8 2 Patterns of Inheritance Key Concepts and

8. 2 Patterns of Inheritance Key Concepts and Vocabulary Key Concepts: 1. What is a test cross? 2. What are ways in which traits can be inherited? 3. What are human blood types? 4. What is a pedigree and how do I read one? Key Vocabulary: • Test cross • Incomplete dominance • Codominance • Multiple allele • Pedigree

Test Crosses • Determines the genotypes of an unknown organism • The unknown individual is crossed with a homozygous, recessive individual to determine genotype • In rabbits black coat is dominant to white coat. What the possible genotypes of a black rabbit?

Test Crosses • Example: You observe a black rabbit in the woods and want to know what the genotype of the rabbit is. You capture the rabbit and breed the rabbit with a white rabbit. The offspring produced are 50% black and 50% white. What is the genotype of the black rabbit? Use a test cross to prove your results.

Incomplete Dominance • Heterozygous individuals show a “in between” or blending in the phenotype. • Neither allele is dominant recessive or • What are some examples of incompletely dominant traits?

Incomplete Dominance How to set up incomplete dominance problems: • Use • Three possible phenotypes • What letter represents red? White? • RR • WW • RW -

Incomplete Dominance • Example: In Japanese four o’clock flowers, red and white flower colors are incompletely dominant. Predict the results of a cross between homozygous red flowered plant and a homozygous white flowered plant

Codominance • When two different phenotypes produce offspring which display parental traits together. • Both alleles are dominant • Codominance problems are set up the same way as incomplete dominance problems • What are some examples of codominant traits?

What is the difference between incomplete dominance and codominance? Parents

Codominance and Blood Types • Human blood types are Codominant • There are multiple alleles for human blood type: – A - type A blood markers – B - type B blood markers – O - neither A nor B blood markers • A person with genes for type A and B blood markers has type AB blood • What are the possible genotypes for Type A blood? Type B blood? Type O blood?

Codominance and Blood Types • Who can donate blood to someone with type A blood? • Who can donate blood to someone with type O blood? • Who can donate blood to someone with type AB blood?

Codominance • Example: Predict the results of a cross between an individual homozygous for type A blood and heterozygous for type B blood

Example • Predict the results of a cross between an individual with a type A blood (AA) and type B blood (BB)

Sex-linked Traits • Traits that are determined by alleles on the sex chromosomes X Y= Male X X = Female Discovered by Thomas Hunt Morgan! • Males only need one copy of the gene to get the trait, females need two • What are some examples of sexlinked traits?

Sex-linked Traits How to set up sex-linked problems: • Start with the sex chromosomes • Add traits as _______ on X chromosomes • Many possible outcomes: – Female - normal, carrier has trait – Male - normal, has trait • Can a male ever be a carrier?

Sex-linked Traits • Example: Color-blindness is a sex-linked trait. Normal vision is dominant over colorblindness. Cross a male who is color-blind with a female carrier of the trait. Give the sex of all four offspring and tell whether they are color-blind.

Pedigrees • Charts that Symbols in a Pedigree: – Circles represent females – Squares represent males – Shaded shapes means the person has a trait – Half-shaded shapes means the person is a carrier for a trait – Lines between a male and female indicate a marriage – Children are shown in a line underneath a marriage line – Generations are numbered using roman numerals

Pedigrees