1. Gamete Formation
Genetics

2. Human Gamete Formation
Gametes are the sperm and egg
Both haploid (n), meaning they have only one of each type of chromosome
Produced through a special cell division called meiosis
Somatic cells are diploid (2n) with 46 chromosomes; gametes have 23

3. Flowering Plant Gamete Production
Ovule: a compartment inside the ovary where female gametes are produced
Anther: where male gametes (pollen grains) are produced
Gametes are always haploid; the zygote is always diploid

4. Gamete Formation

5. Meiosis
Two divisions: goes through prophase, metaphase, anaphase, and telophase twice
In Meiosis I the pairs of chromosomes (and their copies) separate in anaphase
In Meiosis II, the individual chromatids separate

7. Mitosis vs Meiosis

8. Gamete Formation
Spermatogenesis begins with a germ cell called a spermatogonium
Two divisions follow (meiosis I and II)
End result is four haploid sperm

10. Spermatogenesis Sperm formation passes through these cell stages:
Spermatogonium
Primary spermatocyte
Secondary spermatocyte
Spermatid
Mature sperm

11. Oogenesis Oogenesis begins with a diploid cell called a oogonium
Two divisions follow (meiosis I and II)
Result is 3 polar bodies and 1 mature ovum (egg)

13. Oogenesis

14. Oogenesis Ovum formation passes through the following cells stages:
Oogonium
Primary oocyte
Secondary oocyte
Ovum

15. Oogenesis
At birth, a female has all the primary oocytes already formed
Frozen in prophase I
After puberty, meiosis continues with 1 or 2 oocytes each month
Only complete meiosis if fertilized

16. 4 Sperm; 1 Ovum

17. Variety: arrangement and crossing over

18. Fertilization

19. Twinning Dizygotic: two eggs and two sperm
No more closely related than any siblings
“Fraternal”

20. Twinning Monozygotic: one egg and sperm
The embryo separates at an early stage and each continues normal development
Genetically identical

21. Twinning
Conjoined twins: a monozygotic pair that does not separate all the way
May or may not share vital organs
Most often, if separated, one lives and the other dies

22. Aging
Genes control cell division and apoptosis, so aging is somewhat genetically regulated
By about age 30, the body begins to decline
Genes control aging both passively (structures break down, cells are not replaced) and actively (causing new activities)

23. Aging The disease progeria can give clues as to what causes aging
In one type, the gene for helicase is altered. Helicase unzips the DNA for repair and replication. This enzyme is missing in progeria

24. Aging

25. Aging

26. Aging Environment influences aging as well as genes
America’s oldest person is 113, and is the second oldest person in the world