02 Meiosis & Fertilisation Flashcards
What is meiosis?
the formation of sec cells in the male testes and female ovaries
How is meiosis similar to mitosis?
New cells are formed
How is meiosis different from mitosis?
New cells have 23 chromosomes and they’re genetically varied
Sperm and sex cells are haploid. What does this mean?
It means that each has 23 chromosomes (n) which come together to form a diploid zygote (2n) with 46 chromosomes
Why are unique individuals made?
Because each gamete is genetically different
How many times does meiosis go through pmat?
2 times
What happens in meiosis 1?
Genetic variation is created, and the # of chromosomes is halved from 46 to 23
What happens in meiosis 2?
Sister chromatids are separated
Name 4 things that happen in prophase 1
chromatin condenses into x-shaped chromosomes, and the nuclear membrane disappears. Centromeres move towards opposite sides of the cell and form spindle fibers. Crossing over occurs
What is crossing over?
Homologous chromosomes overlap and randomly exchange genetic information
What happens in metaphase 1?
Homologous chromosomes line up side-by-side at the centre of the cell
What is the law of independent assortment?
It states that a resulting gamete’s chromosomes can differ depending on how homologous chromosomes line up during metaphase 1
Name 2 things that happen in Anaphase 1
The homologous chromosomes are pulled apart towards opposite sides of the cell, and the number of chromosomes are halved (2n to n)
Name 4 things that happen in telophase 1 and cytokinesis
Nuclear membrane starts to reform (not fully). Chromosomes start to loosen back to chromatin. Resulting (n) cells’ membranes cleave/split. Results in 2 daughter cells
What is meiosis 2 conducted with?
haploid cells with 23 chromosomes
how many chromosomes does meiosis 2 result in?
23
What happens is prophase 2?
Chromatin re-condenses into fully x-shaped chromosomes. nuclear membrane disappears again. Centrosomes move toward opposite sides of the cell and form spindle fibers
What happens in metaphase 2?
23 chromosomes line up single file at the centre of the cell
What happens in anaphase 2?
sister chromatids pull apart towards opposite sides of the cell
What happens in telophase 2?
Nuclear membrane reforms, chromosomes loosen back to chromatin, and resulting n cells’ membrane cleave. 4 egg/sperm cells are formed
What are all the ways in which meiosis creates genetically varied sex cells?
Crossing over, independent assortment during m1, random joining of sperm and egg cells
What is spermatogenesis?
The formation of sperm cells in the male testes, results in 4 sperm cells
What is oogenesis?
The formation of egg cells
When are primary oocytes in a woman formed?
prenatally
