1. Sperm & Eggs & Variation!
MEIOSIS
Sperm & Eggs & Variation!

2. Sexual Reproduction requires Cells Made by Meiosis

3. Genome

4. Genes

5. Heredity

6. Sexual reproduction

7. Chromosomes
Karyotype

8. In humans e.g. 23 chromosomes in haploid 2n = 46; n = 23
2n = 223 = ~ 8 million possible combinations!

9. Karyotyping

12. HomologOUs CHROMOSOMES

13. HomologOUs CHROMOSOMES

14. In humans …

15. Chromosome numbers
All are even numbers – diploid (2n) sets of homologous chromosomes.
All even, as all are diploid, contain pairs of chromosomes.

16. Meiosis – key differences from mitosis

19. Crossing over
Chiasmata
Synapsis
Recombinant chromosomes.

21. Animation

22. Meiosis I
Prophase 1
Metaphase 1

23. Meiosis I
Anaphase 1
Telophase 1

24. Meiosis II Second division of meiosis: Gamete formation Prophase 2
Metaphase 2

25. MEIOSIS II
Anaphase 2
Telophase 2

26. Mitosis vs. meiosis

28. Meiosis creates genetic variation
Mitosis produces daughter cells identical to parent cell (2n to 2n)
Meiosis results in genetic variation
Shuffling
Crossing over

29. Independent assortment

30. Independent assortment
Number of combinations: 2n
e.g. 2 chromosomes in haploid
2n = 4; n = 2
2n = 22 = 4 possible combinations

31. Crossing over
Chiasmata
Synapsis.
Recombinant chromosomes.

32. HOW SEX IS DETERMINED IN HUMANS
Females don’t have a Y chromosome
Y chromosome is not necessary.

33. SEX DETERMINATION IN OTHER SPECIES

34. Random fertilization
At least 8 million combinations from Mom, and another 8 million from Dad …
>64 trillion combinations for a diploid zygote!!!

35. Meiosis & sexual life cycles
Somatic cells
Gametes

36. Meiosis & sexual life cycles
Generalized animal life cycle

37. principles of Heredity summary of Mendel’s Principles
The inheritance of biological characteristics is determined by individual units known as genes. Genes are passed from parents to their offspring.

38. Summary of Mendel’s Principles
The inheritance of biological characteristics is determined by individual units known as genes. Genes are passed from parents to their offspring.
In cases in which two or more forms (alleles) of the gene for a single trait exist, some forms of the gene may be dominant and others recessive.

39. Summary of Mendel’s Principles
3. In most sexually reproducing organisms, each adult have two copies of each gene – one from each parent. These genes are segregated from each other when gametes are formed.

40. Summary of Mendel’s Principles
3. In most sexually reproducing organisms, each adult have two copies of each gene – one from each parent. These genes are segregated from each other when gametes are formed.
4. The alleles for different genes usually segregate independently

41. Sex is costly! Large amounts of energy required to find a mate
Infection
Genetic costs:
Males contribute little to rearing offspring.

42. genetic diversity:
Linked Genes:

43. Why are linked genes inherited together
Why are linked genes inherited together? To answer this, we must revisit the behavior of chromosomes during the production of gametes, discussed in the previous chapter. Imagine that you have a child. Let’s focus on the gamete of yours that took part in the fertilization to produce that child. When you made that sperm or egg by meiosis, only one of your two copies of each chromosome ended up in the new gamete. It may have been the one from your mother or it may have been the one from your father. In either case, all of the alleles that were on the chromosome from that one parent of yours will be passed on as a group to the child that results from the fertilization involving that gamete. This process continues generation after generation. The linked alleles never get split up unless, during meiosis, recombination occurs between them, moving one or more to the other chromosome in the pair and become linked with the alleles on that chromosome.
When alleles are linked closely on the same chromosome, Mendel’s second law doesn’t hold true. It is very surprising—and was fortunate for Mendel—that of the seven pea traits he studied, none of them were on the same chromosome. For this reason they all behaved as if they weren’t linked, and in his crosses of different pea plants Mendel never noticed any linked genes.
Figure Gene linkage. 43

44. NONDISJUNCTION

45. Down's Syndrome

46. TOO MANY OR TOO FEW CHROMOSOMES