A research group has isolated ten Arabidopsis mutants (A to J) which had a defec

Question

A research group has isolated ten Arabidopsis mutants (A to J) which had a defect in maintaining the 24 hr circadian rhythm. Genetic analysis showed that these mutants were all monogenic recessive. To determine how many loci/alleles these mutants would represent, a complementation test was performed. The result is shown in the following table. Note that in the table "-" represents the aberrant circadian rhythm for the Fl derived from the corresponding crosses, and "+" indicates the normal circadian rhythm as observed in wild-type. Please draw a conclusion based on this complementation test result by designating a genotype for each of these mutants in the "Mutant genotype" column.

Explanation / Answer

Answer) We know that monogenic disorder results from a damaged/defected/mutated single gene. and a monogenic recessive mutation means that the phenotype will be reflected only in homozygous recessive individuals where both the affected alleles for the same gene are present in those individuals.

To identify the number of alleles in the given case, we need to identify the total complementation groups. each complementation group will represent each allele.

In the complementation assay, when the same allele is affected in both the parent. then they will show the mutant phenotype (- sign) in the complementation test. and they can be assigned to a single complementation group having same affected allele. while the parents which show wild-type phenotype (+ sign) in the complementation tests fall in two different complementation groups. also, there may be some individuals which show wild-type phenotype (+ sign) in all the complementation tests. such individuals are outliers and have a separate complementation group.

after analyzing the given table on this knowledge, we identify these complementation groups;

group 1 - A

group 2 - B, D, H, J

group 3 - C

group 4 - E, I

group 5 - F, G

hence, there are five complementation groups which represent the five different loci/alleles. let's name them as V, W, X, Y, Z.

group 1 - A

group 2 - B, D, H, J

group 3 - C

group 4 - E, I

group 5 - F, G

now, denote the genotype for the given mutants;

Genotype of mutant A will be; V-W+X+Y+Z+ (complementation group 1)

Genotype of mutant B will be; V+W-X+Y+Z+ (complementation group 2)

Genotype of mutant C will be; V+W+X-Y+Z+ (complementation group 3)

Genotype of mutant D will be; V+W-X+Y+Z+ (complementation group 2)

Genotype of mutant E will be; V+W+X+Y-Z+ (complementation group 4)

Genotype of mutant F will be; V+W+X+Y+Z- (complementation group 5)

Genotype of mutant G will be; V+W+X+Y+Z- (complementation group 5)

Genotype of mutant H will be; V+W-X+Y+Z+ (complementation group 2)

Genotype of mutant I will be; V+W+X+Y-Z+ (complementation group 4)

Genotype of mutant J will be; V+W-X+Y+Z+ (complementation group 2)

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