Q.11 Assume that the gene UNC is essential for the coordinated movement of a nematode and that the
wild-type allele U is dominant over the mutant allele u. Similarly, the wild-type allele D of another
gene DPY, which is responsible for the normal body length, is dominant over the mutant allele d.
Assume the UNC and DPY are on two different chromosomes. If a female of genotype UUDD
mates with a male of the genotype uudd, the percentage of the F2 progeny that will display
uncoordinated movement but will have normal body length is _____
The cross involves a dihybrid inheritance pattern in nematodes where UNC (U dominant for coordinated movement) and DPY (D dominant for normal body length) assort independently on different chromosomes. The F1 generation from UUDD × uudd produces all UuDd offspring, and the F2 generation follows a classic 9:3:3:1 phenotypic ratio.
Parental Cross
Female UUDD (homozygous dominant: coordinated, normal length) mates with male uudd (homozygous recessive: uncoordinated, dumpy). All F1 progeny are heterozygous UuDd, showing dominant phenotypes (coordinated movement, normal body length).
F1 Selfing and F2 Genotypes
F1 UuDd self-fertilizes to yield F2 genotypic ratios of 1 UU DD : 2 UU Dd : 2 Uu DD : 4 Uu Dd : 1 uu DD : 2 uu Dd : 1 UU dd : 2 Uu dd : 1 uu dd. Since genes assort independently, Punnett square analysis confirms equal segregation for each locus (3/4 dominant, 1/4 recessive per trait).
F2 Phenotypic Ratio
Standard dihybrid ratio: 9/16 coordinated normal (U_ D_) : 3/16 uncoordinated normal (uu D_) : 3/16 coordinated dumpy (U_ dd) : 1/16 uncoordinated dumpy (uu dd).
Target Phenotype Calculation
Uncoordinated movement requires homozygous recessive uu (1/4 progeny). Normal body length requires at least one D allele (D_ = 3/4 progeny). Combined probability: (1/4) × (3/4) = 3/16 = 18.75%.
In nematode genetics, the nematode UNC DPY F2 percentage uncoordinated normal body length question tests dihybrid cross principles. UNC gene (U dominant: coordinated movement) and DPY gene (D dominant: normal length) on separate chromosomes ensure independent assortment from UUDD female × uudd male cross.
Phenotypic Outcomes Explained
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9/16 (56.25%): Coordinated, normal (U_ D_) – wild-type appearance.
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3/16 (18.75%): Uncoordinated, normal (uu D_) – target phenotype (homozygous recessive UNC, dominant DPY).
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3/16 (18.75%): Coordinated, dumpy (U_ dd).
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1/16 (6.25%): Uncoordinated, dumpy (uu dd).
No linkage deviations occur; multiply individual ratios for target class. This matches CSIR NET/IIT JAM patterns emphasizing Mendelian ratios in model organisms like C. elegans.
