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Sex- Linked Traits, Multiple Alleles and Human Genetics ch14 Review Question Which parent determines the sex of an offspring? ________________ How? _______________________________________________ Sex linked traits… what are they? those traits that are controlled by genes on the X or Y chromosomes. The Y chromosome is much smaller than the X chromosome and only contains fewer genes. Most sex-linked traits are on the X chromosome. Question: Why is a male more likely to inherit a sexlinked genetic disorder? A male can inherit a recessive trait if the gene for the trait is present on his X chromosome, because Y chromosome cannot hide the trait. A female must have the recessive trait on both X chromosomes for that trait to show Previous Knowledge : What are some sex-linked genetic disorders that you already know? __________________________________________ __________________________________________ ________________________________________. Duchenne Muscular Dystrophy SCID- severe combined immune deficiency disorder Colorblindess Hemophilia * Klinefelter’s Syndrome and *Turner’s syndrome caused by chromosome abnormalities of the sex chromosomes but, the genes are not located on the X chromosome. Punnett Squares with Sex-Linked Traits In humans, hemophilia is a sex-linked trait. Having hemophilia is recessive (Xh) to being normal (XH).The heterozygous female is called a carrier. Cross a carrier female with a normal male. __ XHXh __ X __ XHY ___ What are the phenotypic ratios? XH X H Y Xh Multiple Alleles Multiple Alleles: when more than two different alleles exist for the same trait. (Remember: each individual will only have two alleles for a trait but there are several alleles to choose from.) Example: In humans, blood type has multiple alleles. IA and IB are codominant and i (type O blood) is recessive. Blood Types Blood Type Type of Antigen Possible Genotypes Type A A antigen IA IA ,IA i Type B B antigen IB I B, IB i Type AB A and B antigens IA I B Type O No antigens ii Complete Sample problems on Worksheet With Blood type lab! Polygenic Inheritance the inheritance pattern is controlled by two or more genes each with two alleles. Example: eye color is the result of polygenic inheritance. At present, three gene pairs controlling human eye color are known Polygenic inheritance usually shows up as a range of variation such has height, skin color or hair color. The results of an average population will result in a bell-shaped curve. TRACKING TRAITS AND GENETIC DISORDERS WHAT CAN WE USE TO DO THIS? Pedigrees! What is a pedigree? A chart that shows relationships within a family that is used to show inheritance of traits. INTERPRETING AND DRAWING PEDIGREES 1. squares represent males, circles represent females 2. shaded shapes represent those family members having the trait being traced (or disease) 3. un-shaded shapes represent family members not affected by trait or disease. 4.½ shaded square or circle indicates a carrier (heterozygous) individual. 5.Horizontal line connecting circle to square indicates a marriage. 6.Vertical line with a bracket connecting circles or squares to a marriage line indicates siblings (oldest child first) 7. Roman numerals or capital letters indicate generations. 8. The oldest children are placed on left, and youngest are on the right. 9. Each horizontal line represents a generation. Symbols used : do not write Royal disease