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

2. Incomplete Dominance
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 r R

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

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

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

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 Answer: IB IA i IAIB ii 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 Example: Eye color in fruit flies Sex Chromosomes
XX chromosome - female
Xy chromosome - male
fruit fly
eye color

20. Genes on the Male Sex ChromosomesY h Y XH Xh
XHXH
XHXh
XHY
XhY 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
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 XR Xr Y

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

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
Mating
Death

31. Pedigrees Illustrate Inheritance
Human Heredity
Pedigrees Illustrate Inheritance I
Female
Male
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 1 2 3 4 5
III 1 2 3 4 ? IV 1 2 3 4 5

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

33. Pedigrees Illustrate Inheritance
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 1 2 3 4 5
III ? 1 2 3 4 IV 1 2 3 4 5

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. Fusion OR fission in utero
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 acids Ex. (GCA-TCA  GCA-GTC-A
Deletion – base is removed, affects several amino acids Ex. (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

51. Patau’s Syndrome 1 out of 6,000 births Trisomy 13
80-90% do not survive past 1 yr old

52. Edward’s Syndrome Trisomy 18
Second most common trisomy after down’s syndrome
Only 5% live to age 1
1 out of 8,000 births
Severely retarded, many die from malformed heart
Polydactyly or syndactyly

53. Cri du Chat “ Cry of the Cat” Osteogenesis imperfecta
Lobstein syndrome
Brittle bone syndrome
1 in 50,000 births
Severe mental retardation
Low mortality rate

54. Down’s Syndrome Trisomy 21 1 in 700 births Mental retardation
Males are sterile but females are not

55. XYY-Jacob’s Syndrome a.k.a. “Super Males”
1 in 1,000 men
Normal appearance, very tall
Low IQ, prone to violence

56. Klinefelter’s Syndrome
XXY
1 in 1,000
Usually sterile because of low sperm count
Tall, sparse body hair
Suffer from gynecomastia- male breast tissue
Testosterone treatments

57. Turner’s Syndrome XO genotype—Monosomy X 1 in 2,500 births
Short, sterile
75% result in non-disjunction from the father

58. Other Diseases
Sickle Cell Anemia – codominant, causes sickle cell shaped red cells in hemoglobin, common in people with African descent
Tay-Sachs – metabolic disorder, deteriorates brain, death by age 4, recessive is lethal
Cystic Fibrosis – thick mucus clogs, lungs, pancreas, liver. Death by age 20 without proper diet/medication

59. Sickle cell

60. How to know… Family history (mostly probabilities)
Genetic testing (ex: spit test)
Karyotyping
Amniocentesis

61. Amniocentesis – remove amniotic fluid to check for genetic disorders