Flashcards in Linkage, sex linkage and sex determination Deck (21):
What is the three-point test-cross?
The standard procedure for determining the order and relative distances between genes on a chromosome.
What would be the result if the three genes were unlinked?
They would independently segregate to give 8 different phenotypes from within 64 genotypes in a 1:1:1:1:1:1:1:1 ratio
What would be the result if the three genes were linked?
8 phenotypes will result from 8 different genotypes, the ratio would depend on the number of map units between different loci.
What is the result of a double recombination?
The middle gene 'changing partners'
What are the three steps in determining the distance between relative genes on a chromosome?
1. Identify the parental combination of alleles (most frequent)
2. Identify the middle locus (the least frequent class)
3. Calculate the recombination frequency between each pair of loci
What does the least frequent combination indicate?
That double recombination has occurred and so gene order can be determined.
How can a species ensure outcrossing?
If the species has sexually dimorphic individuals.
What is genotypic sex determination?
Gender is determined by the genotype of the individual. Based on organisms having specific sex chromosomes that can segregate from one another in meiosis
What is environmental sex determinism?
Gender is determined by environmental conditions.
What is a dominant Y system?
Presence of a Y chromosome determines maleness. Occurs in mammals
Give an example of a hermaphrodite flower?
What happens in hermaphrodite flowers?
The presence of a Y chromosome suppresses carpel development and promotes stamen development. XXY is male.
What determines the gender in Drosophila?
The X to autosome ratio
What is heterogametic sex?
Produces two types of gametes, each carrying a different sex chromosome (male mammals).
What is homogametic sex?
Produces one type of gamete, all carrying the same autosome (female mammals).
What was sex-linkage first observed in?
Why is having two X chromosomes a problem?
You may end up with over expression of a gene
What is X-inactivation
Causing one random X chromosome and condensing it tightly with histones until it is inaccessible by gene expression machinery.
Which X chromosome is inactivated?
A random one in every cell in the body
In female cats why can't the co-dominant O alleles be expressed at the same time?
because one chromosome is inactivated.