Topic 11 pt 1: Sex Chromosomes Flashcards
What are autosomes? What kind of ratios do they show
Non-sex chromosomes (not X or Y) carry the majority of genes
Show normal mendelian ratios for monohybrid, dihybrid and test crosses
How do we tell if a gene is autosomal
Perform a reciprocal cross, do we get mendelian ratios?
Most organisms have how many sexual phenotypes? What are they (usually)
Two:
- male: small and numerous gametes
- female: large and limited gametes
What is the XX-XY chr system? Who uses it
Humans, flies, most mammals, some plants
Homogametic = female
heterogametic = male
What is the ZZ-ZW chr system? Who uses it?
Birds, some reptiles, butterflies
Male = homogametic
Female = heterogametic
Mechanism by which sex is established is termed
Sex determination (e.g. XX/XY, ZZ/ZW)
What is the XX-X0 chr system? Who uses it
Insects, worms
XX = females or hermaphrodites
X0 = males missing a chr (heterogametic)
Who has no sex chromosomes, only sex-determining genes. This is called
Genic sex determination (on various autosomes)
Some plants, fungi, protozoans, fish
What are some ways that sex is determined in nature
Temperature (or other environmental conditions e.g. turtles, alligators)
Nutrient status (poor = usually male, rich = female)
Population density
Age
Describe sex determination in the slipper limpet
Lone larva settle as female
She releases a chemical to attract more larva, which settle on top of female, become male
Limpets at bottom are female
Are all sex related traits found on the sex chromosomes (in ppl)
No
Some genes for non-sex traits are on sex chromosomes
In humans, who determines the sex of the offspring
Males
What is the male determining gene in ppl
Sex determining region Y, located on y chr
Turns on genes needed to be male
Characteristics of the X chromosome in humans
Contains many genes and is essential (at least one)
Y has few genes
Where are fertility genes located
Both X and Y
