Answer to Question #163790 in Inorganic Chemistry for Mady

Question #163790

On crossing a plant with red fruit and hairy stem, with one that was yellow fruit 

and hairy stem, the following progeny were obtained: 

 30 red, hairy / 11 red, smooth / 29 yellow, hairy / 9 yellow, smooth 

Give a reasoned explanation along with the use of full genetic diagrams to 

proof your answer, to explain these results in terms of the simultaneous 

transmission of characteristics.

Expert's answer

The parental phenotypes are; Red-hairly and Yellow-hairly

The offspring data provided is;

(i) Red - hairy =30

(ii) Red -Smooth = 11

(iii) Yellow - hairy =29

(iv) Yellow - smooth = 9

If we calculate the ratios;

(i) "=\\dfrac{30}{9}=3"


(iii) "=\\dfrac{29}{9}=3"

(iv) "=\\dfrac{9}{9}=1"

The ratio is 3:3:1:1 dihybrid phenotypic ratio. This suggests that Red is dominant over yellow and the parental genotypes were heterozygous and homozygous recessive for fruit colour, i.e. Rr and rr. (Where R is gene for red color, and r is the gene for yellow color). The ratio also suggests that hairy stem is dominant over smooth, hence the parents were heterozygous for stem texture, i.e. Hh (Where H is the gene for hairy stem and h is the gene for smooth).

Thus the parental genotypes were;

Parental phenotypes: Red and Hairy Yellow and Hairy

Parental genotypes RrHh x rrHh

Parental gametes RH, Rh, rH, rh rH and rh

Punnet square will give the following combinations in the offspring;

  • RrHH, RrHh, RrHh which will all be red and hairy (3 red and hairy)
  • rrHH,rrHh,rrHh which will all be yellow and hairy (3 yellow and hairy)
  • Rrhh which is red and smooth (1 red and smooth)
  • rrhh which is yellow and smooth (1 yellow and smooth)

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