Genetics Spring 2015 Chromosomes and Sex-Chromosomes Inheritance I

Outline Sex-Chromosome Inheritance Mitosis Meiosis

Sex-Chromosome Inheritance – Sex Determination Females are homogametic (X); males are heterogametic (X or Y). Autosomes are all the other chromosomes. X an Y associate during meiosis, at a small region of homology.

Reciprocal crosses for X-linked eye color gene (w+ or w allele) give different results (not the same progeny). Males therefore exhibit recessive traits carried on the X ch: X-linked traits Sex-Chromosome Inheritance – X-linked Inheritance in Drosophila (reciprocal crosses) To test the role of parental sex chromosomes on a given inheritance. Is the trait sex linked or autosomal? (sex linkage)

Seen in homozygous dominant and heterozygous in female and hemizygous dominant in males. X-linked dominant traits occur in both sexes, but affect more females than males. X-linked dominant traits do not skip a generation, as the mother potentially passes the trait on to all her children (sons and daughters equally affected). X-linked dominant traits do not skip a generation, as the father passes the trait on to all his daughters but not to his sons (as the Y needs to be passed on). Human Pedigree Analysis – X-linked Dominant Inheritance Write a genotype underneath each individual using X, Y, A and a as symbols.

Pedigree showing full penetrance Rett syndrome (dominant) is a progressive neurodevelopmental disorder almost exclusively affecting females. Find characteristics

Human Pedigree Analysis –X-linked Recessive Inheritance Seen in homozygous recessive in female and hemizygous recessive in males. X-linked recessive traits occur in both sexes, but affect more males than females. X-linked recessive traits tend to skip a generation. X-linked recessive traits are not passed on from father to son, as the son inherits the Y-chromosome from his father and not the X-chromosome (affected males receive allele from mother). Write a genotype underneath each individual using X, Y, A and a as symbols.

Hemophilia (recessive) transmission among Queen Victoria's descendants Find characteristics

Human Pedigree Analysis –Y-linked Inheritance Seen in males only as and traits are passed on from father to sons. Y-linked traits are very rare as the Y chromosome is small and does not contain many genes. Write a genotype underneath each individual using X, Y, A and a as symbols.

Hypertrichosis of the ears Find characteristics

Little round shapes denote miscarriages (Macias-Flores et al., 1984) Not all hypertrichosis cases are Y-linked …….in this case, hypertrichosis is ……. Check a few characteristics of all the inheritance patterns and make a diagnosis. Xxxxx My diagnosis is:

Not all hypertrichosis cases are Y-linked and XXXXXX (your previous diagnosis) …….in this case, hypertrichosis is ……. Check a few characteristics of all the inheritance patterns and make a diagnosis. Xxxxx My diagnosis is: (2006)