Basic principles of genetics University of Utah Review of Genes etc! Genetics from the beginning!

The study of Heredity Inheritance of traits coded for by genes

What is a gene pool? All the genes in a given population

Evidence for Heredity Similar phenotype caused by similarities in genotype

Gregor Mendel Austrian Monk!

Mendel’s Pea Plants Showed Traits that were Markedly Contrasting Could tell tall from short easily

Traits studied by Mendel Markedly contrasting

Female part with egg Male part with pollen

Cross Pollination/Cross Fertilization Pollen from anther transferred to stigma of female part

Gregor Mendel Cross pollinated pea plants Studied traits whose expression were markedly contrasting eg Height: tall vs. short…..no in between Pure Tall X Pure Short…….cross 1 All offspring Tall

He then crossed offspring from cross 1 Offspring: 75% Tall : 25% Short He reasoned that…… Gene for tall is dominant Gene for short is recessive

Summary of Mendel’s Cross TT x tt Tt Tt x Tt Tall : 1 Short Parents referred to as P1 First generation referred to as F1 (F=Filial) Second generation referred to as F2

T T t t Tt Monohybrid Cross: Involving 1 trait Phenotypes All Tall Genotypes All Tt Heterozygous Punnett Square

T t T t TT Tt tt Monohybrid Cross Phenotypes 3Tall: 1Short Genotypes 1 TT : 2 Tt : 1 tt

Genotypes of parents F1 F2 Punnett Square

Which characteristic appears to be recessive? Crossing Tall and Short Plants

Genetics Terminology Physical appearance = phenotype Genetic make up causing pheno = genotype Genotype described using minimum of 2 letters All traits controlled by at least 2 genes These referred to as alleles of a pair For height: alleles are T and t

If genotype is TT, plant is tall (homozygous dominant) If genotype is Tt, plant is also tall but also a carrier for short (heterozygous) No need to say Heterozygous dominant…why?? Hybrid & Heterozygous often confused

More terminology…Yikes!!. If genotype is tt, plant is short (homozygous recessive or just recessive) Phenotypic ratio in cross 1 = all tall Phenotypic ratio in cross 2 = 3 tall : 1 short Genotypic ratio in cross 2 = 1 TT: 2 Tt: 1 tt G.R. & P.R. found easily using punnett square

Identify the recessive allele & phenotype Using the following punnett square

Monohybrid Cross Phenotypes 1 Tall: 1 Short Genotypes 1 Tt : 1 tt t t T t Tt tt

Conclusions from Mendel’s work Inherited characteristics controlled by factors (genes) found in gametes All traits controlled by 2 alleles (minimum). –Some alleles mask effect of others. These are called dominant alleles

Law of Segregation: Pairs of genes segregate when homologous chromosomes move to opposite poles during meiosis Law of Independent Assortment: Different pairs of alleles segregate independently of each other

Mendel’s law of segregation

Independent Assortment

Test Cross Used to determine genotype of individual expressing dominant characteristic eg. If pea plant is tall Genotype could be TT or Tt Only one way to find out! Cross with homozygous recessive

Test Cross Phenotypes All Tall Genotypes All Tt t t T T Tt No short offspring

Test Cross Phenotypes 2 Tall : 2 short Genotypes 2 Tt : 2 tt t t T t Tt tt Short offspring

Summary of Test Cross Results If some recessive individuals show up….. Genotype of unknown must be heterozygous If no recessives show up…. Genotype is probably homozygous dominant

Testcross with monohybrids

Test Crossing Sheep Sheep ranchers like producing white wool Easier to dye and less brittle than black White is dominant, black recessive If farmer suspects white sheep in herd are heterozygous…what can she/he do????

Farmer may find out for certain by crossing suspected carriers with homozygous recessive (ww) If some black sheep show up as offspring… Sheep was a carrier for black wool! (heterozygous) These sheep make better meat!!!!