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"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