Meiosis (Pre-IB SC 9)
What are gametes?
Reproductive cells of an animal or plant.
Names of gametes in animal cells?
Female gamete: Egg cells
Male gamete: Sperm cells
What are homologous chromosomes?
Homologous pair of chromosomes consists of one chromosome from each parent. They carry the same genes, but they may have different EXPRESSIONS of that gene.
Sex determining chromosomes are the _______ pair.
23rd
How does meiosis start, diploid or haploid?
The cells which produce eggs and the cells which produce sperm are DIPLOID.
State: What is meiosis?
A process of REDUCTION DIVISION in which the number of chromosomes per cell is cut in HALF through the SEPERATION of HOMOLOGOUS CHROMOSOMES.
In prophase 1 meiosis 1, each chromosome pairs with its corresponding homologous chromosome. What does this form?
A tetrad: 4 chromatids together.
What is crossing over, what phase does it happen in?
In meiosis 1, prophase 1, crossing over = the exchange of genetic information (genes) between segments of homologous chromosomes.
What is independent assortment?
When homologous chromosomes are randomly distributed to daughter cells, and different chromosomes segregate independently of other pairs. This leads to genetic variation!
What is the result of crossing over?
Crossing over results in non-identical chromatids that comprise the genetic materical of gametes. Because of this, the millions of sperm and egg cells produced in an organism are different from each other.
What happens in meiosis 1, metaphase 1?
The tetrads (homologous PAIRS) line up at the center of the cell.
What happens in anaphase 1, meiosis 1?
The tetrads break apart and are pulled away to opposite sides of the cells. The sister chromatids are still attatched to their centromeres.
What happens in telophase 1?
Now there are two newly formed nuclei, and meiosis 1 will end with two cells.
What is the result of meiosis 1?
Two haploid daughter cells
What happens in prophase 2, meiosis 2?
The pairs of sister chromatids begin moving towards the center, and the spindles are starting to form.
NO CROSSING OVER
What happens in metaphase 2, meiosis 2?
Chromosomes line up at the center.
What happens in anaphase 2, meiosis 2?
The chromatids seperate and move to opposite ends of the cell.
What happens in telophase 2, meiosis 2?
The nuclei reforms, and 4 new cells form. They are HAPLOID and DIFFERENT from each other.
What is the result of meiosis 2?
4 haploid daughter cells with combination of chromosomes from both parents.