Sex Determination Flashcards
Why is sexual reproduction described as having a 2 fold cost to asexual
Only half the population produces offsprings- asexual reproduce twice as fast
Why is sexual reproduction desired more for survival than asexual
It produces recombinant genotypes and causes diversity in a population
What is the evidence using yeast that sexual reproduction is better survival
When a sexual and asexual strain were put in harsh conditions. The sexual strain had faster growth
In protenor insects, what was found to determine if the offspring was male or female
There were 2 gamete variations from the male, either autosomes with no X chromosome or auto some with 1 X. If the gamete with the X inherited then it would be female (1 X from mother 1 X from father)
Why are males called hetereogametic sex and female called homogametic sex
Males- produces 2 variants of gametes
Females are always uniform (XX gamete)
What are the heterogametic females and homogametic males called (rare)
ZW- hetereogametic female
ZZ- homogametic male
Which syndromes showed evidence in the Y chromosome being sex determinator
Kline felter syndrome - XXY
Turner - XO (1 sex chromosome)
How did Klinefelter syndrome (XXY) in males suggest Y chromosome was sex determining
Even in the presence of 2 XX, people with the syndrome developed male characteristics eg beards
The Y chromosome has 3 regions on it. Explain them
Par- pseudoautosomal regions - homolog to X
MSY - male specific region - male genes
SRY - sex determining region - testes determining factor - produces testes in tissue of embryo
How does temperature of the incubation of eggs in some reptiles like crocodiles determine sex
The temperature affects the enzymes in steroid hormone production - if higher temp these denature and produce females
What is dosage compensation
A process which keeps the number of x linked genes similar in female and males despite the female having double the Xs
What are Barr bodies and where were they discovered
Barr bodies are condensed X chromosomes found to be inactivated in female nucleus
What does the discovery of Barr bodies mean
Only 1 X is ever active in a human
Eg in females on 1 X is active despite having 2
This keeps x linked genes same
What was the Lyon hypothesis about Barr bodies
Inactivation of an X is random whether it is the x from the male or the female
Once inactivated , all Progeny cells have the same X inactivated
How are X chromosomes inactivated
Initiated from the XIC(x inactivation centre)
The rna non coding transcript XIST packages around 1 X chromosome
This then forms into heterochromatin (condensed silenced)
