BIOL1006 Lecture 17: SEX AND THE SINGLE CHROMOSOME L17
31 Jul 2018
School
Department
Course
Professor
SEX AND THE SINGLE CHROMOSOME L17 (7/05)
• Chromosomal basis of sex
• Abnormal sexual phenotypes
• Molecular basis od sex determination
• Sex-linked pedigrees
• Evolutionary importance
Chromosomal basis ofsex determination in humans
• Female
o 22 pairs of autosomes + XX
o All gametes 22A + X
o Homogametic
• Male
o Half gametes 22A + Y
o Half 22AA + X
o Heterogametic
Turner's syndrome (XO)
• 1/3500 --> female phenotype, sterile
o Late sexual maturity
o Webbing of skin between finders and neck
o Upturned fingernails
XXY Klinefelter's syndrome
• 1/800 --> male phenotype, sterile
XXX triple X
• 1/2000 --> female phenotype,, fertile
XYY Double Y
• 1/550 --> normal male phenotype
Molecular basis of sex
• Controlled by sex determining region Y (SRY) gene
• Males require:
o Testis determining factor
o SRY locus on Y chromosome
o Receptor for male steroid hormones
o Androgen receptor on X chromosome
Sex-linked inheritance
• Genes on part of X and Y that do not pair show sex linkage, eg. Colour blindness
Costs of sex
Document Summary
Sex and the single chromosome l17 (7/05: chromosomal basis of sex, abnormal sexual phenotypes, molecular basis od sex determination, evolutionary importance. Female: 22 pairs of autosomes + xx, all gametes 22a + x, homogametic, male, half gametes 22a + y, half 22aa + x, heterogametic. Turner"s syndrome (xo: 1/3500 --> female phenotype, sterile, late sexual maturity, webbing of skin between finders and neck, upturned fingernails. Xxy klinefelter"s syndrome: 1/800 --> male phenotype, sterile. Xxx triple x: 1/2000 --> female phenotype,, fertile. Xyy double y: 1/550 --> normal male phenotype. Molecular basis of sex: controlled by sex determining region y (sry) gene, males require, testis determining factor, sry locus on y chromosome, receptor for male steroid hormones, androgen receptor on x chromosome. Sex-linked inheritance: genes on part of x and y that do not pair show sex linkage, eg. colour blindness. Stds: costs of finding mate, courting, etc, meiosis, population increase (2-fold cost of sex)
