Chapter 11 - Sexual Reproduction & Meiosis Flashcards
meiosis
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.
somatic cell
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.
sexual reproduction
A biological process that creates a new organism by combining the genetic material of two organisms in a process that starts with meiosis.
synaptonemal complex
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.
nondisjunction
The failure of homologous chromosomes or sister chromatids to separate properly during cell division.
gamete
A mature sexual reproductive cell, as a sperm or egg, that unites with another cell to form a new organism.
zygote
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.
meiosis I
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.
prophase I
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.
prophase II
The first stage in meiosis II wherein the nucleolus and nuclear envelope disintegrate whereas the chromatin condenses forming shorter, thicker chromatid.
metaphase I
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.
metaphase II
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.
aneuploid gamete
Having a chromosome number that is not an exact multiple of the haploid number, caused by one chromosome set being incomplete.
egg
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.
fertilization
(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.
meiosis II
Prophase II, metaphase II, anaphase II, and telophase II. Begins with two haploid (n = 2) cells and ends with four haploid (n = 2) cells.
crossing over
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.
anaphase I
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.
anaphase II
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
sperm
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.
syngamy
The fusion of two cells, or of their nuclei, in reproduction.
synapsis
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.
cell biology
A point of overlap of paired chromatids at which fusion and exchange of genetic material take place during prophase of meiosis.
telophase I
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.
