1. Mendelian Genetics
Gregor Mendel – Austrian monk – performed extensive genetics experiments with garden peas

2. Important Mendelian Genetics terms:
trait: physical attribute or characteristic displayed by an individual (i.e. seed shape, seed colour, etc.)
allele: forms of a trait (i.e. round or wrinkled allele for the trait seed shape)
dominant allele: allele that is displayed when both dominant and recessive alleles are present (dominant allele masks the recessive allele)
recessive allele: allele that is hidden when both dominant and recessive alleles are present (dominant allele masks the recessive allele), and only expressed when both recessive alleles are present)
genotype: actual gene (allele) combination present (RR or Rr)
phenotype: physical outward appearance shown (round seed or wrinkled seed)

3. homozygote: an individual which contains only one allele at the allelic pair; for example DD is homozygous dominant and dd is homozygous recessive; pure lines are homozygous for the gene of interest
heterozygote: an individual which contains one of each member of the gene pair; for example the Dd heterozygote
Human Eye color

4. Multiple Alleles
Multiple Alleles – the existence of several (more than two) alleles for a gene (e.g. ABO blood group)
Genotype
Blood Type
(Phenotype)
IAIA or IAi A
IBIB or IBi B
IAIB AB ii O

5. Incomplete Dominance
shown when a heterozygote has a different phenotype (blending of both homozygotes) than either homozygote (e.g. Snapdragons:
2 alleles - Red – R, White – W
RR (red) x WW (white) produce RW (pink)
RED
PINK
PINK
WHITE
PINK
PINK

6. Codominance Similar to incomplete dominance “co” – together
recessive & dominant traits appear together in the phenotype of hybrid organisms
Ex: roan coat color in cattle (red and white hair on same animal)
2 allelles - R – red, W – white
3 different phenotypes – red (RR), white (WW) and roan (RW)

7. X-linked Inheritance Sometimes called sex-link inheritance
Males – XY, Females – XX
Some traits are present on the X chromosome
E.g. – hemophilia – X-linked disease (“bleeder disease”)
Normal female – XX, carrier female – XXh
Female with hemophilia – XhXh (only if they have both Xh chromosomes)
Normal male – XY, male with hemophilia – XhY
Color blindness – X-linked

8. Dihybrid Cross Monohybrid cross – dealing with only one trait
Dihybrid cross – dealing with two traits (seed shape and seed colour)
(P1)Yellow, round pea plant crossed with wrinkled, green plants produced 100% Yellow, round plants (F1 - YyRr)

9. F1 generation crossed – YyRr x YyRr
Four possible gametes – YR, yR, Yr, yr

10. F2 Generation

11. F2 Generation – phenotypic ratio
9 yellow, round
3 green, round
3 yellow, wrinkled
1 green, wrinkled

12. Mendel’s Laws
3 laws:
Law of dominance – In a cross of parents that are pure for contrasting traits, only one form of the trait will appear in the next generation.  Offspring that are hybrid for a trait will have only the dominant trait in the phenotype.
Law of segregation - During the formation of gametes (eggs or sperm), the two alleles responsible for a trait separate from each other.  Alleles for a trait are then "recombined" at fertilization, producing the genotype for the traits of the offspring.
Law of independent assortment - Alleles for different traits are distributed to sex cells (& offspring) independently of one another.

13. Linked Genes
Linked genes - genes that are on the same chromosome and subsequently are inherited together as a package unless crossing-over separates them.
Crossing over - process of sections of homologous chromosomes breaking and reconnecting onto the other homologous chromosome.
Recombination - creation of combinations of alleles in chromosomes not present in either parent.

14. Linked Genes??

15. Crossing Over & Recombination

16. Hardy Weinberg Equation
p + q = 1.0
p2 + 2pq + q2 = 1.0
Where:
p = Percentage of dominant alleles present in population
q = Percentage of recessive alleles present in population
p2 = homozygous dominant
pq = heterozygous
q2 = homozygous recessive

17. Hardy Weinberg Equation
p + q = 1
p pq + q2 = 1
“Unibrow” is a recessive genetic trait in humans in which it occurs 1 in 30 people.
N – separate eyebrow
n - “unibrow”

18. q2 = 1 / 30 =
q = √q2 = √0.033 = = 18.3% of the genes in the population are “unibrow” (n)
p = 1 – q = = = 81.7% of the genes in the population are separate eyebrow (N).
p2 = = = 66.8% of the population is NN.
2pq = 2 (0.817)( 0.183) = = 29.8% of the population is Nn (carriers for the “unibrow” gene)
Check: 66.7% % + 3.3% = 99.9% ~ 100%

19. Probability the study of outcomes of events or occurrences
Probability = # of chances for an event / # of possible outcomes
Probability of a red card = ½ (26/52)
Probability of a red 6 = 1/26 (2/52)
How does this apply to genetics?
Rr - probability of R = ½, probability of r = ½