MEIOSIS "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

Section vocab: meiosis mitosis sex chromosomes pedigree sex cells homologous chromosomes X chromosome Y sex-linked disorder

Sexual Reproduction Asexual Reproduction

MCAS: 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? Meiosis (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

These cells are produced by meiosis. 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? Variation !

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