Lesson 20: Meiosis Flashcards
What is synapsis?
The homologous chromosomes come together
What is a tetrad?
The synapse pairs (one chromosome inherited from the mother and one from the father)
What is a chiasma?
An X-shaped structure.
–The point at which the homologous chromosomes overlap, where chromosomes exchange segments resulting in genetic variability in daughter cells
What happens during Prophase 1?
Synapsis and chromosome segment exchange
What happens during Metaphase 1?
Chromosome pairs line up along the centerline of the cell DOUBLE-FILE (because the chromosome pairs are still synapsed)
What happens during Anaphase 1?
Synapsed chromosomes separate. Chromosome pairs move to opposite ends of the cell (homologous chromosomes are separated as opposed to the separation of sister chromatids in Mitosis)
What happens during Telophase 1?
Chromosomes reach the poles of the cell
How do you count the number of chromosomes in a cell?
By counting the number of centromeres present in the cell
What happens during Prophase 2?
Duplicated chromosomes begin to move to the middle of the cell
What happens during Metaphase 2?
The chromosomes line up along the center line of the cell
What happens during Anaphase 2?
The sister chromatids move to opposite ends of the cell becoming independent chromosomes
What happens during Telophase 2?
The chromosomes reach the poles of the cell
What type of division is Meiosis 1 known as?
A reduction division because it results in a reduction in the number of chromosomes
What is the major difference between Mitosis and Meiosis 2?
In Meiosis 2 the cell only has 1 complete set of chromosomes (is haploid), whereas in Mitosis there are two complete sets of chromosomes (diploid)
Is Meiosis 2 considered a reduction division?
NO, only in Meiosis 1 are the number of chromosomes divided in half
What happens during Prophase 1 in both Meiosis and Mitosis?
Chromosomes become visible
How many cells result from Meiosis?
4
How many cells result from Mitosis?
2
What is segregation?
The process by which homologous pairs become segregated (there is a 50% chance that a daughter cell will inherit the maternal chromosome and a 50% chance that it will inherit the paternal chromosome)
What is crossing over or recombination?
The process by which segments of a chromosome are exchanged with its corresponding homologous (non-sister chromatid) chromosome
Suppose the gene for protein XYZ is on chromosome 17. How many copies of gene XYZ are present in a cell in the G1 phase? At the beginning of mitosis?
- -Two. One on each chromosome of the homologous pair
- -Four. One on each sister chromatid of each chromosome of the homologous pair
What main process happens during Meiosis 1?
Homologous chromosomes are separated
What main process happens during Meiosis 2?
Sister chromatids are separated
Suppose the gene for protein XYZ is on chromosome 17. How many copies of gene XYZ are present in a cell in G1 phase?
Two. One on each chromosome of the homologous pair (one from each parent)
What is the formula used to calculate the number of potential combinations for a given chromosome number (assuming no crossing over)?
2^n, where n=number of homologous pairs
After telophase 1 of Meiosis, what is the chromosomal makeup of each daughter cell?
Haploid; and the chromosomes are each composed of two chromatids
What is Meiosis?
The process in the nucleus which divides the chromosome number in half
What are homologous chromosomes?
Chromosomes which contain genes which regulate the same phenotypes, but may or may not have the same genotype
–One chromosome from the father and one from the mother
