Flashcards in 8.4 Meiosis And Genetic Variation Deck (15):
What two components make up the division of a cell?
1. The division of the nucleus
2. The division of the cell as a whole
In which ways does the division of the nucleus of cells occur?
1. Mitosis: produces two daughter nuclei with the same number of chromosomes as the parent cell.
2. Meiosis: produces four daughter nuclei, each with half the number of chromosomes as the parent cell.
Why is halving the number of chromosomes necessary in meiosis?
In order to maintain a constant number of chromosomes in the adult species.
How many chromosomes does a human diploid cell have?
46 (23 homologous pairs)
How many chromosomes does a human haploid cell have?
How is the diploid number restored at fertilisation?
Two haploid gametes fuse.
Describe the two nuclear divisions of meiosis.
1. In meiosis 1, the homologous chromosomes pair up and their chromatids wrap around each other.
Crossing over occurs where equivalent proportions of these chromatids are exchanged.
The homologous pairs separate, with one chromosome from each pair going into one of the two daughter cells
2. In meiosis 2, the chromatids move apart.
How does meiosis produce genetic variation among offspring to allow an organism to adapt and survive in a changing world?
Independent segregation of homologous chromosomes
Recombination of homologous chromosomes by crossing over
Describe independent segregation.
In meiosis 1 each chromosome lines up alongside its homologous partner - arranged randomly.
One of each pair will pass to each daughter cell, this depends on how the pairs are lined up in the parent cell.
Since the pairs are lined up at random, the combination of chromosomes that goes into the daughter cell at meiosis 1 is also random. This is independent segregation.
Genetic combinations are produced as a result of the different alleles on the homologous chromosomes. E.g brown eyes and blood type A
What is the saying for meiosis?
Hi dick cocks suck sick
How does crossing over occur?
The chromatids of each pair become twisted around each other
Tensions are created and portions of the chromatids break off
The homologous pairs rejoin
In this way new genetic combinations are produced
During crossing over, broken-off portions of chromatid recombine with another chromatid. What is this process called?
Crossing over increases...