Chapter 13: Meiosis and Sexual Life Cycles

Question 1

Distinguish between haploids and diploids.

Answer 1

Haploid: Contain one set of chromosomes, are involved in sexual reproduction, and contain half the number of chromosomes found in diploid cells. (Sperm, Ova)

Diploid: Contain two sets of chromosomes, are not involved in sexual reproduction, and are mostly found in body tissues. (Somatic cells: skin cells, muscle cells)

Question 2

Distinguish between somatic cells and gametes.

Answer 2

Somatic Cells: Diploid cells found in multicellular organisms that undergo mitosis. They make up the tissues, organs, and other structures of the body.

Gametes: Haploid cells involved in sexual reproduction that undergo meiosis. Male gametes are sperm cells (23), female gametes are egg cells or ova (23).

Question 3

How do gametes give rise to more cells?

Answer 3

By fertilizing and making zygotes (the cell formed by the fusion of two gametes during fertilization)

Question 4

Distiguish between Autosomes and Sex Chromosomes (X-linked).

Answer 4

Autosomes: Non-sex chromosomes that are found in both males and females that determine an organisms traits. (1-22)

Sex Chromosomes: Determine an individual’s sex. Females have two X chromosomes (XX), while males have one X and one Y (XY).

Question 5

What is a karyotype?

Answer 5

A visual representation of the chromosomes in the nucleus of a cell, arranged in a specific order based on size, shape, and other characteristics

Question 6

Define Meiosis.

Answer 6

Cell division that occurs in sexually reproducing organisms to produce gametes with half the number of chromosomes as the parent cell, resulting in 4 haploid daughter cells that are all genetically unique.

Question 7

Define homologous chromosomes.

Answer 7

Pairs of chromosomes that contain genes for the same traits, arranged in the same order.

Question 8

Describe the events that characterize each phase of Meiosis I.

Answer 8

Prophase I: Homologous chromosomes pair up (synapsis) and crossing over occurs (certain sections of chromatids are exchanged, leading to genetic recombination).

Metaphase I: Homologous chromosome pairs line up at the metaphase plate, with one chromosome from each pair facing opposite poles of the cell.

Anaphase I: Homologous chromosomes separate and move toward opposite poles of the cell, pulled by spindle fibers.

Telophase I: Chromosomes arrive at opposite poles, and cytokinesis typically occurs, resulting in two haploid daughter cells, each with half the number of chromosomes as the original cell.

Question 9

Describe the events that characterize each phase of Meiosis II.

Answer 9

Prophase II: If the nuclear envelope broke down during telophase I, it reforms around the chromosomes. Chromosomes condense again, and a new spindle apparatus forms.

Metaphase II: Chromosomes line up at the metaphase plate of each haploid daughter cell.

Anaphase II: Sister chromatids separate and move toward opposite poles of the cell.

Telophase II: Chromatids arrive at opposite poles, and nuclear envelopes re-form around them. Cytokinesis then occurs, resulting in a total of four haploid daughter cells, each with a single set of chromosomes.

Question 10

Compare and contrast Mitosis and Meiosis.

Answer 10

Similarities:
1. Both start with cell growth and DNA replication.
2. Both processes involve the division of a single cell into multiple daughter cells.
3. Both processes involve the formation of a mitotic spindle, which helps separate chromosomes.

Differences:
1. Number and uniqueness of daughter cells and chromosomes produced (mitosis - 2 identical, meiosis 4 unique)
2. What they are involved in (mitosis - growth, repair, asexual reproduction. meiosis - sexual reproduction and genetic variation)

Question 11

How many chromoSOMES…
(a) before interphase
(b) after interphase
(c) after meiosis I
(d) after meiosis II

Answer 11

(a) 46
(b) 46
(c) 23
(d) 23

Question 12

How many chromaTIDS…
(1) before interphase
(2) after interphase
(3) after meiosis I
(4) after meiosis II

Answer 12

(a) 46
(b) 92
(c) 46
(d) 23

Question 13

Describe three events that occur during meiosis I but not mitosis.

Answer 13

1. Synapsis and Crossing over in prophase I: Homologous chromosomes pair up (synapsis) and crossing over occurs (certain sections of chromatids are exchanged, leading to genetic recombination).
2. Independent Assortment: Homologous pairs of chromosomes randomly align at the metaphase plate without being dependent by the alignment of other pairs.
3. Reductional DIvision: During anaphase I, homologous chromosomes (instead of sister chromatids) separate and migrate to opposite poles of the cell.

Question 14

Name and explain the three events that contribute to genetic variation in sexually reproducing organisms.

Answer 14

1. Independent assortment: The maternal and paternal chromosomes of each homologous pair can align in different orientations relative to each other, resulting in the random distribution of maternal and paternal chromosomes leading to a multitude of possible combinations of chromosomes in gametes.
2. Crossing over (recombination): Portions of chromatids are swapped between non-sister chromatids of homologous chromosomes, resulting in new combinations of alleles on the chromatids and increasing genetic diversity by creating chromosomes with combinations of new alleles
3. Random fertilization: When gametes combine during fertilization, the specific sperm that fertilizes a particular egg is a matter of chance. The random combination produces a genetically unique zygote.

Question 15

What are the results of genetic variation in evolution?

Answer 15

The result of genetic variation in evolution is natural selection as favored by the environment.

Question 16

What is nondisjunction?

Answer 16

When a cell can receive too many or too few chromosomes in seperation. Contributes to genetic disorders.