"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”

– also known as reduction division

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 !

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, a form of asexual reproduction-(review on next slide)

Review of 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. (this process is needed for sexual reproduction)

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

found in the original cell !

MEIOSIS PROVIDES___ IN A SPECIES.

?

8 Steps in Meiosis

Steps of Meiosis

MEIOSIS PRODUCES:

•Sex cells:

–Eggs

–Sperm

Tap me (best meiosis video ever)

Comparison of Mitosis and Meiosis

mitosis

meiosis

both

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?

BRAIN POP

Karyotype:a picture of human

chromosomes all lined up:

Sex-linked Disorders

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

Females have 2 “X” chromosomes

recessive

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

• (this allows the recessive disorder gene 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– Examples are Color Blindedness,

Hemophilia (bleeder’s disease), and Cystic Fibrosis

Colorblind tests

Hemophilia

Cystic FibrosisCystic fibrosis is an inherited chronic disease that affects the lungs and digestive system of about 30,000 children and adults in the United States (70,000 worldwide). A defective gene and its protein product cause the body to produce unusually thick, sticky mucus.

To tell a sex linked disorder in a pedigree…

• Females are carriers of the trait

• Males have the trait

Pedigree:

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

Pedigree Rules

• Squares represent males• Circles represent females• Vertical lines connect children to

parents• Solid circle or square indicates that

the person has a certain trait• A half-filled square or circle indicates

the person is a carrier of the trait.

Pedigree

Selective Breeding• Organisms with desirable

characteristics are matedHigh egg

layers

White colored

pumpkins

Bigger,fatter,

tastier

Bigger petalsNewer

colors

Faster race horses

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

•Loyal

Golden Doodle

•Hair, not fur

•Smart

•Retrieves

•Loyal