Please answer all parts. 1. In a species of tree, seed color is determined by 4

Question

Please answer all parts.

1. In a species of tree, seed color is determined by 4 independently assorting genes: A, B, C, and D. The recessive alleles of each of these genes (a, b, c, and d) produce abnormal enzymes that cannot catalyze a reaction in the biosynthetic pathway for seed pigment. This pathway is diagrammed as follows: White precursor - Yellow Orange Red Blue When both red and blue pigments are present, the seeds are purple. Trees with the genotypes Aa Bb CC dd and Aa Bb cc dd were crossed. What color are the seeds in these two parental genotypes? What proportion of the offspring from the cross will have white seeds? What proportion of the offspring from the cross will have blue seeds? What proportion of the offspring from the cross will have red seeds? a) b) c) d)

Explanation / Answer

1) In parent with genotype AaBbCCdd, the colour of the seed is Red. It is because, a dominant allele 'A' causes the conversion of white precursor to yellow, dominant 'B' allele causes the coversion of yellow to orange and dominant allele 'C' coverts orange to red. Since the d allele is recessive, orange cannot be converted to blue and hence purple colour is also absent.

In parent with genotype AaBbccdd, the colour will be orange. It is because, there is only domiannt alleles 'A' and 'B'. Hence, white precursor can be converted to yellow which gets converted to orange.

2) The genotypes of gametes that are possible from the above parents, and that could have white flowers are,

aaBBCcdd OR aaBbCcdd OR aabBCcdd OR aabbCcdd

= (1/2*1/2*1/2*1/2*1*1*1*1 )+ (1/2*1/2*1/2*1/2*1*1*1*1) + (1/2*1/2*1/2*1/2*1*1*1*1 )+ (1/2*1/2*1/2*1/2*1*1*1*1)

= 1/16 +1/16 + 1/16 +1/16

= 4/16

= 1/4

(Note : OR- Addition Rule & AND - Multiplication rule)

3) None of the offsprings from the above cross have blue seeds. It is because, to have blue seeds the 'D' allele should be either in a homozygous dominant ( DD ) or in a heterozygous (Dd) condition in the offspring. Since both of the parents doesnot conatin a dominant 'D' allele, this phenotype of blue colour is not possible.

4) The possible genotypes from the above cross that contain red seeds are,

AABBCcdd OR AaBbCcdd OR aAbBCcdd OR aABbCcdd OR AabBCcdd OR AABbCcdd OR AAbBCcdd OR aABBCcdd OR AaBBCcdd

= (1/2*1/2*1/2*1/2*1*1*1*1 ) + (1/2*1/2*1/2*1/2*1*1*1*1) + (1/2*1/2*1/2*1/2*1*1*1*1) + (1/2*1/2*1/2*1/2*1*1*1*1) + (1/2*1/2*1/2*1/2*1*1*1*1) + (1/2*1/2*1/2*1/2*1*1*1*1) + (1/2*1/2*1/2*1/2*1*1*1*1) + (1/2*1/2*1/2*1/2*1*1*1*1) + (1/2*1/2*1/2*1/2*1*1*1*1)

= (1/16 +1/16 +1/16 +1/16 +1/16 +1/16 +1/16 +1/16 +1/16)

= 9/16

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