Fundamentals of Genetics Early Genetics Gregor Mendel Austrian

Fundamentals of Genetics

Early Genetics Gregor Mendel- Austrian monk—mid 1800 s “Father of Genetics” - studied garden peas Pisum sativum

Reasons for Mendel’s Success 1. Chose subject carefully- could manipulate which plants were crossed 2. Careful Research- studied one variable at a time * carefully controlled each experiment * analyzed data mathematically

Ex: Purple flowers X White Flowers P 1 Purple flowers X White flowers F 1 All Purple flowers (self-pollinate) F 2 3 Purple flowers: 1 White flower

Conclusions • Mendel concluded that there must be 2 factors controlling each trait • these “factors” are now called alleles • Recessive- allele that is masked by dominant (does not show up in F 1) • Dominant- allele that masks other trait, or appears in F 1

Mendel’s Laws 1. Law of segregation- states that a pair of factors is segregated, or separated, during the formation of gametes *when gametes unite, offspring will have two factors for a specific trait

Mendel’s Laws 2. Law of Independent Assortmentfactors for different characteristics are distributed to gametes independently *only observed for genes on separate chromosomes or located far apart on same chromosome

Genetic Cross Terminology • Genotype- genetic make-up of an organism (Ex: PP, Pp, pp) • Phenotype- appearance of an organism (Ex: tall or short, purple or white flowers)

Genetic Cross Terminology • Homozygous- both alleles of a pair are alike (PP or pp) • Heterozygous- alleles in a pair are different (Pp)

Genetic Cross Terminology • Probability- likelihood that an event will occur • Probability = ___________ • can be written as a fraction, decimal, or percentage

Monohybrid Crosses • Mono = “one” • cross involving only one trait • to predict probability of offspring inheriting certain traits, biologists use Punnett squares

3 Types of Monohybrid Cross 1. Homozygous x Homozygous 2. Homozygous x Heterozygous 3. Heterozygous x Heterozygous

Test Crosses • To determine genotype of an unknown individual that has a dominant phenotype, a test cross is performed • to do this, cross the unknown individual with a homozygous recessive individual

Incomplete Dominance • offspring have a phenotype in between that of the parents • 2 or more alleles influence phenotype (get an intermediate phenotype)

Incomplete Dominance • Example: four o’clocks (flowers) R = red flowers r = white flowers Red x White

Codominance • both alleles for a gene are expressed in a heterozygous offspring • Example: Roan colored horses R= red R’=white • Individual that is RR’ will have both white and red hairs in coat.

Dihybrid Crosses • Di = “two” • cross involving two traits • more complicated- more squares to fill in because there are more possible allele combinations

Types of Dihybrid Crosses 1. Homozygous x Homozygous 2. Heterozygous x Heterozygous 9 different genotypes 4 different phenotypes in a 9: 3: 3: 1 ratio