1. The rest of heredity

2. Law of Independent Assortment:
Each pair of alleles segregates (separates) independently during gamete formation
Eg. color is separate from shape

3. The laws of probability govern Mendelian inheritance
Multiplication Rule:
Probability that 2+ independent events will occur together in a specific combination → multiply probabilities of each event
Ex. 1: probability of throwing 2 sixes
1/6 x 1/6 = 1/36
Ex. 2: probability of having 5 boys in a row
½ x ½ x ½ x ½ x ½ = 1/32
Ex. 3: If cross AABbCc x AaBbCc, probability of offspring with AaBbcc is:
Answer: ½ x ½ x ¼ = 1/16

4. The laws of probability govern Mendelian inheritance
Addition Rule:
Probability that 2+ mutually exclusive events will occur → add together individual probabilities
Ex. 1: chances of throwing a die that will land on 4 or 5?
1/6 + 1/6 = 1/3

5. Segregation of alleles and fertilization as chance events

6. Extending Mendelian Genetics
The relationship between genotype and phenotype is rarely simple
Complete Dominance: heterozygote and homozygote for dominant allele are indistinguishable
Eg. YY or Yy = yellow seed
Incomplete Dominance: F1 hybrids have appearance that is between that of 2 parents
Eg. red x white = pink flowers

7. Codominance: phenotype of both alleles is expressed
Eg. red hair x white hairs = roan horses
Multiple Alleles: gene has 2+ alleles
Eg. human ABO blood groups
Alleles = IA, IB, i
IA,IB = Codominant

8. Blood Typing Phenotype (Blood Group) Genotype(s) Type A IAIA or IAi
IBIB or IBi
Type AB
IAIB
Type O ii

9. Practice Problem #1:
A man who is heterozygous with type A blood marries a woman who is homozygous with type B blood. What possible blood types might their children have?

10. Blood Transfusions Blood transfusions must match blood type
Mixing of foreign blood → clumping → death
Rh factor: protein found on RBC’s (Rh+ = has protein, Rh- = no protein)

11. Practice Problem #2:
Babies Jane (blood type B), John (blood type O), and Joe (blood type AB) were mixed up in the hospital. Who are their parents?
Couple #1: A, A
Couple #2: A,B
Couple #3: B,O

12. Polygenic Inheritance: the effect of 2 or more genes acting upon a single phenotypic character (eg. skin color, height)

13. Nature and Nurture: both genetic and environmental factors influence phenotype
Hydrangea flowers vary in shade and intensity of color depending on acidity and aluminum content of the soil.

14. Mendelian Inheritance in Humans
Pedigree: diagram that shows the relationship between parents/offspring across 2+ generations
Woman =
Man =
Trait expressed:

15. Pedigree Analysis: Widow’s Peak Trait

16. Pedigree Analysis: PTC Tasting

17. Practice Problem
The pedigree below traces the inheritance of alkaptonuria, a biochemical disorder. Affected individuals are shaded. Does alkaptonuria appear to be caused by a dominant or recessive allele?

18. Genetic Disorders Autosomal Recessive Autosomal Dominant Albinism
Cystic fibrosis (CF)
Tay-Sachs disease
Sickle-cell disease
Phenylketonuria (PKU)
Achondroplasia
Huntington’s disease (HD)
Lethal dominant allele

19. Multifactorial Disorders
Heart disease
Diabetes
Cancer
Alcoholism
Mental illnesses (schizophrenia, bipolar disorder)

20. Genetic Counseling

21. Practice Problems
Cystic Fibrosis is an autosomal recessive disorder. What are the chances that 2 carriers for this disease will have a child with CF?
Huntington’s Disease is an autosomal dominant disorder. If a woman with this disease marries a normal man, what are the chances that their children will have the disease?

24. Chromosome Theory of Inheritance
Genes have specific loci (positions) along chromosomes
Chromosomes undergo segregation and independent assortment
Chromosomes tagged to reveal a specific gene (yellow).

25. Thomas Hunt Morgan Drosophila melanogaster – fruit fly
Fast breeding, 4 prs. chromosomes (XX/XY)
Sex-linked gene: located on X or Y chromosome
Red-eyes = wild-type; white-eyes = mutant
Specific gene carried on specific chromosome

26. Sex-Linked Genes Sex-linked gene on X or Y Females (XX), male (XY)
Eggs = X, sperm = X or Y
Fathers pass X-linked genes to daughters, but not sons
Males express recessive trait on the single X (hemizygous)
Females can be affected or carrier

27. Transmission of X-linked recessive traits

28. Sex-Linked Disorders Colorblindness Duchenne muscular dystrophy
Hemophilia

30. X-Linked Genetics Practice Problem
A man with red-green colorblindness (a recessive, sex-linked condition) marries a woman with normal vision whose father was color-blind. What is the probability that they will have a color-blind daughter? That their first son will be color-blind?

31. X Inactivation
Barr body = inactive X chromosome; regulate gene dosage in females during embryonic development
Cats: allele for fur color is on X
Only female cats can be tortoiseshell or calico.

32. Human Development Y chromosome required for development of testes
Embryo gonads indifferent at 2 months
SRY gene: sex-determining region of Y
Codes for protein that regulates other genes

33. Linked Genes
Genes located near each other on same chromosome tend to be inherited together

34. Genetic Recombination: production of offspring with combination of traits different from either parent
If offspring look like parents → parental types
If different from parents → recombinants

35. Calculating Recombination Frequency=
# Recombinants
Total # Offspring
x 100%

36. Sample Problem 1: Calculate the recombination frequency
# of offspring produced:
244 yellow-round
256 green-wrinkled
251 yellow-wrinkled
249 green-round

37. Sample Problem 2: Calculate the recombination frequency
Original homozygous parents (P): Gray body, normal wings x black body, vestigial wings → F1 dihybrid offspring
Dyhybrid testcross (F1): Gray, normal (heterzygous) x Black, vestigial (homozygous recessive)
F2 results shown below:

38. If results do not follow Mendel’s Law of Independent Assortment, then the genes are probably linked

39. Crossing Over: explains why some linked genes get separated during meiosis
The further apart 2 genes on same chromosome, the higher the probability of crossing over and the higher the recombination frequency

40. Linkage Map: genetic map that is based on % of crossover events
1 map unit = 1% recombination frequency
Express relative distances along chromosome
50% recombination = far apart on same chromosome or on 2 different chromosomes

41. Partial genetic (linkage) map of a Drosophila chromosome

42. Linkage Map Sample Problem
Genes A, B and C are located on the same chromosome. Testcrosses show that the recombination frequency between A and B is 28% and between A and C is 12%. Can you determine the linear order of these genes? Explain.