Mendelian Genetics Gregor Mendel – Austrian monk – performed extensive genetics experiments with garden peas Gregor Mendel – Austrian monk – performed extensive genetics experiments with garden peas du/mendelian_genetics/mend elian_genetics.html du/mendelian_genetics/mend elian_genetics.html du/mendelian_genetics/mend elian_genetics.html du/mendelian_genetics/mend elian_genetics.html html html html html

Gregor Mendel

Important Mendelian Genetics terms: trait: physical attribute or characteristic displayed by an individual (i.e. seed shape, seed colour, etc.) 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) 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) 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) 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) genotype: actual gene (allele) combination present (RR or Rr) phenotype: physical outward appearance shown (round seed or wrinkled seed) 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 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 heterozygote: an individual which contains one of each member of the gene pair; for example the Dd heterozygote Human Eye color Human Eye color Human Eye color Human Eye color

Multiple Alleles Multiple Alleles – the existence of several (more than two) alleles for a gene (e.g. ABO blood group) Multiple Alleles – the existence of several (more than two) alleles for a gene (e.g. ABO blood group) Genotype Blood Type (Phenotype) I A I A or I A i A I B I B or I B i B IAIBIAIBIAIBIAIBAB iiO

Incomplete Dominance shown when a heterozygote has a different phenotype (blending of both homozygotes) than either homozygote (e.g. Snapdragons: 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) RR (red) x WW (white) produce RW (pink) RED WHITE PINK

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

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

Dihybrid Cross Monohybrid cross – dealing with only one trait Monohybrid cross – dealing with only one trait Dihybrid cross – dealing with two traits (seed shape and seed colour) Dihybrid cross – dealing with two traits (seed shape and seed colour) (P 1 )Yellow, round pea plant crossed with wrinkled, green plants produced 100% Yellow, round plants (F 1 - YyRr) (P 1 )Yellow, round pea plant crossed with wrinkled, green plants produced 100% Yellow, round plants (F 1 - YyRr)

F 1 generation crossed – YyRr x YyRr F 1 generation crossed – YyRr x YyRr Four possible gametes – YR, yR, Yr, yr Four possible gametes – YR, yR, Yr, yr

F 2 Generation

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

Mendel’s Laws Mendel’s Laws 3 laws: 3 laws: a. 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. b. 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. c. Law of independent assortment - Alleles for different traits are distributed to sex cells (& offspring) independently of one another.

Linked Genes Linked Genes Linked genes - genes that are on the same chromosome and subsequently are inherited together as a package unless crossing-over separates them. 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. 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. Recombination - creation of combinations of alleles in chromosomes not present in either parent.

Linked Genes??

Crossing Over & Recombination

Hardy Weinberg Equation 1. p + q = p 2 + 2pq + q 2 = 1.0

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

1. q 2 = 1 / 30 = q = √q 2 = √0.033 = = 18.3% of the genes in the population are “unibrow” (nn) 3. p = 1 – q = = = 81.7% of the genes in the population are separate eyebrow. 4. p 2 = = = 66.8% of the population is NN. 5. 2pq = 2 (0.817)( 0.183) = = 29.8% of the population is Nn (carriers for the “unibrow” gene)

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