Final Concepts for Chapter 11 Mendelian Genetics Codominance Complete dominance Dihybrid cross Genotype Genotypic ratio Heterozygous Homozygous Incomplete dominance Monohybrid cross Phenotype Phenotypic ratio Probability Punnett square Testcross Expected/predicted results Actual/observed results Karyotype Amniocentesis Linked genes Sex-linked disorders Autosomal disorders Allele Dominant Recessive P-generation F1 generation F2 generation Law of independent assortment Law of segregation Chromosomes Pure breed Trait

Independent Assortment vs. Linked Genes Mendel did not know about chromosomes when he proposed the Law of Independent Assortment. The pea traits he studied happened to be located on different chromosomes – so they did assort independently.

Independent Assortment vs. Linked Genes Question: How many traits do you have? Question: How many chromosomes (per cell) do you have? Question: Is it possible to have only one trait per chromosome? No, lots of genes are carried or linked together on the same chromosome.

Independent Assortment vs. Linked Genes Do the punnett square for the following cross – assume independent assortment. Cross two heterozygous tall, heterozygous red flowered plants T=tall R=red flower t= short r = white flower

Independent Assortment vs. Linked Genes What is the phenotypic ratio? TtRr x TtRr TR Tr tR tr TTRR TTRr TtRR TtRr TTrr Ttrr ttRR ttRr ttrr TR Tr tR tr

Independent Assortment vs. Linked Genes 9:3:3:1 ratio 9 = tall and red 3 = tall and white 3 = short and red 1 = short and white PROBABILITY: From this cross, 48 offspring were produced. How many offspring would you expect to be tall and red? How many would expect to be tall and white? How many would you expect to be short and white?

Independent Assortment vs. Linked Genes Now, do the following cross BUT the genes for tallness and red flowers are linked. Cross two heterozygous tall, heterozygous red flowered plants T=tall R=red flower t= short r = white flower

Independent Assortment vs. Linked Genes Hint T t R r TtRr X TtRr Is it possible to produce a Tr gamete?

Independent Assortment vs. Linked Genes TtRr X TtRr What is the phenotypic ratio? tr TR TTRR TtRr ttrr 3:1 3 = Tall and Red 1 = Short and white TR tr

Independent Assortment vs. Linked Genes So… out of the 48 offspring, if the genes are linked, how many would be 1. tall and red? 2. tall and white? 3. short and red? 4. short and white? Answer: tall and red = 36 tall/white = 0 short and white = 12 short/red = 0 EXPECTED RESULTS!

Independent Assortment vs. Linked Genes Is it possible for our Actual Results to show any flowers that are tall/white or short/red? Yes – how? Crossing over

Crossing over occurs in meiosis Pieces of the chromosomes actual switch places.

Complete vs Incomplete Dominance

Codominance – the alleles are equally dominant Roan Cow Human Blood Type

Fill in the genotypes on the pedigree. Sex-linked Traits Traits carried on the X chromosome Fill in the genotypes on the pedigree.

Autosomal disorders Disorders carried on non-sex chromosomes (first 22 pairs) Some are autosomal dominant Huntington’s disease Most are autosomal recessive Sickle-cell anemia Cystic fibrosis

Question: How do you know if the pure bred dog you just paid big bucks for is actually pure? GG? Gg?

Test Cross Cross using a homozygous recessive individual with a dominant individual to determine if the dominant individual is heterozygous or homozygous dominant (pure) Why use a homozygous recessive individual?

Test Cross Do the punnett squares for each case: GG x gg Gg x gg

Test Cross All offspring produced should show the dominant characteristics if the dominant parent is pure (GG) for the trait.