Question

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.

Answer 1

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) $=\dfrac{30}{9}=3$

(ii)$=\dfrac{11}{9}=1$

(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)