You’re interested in human disorders that result from deficiencies in synthesizi

Question

You’re interested in human disorders that result from deficiencies in synthesizing the compound heme (“poryphrias”).  Heme is the molecule that carries oxygen in the blood, but deficiencies in heme synthesis mainly cause disease phenotypes through the buildup of toxic intermediates called porphyrins that damage skin and other tissues in response to sunlight. The light sensitivity caused by these poryphriasis thought to have potentially contributed to the origin of vampire mythologies.  

To model and understand these diseases and work toward a cure, you perform genetic screens in the zebrafish Danio rerio in order to find mutations that mimic human porphyrias.  You find a series of 6 true-breeding mutants that have porphyria-like symptoms in zebrafish (light sensitive, lis-1 through lis-6). You cross together each of these mutants and examine their progeny (the F1 generation) and note their phenotypes in the table below.  (S is light sensitive phenotype, I is normal light insensitive phenotype).

lis-1    lis-2    lis-3    lis-4    lis-5    lis-6    

lis-1      S         I           I         I          S          I           

lis-2     I           S         I         S        I            I           

lis-3      I           I           S       I          I           I          

lis-4      I           S         I         S        I            I          

lis-5      S         I           I          I          S         I           

lis-6      I           I           I         I          I            S         

A. Are lis-1 through lis-6 dominant or recessive?

B. How many distinct recessivegenes did you find?

C. What alleles correspond to the recessive genes?

Explanation / Answer

According to the tabulated result after genetic screening in zebra fish,the following are the coclusion I could come up with

lis1xlis1---->Sensitive

lis 1 is recessive,when two recessive lis1 is crossed the F1 progeny obtained is sensitive.

lis 1 X lis 5-------->Sensitive

lis 1 is recessive and lis 5 is dominant,,

lis 2xlis 2---------->Sensitive

lis 2 is recessive ,two recessive leads to sensitive

lis 2x lis 4-------->Sesitive

lis 2 is recessive and lis 4 is dominant

lis 3X lis 3------>Snsitive

lis 3 is resessive

lis 4 x lis 2------>Senstive

lis 4 is dominant and lis 2 is recessive

lis 4 x lis 4

dominant crossed with dominant leads to sensitive

lis 5 x lis 1-------->Sensitive

lis 5 dominat and lis 1 recessive

lis 5 x lis 5----->sensitive

lis 5 is dominant

lis 6 x lis 6------------->sensitive

lis 6 is recessive

When certain gene pairs are crossed the sensitive gene loose it sensitivity and act as normal,which might be the reason behind Normal progeny .eg;lis 1 x lis 3----->Normal light sesitivity.

B)I could find 4 recessive gene ana 2 dominant gene

C)lis 1,2 3 and 6

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