1. Human Genetics
Chapter 14

2. In the beginning. . .
Life starts when the male gamete (sperm) combines with the female gamete (ovum). Produced from Meiosis.
All gametes are haploid (containing only one set of chromosomes)

3. Fertilization When a sperm and an egg combine, they produce a zygote.
This process is called fertilization.

4. We have contact!

5. And then there was life...
The zygote is now diploid (it contains two sets of chromosomes), one from mom and one from dad.
50% from dad
50% from mom

6. Producing Variation
Every zygote contains a brand new combination of alleles.
Half of mom’s and half of dad’s.

7. What are the two major sources of genetic variation?
Gene shuffling (Crossing over) – during Meiosis.
Mutation (Random changes in an individual’s DNA)

8. Human Chromosomes
There are 23 pairs of homologous chromosomes in a typical human cell.
Karyotype 
The last pair
are the sex
Chromosomes
XX = female
XY = male

9. Because females are XX, all eggs contain an X chromosome.
Boy or Girl?
Because females are XX, all eggs contain an X chromosome.

10. Males, on the other hand, are XY so 50% of the sperm carry a Y and 50% carry an X.
So, the male determines the sex of the baby.

11. What are the odds of having a boy/girl?X X X Y

12. 1 out of 2
Or 1:1
Or 50%

13. Name that karyotype!
Female Male

14. Modes of Inheritance Autosomal Sex-linked aka X-linked Dominant
Recessive
Sex-linked aka X-linked

15. Autosomal
The gene is found on one of the first 22 chromosomes – NOT ON THE SEX CHROMOSOMES!
Males and females
equally affected

16. Sex-Linked The gene is found on the sex chromosomes (X or Y)
Males affected more than females

17. Why are males affected more?
If the “bad” gene is on the Y, it is impossible for girls to get it (they don’t have a Y chromosome)
If it is on the X, but recessive, females would have to inherit 2 bad copies, but males would only need to get one.

18. Some Common Sex-linked disorders
Colorblindness

19. Male pattern baldness

20. Hemophilia (unable to form blood clots)

21. Pedigree
Charts that scientists use to determine the mode of inheritance.

22. Pedigree symbols Males are represented by squares
Females are represented by circles
Male
Female

23. Pedigree symbols cont…
If they are shaded in, then the individual has the trait
If they are left white, the individual does not have the trait
If they are half and half, the individual is a carrier, but does not have it

24. More Symbols…
Non-Identical Twins
Identical Twins
Deceased Individuals

25. More Symbols
Adopted Individuals
Out of a Family
Into a Family

26. Draw and Label

27. Dominant vs. Recessive
If it is dominant, you will see at least one person per generation that is affected.
If it is recessive, it can “skip” generations.

28. PATTERNS OF INHERITANCE
Autosomal (1-22) Recessive Traits
Trait is rare in pedigree
Trait often skips generations (hidden in heterozygous carriers)
Trait affects males and females equally

29. PATTERNS OF INHERITANCE
Autosomal (1-22) Dominant Pedigrees
Trait is common in the pedigree
Trait is found in every generation
Affected individuals transmit the trait to ~1/2 of their children (regardless of sex)

30. Dominant or recessive? Autosomal or X-linked?

31. Dominant or recessive? Autosomal or X-linked?

32. Hemophilia in European royalty
X-linked recessive

33. Dominant or Recessive? Autosomal or X-linked?

34. Gene Map
A diagram that shows you the approximate positions of genes on a chromosome.

35. Linked Genes
The closer two genes are on a chromosome, the less likely it is that they will be separated during crossing over.
This means that they are usually inherited together.