Stages of mieosis

Interphase

The same as mitotic interphase

G1

• The cell grows and develops mRNA and proteins for DNA synthesis

S

• Chromosomes are copied

G2

• The cell grows and checks for any mistakes and such

2n, 46 chromosomes, 92 chromatids (Diploid)

Prophase 1

• The nuclear membrane breaks down

• The DNA (Chromatin) condenses into chromosomes

• The chromosomes then pair with their homologous pair (same size and placing of genes)

• They create a tetrad shape

• Crossing over occurs (parts of each chromosome switching sides)

• Centrosomes begin to appear at different ends of the cell

Metaphase 1

• The homologous chromosomes line up across the middle of the cell (Metaphase plate)

• The Spindle fibres then attach to the centromeres

• The way they align is also random which introduces more genetic variation

How is genetic variation introduced in meiosis

• By crossing over which is the homologous chromosomes switching parts of their genetic code to each other while they are paired up

• By the order the chromosomes are aligned during metaphase since it is random

what is an Allele

A version of genes that could be inherited. Like

Anaphase 1

• The spindle fibers pull the homologous chromosomes to opposite poles of the cell

• The sister chromatids are still attached at the centromere

Telophase 1

• A new nuclear membrane forms around to 2 groups of DNA

• The chromosomes then decondense into chromatin again

• Spindle fibers disappear

• 2 nucleus are at opposite poles

Cytokinese 1

• A bunch of proteins called a contractile ring form around the equator of the cell and pinches the cytoplasm, creating a cleavage furrow until the cell divides

  n, 23 chromosomes, 46 chromatids (haploid)

Prophase 2

• The nuclear membrane dissolves and the chromatin reforms into chromosomes and spread out

• Centrosomes form and move to opposite poles of the cell

Metaphase 2

• The chromosomes move to the metaphase plate of the cell

• Spindle fibers attach to each sister chromatid of the chromosome

Anaphase 2

• The sister chromatids are pulled apart by the spindle fibers and are moved to the opposite poles

Telophase 2

• The nuclear membrane reforms around the chromosomes

• The sister chromatids unravel back into chromatin

Cytokinesis 2

• A bunch of proteins called a contractile ring form around the equator of the cell and pinches the cytoplasm, creating a cleavage furrow until the cell divides

  n, 23 chromosomes, 23 chromatids, (haploid)

Difference between males and females in meiosis

• The males create 4 equal size sperm cells

• The females create 1 large egg cell and 3 smaller cells

• The large cell is called the Ovum and the smaller ones are called polar bodies (They are byproducts and just die)

What would happen if mieosis occured without DNA replication

• 2 of the 4 cells created would have no genetic material

• But the good thing is that this wouldn’t happen because the G2 phase checks for mistakes like this

What would happen if the spindle fibers never attached during metaphase 1

• This would cause the cells to miss out on some genetic information

• This is because only some chromosomes would be on either side (whole homologous chromosomes would be on each side)

What would happen if sister chromatids were not pulled apart at anaphase 2

• This would cause the chance of both sister chromatids ending up in a cell

• This would cause some cells miss out on a full set of chromosomes

What would happen if cytokinesis 2 didn’t occur

• The cell would have 2 amounts of DNA in 1 cell

Why is the egg cell the biggest cell in the human body and the sperm cell the smallest

• So that the whole sperm cell can fit inside the egg cell and create a zygote