Fundamentals of Genetics

Introduction to Genetics 1. GREGOR MENDEL - “Father of Genetics” Austrian monk, teacher, scientist, gardener Formulated basic laws of heredity in the early 1860s Used quantitative data

2. Worked with garden peas because: Easy to grow and had a short generation time Could be self-pollinated 3. Chose true-breeding varieties for his experiments NO genetic variation for a trait Studied 7 simple traits

P1 = parental generation F1 = first-generation (sons/daughters) 4. Mendel cross-pollinated plants P1 = parental generation F1 = first-generation (sons/daughters) F2 =second-generation

5. Principle of Dominance and Recessiveness F1 plants resembled only one of the parents F1 hybrids contained two factors for each trait one dominant; (stronger, masks recessive); one recessive; (seems to disappear)

6. Principle of Segregation Organism contains two factors for each trait. Factors segregate during formation of gametes. Each gamete contains one factor for each trait.

7. Principle of Independent Assortment Each trait is independent of another Genes of one pair of traits assort independently All combinations of genes occur in gametes

Chromosomes, Genes, and Genetic Crosses Homologous Chromosomes contain genes (locations) for the same traits Traits are controlled by alleles (alternative forms of a gene). Genotype refers to the alleles an individual receives at fertilization Phenotype refers to the physical appearance of the individual.

5. Homozygous dominant genotypes = two dominant alleles for a trait. (BB) 6. Homozygous recessive genotypes = possess two recessive alleles for a trait (bb) 7. Heterozygous genotypes = one of each allele for a particular trait (Bb)

Show probabilities of future offspring 8. Punnett Squares Show probabilities of future offspring Monohybrid crosses = crosses between individuals that involve one pair of contrasting traits.

9. Monohybrid Crosses (Examples) Ex 1: Pure Tall x Pure Short TT=Tall tt =short F1 F2 T T t Tt Tt T t T t TT tt Genotype: 25% TT homozygous dom. 50% Tt heterozygous 25% tt homozygous rec. Genotype: 100% Tt (heterozygous) Phenotype: 100% Tall (hybrid tall) Phenotype: 75% tall 25% short

10. Test Crosses A cross of an individual of unknown genotype with an individual of known genotype Tells if individual is heterozygous or homozygous Very important to breeders

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Incomplete Dominance

Dominance Has Degrees 1. Incomplete dominance Offspring are intermediate between two parental phenotypes Neither allele is completely dominant over the other Both alleles influence phenotype 3 phenotypes

Ex: Japanese Four o’clocks RR = red RR’ = pink R’R’ = white All Pink 1 red : 2 pinks : 1 white

2. Codominance Both alleles of a gene are expressed. A person with AB blood has both A and B antigens on their red blood cells. Neither allele is dominant or recessive

RED WHITE ROAN

White & Red Mixed – RW (“roan”) Ex: Red Coat - RR White Coat – WW White & Red Mixed – RW (“roan”) R R R W RW RW RW R W RR W RW RW RW WW All Roan – both red and white hair 1 red : 2 roan : 1 white

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Feather color = ORANGE or blue Dihybrid Cross  Feather color = ORANGE or blue   CREST or no crest

A cross involving two pairs of contrasting traits Example: Dominant Recessive Yy, YY = yellow yy = green Rr, RR = round rr = wrinkled

Example cont. P1 RRYY x rryy round, yellow wrinkled, green (homozygous) (homozygous) RY RY ry RrYy RrYy ry RrYy RrYy Offspring are all heterozygous

RrYy X RrYy Law of Independent Assortment Genes for different traits are inherited independently R, r, Y, y go to sperm/egg independently of each other Can recombine in four ways: RY, Ry, rY, ry

RY Ry rY ry RRYY RY Ry rY ry

. 9 round,yellow : 3 round, green : 3 wrinkled, yellow : 9:3:3:1 1 wrinkled ,green RY Ry rY ry RY RRYY RRYy RrYY RrYy Ry RRYy RRyy RrYy Rryy rY RrYY RrYy rrYY rrYy ry RrYy Rryy rrYy rryy