L#32 Ch15 sex determination X-inactivation sex linkage nondisjunction sex chromosome abnormalities

L#32 Ch15 sex determination X-inactivation sex linkage nondisjunction sex chromosome abnormalities

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1 Biology 1107 Lecture # 32 Wednesday March 31, 2010 Lecture based on Chapter 15 1. Sex determination 2. Sex linkage 3. Sex linkage in humans a) Hemophilia (How Queen Victoria contributed to the Bolshevik revolution) b) Red-green color blindness 4. X inactivation in female mammals (Barr body formation) 5. The tortoiseshell and calico cat 6. Sex influenced genes (male pattern baldness) 7. Autosome nondisjunction a) Trisomy 21 8. Sex chromosome nondisjunction b) Klinefelter syndrome c) Turner syndrome d) XYY males 1. Sex determination Read the chromosomal basis of sex on pages 289 and 290. Play attention to figure 15. 6 Some chromosomal systems of sex determination. What is the SRY gene on the Y chromosome? How many genes have been identified on the Y chromosome? How many different proteins? 1.Sex-linked genes have unique patterns of inheritance In addition to their role in determining sex, the sex chromosomes, especially the X chromosome, have genes for many characters unrelated to sex. These sex-linked genes follow the same pattern of inheritance as the white-eye locus in Drosophila . If a sex-linked trait is due to a recessive allele, a female will have this phenotype only if homozygous. Heterozygous females will be carriers. Because males have only one X chromosome ( hemizygous ), any male receiving the recessive allele from his mother will express the trait. The chance of a female inheriting a double dose of the mutant allele is much less than the chance of a male inheriting a single dose. Therefore, males are far more likely to inherit sex-linked recessive disorders than are females. See figure 15.7 The transmission of sex-linked recessive traits. Several serious human disorders are sex-linked. Hemophilia is a sex-linked recessive trait defined by the absence of one or more clotting factors. These proteins normally slow and then stop bleeding. Individuals with hemophilia have prolonged bleeding because a firm clot forms slowly. Bleeding in muscles and joints can
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This note was uploaded on 10/12/2010 for the course BIO 3453 taught by Professor Dervartarian during the Spring '09 term at UGA.

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L#32 Ch15 sex determination X-inactivation sex linkage nondisjunction sex chromosome abnormalities

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