Chromosomes and inheritance

Sex determination XX X Y XXXX XXYY –Female and males have same autosomes. –Females have “XX” for sex chromosomes. Gametes only XGametes only X –Males have “XY” for sex chromosomes. Gametes x or yGametes x or y

Sex Linked Traits Sex linked traits are located on the X sex chromosome.Sex linked traits are located on the X sex chromosome. Males:Males: –XRY–XRY–XRY–XRY –XrY–XrY–XrY–XrY Females:Females: –XRXR–XRXR–XRXR–XRXR –XRXr–XRXr–XRXr–XRXr –XrXr–XrXr–XrXr–XrXr Males: ½ chance of recessive phenotype Females: 1/3 chance of recessive phenotype

XRXRXRXR XrXrXrXr XrXrXrXr Y Y Y XrXrXrXr XrXrXrXr XRXRXRXR XrXrXrXr XRXRXRXR XrXrXrXr P = X R X r x X r Y Cross a carrier female for white eyes with a male that is white eye. What percent of the offspring will have white eye?

Multiple Alleles Instead of two versions or alleles there are 3 or more alleles.Instead of two versions or alleles there are 3 or more alleles. I A, I B, i are the alleles for blood type.I A, I B, i are the alleles for blood type. Possible genotypes would bePossible genotypes would be –I A I A, I a i –I B I B, I B i –I A I B –ii

White board: What blood types might result in a family in which the mother is O and the father is AB? P = I A I B x iiP = I A I B x ii i i i i i i IAIAIAIA IBIBIBIB IAIAIAIA IBIBIBIB IBIBIBIB IAIAIAIA 50% A, 50%B

Chromosome Mutations Germ cell mutationsGerm cell mutations –Occurs in cells that will become sperm or eggs Somatic mutationsSomatic mutations –Occurs in body cells.

Chromosome Mutation: deletion When a portion of the chromosome is lost.When a portion of the chromosome is lost.

Chromosome Mutations: inversion occurs when a piece of the chromosome detaches and then reattaches in the opposite position.occurs when a piece of the chromosome detaches and then reattaches in the opposite position.

Chromosome Mutations : translocation When a part of a chromosome breaks off and reattaches to another chromosome.When a part of a chromosome breaks off and reattaches to another chromosome.

Chromosome Mutations: Nondisjunction When chromosomes do not segregate properly during meiosis.When chromosomes do not segregate properly during meiosis. Nondisjunction results in missing or extra chromosomesNondisjunction results in missing or extra chromosomes

Disorders Due to Nondisjunction Trisomy means 3 chromosomes instead of normal pair.Trisomy means 3 chromosomes instead of normal pair. Monosomy means 1 chromosome instead of normal pair.Monosomy means 1 chromosome instead of normal pair.

Review 1.For a sex-linked trait what are the odds that a male will have the recessive phenotype? 2.What happens with deletion? 3.Think back to the karyotyping lab. Name a disorder that can occur due to trysomy. Answers: 1.½ 2.A portion of a chromosome is lost. 3.Downs syndrome, or Edward’s syndrome, or Turner’s syndrome…