Chapter 11 - Sexual Reproduction & Meiosis

Question 1

meiosis

Answer 1

Type of cell division which reduces the chromosome number by half. Occurs in all sexually reproducing eukaryotes (both single-celled and multicellular) including animals, plants, and fungi. DNA replication is followed by two rounds of cell division to produce four daughter cells with half the number of chromosomes as the original parent cell.

Question 2

somatic cell

Answer 2

Any cell of the body except sperm and egg cells. Somatic cells are diploid, meaning that they contain two sets of chromosomes, one inherited from each parent.

Question 3

sexual reproduction

Answer 3

A biological process that creates a new organism by combining the genetic material of two organisms in a process that starts with meiosis.

Question 4

synaptonemal complex

Answer 4

A protein structure that forms between homologous chromosomes (two pairs of sister chromatids) during meiosis and is thought to mediate chromosome pairing, synapsis, and recombination.

Question 5

nondisjunction

Answer 5

The failure of homologous chromosomes or sister chromatids to separate properly during cell division.

Question 6

gamete

Answer 6

A mature sexual reproductive cell, as a sperm or egg, that unites with another cell to form a new organism.

Question 7

zygote

Answer 7

Cell formed when two gamete cells are joined by means of sexual reproduction. In multicellular organisms, it is the earliest developmental stage of the embryo.

Question 8

meiosis I

Answer 8

Prophase I, metaphase I, anaphase I, and telophase I. In meiosis I, chromosomes in a diploid cell resegregate, producing four haploid daughter cells. It is this step in meiosis that generates genetic diversity.

Question 9

prophase I

Answer 9

DNA replication precedes the start of meiosis I. During prophase I, homologous chromosomes pair and form synapses, a step unique to meiosis. The paired chromosomes are called bivalents, and the formation of chiasmata caused by genetic recombination becomes apparent. Chromosomal condensation allows these to be viewed in the microscope. Note that the bivalent has two chromosomes and four chromatids, with one chromosome coming from each parent.

Question 10

prophase II

Answer 10

The first stage in meiosis II wherein the nucleolus and nuclear envelope disintegrate whereas the chromatin condenses forming shorter, thicker chromatid.

Question 11

metaphase I

Answer 11

Homologous chromosomes (four chromatids) align at the metaphase plate. The orientation is random, with either parental homologue on a side. This means that there is a 50-50 chance for the daughter cells to get either the mother’s or father’s homologue for each chromosome.

Question 12

metaphase II

Answer 12

Each of the two daughter cells produced by the first meiotic division (which are known as secondary germ cells), the spindle again draws the chromosomes to the metaphase plate. This time, unlike metaphase I, the two kinetochores of each centromere bind to spindle fibers from opposite poles (as in mitotic metaphase). This results in separation of the sister chromatids of each chromosome during the next phase of meiosis, anaphase II.

Question 13

aneuploid gamete

Answer 13

Having a chromosome number that is not an exact multiple of the haploid number, caused by one chromosome set being incomplete.

Question 14

egg

Answer 14

A structure which the females of certain animal species lay as a means of reproduction, it contains a fertilized zygote and nutrition in the form of yolk for the developing offspring.

Question 15

fertilization

Answer 15

(Also known as syngamy). The fusion of gametes to initiate the development of a new individual organism. In animals, the process involves the fusion of an ovum with a sperm, which eventually leads to the development of an embryo.

Question 16

meiosis II

Answer 16

Prophase II, metaphase II, anaphase II, and telophase II. Begins with two haploid (n = 2) cells and ends with four haploid (n = 2) cells.

Question 17

crossing over

Answer 17

The exchange of genetic material between homologous chromosomes that results in recombinant chromosomes. It is one of the final phases of genetic recombination, which occurs during prophase I of meiosis during a process called synapsis.

Question 18

anaphase I

Answer 18

Chiasmata separate. Chromosomes, each with two chromatids, move to separate poles. Each of the daughter cells is now haploid (23 chromosomes), but each chromosome has two chromatids.

Question 19

anaphase II

Answer 19

The sister chromatids of each chromosome separate and move toward opposite poles. Once they are no longer connected, the former chromatids are called unreplicated chromosomes. As the chromosomes are dragged along by the spindle apparatus, their arms can be seen dragging along behind so that the chromosomes form V-shapes. The poles themselves move further apart as cytokinesis begins and the cell lengthens

Question 20

sperm

Answer 20

The male gamete or reproductive cell involved in sexual reproduction. It is produced by a male organism that unites with the egg of a female organism forming a zygote.

Question 21

syngamy

Answer 21

The fusion of two cells, or of their nuclei, in reproduction.

Question 22

synapsis

Answer 22

The pairing of two homologous chromosomes that occurs during meiosis. It allows matching-up of homologous pairs prior to their segregation, and possible chromosomal crossover between them. Synapsis takes place during prophase I of meiosis.

Question 23

cell biology

Answer 23

A point of overlap of paired chromatids at which fusion and exchange of genetic material take place during prophase of meiosis.

Question 24

telophase I

Answer 24

At each pole, during this stage, there is a complete haploid set of chromosomes (but each chromosome still has two sister chromatids). A cleavage furrow appears, and by the end of this stage the parent cell has divided into two daughter cells. This separation of the cytoplasm is called cytokinesis. In some organisms nuclear envelopes appear briefly at this point (this intermediate stage is called interkinesis). But in others the daughter cells begin immediately to prepare for the second meiotic division.

Question 25

telophase II

Answer 25

The chromosomes reach opposite poles, cytokinesis occurs, the two cells produced by meiosis I divide to form four haploid daughter cells, and nuclear envelopes (white in the diagram) form. When the two cells are entirely separated and their nuclear membranes are fully formed, meiosis will be complete.