"Biology is the only science in which multiplication means the same thing as division."

Meiosis

• Comes from a Greek word that means:

–“to make smaller”

Learning Goals:(for this section)

• 1. Explain the difference between Mitosis and Meiosis

• 2. Descibe how chromosomes determine sex.

• 3.Explain why sex-linked disorders occur in one sex more than in the other.

• Interpret a pedigree

meiosis mitosis

sex chromosomes

pedigree

sex cells

homologous chromosomes

Xchromosome

Ychromosome

sex-linked disorder

Section vocab:

Sexual Reproduction

Asexual Reproduction

Unit: Heredity 

E.U: Organisms reproduce either

asexually or sexually. Sexual reproduction leads to a genetic

variation.

Why does a pug….

Look so different from a…

Doberman

pincher?

Answer?

(And Selective Breeding)

Two Kinds of Reproduction

• Asexual– One parent cell is needed to

reproduce ex. Mitosis

• Sexual – Two parent cells join together to form

a new individual.– Requires meiosis !

Review of mitosis:

There are two categories of cells in the human

body:• 1.) Somatic cells (body cells)

– These have 46 chromosomes in every nucleus of every cell.

–These cells are produced through mitosis

2.) Sex cells:– Eggs in females– Sperm in males

• All contain only 23 chromosomes (1/2 that of body cells)

These cells are produced by meiosis.

WHEN SEX CELLS ARE MADE, CHROMOSOMES ARE COPIED ONCE AND

THEN THE NUCLEUS

DIVIDES TWICE.

HOW DOES MEIOSIS HAPPEN?

•One cell produces 4 cells with ½ the DNA

• Meiosis: An Interactive Animation

EACH OF THE NEW CELLS HAS HALF THE NUMBER

OF CHROMOSOMES

THAT WERE FOUND IN THE ORIGINAL CELL!

WHAT DOES MEIOSIS PROVIDE IN A SPECIES?

MEIOSIS PRODUCES:

•Sex cells:

–Eggs

–Sperm

SEX CHROMOSOMES:

• Contain genes that determine an offspring’s sex

• HUMAN FEMALES HAVE: Xand X

• HUMAN MALES HAVE: X and Y

What are the chances of getting a boy or a girl?

Karyotype:a picture of human

chromosomes all lined up:

Sex-linked Disorders

• The Y gene is small and does not carry all of the genes of an X chromosome

Females have 2 “X” chromosomes

• Females therefore carry a copy of each gene found on the X chromosome.

• (this allows the trait to be masked)

• Males have only one copy of each gene on their X chromosome– If they inherit the disorder on this

chromosome, they will have the disorder

Tests for colorblindness:

Meiosis diagram:

Pedigree:

• A diagram that shows the occurrence of a trait in several generations of a family.

Selective Breeding

• Organisms with desirable characteristics are mated

Ex:

People have been breeding dogs for desired traits for thousands of years.

Example:

• Mate a poodle and a golden retriever

Hair, not fur

smart

Fur that sheds,

retrieves

Golden Doodle

•Hair, not fur

•Smart

•Retrieves