Chapter 14 Genetics

Introduction Pre 1800s – blending hypothesis 1850s – Gregor Mendel

Pisum sativum – what makes pea good genetic model? Pea character (gene) = Pea trait (allele) =

self fertilization Vs. cross fertilization

The monohybrid cross Cross true breeding parental plants (P) produces F1 generation

-character (gene) -trait (allele) - dominant phenotype - recessive phenotype

F1 plants all purple

Cross F1 plants F2 plants = ~250 white ~750 purple A monohybrid Is this quantitative or qualitative data?

Mendel’s Conclusions

Dominance Allele = Alternative version of gene Dominant allele P Recessive allele p Each individual inherits 2 alleles/gene GenotypePhenotype? PP homozygous dominant pp homozygous recessive P p heterozygous

Dominant allele masks expression of recessive allele Find the dominant allele Pick symbols What is the phenotype of plant with genotype Rr? What is genotype of a green plant?

Genotype?

Segregation The 2 alleles segregate in gametes during meiosis Random segregation Human chromosome 11 gene for beta globin Genotype Hbb/Hbb Pea chromosome 1 Genotype of plant? Phenotype of plant?

Mendel did not know about: – DNA/chromosomes/genes – Crossing over or the cell cycle – Linked alleles

In mice, black fur is dominant over white fur Cross heterozygous mouse with homozygous recessive mouse Possibilities?

In mice, black fur is dominant over white fur Cross heterozygous mouse with homozygous recessive mouse 1.Make an allele key 2.Show the cross 3. Write the phenotypes under the genotypes 4. Determine the parental gametes (random segregation) 5. Add to Punnett square 6. Determine offspring

Punnett square What is the expected ratio of phenotypes? Genotypes? In a litter of 3, how many are expected to be white? Which phenotype is the recessive phenotype?

In cats striping is dominant over non-stripes. Mate two heterozygous cats.

The Scottish fold is a dominant trait Genotypes FF Ff ff Phenotypes? The original Scottish Fold was a white barn cat named Susie, found in Scotland

Test cross Scottish fold cat -> Is she Ff or FF? If FF, then cross to ff  kittens? If Ff, then cross to ff  kittens? A test cross is always a cross to a homozygous individual.

Review All possible one gene crosses B = black fur allele b = white fur allele BB X BB  all black BB X Bb  BB X bb  Bb X Bb  Bb X bb  bb X bb  all white

The Dihybrid cross (2 genes)

Independent Assortment 2 genes Y = yellow pea allele R = round pea allele y = green pea alleler = wrinkled Phenotypes of peas

True-breeding yellow, round X true-breeding green, wrinkled Allele key? P Genotype? Gametes? (always 4 per parent in 2 gene cross) X R = round allele Y = yellow r = wrinkled y = green rryy RRYY RY and ry

Parental generation: RRYY X rryy Gametes ? F1 generation? Gametes of F1 generation? F2 generation?

F2 generation Ratio of genotypes? Ratio of phenotypes?

Extensions of Mendel Codominance Both alleles expressed in phenotype Ex. Blood type I gene Alleles I A I B Phenotype of I A I B ?

multiple alleles Ex. blood type Alleles I A I B i I A I A I B I B I A I B I A i I B iii

polygenic inheritance multiple genes affect characteristic Ex. skin – at least 3 genes Height

environmental effects A particular genotype may have a phenotypic range Ex – Does blood color have a norm? – Skin color?

?

Recessively inherited disorders A allele  normal protein a allele  malfunctioning or no protein AA Aa heterozygotes are carriers aa disorders range from fetal lethal to mild

Ex. albinism a allele does not code for functional melanin protein Chromosome 11

Recessive traits bb = blond hair bb = blue eyes ii = type O blood

Dominantly inherited disorders A allele  abnormal protein a allele  normal protein AA Aa aa

Achondroplasia D allele causes dwarfism

Multifactorial disorders Genetic component + environment (aging, diet, chemicals, radiation, etc.)