Dominant and Recessive Physical Traits

1. Dominant and Recessive Physical Traits

2. BioEd Online Pedigree Diagrams: I • Basic Symbols

3. normal male normal female affected male affected female male carrier female carrier

4. BioEd Online Pedigree Diagrams: II Basic Symbols for offspring and the expression of a trait. • Offspring are depicted below the parents. • Filled in symbol indicates the expression of the studied trait. • Roman numerals – Generations • Arabic numerals – Individuals in a certain generation Parents Generation Siblings

6. BioEd Online Factors to Consider in Pedigrees • Is the trait located on a sex chromosome or an autosome? • Autosomal – not on a sex chromosome #1-22 • Sex Linkage – located on one of the sex chromosomes • Y-linked - only males carry the trait. • X-linked (recessive) - sons inherit the disease from normal parents • How is the trait expressed? • Dominant - the trait is expressed in every generation. • Recessive - expression of the trait may skip generations.

7. Autosomal Dominant Disorders • Requires only ONE allele for the disorder to be passed • Probability of having offspring with the disorder: 50% if one parent has the defective allele

8. Huntington’s Disease • Results in damage to the brain • Symptoms generally occur after the affected reaches 30 years old • Many have children before they show symptoms • Rate of Occurrence: 1 in 15,000 • Life expectancy: 10-20 years after onset of symptoms • Genetic screening can identify those affected before the onset of symptoms

9. BioEd Online Marfan’s Syndrome: An Example • Expressed in both sexes. • Thus, autosomal or sex linked?? • Expressed in every generation. • Thus, dominant or recessive? Marfan Syndrome

10. BioEd Online Marfan’s: Genotype the Normal Individuals • Assign codes for the alleles. • Code “m” for the recessive normal allele. • Code “M” for the dominant allele for Marfan’s syndrome. • Normal individuals must be “_____.”

11. BioEd Online Marfan’s: Genotype the Affected Individuals • Affected individuals must have at least one “____.”

12. BioEd Online Marfan’s: Parent-Offspring Relationships • Possibilities for #1 and #2: Heterozygote (Mm) or homozygous for “M?” • If “MM,” all offspring from a normal mate should be affected. • Therefore, both must be heterozygotes.

13. BioEd Online Marfan’s: Parental Genotypes Known • “M” must have come from the mother. • The father can contribute only “m.” • Thus, the remaining genotypes are “Mm.”

14. Autosomal Recessive Disorders • Autosomes: homologous chromosomes 1-22 • many disorders are autosomal recessive • Requires defective recessive allele to be passed by BOTH parents • Probability of offspring having the disorder: 25% if both parents are carriers/ 0 if only one parent is a carrier.

15. Cystic Fibrosis (CF) • 1 in 20 Caucasians are carriers • Rate of occurrence: 1 in 2000 • Characteristics: accumulation of mucus in lungs and digestive tract. • Life expectancy: ~30 years (before treatment became available), but now depends heavily on the age at when treatment is started.

16. Phenylketonuria (PKU) • Metabolic disorder in which phenylalanine cannot be broken down • Rate of occurrence: 1 in 15,000 • Can result in mental retardation • All infants in US are screened • Reducing intake of phenylalanine until puberty can prevent retardation

17. PKU

18. Sickle cell anemia • Disorder of the Red Blood Cells • Causes sickling of cells preventing normal function • Lack of oxygen to organs can cause tissue damage resulting in intense pain • Affects mostly those of African descent • 1 in 12 African-Americans are carriers • >70,000 have the disease

19. BioEd Online Albinism: An Example • Expressed in both sexes at approximately equal frequency. • Thus, autosomal. • Not expressed in every generation. • Thus, recessive.

20. BioEd Online Albinism: Genotype the Affected Individuals • Assign codes for the alleles. • Code “A” for the dominant normal allele. • Code “a” for the recessive allele for albinism. • Affected individuals must be homozygous for “a.” • First generation parents must be “Aa” because they have normal phenotypes, but affected offspring.

21. BioEd Online Albinism: Genotype the Normal Individuals • Normal individuals must have at least one “A.”

22. BioEd Online Albinism: Parent-Offspring Relationships • #1 must transmit “a” to each offspring. • The “A” in the offspring must come from the father. • Normal father could be either heterozygous or homozygous for an “A.” **

23. BioEd Online Albinism: Parental Genotypes are Known • Both parents are heterozygous or homozygous? • Normal offspring could have received an “A” from either parent, or from both.

24. BioEd Online Albinism: One Parental Genotype is Known • Only the genotype of the offspring expressing albinism are known. • Normal offspring must have received an “a” from their affected father.

25. Tay-Sachs Disease • Metabolic disorder that affects the nervous system • More common in those of Central and Eastern European Jewish descent • 1 in 30 are carriers • Life expectancy: ~5 years

26. Sex-Linked Inheritance • Alleles that are inherited on the sex chromosomes • Written as superscripts on the X and Y chromosomes • XªX or XªY • Most sex-linked traits are associated with the female (X) chromosome

27. Red-Green Color Blindness • Disorder in which a person cannot differentiate between red and green • Allele passed on the X chromosome • Disorder more common in males • Males: one copy results in color blindness • Females: one copy (carrier) two copies result in color blindness

28. Red-Green Color Blindness

29. BioEd Online Hairy Ears: An Example • Only males are affected. • All sons of an affected father have hairy ears. • Thus, hairy ears is Y-linked.

30. BioEd Online Hairy Ears: Female Sex Determination • All females are XX.

31. BioEd Online Hairy Ears: Male Sex Determination • All males are XY.

32. BioEd Online Hairy Ears: Gene on the Y Chromosome • Code “H” indicates the allele on the Y chromosome for hairy ears.

33. Hemophilia • Disorder that prevents blood from clotting properly • Allele passed on the X chromosome • Males more commonly affected • males: one copy results in disorder • Females: one copy (carrier) two copies results in disorder

34. BioEd Online Hemophilia: An Example • In this pedigree, only males are affected, and sons do not share the phenotypes of their fathers. • Thus, hemophilia is linked to a sex chromosome–the X. • Expression of hemophilia skips generations. • Thus, it is recessive. Extensive bruising of the left forearm and hand in a patient with hemophilia.

35. BioEd Online Hemophilia: Expression of the Female Sex Chromosomes • All females are XX.

36. BioEd Online Hemophilia: Expression of Male Sex Chromosomes • All males are XY.

37. BioEd Online Hemophilia: Genotype the Affected Individuals • Assign codes for the alleles. • Code “h” for the recessive hemophilia allele. • Affected individuals must have an “h” on an X chromosome.

38. BioEd Online Hemophilia: Father-Daughter Relationship • All daughters of an affected father receive an X chromosome with the “h” allele.

39. BioEd Online Hemophilia: Homozygous or Heterozygous? • Only males affected • Not Y-linked • Skips a generation: recessive • X-linked

40. Incomplete Dominance • When traits exhibit incomplete dominance, heterozygotes exhibit intermediate characteristics Ex. Snapdragons Red flowers (RR)X White flowers (R´R’) F1: Pink flowers (RR’)

41. Codominance • Heterozygotes exhibit both characteristics ex. Chickens Black rooster (BB) X White hen (WW) F1 : black & white checkered pattern (BW)

42. Polygenic Inheritance • when traits are controlled by two or more genes ex. Hair color, eye color, skin color, height, fingerprint patterns

43. Multiple Alleles • Many traits are controlled by more than two alleles ex. Fur color in many animals

44. Blood Types • An example of several different hereditary patterns • Multiple alleles: A, B, and O • Codominance: A and B • Recessive and Dominant:O is recessive to both A and B

45. Blood Types *Notice how the genotype is written for each type

46. Blood Transfusion Facts • People with type O- blood can donate to anyone (universal donor), but can only receive type O- blood. • People with type AB+ blood can receive blood from anyone (universal recipient), but can only donate to someone who is type AB+.