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

2. Meiosis
Comes from a Greek word that means:
“to make smaller”

3. Learning Goals: (for this section)
1. Explain the difference between Mitosis and Meiosis

4. 2. Descibe how chromosomes determine sex.

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

6. Interpret a pedigree

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

8. Sexual Reproduction
Asexual Reproduction

9. MCAS:
Unit: Heredity   E.U: Organisms reproduce either asexually or sexually. Sexual reproduction leads to a genetic variation.

10. Why does a pug….

11. Look so different from a…
Doberman
pincher?

12. Answer?
Meiosis
(And Selective Breeding)

13. 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 !

14. Review of mitosis:

15. 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

17. 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.

18. WHEN SEX CELLS ARE MADE, CHROMOSOMES ARE COPIED ONCE AND THEN THE NUCLEUS DIVIDES TWICE.

19. HOW DOES MEIOSIS HAPPEN?
One cell produces 4 cells with ½ the DNA
Meiosis: An Interactive Animation

20. EACH OF THE NEW CELLS HAS HALF THE NUMBER OF CHROMOSOMES
THAT WERE FOUND IN THE ORIGINAL CELL!

21. WHAT DOES MEIOSIS PROVIDE IN A SPECIES?
Variation !

22. MEIOSIS PRODUCES:
Sex cells:
Eggs
Sperm

23. SEX CHROMOSOMES: Contain genes that determine an offspring’s sex
HUMAN FEMALES HAVE: Xand X
HUMAN MALES HAVE: X and Y

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

25. Karyotype: a picture of human chromosomes all lined up:

27. Sex-linked Disorders
The Y gene is small and does not carry all of the genes of an X chromosome

28. Females have 2 “X” chromosomes

29. 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

30. Tests for colorblindness:

31. Meiosis diagram:

32. Pedigree:
A diagram that shows the occurrence of a trait in several generations of a family.

34. Selective Breeding
Organisms with desirable characteristics are mated

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

36. Example: Mate a poodle and a golden retriever Hair, not fur smart
Fur that sheds,
retrieves

37. Golden Doodle
Hair, not fur
Smart
Retrieves