MEIOSIS

1
MEIOSIS

• The Source of Genetic Variation in Eukaryotes

2
Whats good about asexual reproduction by mitosis?

• Rapid rate of reproduction is possible
• Offspring are clones of their parents
• Successful organisms continue to be successful in
  their environment
• Doesnt require specialized cells or organs
• Examples Cuttings, budding yeast, binary
  fission in bacteria, parthenogenesis, runners

3
Whats wrong with asexual reproduction?

• All members of a population are genetically
  identical
• If one member of the population is susceptible to
  a disease, they are all susceptible
• No ability to adapt to changes in the environment
• Evolution is not possible except in the case of
  bacteria or viruses

4
Corn Blight of 1970

• As it was, the Southern Corn Leaf Blight
  devastated 15 percent of America's 1970 corn
  crop, reducing the average national corn yield
  from 83.9 to 71.7 bushels per acre, costing
  farmers about 1 billion in losses. Some southern
  states lost more than 50 percent of their corn
  crop. In all, more than 1.02 billion bushels of
  corn were lost in 1970. But the crisis wasn't
  over.

http//www.unsafescience.com/cms-sclb.html
5
Terms to Review

• Genes Hereditary units
• Karyotype
• Homologous chromosomes
• Sex chromosomes
• Autosomes
• Haploid vs. Diploid n vs. 2n
• Zygote
• Syngamy

6
(No Transcript)
7
(No Transcript)
8
Meiosis produces 4 haploid gametes from a diploid
mother cell
2n
Chromosomes segregate by independent assortment
at Metaphase 1
Single chromosomes consisting of two sister
chromatids are present after the first meiotic
division
n
Four haploid gametes result after the 2nd meiotic
division. Each cell contains one member of each
original pair of chromosomes
n
9
Synapsis occurs, tightly locking the
chromosomes together
4 chromosomes become visible, connected by
chiasmata crossing over of non-sister chromatids
Homologous chromosomes attach to the same spindle
fiber
Homologous chromosomes separate (Segregate)
independently
Sister chromatids separate
10
Spermatogenesis
11
Oogenesis
12
COMPARE
13
(No Transcript)
14
Three Sources of Genetic Variation

• Independent assortment of homologous chromosomes
  during meiosis 1 and of non-identical sister
  chromatids during meiosis 2
• Crossing over between homologous chromosomes
  during prophase of meiosis 1
• Random fertilization of an ovum by a sperm