Mendelian Genetics Gregor Mendel – Austrian monk – performed extensive genetics experiments with garden peas http://www.biology.arizona.edu/mendelian_genetics/mendelian_genetics.html http://www.quia.com/jfc/65851.html

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)

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

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

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

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)

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

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)

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

F2 Generation

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

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.

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.

Linked Genes??

Crossing Over & Recombination

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

Hardy Weinberg Equation p + q = 1 p2 + 2pq + q2 = 1 “Unibrow” is a recessive genetic trait in humans in which it occurs 1 in 30 people. N – separate eyebrow n - “unibrow”

q2 = 1 / 30 = 0.033 q = √q2 = √0.033 = 0.183 = 18.3% of the genes in the population are “unibrow” (n) p = 1 – q = 1- 0.183 = 0.817 = 81.7% of the genes in the population are separate eyebrow (N). p2 = 0.8172 = 0.668 = 66.8% of the population is NN. 2pq = 2 (0.817)( 0.183) = 0.298 = 29.8% of the population is Nn (carriers for the “unibrow” gene) Check: 66.7% + 29.8% + 3.3% = 99.9% ~ 100%

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