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Lecture 4 - Lecture 4 Sex linked single gene inheritance...

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Lecture 4 Sex linked single gene inheritance Introduction to pedigrees Mendel’s Second Law
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Many plants and animals exhibit sexual dimorphism. Individuals are either male or female as a result of inheriting either an X or Y chromosome paternally. X and Y chromosomes are termed sex chromosomes, as opposed to autosomes (all other chromosomes). At meiosis in females the one copy of the X chromosome is distributed into each gamete. In males the X and Y are distributed so that there are two types of gametes; two carry the X and two carry the Y. This equal distribution accounts for the equal probability of male and female progeny in Diploid number (46) Females: 44 autosomes + X X Males: 44 autosomes + X Y Very little in the differential region is related to sex determination/function.
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Sex-Linked Single Gene Inheritance Patterns Eye color in fruitfly…Note that eye color is unrelated to sex determination, the gene that specifies this characteristic is situated in the differential region of the X chromosome. Remember male and female have X…only male has Y. Therefore this gene is hemizygous. Hemizygous: a gene present only in one copy in a diploid organism – for example an X-linked gene in a male mammal (or arthropod in this case!)
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Reciprocal cross: a pair of crosses where genotype A (female) X genotype B (male) and B (female) X (A male)
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Figure 2-27 part 2 Sex linked inheritance will show different phenotypic ratios the two sexes of progeny and in the reciprocal cross.
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Human pedigrees: predicting outcomes of matings when progeny are few.
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