Lecture 2 Flashcards
What 4 processes contribute to genetic variation?
Mutation.
Independent assortment.
Crossing-over.
Random fertilisation.
What are the number of possible offspring combinations from one couple?
2^46.
What is a recombinant phenotype?
The combination of phenotypes differs from that found in either parent.
2 ways recombinant phenotypes can occur?
Independent assortment.
Crossing over.
What is crossing over?
Process of genetic recombination that gives rise to new combinations of linked genes.
When does crossing over occur?
Pachytene phase of prophase I.
Crossing over begins with synapsis. What is this?
Pairing of homologous chromosomes.
What is the synaptonemal complex?
Protein zipper that holds homologous chromosomes together in the tetrad.
What does the synaptonemal complex lead to?
Crossing over between homologous chromosomes.
What is the result of crossing over?
Recombinant chromosomes with new combinations of linked genes.
What is recombination frequency?
Percentage of progeny that inherit a combination of alleles that differs from either parent.
How do you calculate recombination frequency?
(No. of recombinants/Total no. of progeny)*100.
How can recombination frequencies be estimated?
Studying results of a testcross.
What does the recombination frequency depend on?
What will the recombinant frequency be for genes on different chromosomes?
Whether the genes are on same or different chromosomes.
50%.
Who was the first to observe gene lineage, and in what scenario?
T.H.Morgan.
Vestigial Wing mutant of Drosophila melanogaster.
How is a wild type (normal) allele usually represented?
Superscript +.
What did A.H. Sturtevant notice in 1913?
Recombination frequency between two genes should be related to distance apart on chromosomes.
What does 1% recombination frequency equal when creating recombination maps?
1cM - 1 centimorgan.
Why do map distances not add up in multiple crossovers? (3)
Lead to underestimate of distance between two loci.
Mean recombination frequencies >50% are not possible.
Genes far apart on same chromosome appear to assort independently.
What do the largest and smallest numbers indicate in a 3 point cross?
Largest = parental types. Smallest = result of a double crossover.
What are the 2 possible arrangements of alleles in a double heterozygote?
Will these affect the outcome of a testcross with the double mutant?
Coupling heterozygote.
Repulsion heterozygote.
Will affect testcross outcome with double mutant.
6 instances of deviations from Mendelian ratios?
Sex-linkage, Incomplete dominance, Co-dominance. Pleiotropy, Polygenic inheritance, Epistasis.
What are autosomes?
Chromosomes that aren’t sex chromosomes.
What does the Y chromosome lack in Drosophila, and what does this mean for the amount of alleles required for a male fruit fly to have white eyes?
Only needs one copy of XW.
