Linkage and Mapping in Eukaryotes Flashcards
What is linkage?
The tendency for genes or segments of DNA closely positioned along a chromosome to segregate together at meiosis, and therefore be inherited together
What is the chance of chromosomes lining up at centre of a nucleus during meiosis and randomly associate in any of the potential combinations of heterozygous individuals?
Equal chance
What is the chance of independent segregation of genes on different chromosomes?
Equal
What is the chance of two genes on the same chromosomes lining up at centre of a nucleus during meiosis and randomly associate in any of the potential combinations of heterozygous individuals?
Certain, linkage
What is way only way that two genes on the same chromosome will segregate two different chromosomes?
Recombination occur between genes during meiosis I
How linkage discovered?
As in certain crosses, a greater number of offspring with ‘parental’ genotypes were generated than expected
Who discovered linkage?
Bateson, saunders and punnent
What indicated linkage?
A greater number of parental offspring than expected
Where do non-parental genotypes arise from?
Crossing over during meiosis I
What are non-parental genotypes called?
Recombinants
What can be used to make linkage map of chromosomes ?
recombination
What does the frequency of recombination and distance show?
The frequency of recombination between two genes will depend on distance between genes
Finish the sentence:
The great the distance between two genes…
the greater the frequency of recombination
What experiment did Morgan do?
Genetics of fruit fly Drosophila melanogaster
What does one genetic map unit (m.u) show?
The distance between genes for which 1% products of meiosis are recombinant
What is a map unit equal to?
centimorgan (cM)
In a particular species of mammal black hair (B) is dominant to green hair (b) and red eyes (R) are dominant to white eyes (r). If a BbRr individual is mated with a bbrr individual the expected phenotypic ratio of the offspring is 1 black-red : 1 black-white: 1 green-red : 1 green-white. However, when you mate these individuals you find that the phenotypic ratio of the offspring is: black-red 450; black-white 50; green-red 50; green-white 450. Based on these data, what is the recombination frequency?
A) 5 %
B) 10 %
C) 20 %
D) 30 %
C
What are genetic maps?
Linear and additive
What are most common classes?
Parental types
What are least common classes?
Recombinant types
How to deduce gene order?
- Gene in the middle must be only one to undergo double recombination
- Double recombinants are found alongside alleles which is not found alongside in the parents
