Additional slides from lecture 5

Genetics: A Conceptual Approach

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Unformatted text preview: Last time Sex Determination- the sex of an organism is controlled by its genes- in many species, these genes are carried on chromosomes that look different in the two sexes (sex chromosomes)- XX-XY system for sex determination: in humans , it is the presence of the Y chromosome ( SRY gene) that determines maleness in flies , it is the X:A ratio that determines the sex X:A = 1 = female X:A = 0.5 = male Sex-linked characteristics- are controlled by genes carried on the sex chromosomes- pattern of inheritance for sex-linked characteristics differ from the pattern described by Mendel alleles controlling characteristics studied by Mendel are carried on autosomes, so males and females possess two alleles for each characteristic for sex-linked characteristics, females have two alleles but males have only one (male is hemizygous ) phenotypic ratios for sex-linked characteristics often differ among male and female offspring when reciprocal crosses are performed 1. Autosomal Recessive Trait aa Aa Aa aa Aa Aa 1. Autosomal Recessive Trait aa AA Aa Aa Aa Aa If recessive trait is rare persons from outside the family are usually homozygous for the normal allele In this case, none of their children will display the trait (skips generations) Homework Problem: 6-17 Joe is color blind. His father & mother have normal vision, but his mothers father (Joes maternal grandfather) is color blind. All Joes other grandparents have normal color vision. Joe has three sisters: Patty, Betsy, and Lora, all with normal color vision. Joes oldest sister, Patty is married to a man with normal color vision; they have two children, a 9-year- old color-blind boy and a 4-year-old girl with normal color vision. a. Draw a pedigree of Joes family. Homework Problem: 6-17 Joe is color blind. His father & mother have normal vision, but his mothers father (Joes maternal grandfather) is color blind. All Joes other grandparents have normal color vision. Joe has three sisters: Patty, Betsy, and Lora, all with normal color vision. Joes oldest sister, Patty is married to a man with normal color vision; they have two children, a 9-year- old color-blind boy and a 4-year-old girl with normal color vision. a. Draw a pedigree of Joes family. Joe Homework Problem: 6-17 Joe Joe is color blind. His father & mother have normal vision, but his mothers father (Joes maternal grandfather) is color blind. All Joes other grandparents have normal color vision. Joe has three sisters: Patty, Betsy, and Lora, all with normal color vision. Joes oldest sister, Patty is married to a man with normal color vision; they have two children, a 9-year- old color-blind boy and a 4-year-old girl with normal color vision....
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This note was uploaded on 05/06/2010 for the course BIO 311 taught by Professor Otto during the Spring '10 term at George Mason.

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Additional slides from lecture 5 - Last time Sex...

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