Gamete Formation

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

6
(No Transcript)
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

9
(No Transcript)
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)

12
(No Transcript)
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
• Americas oldest person is 113, and is the second
  oldest person in the world