Zoo 317 Heredity, Evolution and Society

Lecture 14 Cummings 7:181-192
SEX DETERMINATION

I. Genetic bases of sex determination.

II. Sex determination in mammals.

III. X-chromosome inactivation.

IV. Sex and gene expression.

Terms

Notes
Page 188: Pseudohermaphrodite should be defined as any person in whom the phenotypic sex does not agree with the genetic sex.
Page 189: Not all genes in the "inactive" region of the X chromosome are inactive.
Figure 7.22 and several places in text: Persons with XY chromosome constitution are referred to as "males," even though they are females phenotypically. The common practice among professionals is to assign gender on the basis of phenotype rather than genotype. Therefore, these persons should be considered females.

I. Sex can be defined as a means whereby individuals can exchange genes, leading to new combinations of alleles.

II. Sex determination in mammals

III. X-chromosome inactivation refers to the random inactivation of one of the X chromosomes in each cell of very early XX embryos. As a result, females are a mosaic of tissues in which one or the other X is active. This makes males and females equivalent for activity of most X-linked genes. This explanation was proposed by Mary Lyon and is known as the Lyon hypothesis.

IV. The expression of many inherited traits depends on sex of the individual.



Terms
sex homogametic heterogametic
sexual dimorphism SRY testosterone
androgen anti-Mullerian hormone Mullerian duct
estrogen testicular feminization   androgen insensitivity  
pseudohermaphrodite XX male XY female
  congenital adrenal hyperplasia     X-chromosome inactivation   mosaic
Lyon hypothesis Barr body sex chromatin
sex-influenced trait sex-limited trait Wolffian duct

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last revision: 24 September 1999
owned by: Dr. Eldon Sutton