Meiosis

Crossing over is a very important event in prophase I of meiosis! What happens during crossing over and what is the significance?

1. Exchange of genetic material 2. Leads to genetic variation- explains why we all look different

In the process of meiosis , chromosomes begin to match up in homologous pairs. How would you know if two chromosomes were homologous?

1. Same size 2.same time of gene, same location

Remember that a cell that begins meiosis has

23 chromosomes inherited from mother and 23 chromosomes inherited from father

Interphase occurs once before the process begins

Both mitosis and Miosis

Meiosis does not always occur without any difficulties. Describe what occurs during nondisjunction and the effect on the resulting cells.

Cells ends up with chromosomes than it should have

Interphase must occur once before meiosis can happen. (Same thing for mitosis) . What would happen if interphase didn't occur first?

Chromosomes would not duplicate

Nondisjunction always results in a zygote with an extra chromosomes

False- could have too many or not enough

Down Syndrome is a result of polyploidy

False- it's a result of nondisjunction

Why meiosis ?

It maintains a constant number of chromosomes within a species

Crossing over occurs

Meiosis

Produces 4 cells that each have 23 chromosomes

Meiosis

Produces gametes

Meiosis

If the chromosomes are in the middle of the cell, how would you know whether it was in metaphase I or metaphase II?

Metaphase I because the homologous pair are leveled up along the center of the cell

Process ends with identical cells

Mitosis

Process is important for growth and repair

Mitosis

Meiosis does

PMAT twice! Which means there's a prophase I and prophase II etc.

The purpose of meiosis is to make gametes, Also known as sperm and egg cells. In humans, your body cells have 46 chromosomes. How many chromosomes are in a sperm or egg cell if, when they come together to form a fertilized zygote, there are 46 chromosomes?

Sperm= 23; Egg=23 ; =46

Reassortment of chromosomes can occur during meiosis by crossing over of nonsister chromatids or by independent segregation of homologous chromosomes

True

The random segregation of chromosomes during meiosis explains Mendel's observation that genes for different traits are inherited independently of each other

True

genetic recombination is a major source of variation among organisms

True