Sexual Reproduction and Meiosis

1
Sexual Reproduction and Meiosis
2
Reproduction

• Organisms can reproduce asexually -mitosis,
  fission, budding

3

• Organisms can also reproduce sexually
• Two sex cells (usually egg and sperm) join
  together
• Males produce sperm, females produce eggs

4

• Sex cells do not have pairs of chromosomes
• They are called haploid (single- not paired up
  sometimes represented as the letter N).
• They only have half the number of chromosomes as
  body cells.
• 23 total chromosomes

5

• All other body cells are diploid (paired up 2N).
• Humans have 23 pairs of chromosomes
• 46 chromosomes total

6

• When an egg and sperm join together, it is called
  fertilization.
• The resulting cell is called a zygote
• The zygote will begin to undergo cell division

http//www.exploratorium.edu/imaging-station/galle
ry.php?AssetZebrafish20developmentGroupCatego
ryDevelopmentSectionIntroduction
7

• The zygote formed following fertilization has a
  diploid set of chromosomes (46 total).
• Half (23) from mom, half (23) from dad.

8

• Sexual reproduction occurs when the genes of two
  parents are combined to form an offspring.
• The offspring is a unique genetic combination of
  its two parents.

9
So how do we get specialized sex cells with only
half the chromosomes?
10
Meiosis

• Meiosis is a process that produces haploid sex
  cells.

11
Why does meiosis happen?

• Meiosis allows for the production of sex cells so
  sexual reproduction can occur.

12

• In meiosis I, the nucleus divides and produces
  two new cells with one duplicated chromosome
• Exactly like mitosis.

13

• In meiosis II, the division happens again and the
  sister chromatids separate, producing four cells
  with half (haploid) the number of chromosomes of
  the original nucleus.

http//www.youtube.com/watch?vkVMb4Js99tA
14

• The end result of meiosis
• A cell undergoes division twice.
• This produces four sex cells, with half the
  number (haploid) of chromosomes of the original
  cell

15
(No Transcript)
16
Mitosis vs. Meiosis
http//www.youtube.com/watch?vBa9LXKH2ztU
17
Asexual vs. Sexual reproduction

• Asexually produced organisms are genetically
  identical to their parent.

18

• Sexually produced organisms are genetically
  different from their parent.
• This produces unique organisms who may be more
  (or less) resistant to disease, more (or less)
  intelligent, more (or less) physical abilities,
  adaptable to environment, etc.
• There is variety among the offspring.