Linkage

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  • Created by: ppogba
  • Created on: 18-08-19 16:29
Why are Drosophila melanogaster (fruit fly) good organisms to use when studying genetics?
at least 144 drosophila species. Easy to rear. Rapid generation time. Genome sequenced before humans.
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How many pairs of chromosome are their in drosophila compared to humans (and how many genes)
4 pairs (with 14,000 genes) compared to 23 (with 20,000)in humans. (ie. there are many genes on each chromosome)
2 of 10
Recap what Mendel's theory of Independent Assortment is?
alleles of 2 genes would get sorted into gametes independently.
3 of 10
Geneticist, Morgan, did a similar experiment to Mendel's peas (to prove independent assortment), using flies eye colour and wings. However when crossed, the 2 genes didn't assort independently. What was concluded from this?
they must be linked (ie. on the same chromosome)
4 of 10
What is Recombination?
the process by which DNA is switched between homologous chromosomes.
5 of 10
What are the 2 enzymes used in Recombination, involved in inserting the cut strand and annealing the new combinations together?
recombination enzyme and Ligase.
6 of 10
What is the recombinant fraction a measure of? What are the units used?
the distance between 2 genes. centiMorgans (cM).
7 of 10
1339, 1195 (non-recombinant), 151, 154 (recombinant). How would we calculate the recombinant distance from this?
recombination fraction = (151+154)/2829 = 0.107 (ie. 10.7% of flies were recombinants. This also equates to 10.7cM.
8 of 10
Recombination fractions are additive. 6 genes are on a genetic map , with the additive map distance being 0.08+0.07+0.07+0.07+0.06=0.35. But if a test cross is done between the start and finish, and only gives 0.23, why?
Double recombinants- if recombination fraction is 0.35, the proportion of double recombinant is 0.35x0.35=0.12. 0.35-0.12=0.23 (phenotypically we cannot detect double recombinants).
9 of 10
What do we conclude if the recombination fraction is around 0.5? If the value is much less than 0.5, what do we conclude?
the 2 genes are therefore not linked- ie. independent assortment is taking place). If its less than 0.5, we conclude that the genes are linked.
10 of 10

Other cards in this set

Card 2

Front

How many pairs of chromosome are their in drosophila compared to humans (and how many genes)

Back

4 pairs (with 14,000 genes) compared to 23 (with 20,000)in humans. (ie. there are many genes on each chromosome)

Card 3

Front

Recap what Mendel's theory of Independent Assortment is?

Back

Preview of the front of card 3

Card 4

Front

Geneticist, Morgan, did a similar experiment to Mendel's peas (to prove independent assortment), using flies eye colour and wings. However when crossed, the 2 genes didn't assort independently. What was concluded from this?

Back

Preview of the front of card 4

Card 5

Front

What is Recombination?

Back

Preview of the front of card 5
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