Meiosis

Where are genes located and how do they pass information?Understanding reproduction is the first step to finding answers.

Meiosis Two kinds of

reproduction: asexual and sexual. The name for the way cells divide in asexual reproduction is mitosis.

Asexual = not sexual = example: skin cell

Asexual Reproduction In asexual

reproduction, only one parent cell is needed.

This type of cell reproduction is known as mitosis. Most of the cells in your body reproduce this way.

Sexual Reproduction In sexual

reproduction, two parent cells join together to form offspring that are different from both parents.

Parent cells are called sex cells. Sex cells are different from regular body cells because they only have 23 chromosomes, which is half of our other body cells.

Meiosis Sex cells are made

during a process called meiosis.

Meiosis is a copying process that produces cells with half the usual number of chromosomes.

Genes and Chromosomes

Walter Sutton was a graduate student who studied grasshopper sperm and egg cells.

Walter Sutton’s important observation was that egg and sperm cells were different, but they did have something in common: Their chromosomes were located inside a nucleus.

Sutton proposed that genes are located on chromosomes!

The Steps of Meiosis Chromosomes are

copies once, and then the nucleus divides twice. The resulting sperm and eggs have half the number of chromosomes of a normal body cell.

Sex chromosomes carry genes that determine sex Female chromosomes XX Male chromosomes XY

Sex Linked Disorders Because males

have only one X chromosome, what is more likely to happen to them? More likely to

have a sex-linked disorder

Name two sex-linked disorders: hemophilia, color blindness

Genetic Counseling & Selective Breeding To trace a trait

through generations of a family, you can use a pedigree

A genetic counselor can often predict if a person is a carrier of hereditary diseases.

People with cystic fibrosis have two recessive alleles.

When organisms with desirable characteristics are mated by humans, it is called selective breeding.

Examples of selective breeding: race horse, show dogs, roses