2 Two copies of each autosomal gene affect phenotype Mendel studied autosomal gene traits (these genes are on autosomes), like hair texture.The “either-or” traits that were seen in your tutorial.Genes found on autosomes (1-22 for humans) = autosomal traitsGenes found on sex chromosomes (pair 23 for humans) = sex-linked traits
3 There is a 50/50 chance of child being a boy/girl Sex DeterminationSex determined by genes found on the X and Y chromosomeFemales: egg produced with an X chromosomeX chromosome genes in mammals affect many traits.Males: ½ sperm cells contain X; and the other ½ contain YChromosome genes in mammals are responsible for male characteristics.X XXYXXXXXYXYThere is a 50/50 chance of child being a boy/girl
4 Males & Females have Different Inheritance PatternsALL of a male’s sex-linked genes are expressed.Males have no second copies of sex-linked genes.Because of this, males can NEVER be “carriers” of sex-linked traits or disorders.Ex: Colorblindness, Hemophilia, Muscular dystrophy
5 Sex-Linked DisordersDefined: Inherited conditions found on X chromosomeUsually recessiveFemales: XX chromosomesXH XH = healthyXH Xh = healthy carrierXh Xh = diseaseMales: XY chromosomesXHY = healthyXhY = diseaseRare in women (back-up X chromosome)Ex: Colorblindness, Hemophilia, Muscular dystrophy
7 Sex-Linked Punnett Squares Let’s take a look at…Sex-LinkedPunnett Squares
8 Jen is a healthy carrier (XH Xh) of hemophilia and Adam has no history in his family (XH Y). What is the probability ofgetting:Daughter with hemophilia?0%Carrier child?25%Child with hemophilia?Two healthy children?¾ x ¾ = 9/16 (56%)Healthy girlHealthy boyHealthy girl (carrier)Disease boy
9 Kelly is a healthy carrier of hemophilia, but Jim suffers from the disease. What is the probability of getting a:Healthy son?25%Healthy daughter?Child with hemophilia?50%Carrier child?Healthy girl (carrier)Healthy boyDisease girlDisease boy
10 If the phenotype is more common in males, the gene is likely sex-linked.
11 Let’s try a sex-linked problem: A man and a woman marry.The woman is a carrier of colorblindness, an X-linked disorder.They have 4 children, 3 boys and one girl.Two of the boys are colorblind, and the girl is a carrier.The carrier daughter marries a healthy man.a)What is the probability they will have a carrier?b)What is the probability they will have a child that is colorblind?XD XdXD YXd YXd YXD YXD XdXD Y?XD XdXD XD XD XdXDY25%XD Y Xd Y25%
12 REVIEW How are sex-linked disorders different from autosome disorders? Why are sex-linked disorders more common in males?Write the genotype of a heterozygous dominant female.Write the genotype of a carrier female.Examine Kelly and Jim’s Punnett square. What are the chances they would have three children, all of whom are healthy?