mcb104 _101-106_ week 2 - MCB 104 Discussion (sections 101...

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MCB 104 Discussion (sections 101 &106) Sept. 8-10, 2009 Dihybrid Cross: A cross examining the outcome of 2 traits, each controlled by a separate gene AaBb X AaBb: (Make sure you understand this!!!) When both traits are considered, the progeny will have 4 possible phenotypes, occurring in a 9:3:3:1 ratio. When a single trait is considered, there are 2 phenotypic outcomes, and these will occur in a 3:1 ratio. SEX-LINKED TRAITS Genes responsible for sex-linked traits are encoded on the sex chromosomes (usually X). Due to the differential inheritance of X chromosomes between males and females, the inheritance of sex-linked traits does not follow the typical Mendelian pattern of inheritance. In terms of autosomal recessive traits, it is said that an individual must be homozygous recessive in order to display the recessive trait. However, XY individuals cannot be homozygous for a gene encoded on the X chromosome because they only have 1 copy of X, but they can have an X-linked recessive trait. What is a more accurate description of the requirements needed for someone to display a recessive trait – one that would include both autosomal and X-linked traits? If a gene responsible for a recessive trait is encoded on the X chromosome, people of which sex are more likely to display the recessive trait? Why? GENETIC LINKAGE
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mcb104 _101-106_ week 2 - MCB 104 Discussion (sections 101...

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