Lecture 5 Flashcards
TDF Protein
Testis Determining Factor
SRY Gene
Sex-determining Region Y
Heteromorphic Chromosomes
Chromosomes that are paired X to Y
Ex: The platypus has 5 heteromorphic chromosomes (X1Y1, X2Y2, X3Y3, X4Y4, X5Y5); the Y chromosomes always segregate together and all the X chromosomes separate to the same pole
Sexual Reproduction
Alternates between haploid and diploid states
Heterogametic Sex
Produces 2 different gamete types with 2 different sex chromosomes
Hermaphroditism
Both sexes in the same organism, mostly invertebrates, snails, slugs, and earthworms
Monoecious
Both male and female reproductive structures in the same organism
Ex: Corn, sagebrush, buttercup
Dioecious
Either male or female reproductive structures but not both in one organism
Ex: Cottonwood trees
Why is the X chromosome important in humans, whether they are male or female?
X chromosome contains genetic information essential for both sexes; at least one copy of an X is required
What happens if there is a Y chromosome present, even if there are multiple X chromosomes?
Still produces a male phenotype
What happens in the absence of a Y chromosome?
Results in a female phenotype
Pseudoautosomal Regions
Regions on the X and Y chromosomes where they are considered homologous; these are essential for X-Y chromosome pairing in meiosis in the male; primary region is located at the ends of the short arms of the chromosomes and the secondary region is located at the ends of the long arms of the chromosomes
Genic Sex-Determining System
No sex chromosomes, only sex-determining genes
Environmental Sex-Determining System
Found in Limpet’s; Limpet’s position in the stack determines sex
Ex: Larva settles on unoccupied substrate = female (attracts other larvae)
Larvae settle on top of female = males (become mates for original female); eventually the males on top switch sex, developing into females and the stacking process repeats
Temperature-Dependent Sex-Determining System
In red eared turtles, as temperatures increase, the percentage of males decreases; in alligators, as temperatures rise, the percentage of males increases to a point, and then they begin to decrease
