Meiosis Flashcards
What is formed when an egg cell and a sperm cell fuse together during fertilisation?
A zygote.
What is a haploid cell?
Cells that have half the number of chromosomes than a normal cell.
Where in the body does meiosis occur?
In the reproductive organs
How many divisions are involved in meiosis?
2 divisions.
Meiosis l and Meiosis ll
What happens in a reduction division?
The chromosome number is halved.
What is a homologous pair of chromosomes?
A pair of chromosomes, one that is paternal and one maternal. They are the same size and have the same genes in the same loci.
What are alleles?
Different versions of the same gene.
What happens in prophase l?
Chromosomes condense.
Chromosomes arrange themselves into homologous pairs and they cross over.
Centrioles move to opposite ends of the cell.
Nuclear envelope condenses.
What happens in metaphase l?
Homologous pairs line up along the metaphase plate INDEPENDENTLY and RANDOMLY.
They attach to the spindle by their centromeres.
What happens in anaphase l?
Spindles contract separating the homologous pair.
One chromosome goes to each end.
What happens in telophase l?
Nuclear envelope forms around each group of chromosomes.
What happens in the first cytokinesis?
The cell divides into two, forming 2 haploid daughter cells.
What is produced at the end of meiosis?
Gametes (sex cells) for sexual reproduction.
What is a bivalent?
When homologous pairs of chromosomes come together and cross over. Bits of the chromatids swap over forming different combinations of alleles.
What happens in metaphase ll?
Chromosomes align along the equator.
What happens in anaphase ll?
The sister chromatids are separated as the spindles contract.
What happens in telophase ll?
Nuclear envelope forms around the chromatids.
What happens in the second cytokinesis?
The two cells divide again, forming 4 genetically different haploid daughter cells (gametes).
What two events lead to genetic variation in meiosis?
Crossing over and independent assortment.
How does crossing over of chromatids lead to genetic variation?
When they cross over, the chromatids in each cell end up with a different set of alleles. So each is different.
How does independent assortment lead to genetic variation?
When the chromosomes line up in metaphase l, it is random which way they line up. The final daughter cells will have different combinations of chromosomes to each other.
What happens in prophase ll?
The centrioles move to opposite ends.
Spindles form.
Nuclear envelopes break down in both cells.
