1. Human Genetic Traits

2. Importance of genetics
Understanding hereditary diseases and to develop new treatments
Donor matches
Paternity
Forensics
Evolution

3. Genes- genetic material on a chromosome that codes for a specific trait
Genotype- the genetic makeup of the organism
Phenotype- the expressed trait
Allele- an alternative form of a gene

4. Dominance Mechanism
Two alleles are carried for each trait
In true-breeding individuals, both alleles are the same (homozygous).
Hybrids, on the other hand, have one of each kind of allele (heterozygous).
One trait is dominant, the other trait is recessive

5. Genetic Information Genes are traits “Eye color”
Ear lobe connectedness
Genes produce proteins
Enzymes are proteins

6. Homologous Chromosomes
gene: location
allele: specific trait

7. Allele Example
Gene = “eye color”
Alleles
brown
blue
green
lavender

8. Allele Examples
appearance
eye color: homozygous

9. Allele Examples appearance eye color: heterozygous,
brown dominant over blue

10. Genotype vs Phenotype genotype phenotype homozygous (dominant)
heterozygous
homozygous
(recessive)
appearance
Phaner = visible

11. Punnett Square If male & female are heterozygous for eye color maleX
brown: 3/4 offspring
blue: 1/4 offspring

12. Each parent carries one gene for PKU.X P p P
How is PKU inherited?
Phenylketoneuria (PKU) affects people who inherit two copies of an altered gene from their carrier parents. Carrier parents have a one-in-four chance of having an affected child, a one-in-two chance of having a child who is an unaffected carrier and a one-in-four chance of having a child with no altered genes at all. Carriers of PKU are not affected themselves, as they have a working gene as well as an altered one.
If some genes 'cause' PKU and Huntington's chorea why haven't they been removed from our species by the process of natural selection?
1. PKU is an autosomal recessive disorder with an incidence of 1 in 5,000 homozygous (carrying two copies of the mutation) affected people in Celtic populations. Using the Hardy Weinberg equation we can calculate that 1/36 of the population are healthy heterozygotes carrying only 1 copy of the PKU mutation. The vast majority of PKU alleles in the population are in  healthy carriers. Even if all the PKU alleles in the relatively small affected population are removed from the whole population each generation (because affected people do not reproduce) then it would take very many generations to reduce the total frequency of the gene in the population. As the gene became rarer then the chance two carriers would meet would reduce so the number of affected offsprings' PKU alleles that would be removed from the population would also go down. Very complex, a computer model would help!
In practice other factors will also be at work; e.g. treated PKU patients can now have families and their genes will maintain or increase the PKU mutation pool. 
Why is the PKU gene so common in the Celtic population? We do not know. Maybe if the population was founded by a relatively small number of individuals and by chance one carried a PKU mutation, the resulting high PKU incidence would be maintained as the population grew. Perhaps the carriers have a greater reproductive fitness than the non carriers; c.f. sickle cell disease in malarial areas. See the following for more details: GENETICS
2. Huntington disease is an autosomal dominant disease causing progressive dementia and a movement disorder. The mutation is caused by a length expansion of a trinucleotide repeat sequence in the Huntingtin gene.  It is likely that the vast majority of cases in the world are descended from a relatively small number of founder mutations. One founder mutation has arisen in Western Europe and spread with European colonisation, another has arisen in Japan. Although Huntington disease is ultimately fatal, it is a late onset disease and does not seem to affect reproductive fitness. Indeed, many clinical geneticists have an  impression that affected patients have larger families than their unaffected relatives. This was confirmed in a study of the Northern Irish population by Morrison et al., 1995,  J. Med. Genet. 32: Some molecular studies of human and primate populations has suggested that the key element in HD evolution is a tendency to ever-lengthening repeats in the normal population and this will lead to an ever-increasing incidence of HD. See the following for more details: GENETICS p p p p
Possible genotypes: 1PP 2Pp 1pp
Possible phenotypes:no PKU PKU

13. Compare this to what would have happened if one parent was homozygous for sickle cell.
HbA
HbA
HbA
HbA
HbS
HbA
HbA
HbS
HbS X
HbA
HbA
HbS
HbS
HbS
HbS
HbS
all offspring are carriers of sickle cell trait

14. Autosomes and Sex Chromosomes

15. Red-Green Color Blindness
Sex-linked trait XC Y XC Y XC XC XC
Normal male XC Y X XC Xc XC Xc Xc Xc Y
Normal female recessive gene
Possible outcomes: XCXC XCXc XCY XcY
Normal
female
Normal
Female
(carrier)
Normal
male
Color-blind male

16. Dominance
Most traits show complete dominance
Blending unexpected

17. E unconnected earlobe e connected earlobe P EE x ee E e F1 Ee allele
gene
E unconnected earlobe
e connected earlobe
unconnected P
EE x ee
connected
gametes
E e F1 Ee

18. F1 Ee x Ee 1/2 E 1/2 e 1/2 E 1/2 e E e E EE Ee e Ee ee F2
gametes E e E EE Ee
Punnett Square e Ee ee F2
1 EE 2 Ee 1 ee

19. P EE, ee 50% 1:1 F1 Ee 100% 1:1 F2 EE, 2 Ee, ee 75% 1:1 phenotypes
generation genotypes unconnected E:e P
EE, ee
50%
1:1 F1 Ee
100%
1:1 F2
EE, 2 Ee, ee
75%
1:1
phenotypes
ratio of alleles in the population
Basis of the Castle-Hardy-Weinberg Law

20. Genotypes Phenotypes
Experiment to determine dominant vs. recessive

21. Genetic Sleuthing My eye color phenotype is brown.
What is my genotype?

22. Pedigree phenotypes infer genotypes Alternative:
look directly at the DNA

23. Complexities Multiple genes for one trait Example: eye color
Blended traits (“incomplete dominance”)
Influence of the environment

24. Disorders Down’s Syndrome (chrom 21)
Alzheimer’s (chrom 1, 10, 14, 19, 21)
Huntington’s (chrom 4)

25. Human Genetic Traits

26. R = Tongue Roller r = Unable to Roll Tongue

27. W = Widows Peak w = Lack of Widow’s Peak

28. E = Free Ear Lobe e = Attached Ear Lobe

29. Hi = Straight Thumb hi = Hitchhiker’s Thumb

30. Bf = Bent Little Finger bf = Straight Little Finger

31. M = Mid-Digital Hair m = Absence of Mid-Digital Hair

32. D = Dimples d = Absence of Dimples

33. Ha = Short Hallux ha = Long Hallux

34. Ss = Short Index Finger S1 = Long Index Finger
*Sex-Influenced Trait

35. Presentation created by J. Kenyon
Kiss me, you fool.
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Presentation created by J. Kenyon