Meiosis Flashcards
(12 cards)
Define sister chromatids
Replicated DNA - genetically identical
Define homologous chromosomes
Two chromosomes that determine the same genetic characteristics but may have different alleles
Define gene
A section of DNA that codes for a polypeptide
Define locus
The position of a gene on a chromosome or DNA molecule
Define allele
One of the different forms of a particular gene
How do we calculate the possible combinations of each daughter cell after meiosis?
2^n
n = number of pairs of homologous chromosomes
How to calculate the number of possible chromosome combinations from two parents?
(2^n)^2
What are the two ways in which meiosis produces genetic variation?
- independent segregation of homologous chromosomes
- recombination of homologous chromosomes by crossing over
Describe independent segregation
As the chromosomes line up they do it randomly
Which one pair goes into the daughter cell is at random
The combination of chromosomes to go into the daughter cell is random
Independent segregation increases variation
Describe crossing over
When the chromosomes line up the chromatids of each pair twist around each other
Tension is created and pieces break off
The broken pieces rejoin with the chromatids of the homologous partner
Usually equivalent portions are exchanged
Crossing over increases variation
How does crossing over increase variation?
All gametes have a different combination of alleles on the chromosomes
Describe the process of meiosis
Late interphase - synapsis crossing over begin - semi-conservative replication
Prophase 1 - crossing over continues. Paired chromosomes condense
Metaphase 1 - homologous chromosomes line up double file
Anaphase / telophase 1 (1st division) - homologous chromosomes separate into haploid daughter cells
- sister chromatids remain joined
Metaphase 2 - chromosomes line up in single file in haploid cells
Anaphase / telophase 2 - sister chromatids separate into non-identical haploid cells
Meiosis produces haploid cells with new genetic combinations
