"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?
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)
– 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!
A 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? (use a Punnett Square!)
Karyotype:a picture of human
chromosomes all lined up:
Pedigree:
• A diagram that shows the occurrence of a trait in several generations of a family.
Sex-Linked Disorders:
• Colorblindness
• Hemophilia
• Cystic Fibrosis
• The genes for these disorders are carried on the sex chromosomes- girls have a 2nd X chromosome to mask it. Boys therefore, have the disorder more than girls.
Selective Breeding
• Organisms with desired characteristics are mated