1. Chapter 13: Meiosis and Sexual Life Cycles

2. Heredity
Heredity: the transmission of traits from one generation to the next
Genes- hereditary units
Transmitted by sex cells

3. Chromosomes: Where genes are located (locus).
Every species has a characteristic number of chromosomes
Humans = 46 chromosomes (23 pairs)

4. Asexual vs. Sexual Reproduction
Asexual Reproduction: clones (mitosis)
Example: budding(hydra)
Sexual Reproduction:
Meiosis
Variation
Life cycle- begins with fertilization of the egg by the sperm

5. Sets of Chromosomes in Human Cells:
Somatic cells: body cells or any cell that is not a gamete
Karyotype
Homologous chromosomes
One exception??
Autosomes??

6. PCA: 1.What is it? 2.What does it show? 3. Is there an exception?
karyotype
2.What does it show?
Homologous chromosomes
3. Is there an exception?
Yes- sex chromosomes
4. Male or female?
5. What is a chromosome consist of?

7. advance

8. Representing Chromosomes:
n = number of chromosomes
2n = diploid ( two sets of chromosomes)
n = haploid (one set of chromosomes)
Human somatic cells = diploid = 23 pairs (46 total)
Human sex cells(gametes) = haploid = 23 chromosomes
22 autosomes and a sex chromosome

9. Meiosis: Cell division that reduces the number of sets of chromosomes
Formation of gametes
What would happen if gametes are formed by mitosis?

10. Chromosome Behavior: Human life cycle =
Fertilization: haploid sperm + haploid egg
Diploid zygote- 46 chromosomes is restored

11. Alteration of life cycles:
Alternation of generations:
All sexually reproducing organisms will alternate between haploid cells and diploid cells.

12. Alteration of life cycles:
Most fungi and some protists:
Haploid gametes form diploid zygote
Diploid zygote divides by meiosis, then by mitosis to produce a haploid multicellular organism
Haploid cells divide by mitosis to produce gametes

13. Alteration of life cycles:
Plants and Some Algae:
sporophyte produces a gametophyte as its offspring, which then produces the next sporophyte generation

15. Alteration of life cycles:
Animals:
Diploid organism produces haploid gametes by meiosis
Fertilization produces a diploid zygote
Divides by mitosis to form a multicellular organism

16. Reduces number of chromosome sets from diploid to haploid
Meiosis:
Reduces number of chromosome sets from diploid to haploid
Two consecutive cell divisions
Meiosis I: separates homologous chromosomes
Meiosis II: separates sister chromatids similar to mitosis
Four daughter cells distinct from each other and the parent cell

17. Meiosis

18. Meiosis I:
Prophase I: pairing of homologous chromosomes, synapsis, chiasmata, tetrads
Metaphase I: tetrads line up on metaphase plate
Anaphase I: chromosomes migrate to respective poles
Telophase I: haploid chromosome, sister chromatids intact
Cytokinesis: cleavage furrow(cell plate)

19. Meiosis II:
Prophase II: spindle apparatus, chromosomes start to migrate
Metaphase II: chromosomes line up on metaphase plate
Anaphase II: sister chromatids migrate towards their respective poles
Telophase II: de-condensing of chromosomes, nuclear envelop re- assembles
Cytokinesis: cleavage furrow

21. Meiosis vs. mitosis

22. Meiosis vs. mitosis

23. Genetic variation: Prokaryotes vs. Eukaryotes:
Transformation- uptake of DNA
Transduction- viral transmission of genetic information
Transposition- movement of DNA segments between and within DNA molecules
Eukaryotes:
Crossing over
Independent assortment of alleles
Fertilization

24. Origins of Genetic Variation
Genetic variation c0ntributes to evolution:
Mutations are responsible for change
Reshuffling of genes

25. Origins of Genetic Variation
Independent assortment: homologous pairs of chromosomes are randomly arranged
(metaphase I)

26. Origins of Genetic Variation
50% chance offspring will get their mothers chromosomes
50% chance offspring will get their fathers chromosomes
Chromosomes sort independently during meiosis I

27. Origins of Genetic Variation
Each daughter cell represents one possible outcome
Combinations possible:
n = haploid number of organisms
2n= the number of possible combinations when chromosomes sort independently

28. Example: Example: what are the total number of combinations when n = 3

30. Origins of Genetic Variation
Crossing over (prophase I):
the reciprocal exchange of genetic material between nonsister chromatids during synapsis of meiosis I (recombinant chromosomes)

31. Origins of Genetic Variation
Random fertilization:
1 sperm (1 of 8 million possible chromosome combinations) x 1 ovum (1 of 8 million different possibilities) = 64 trillion diploid combinations!

34. Back

35. Chapter 12 reveiw Pg. 220, #’s: 1 and 2 Pg. 228, #’s: 1, 4 and 5