Non-Mendelian Patterns of Inheritance: Incomplete Dominance, Codominance and Sex-Linked Traits

1. Non-Mendelian Patterns of Inheritance:Incomplete Dominance, Codominance and Sex-Linked Traits

2. Incomplete Dominance r r R R • F1 hybrids have an appearance somewhat in between the phenotypes of the two parental varieties. • Example:snapdragons (flower) • red (RR) x white (rr) • RR = red flower • rr = white flower

3. Incomplete Dominance r produces the F1 generation Rr Rr R R Rr Rr All Rr = pink (heterozygous pink) r

4. Incomplete Dominance

5. Incomplete Dominance • Blending of alleles to produce a different phenotype from either parent

6. Codominance • Two alleles are expressed (multiple alleles) in heterozygous individuals. • Example: blood type • Phenotype Genotype • 1. type A = IAIA or IAi • 2. type B = IBIB or IBi • 3. type AB = IAIB • 4. type O = ii

7. Codominance Problem IA i IAIB IBi IB 1/2 = IAIB 1/2 = IBi IB IAIB IBi • Example: homozygous male Type B (IBIB) • x heterozygous female Type A (IAi)

8. Another Codominance Problem IA IB IAi IBi i 1/2 = IAi 1/2 = IBi i IAi IBi • Example:male Type O (ii) x female type AB (IAIB)

9. Codominance • Question:If a boy has a blood type O and his sister has blood type AB, what are the genotypes and phenotypes of their parents? • boy - type O (ii) X girl - type AB (IAIB)

10. Codominance IA i IAIB IB i ii • Answer: Parents: genotypes = IAi and IBi phenotypes = A and B

11. Pattern of Inheritance • Complete Dominance - 1 allele overshadows the other allele in a heterozygous individual • Incomplete Dominance – blending of alleles to produce a different phenotype from either parent (Ex. Red rose X White rose = Pink rose) • Codominance– both alleles of a gene are expressed(Ex. Red rose X White rose = red/white rose)

12. Incomplete or Codominance?

13. Incomplete or Codominance?

14. More Patterns of Inheritance • Autosomal inheritance – genes are located on the autosomes, same for both male and female • Sex-linked inheritance – genes located on the sex chromosomes, different for male and female • Sex-influenced traits – sex hormones create different phenotypes in males and females (Ex. Baldness) • Multiple alleles – has more than 2 alleles for the same gene (Ex. blood types) • Polygenic inheritance – coded for by many genes (skin color, hair color, height)

15. Blood Type • Multiple Alleles – 3 or more alleles code for a trait • Codominant Inheritance • Blood types – A, B, AB, O are coded by 3 alleles (A, B, O) • Universal Donor – O • Universal Recipient – AB • RH+ - antigen present • RH- - no antigen present

18. Sex-linked Traits • Traits (genes) located on the sex chromosomes • Sex chromosomes are X and Y • XX genotype for females • XY genotype for males • Many sex-linked traits carried on X chromosome

19. Sex-linked Traits fruit fly eye color XX chromosome - female Xy chromosome - male Example: Eye color in fruit flies Sex Chromosomes

20. H h Y Y Genes on the Male Sex Chromosomes XH Xh XH Y RECESSIVE DOMINANT

21. Sex-linked Inheritance • Color Blindness – recessive, on X chromosome • Normal Vision is dominant • Genotypes: • XCXC – normal female, non carrier • XCXc’ – normal female, carrier (may pass recessive allele on to sons and/or daughters) • Xc’Xc’ – colorblind female (will pass recessive allele to all children • XCY – normal male • Xc’Y – colorblind male (will pass recessive allele to daughters only)

23. ~Hemophilia – bleeder’s disease, recessive, linked to the X chromosome • Protein Factor VIII or IX is missing but is necessary to clot blood • Genotypes: • XHXH – normal female, non carrier • XHXh – normal female, carrier • XhXh – hemophiliac female • XHY – normal male • XhY – hemophiliac male

24. Female Carriers

25. Sex-linked Trait Problem Xr Xr XR Y • Example: Eye color in fruit flies • (red-eyed male) x (white-eyed female)XRY x XrXr • Remember: the Y chromosome in males does not carry traits. • RR = red eyed • Rr = red eyed • rr = white eyed • XY = male • XX = female

26. Sex-linked Trait Solution: Xr Xr XR Xr XR Xr XR Y Xr Y Xr Y 50% red eyedfemale 50% white eyed male

27. Pedigrees

28. Making a Pedigree • A family tree traces a family name and various family members through successive generations. • Through a family tree, you can identify the relationships among your cousins, aunts, uncles, grandparents, and great-grandparents.

29. Pedigrees Illustrate Inheritance • A pedigree is a graphic representation of genetic inheritance. • It is a diagram made up of a set of symbols that identify males and females, individuals affected by the trait being studied, and family relationships.

30. Pedigrees Illustrate Inheritance Male Parents Siblings Female Affected male Known heterozygotes for recessive allele Affected female Death Mating

31. Human Heredity Pedigrees Illustrate Inheritance Female Male I • In a pedigree, a circle represents a female; a square represents a male. • Highlighted circles and squares represent individuals showing the trait being studied. • Circles and squares that are not highlighted designate individuals that do not show the trait. 1 2 II 2 1 4 5 3 III 1 4 2 3 ? IV 5 3 4 2 1

32. Human Heredity Pedigrees Illustrate Inheritance • A half-shaded circle or square represents a carrier, a heterozygous individual.

33. Human Heredity Pedigrees Illustrate Inheritance • A horizontal line connecting a circle and a square indicates that the individuals are parents, and a vertical line connects parents with their offspring. • Each horizontal row of circles and squares in a pedigree designates a generation, with the most recent generation shown at the bottom. • The generations are identified in sequence by Roman numerals, and each individual is given an Arabic number. I 1 2 II 4 2 3 1 5 III ? 1 4 2 3 IV 2 3 5 1 4

34. Dd DD Dd Dd Dd Dd Dd Dd Dd dd dd DD DD dd DD dd dd dd DD DD DD Dd Dd Dd Dd

35. Dd Dd dd dd dd DD dd dd Dd Dd Dd Dd dd dd dd dd

36. Hemophilia pedigree beginning with Queen Victoria

37. Genetic Rarities & Abnormalities • What can happen when meiosis goes awry…

38. Twins • Identical – develop from the same fertilized egg (zygote), genetically identical, always same sex • Fraternal – 2 sperm fertilize 2 different eggs, genetically different

39. Conjoined Twins Fusion OR fission in utero

40. Chromosome Theory • Each gene occupies a specific place on chromosome • Gene Mapping – locating and mapping the position of a gene on the chromosome • Gene Linkage – some genes are linked together and are inherited together • Crossing Over – produces new allele combinations and increases variety

41. Types of Mutations – mistakes • Germ mutations – occur in gametes. Inheritable (colorblindness, hemophilia) • Somatic mutations – affect body cell, not inheritable (cancer) • Chromosomal mutations – most drastic, change in structure or # of chromosomes (Downs’ syndrome)

42. Point Mutations • Substitution– one base exchanges for another, affects 1 amino acid(Ex. GCA-TCA  GCT-TCA • Insertion(frame shift) – 1 base is inserted, affects several amino acidsEx. (GCA-TCA  GCA-GTC-A • Deletion– base is removed, affects several amino acidsEx. (GCA-TCA  GCT-CA

43. Point Mutation

44. Frameshift Mutation

45. Nondisjunction (Chromosomal mutation) – chromosomes do not separate during meiosis • Sex Chromosomes • Turner’s Syndrome – XO – 45 chromosomes, female, sterile • Kleinfelter’s syndrome – XXY – 47, XXXY – 48, or XXXXY – 49 chromosomes, male, sterile • Autosomes • Down’s syndrome (Trisomy 21) extra 21st chromosome • Trisomy 8 and 13 – result in miscarriages

46. Karyotypes

50. Nondisjunction