Unit 8: Mendelian Genetics 8 Unit 8: Mendelian Genetics 8.6 Other Patterns of Inheritance: Sex-Linked Traits

Humans have 22 pairs of autosomes and 1 pair of sex chromosomes. Males are XY Males donate their Y chromosome to their sons only and their X chromosome to their daughters. They determine the sex of the child! Females are XX Females donate one or the other of their X chromosomes to their sons and daughters. Chromosomes

Sex-Linked The gene is carried on a sex chromosome (x or y) Occur most often in males because they only receive one X chromosome from their mother. Most of these genes are recessive, which means mom can be a carrier and pass the trait to her offspring A carrier is a female who is heterozygous for a trait and can pass the trait on to her offspring but does not show symptoms of the trait. Examples: Hemophilia Red-green color blindness Sex-Linked

Using a Punnett Square for Sex-Linked Determine the genotypes of the parents Mom is a carrier: Xx heterozygous Mom is NOT a carrier: XX homozygous Mom shows trait: xx homozygous recessive Dad “normal”: XY Dad with trait: xY Place the traits onto the Punnett square as you have before Cross the traits in the square Determine the genotype and phenotype of the offspring Male = XY, xY Female = XX, Xx Using a Punnett Square for Sex-Linked

Example with Sex-Linked Carol is a “carrier” for a recessive sex-linked trait that causes red- green color blindness. Carol has a baby with Bill, who is normal. a. parent genotype b. offspring genotype c. offspring phenotype d. proportion of male offspring e. Proportion of offspring with red-green color blindness.

Parents: The McBride’s: type O and AB (1 Punnett) The Gonzales’: type A and B (4 Punnetts) The Pepronis: type A and O (2 Punnetts) Children: Baby A is type AB Baby B is type O Baby C is type B 1. Who are the parents of baby A? A: Gonzales 2. Who are the parents of baby B? A: Pepronis 3. Who are the parents of baby C? A: McBride Practice In a hospital, 3 babies were born simultaneously during a thunderstorm. The lights went off and the babies were mixed up. The hospital wants to match the baby with its parents by looking at the blood types. Can you help?