosomes in each cell nucleus
    • Eukaryotic chromosomes consist of chromatin

    Distribution of Chromosomes During Eukaryotic Cell Division

    • In preparation for cell division, DNA is replicated, and the chromosomes condense
    • Each duplicated chromosome has two sister chromatids joined together at the centromere
    • Cohesins: protein complexes that attach sister chromatids
    • Centromeres are located on each sister chromatid

    The Two Major Phases of the Cell Cycle

    • Interphase (G1, S, and G2): -Cell growth and copying of chromosomes in preparation for cell division
      • About 90% of cell cycle
      • G1 phase: First gap, cells increase in size
      • S phase: Synthesis, DNA replication occurs
      • G2 phase: Second gap, cells continue to grow, ready for mitosis
    • Mitotic phase (mitosis and cytokinesis): -Mitosis: the division of the genetic material in the nucleus
      • Cytokinesis: the division of the cytoplasm

    Mitosis Consists of 5 Stages

    • Prophase
    • Prometaphase
    • Metaphase
    • Anaphase
    • Telophase and Cytokinesis

    G2 of Interphase

    • A nuclear envelope encloses the nucleus
    • Two centrosomes have formed
    • Chromosomes duplicated in S phase cannot be seen because they have not condensed

    Prophase

    • Chromatin fibers tightly coil into discrete chromosomes, becoming visible
    • Duplicated chromosomes appear as two sister chromatids
    • Mitotic spindle begins to form
    • Centrosomes move away from each other

    Prometaphase

    • Nuclear envelope fragments, chromosomes are even more condensed
    • Microtubules from each centrosome invade the nuclear area
    • Kinetochore: protein structure at the centromere on each sister chromatid
    • Some microtubules become kinetochore microtubules, jerking chromosomes back and forth
    • Non-kinetochore microtubules elongate the cell

    Metaphase

    • Centrosomes now at opposite poles of the cell
    • Chromosomes arrive at the metaphase plate
    • An imaginary plane at the middle of the cell
    • Centromeres lie at the metaphase plate
    • Kinetochore of each sister chromatid attaches to kinetochore microtubules

    Anaphase

    • Shortest phase of mitosis
    • Cohesins between chromatids are cleaved, allowing each pair to separate
    • Two new daughter chromosomes move towards opposite poles
    • Centromeres lead because microtubules are attached to kinetochores (at the centromere)

    Telophase and Cytokinesis

    • Telophase:
      • Two daughter nuclei form
      • Nuclear envelope reappears
      • Chromosomes start to decondense
      • Mitosis is now complete, creating two genetically identical nuclei
    • Cytokinesis:
      • Division of the cytoplasm
      • Involves formation of a cleavage furrow, pinching cell in two (animal cells)

    Animal Cell Mitosis (time-lapse)

    BioFlix Animation: Mitosis

    Plant cell cytokinesis in onion root cells

    The Mitotic Spindle:

    • A structure made of microtubules that controls chromosome movement
    • In animal cells, assembly of spindle microtubules begins in the centrosome
    • The microtubule-organizing center (MTOC)
      • The centrosome replicates during interphase
      • Two centrosomes migrate to opposite ends of the cell during prophase and prometaphase

    The Mitotic Spindle

    • During prometaphase, some spindle microtubules attach to the kinetochores of chromosomes and begin to move the chromosomes
    • Kinetochores are protein complexes associated with centromeres
    • At metaphase, all chromosomes line up at the metaphase plate

    The Mitotic Spindle

    • In anaphase, cohesins are cleaved by an enzyme called separase
    • Sister chromatids separate and move along the kinetochore microtubules towards opposite ends of the cell
    • Microtubules shorten by depolymerizing at their kinetochore ends

    The Mitotic Spindle

    • Non-kinetochore microtubules from opposite poles overlap and push against each other, elongating the cell
    • At the end of anaphase, duplicate groups of chromosomes arrive at opposite ends of the elongated cell
    • Cytokinesis beings during anaphase or telophase, and the spindle eventually disassembles

    Comparing Cytokinesis in Animal and Plant Cells

    • In animal cells, cytokinesis occurs by a process known as cleavage, forming a cleavage furrow
      • Contractile ring of microfilaments
    • In plant cells, a cell plate forms during cytokinesis
      • Vesicles contain cell wall material derived from the Golgi apparatus

    Comparing Cytokinesis in Animal and Plant Cells (Diagram)

    How Do Cells Know When to Divide?

    • Cell cycle is tightly regulated
    • Some cells divide frequently (e.g., intestinal cells) and others rarely (e.g., neuronal cells)
    • Cancerous cells can escape usual controls and proliferate

    Molecular Clocks

    • The cell cycle is driven by specific chemical signals present in the cytoplasm
    • The cell cycle is directed by a distinct cell-cycle control system, which is similar to a clock
    • The clock has specific checkpoints where the cell cycle stops until a go-ahead signal is received

    Cellular Checkpoints

    • Changes in regulatory protein concentrations drive the cell cycle
    • Three important checkpoints are those in the G1, G2, and M phases
    • If the cell does not receive the go-ahead signal, it will exit the cycle and switch to a non-dividing state called the G0 phase

    Cancer Cells

    • Have lost their cell cycle checkpoints (due to internal and external factors)
    • Can become immortal, dividing continuously provided they have enough nutrients
    • HeLa cells: Harvested from a woman named Henrietta Lacks in 1951

    Chapter 13: Meiosis

    Meiosis

    • A special type of cell division that produces sperm and egg cells (gametes)
    • Produces non-identical daughter cells
    • Heredity: the transmission of traits from one generation to the next
    • Variation is demonstrated by the differences in appearance that offspring show from parents and siblings
    • Genetics is the scientific study of heredity and variation

    Inheritance of Genetic Material

    • Offspring inherit genetic material from parents → genes
    • Genes are the units of heredity made up of segments of DNA
    • Locus (plural, loci): A gene's specific position along a chromosome
    • Genes are passed to the next generation via reproductive cells called gametes (sperm and eggs)

    Inheritance of Genetic Material

    • Offspring acquire genes from parents by inheriting chromosomes
    • Most DNA is packaged into chromosomes
    • Human somatic cells have 23 pairs of chromosomes (total of 46)
    • Karyotype: an ordered display of the pairs of chromosomes from a cell

    Comparison of Asexual and Sexual Reproduction

    • In asexual reproduction, a single individual passes all its genes to its offspring without the fusion of gametes
    • A clone is a group of genetically identical individuals from the same parent
    • In sexual reproduction, two parents give rise to offspring that have unique combinations of genes inherited from the two parents

    Cellular Organization of the Genetic Material (Somatic and Gametes)

    • Somatic cells: non-reproductive cells with two sets of chromosomes (diploid)
    • Gametes: reproductive cells (sperm and eggs) with half the number of chromosomes (haploid)
    • In an unfertilized egg, the sex chromosome is X
    • In a sperm cell, the sex chromosome may be either X or Y

    Sets of Chromosomes in Human Cells

    • Human somatic cells have 23 pairs of chromosomes
    • The sex chromosomes are called X and Y
    • Human females have a homologous pair of X chromosomes (XX)
    • Human males have one X and one Y chromosome
    • The remaining 22 pairs of chromosomes are called autosomes
    • Aneuploidy: abnormal number of chromosomes

    Sets of Chromosomes in a Cell

    • The two chromosomes in each pair are called homologous chromosomes or homologs
    • Chromosomes in a homologous pair are the same length and shape and carry similar genes
    • Each pair includes one chromosome from each parent
    • Non-sister chromatids: chromatids in a homologous pair, one from each parent

    Sets of Chromosomes in a Cell

    • The 46 chromosomes in a human somatic cell are two sets of 23
    • Each replicated chromosome consists of two identical sister chromatids
    • A diploid cell has two sets of chromosomes

    Behavior of Chromosome Sets in the Human Life Cycle

    • A life cycle is the generation-to-generation sequence of stages in the reproductive history of an organism
    • Fertilization: the union of gametes
    • The fertilized egg is called a zygote, having one set of chromosomes from each parent
    • The zygote develops into an adult form by mitosis in somatic cells

    Behavior of Chromosome Sets in the Human Life Cycle

    • At sexual maturity, the ovaries and testes produce haploid gametes
    • Gametes are the only human cells produced by meiosis, not mitosis
    • Meiosis results in one set of chromosomes in each gamete
    • Fertilization and meiosis alternate in sexual life cycles to maintain chromosome number, a common feature of sexually reproducing organisms

    Animal Life Cycles

    • Gametes are the only haploid cells in animals
    • Produced by meiosis and don't divide again before fertilization
    • Gametes fuse to form a diploid zygote, which develops into a multicellular organism by mitosis
    • Only diploid cells can undergo meiosis

    Meiosis

    • Meiosis reduces the number of chromosome sets from diploid (2n) to haploid (n)
    • Like mitosis, meiosis is preceded by the replication of chromosomes
    • Meiosis takes place in two consecutive cell divisions called meiosis I and meiosis II
    • Meiosis I and II follow steps similar to mitosis (PMAT)

    Meiosis

    • The two cell divisions result in four daughter cells, rather than two in mitosis
    • Each daughter cell has only half as many chromosomes as the parent cell
    • Crossing over during meiosis allows for genetic recombination

    Meiosis

    Events Unique to Meiosis, Occurring in Meiosis I

    • Synapsis and crossing over in prophase I
    • Homologous pairs at the metaphase plate
    • Separation of homologs during anaphase I
    • Telophase I creates two haploid cells

    Meiosis II

    • Meiosis II is similar to mitosis
    • During another round of cell division, the sister chromatids separate
    • Produces four haploid daughter cells

    Results of Meiosis

    • Chromosomes duplicate before meiosis
    • Pairs of homologs and crossover at chiasma allows for genetic recombination
    • The chromatids are sorted into four haploid daughter cells

    Comparing Mitosis and Meiosis

    • Mitosis:
      • Conserves the number of chromosome sets
      • Produces cells that are genetically identical to the parent cell
    • Meiosis:
      • Reduces the number of chromosomes sets from two (diploid) to one (haploid)
      • Produces cells that differ genetically from each other and from the parent cell

    Comparing Mitosis and Meiosis (Diagram)

    Comparing Mitosis and Meiosis (Summary)

    • Mitosis:
      • DNA replication occurs during interphase before mitosis begins
      • One division; including prophase, prometaphase, metaphase, anaphase, and telophase
      • No synapsis of homologous chromosomes
      • Two daughter cells; genetically identical to parent cell
    • Meiosis:
      • DNA replication occurs during interphase before meiosis I begins
      • Two divisions; each includes prophase, metaphase, anaphase, and telophase
      • Synapsis of homologous chromosomes occurs during prophase I
      • Four daughter cells; genetically different from each other and the parent cell
      • Enable multicellular animal or plant (gametophyte or sporophyte) to arise from a single cell; produces cells for growth, repair, and sexual reproduction; produces gametes in the gametophyte plant

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    Test your knowledge on key concepts in genetics with this quiz. Questions cover meiosis, chromosomal structure, heredity, and genetic variation, providing a comprehensive overview of genetic principles. Perfect for students studying biology at various levels.

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