Sex Linkage (Genetics) Flashcards
Who is the famous scientist for determining sex linkages in the 1900s?
Thomas Morgan
What organisms were used in experiments for sex linkage?
Fruit flies
What is the wild type allele for the fruit fly?
red eyes
What is the mutant allele for the fruit fly?
white eyes
T or F: the mutant allele was found in both female and male offspring
FALSE. Only F2 generation MALES
What phenotype did the F1 offspring have when a female fruit fly with red eyes was crossed with a male fruit fly with white eyes?
All had red eyes
When the F1 of the fruit flies were crossed, what phenotypes were present? and in which ratio?
3 red eyes: 1 white eye but the only ones with white eyes were the males
Which allele was dominant and which was recessive in Morgan’s experiments?
Red eyes dominant
White eyes recessive
Define sex chromosome
chromosomes involved in determining if an organism is male or female (X or Y)
In humans and fruit flies, what is the typical genotype for biological males?
XY
In humans and fruit flies, what is the typical genotype for biological females?
XX
Where did Morgan determine the gene for eye colour is? Why did he decide this?
On the X chromosome because males have only ONE X chromosome so they have to display whichever genes they get on the X.
How come the females didn’t show the white eyed phenotype?
Because females have two X chromosomes, so they would only show the white eyes if they had two white-eye alleles (one on each X)
So females will show the red eye phenotype if they are hetero- or homozygous for red
Define reciprocal crosses
A pair of matings where the phenotypes of the males and females are different (parents are true bred)
What are reciprocal crosses used for? What do the results show?
Testing for sex linkage
If the results are different, the condition is SEX LINKED
if the results are the same, it’s autosomal
Which sex chromosome is much shorter than the other?
the Y is much shorter than the X
During meiosis in the testes and ovaries, what occurs to the X and Y chromosomes?
They segregate
Which chromosome(s) can females produce in gametes?
Only the X
Which chromosome(s) can males produce in gametes?
50% X and 50% Y
What biological sex will result if a sperm containing a Y chromosome fertilizes an egg?
A male offspring
What biological sex will result if a sperm containing an X chromosome fertilizes an egg?
A female offspring
How do alternatives of sex chromosome numbers and/or pairs occur?
Due to incorrect separation of chromosomes during meiosis
Describe the syndrome related to having only an X chromosome
Turner Syndrome
Occurs in females, usually shorter in height and infertile
Describe the syndrome related to having XXX chromosomes
Trisomy X
2 Xs are inactivated so mild or no symptoms occur but can be taller
