Patterns of Heredity and Human Genetics

1. Patterns of Heredity and Human Genetics A Look at Genetic Complexities Chapter 12 Notes

2. What happens when heredity follows different rules? The Exceptions to Mendel’s Rules Section 12.2

3. Section Objectives • At the end of this lesson, YOU will be able to: • Distinguish between alleles for incomplete dominance and codominance. • Explain the patterns of multiple allelic and polygenic inheritance. • Analyze the pattern of sex-linked inheritance. • Summarize how internal and external environments affect gene expression.

4. Remember Punnett Squares dd Heterozygous Chin Dimple (male) X No Chin Dimple (female) d d D Dd d

5. Remember Mendel? • His 4 conclusions were: • The Rule of Unit Factors • The Rule of Dominance • The Law of Segregation • The Law of Independent Assortment http://www.pbs.org/wgbh/nova/orchid/images/amat_mendel.jpg

6. Exceptions to Mendel’s Rules • Sometimes, patterns of inheritance are not as simple as Mendel’s Rules imply. • The exceptions to Mendel’s Rules are when nature uses a different method of determining traits.

7. Gene Linkage • The Law of Independent Assortment can be broken when genes are found close together on the same chromosome. • The genes will appear linked, or show up together. • The closer the genes are to each other the more they will be inherited together.

8. Breaking the Rule of Dominance • Usually, a dominant gene produces a protein for the trait. • The recessive allele either produces a nonfunctional protein or no protein at all. • So we see the dominant trait in hybrids because it is the only trait expressing a protein. DNA mRNA mRNA Protein

9. Incomplete Dominance • When heterozygous individuals show an intermediate phenotype between the two homozygous phenotypes. • Having one copy of a gene does not produce enough protein to completely mask the recessive allele. http://www.miracosta.edu/home/rmooney/Mendelian%20genetics_files/slide0015_image033.jpg

10. Incomplete Dominance r r • Snapdragons • If you cross a red flower and a white flower, the resulting hybrid will be pink. • RR = red flower • rr = white flower • Rr = pink flower • If you cross two pink flowers (Rr), you get: • 25% Red Flowers • 50% Pink Flowers • 25% White Flowers R Rr Rr R Rr Rr R r R RR Rr r Rr rr

11. Incomplete Dominance • Hair • Straight (HH) • Wavy (Hh) • Curly (hh)

12. Codominance • When a heterozygous individual shows the phenotypic traits of both alleles. • Both alleles produce a protein, which are seen in the hybrids. • The traits do not blend!

13. Codominance B B • Feather Color in Chickens • A black chicken would be BB. • A white chicken would be WW. • A hybrid, BW, would have a checkered appearance. • Both white and black pigments are seen in the offspring. BW BW W BW BW W B W BB BW B BW WW W

14. Codominance • Sickle Cell

15. Multiple Alleles • When a trait is controlled by more than two alleles. • Each individual only owns two alleles, but others in the population may possess different types.

16. cch C ca ch cbcb- Bugs Bunny Multiple Alleles • Fur Color in Rabbits • C = Dominant allele • ch = Himalayan fur • cch = Chinchilla fur • ca = Albino fur

17. Multiple Alleles • Blood Types • IA, IB, or i IAIA or IAi IBIB or IBi IAIB ii

18. Polygenic Traits • When one trait is controlled by more than one gene. • The genes may be on the same or different chromosomes. • Both genes have a single phenotypic effect.

19. Polygenic Traits • Coat Color in Labrador Retrievers • Controlled by two different genes, the B gene and the E gene. • A dihybrid cross of two black labs (BbEe x BbEe) results in: • 9 Black Pups • 3 Chocolate Pups • 3 Golden Pups • 1 Golden Pup with a brown nose and light eyes. http://www.oakhillkennel.com/library/color.html

20. Polygenic Traits • Eye Color • Brown Gene • Green Gene

21. Multifactorial Traits • When traits are determined by several factors from the genetic makeup and the organism’s environment. • The genes only represent the potential. • Environmental influences turn on the genes at different times and in different amounts.

22. Multifactorial Traits • Temperature, nutrition, light, chemicals, and infections can influence gene expression. • Arctic Foxes have coats that change color due to temperature.

24. Multifactorial Traits • Height, Intelligence, Cholesterol, Weight, Mental Illness, etc.

25. How do our chromosomes determine our sex? Sex Determination and Sex-linked Traits Section 12.2

26. Sex Determination • Humans have a total of 46 chromosomes, or 23 pairs: • 22 pairs of autosomes • 1 pair of sex chromosomes • Autosomes • All of the chromosomes that determine the traits other than sex. • Come in different sizes with different genes on them. • Pairs 1-22

27. Sex Determination • Sex Chromosomes • Determine the sex of the individual. • Pair 23 • In females, these chromosomes match in the form of XX. • In males, these chromosomes are different, as in XY.

28. Sex Determination • The combination of sex chromosomes decides if you are a boy or a girl. • A mother (XX) can only supply eggs that have an X chromosome. • The father (XY) has some sperm with a X chromosome and some with a Y chromosome. X X XX XX X Y XY XY G- 50% XX; 50% XY P- 50% female; 50% male

29. Comparing the X and the Y

30. Sex-Linked Traits • Genes that are located on the sex chromosomes. • The X chromosome contain many important genes that are necessary for survival. • The Y chromosome contains the SRY gene which determines maleness.

31. Sex-Linked Traits • First observed in fruit flies (Drosophila). • Fruit flies have either red or white eyes. • Thomas Hunt Morgan noticed that all of the white-eyed flies were male. • Therefore, eye-color in flies is a sex-linked trait.

32. Sex-Linked Traits • Y • Y Chromosome • (no alleles) • XR • X Chromosome • (red-eyed allele) • Xr • X Chromosome • (white-eyed allele) • Because the X chromosome is much larger than the Y, most sex-linked traits are on the X. • When writing the alleles for these traits, you must include the chromosomes that the individual has:

33. Sex-Linked Traits • Because males have only one X chromosome, they are more likely to get a single defective copy. • XRY- red-eyed male • XrY- white-eyed male XRY XrY

34. Sex-Linked Traits • Because females receive two X chromosomes, they are more likely to get a dominant allele that can cover the effects of the recessive trait. • A carrier female has a recessive allele but does not show the trait (heterozygous) • XRXR • Homozygous Red-eyed Female • XRXr • Carrier Female • XrXr • White-eyed female (rare)

35. Xr Y XR XR Xr XR Y XR XR Xr XR Y Sex-Linked Punnett Squares Homozygous Red-eyed Female x White-eyed Male XRXR XrY G- 50% XRXr 50% XRY P- 50% red-eyed female 50% red-eyed male

36. XR Y XR XR XR XR Y Xr XR Xr Xr Y Sex-Linked Punnett Squares Heterozygous Red-eyed Female x Red-eyed Male XRXr XRY G- 25% XRXR 25% XRXr 25% XRY 25% XrY P- 50% red-eyed female 25% red-eyed male 25% white-eyed male

37. How do pedigrees show inherited traits within families? Understanding Pedigrees Section 12.1

38. Pedigrees • A graphic representation of traits inherited within a family. • Allows scientists to trace the history of a genetic disorder. • Uses symbols to represent individuals. • Circles represent females • Squares represent males • If the symbol is shaded, the individual is affected by the trait. Normal Female Normal Male Affected Female Affected Male

39. Pedigrees • Inherited traits can be followed from generation to generation. • Horizontal lines connect two individuals who have mated. • Vertical lines represent the offspring of a union. I Bb Bb 1 2 Bb bb BB Bb II 1 2 3 4 5

40. Rules of Pedigrees • Sex-Linked vs. Autosomal • If more males are affected by a trait than females, it is probably sex-linked. • If it affects males and females equally, it is probably autosomal.

41. Rules of Pedigrees • Dominant vs. Recessive • If a trait skips a generation, it is recessive. • If the trait is found in each generation, it is probably dominant.

42. Rules of Pedigrees • Identifying Genotypes • If any males are carriers, the trait is autosomal. • If a male has a sex-linked trait, his mother was probably a carrier.

43. Autosomal Recessive • Affects males and females equally. • Skips generations (appears in some generations but not in others). • Males can be carriers

44. Autosomal Dominant • Affects males and females equally • Does not skip any generations.

45. Sex-Linked Recessive • Affects males more than females. • Skips generations. • Must use the chromosomes (XY or XX)

46. Example #1: Albinism Are males affected more frequently that females? NO Autosomal Disorder Does the disorder skip generations? YES (P1) Recessive Disorder A- normal a - albino Autosomal Recessive

47. Example #2: Hemophilia Are males affected more frequently that females? YES Sex-Linked Disorder Does the disorder skip generations? YES + = normal H = hemophilia Recessive Disorder Sex-Linked Recessive

48. Pedigree Practice Genetic Trait: ACHOO (Sneezes in response to light) A #1- Is this trait sex-linked or autosomal? #2- Is this trait dominant or recessive? B #3- What is the genotype of individual A? #4- What is the genotype of individual B? C #5- What is the genotype of individual C? #6- What is the genotype of individual D? D

49. Karyotype • A picture of an individuals chromosomes. • Homologous chromosomes are paired up. • Pairs are arranged by size. • Karyotypes can help diagnose chromosomal disorders.

50. Karyotypes • When arranging the chromosomes: • Autosomal Chromosomes are placed in order by size. • The Sex Chromosomes are pair 23.