Genetic Linkage and Mapping Flashcards
What are syntenic genes?
Genes located on the same chromosome
What are linked genes?
Syntenic genes that are so close together that their alleles cannot sort independently.
What are recombinant chromosomes
Chromosomes whose syntenic genes have been reshuffled between homologs during crossing over
What are parental chromosomes?
Homologs that do not reshuffle alleles under study
What is genetic linkage mapping?
Plots the positions of genes on chromsomes?
When does independent assortment of syntenic genes occur?
If they are far apart on a chromosome so that recombination occurs very frequently
What are the characteristics of linked genes?
Are always syntenic and always located near one another
Does genetic linkage lead to the production of more gametes with parental allele combinations or nonparental combinations?
Parental
Is crossing over more likely to occur between closely linked genes or those further apart on a chromosome?
Farther apart
How can genetic linkage be recognized?
By comparing observed frequencies of gamete phenotypes or progeny phenotypes with those expected under independent assortment
What will happen if genes are linked?
Parental allele combinations will be observed at higher frequency than predicted by chance
What is complete genetic linkage?
When only parental gametes are formed
When is complete genetic linkage observed?
When no crossing over occurs
Give an example of organisms that exhibit complete linkage.
Male drosophilas
What is the biological basis for complete linkage?
Unknown
What is incomplete genetic linkage?
Produces mixture of parental and nonparental gametes
How is recombination frequency calculated?
r = # of recombinants / total # of progeny
What is recombination frequency most likely a reflection of?
The physical distance between two genes
What does it mean if linked genes have higher recombination frequencies?
More distant from one another
Explain the experiments conducted by Bateson and Punnett that led to the discovery of genetic linkage.
Crossed pure-breeding purple-flowered, long-pollen plants to red-flowered, round-pollen plants; the purple, long-pollen F1 were interbred to produce F2
What were the observed results of Bateson and Punnett’s experiments?
The expected 9 : 3 : 3 :1 ratio was not observed
In F2 progeny, the purple-flowered, long-pollen plants and red-flowered, round pollen plants were seen in larger proportion than expected
These were the same phenotypes of the P generation
What did Bateson and Punnett conclude?
An unknown mechanism kept the two parental gamete combinations together, which they called coupling
They described the appearance of the nonparental types as repulsion of the parental alleles.
Explain Morgan’s crosses that examined genetic linkage
Crossed pure-breeding white-eyed females with minaiture wings to males wild type for both traits
F1 were wild-type females and white, miniature males
F1 were interbred with a 1:1:1:1 ratio expected
What did Morgan see in his F1 crosses?
Many more parental types than recombinant types
