In: Biology
a. Your dream is to find durum seeds that are white in color (wild type is amber or yellow) and so you mutagenize thousands of amber seeds and identify 6 plants segregating for white seeds
I. How would you identify true breeding white lines?
II. Determine whether the 6 individual white lines contained mutations in the same gene or different genes?
b. The following two genotypes are crossed: Aa Bb Cc dd Ee × Aa bb Cc Dd Ee. What will the proportion of the following genotypes be among the progeny of this cross? (5 points)
I. Aa Bb Cc Dd Ee
II. aa bb cc dd ee
IV. If there were 1000 offspring, how many will have the true breeding recessive genotype?
I. True breeding = Homozygous
To determine if a plant is true breeding, allow it it
self-pollinate.
If all the progeny exhibit white seeds, the plant is
homozygous.
If there is more than one phenotype, the plant is not
homozygous.
II. If two recessive mutants are
crossed and the resulting F1 exhibits the mutant phenotype, both
mutants are said to be allelic i.e. located in the same gene.
If two recessive mutants are crossed and the resulting F1 exhibits
the WT phenotype, both mutants are said to be non-allelic i.e.
located in different genes.
This is applicable only to recessive mutants.
b. Parental cross: AaBbCcddEe X AabbCcDdEe
I. Required progeny = AaBbCcDdEe
Probability = 1/2 X 1/2 X 1/2 X 1/2 X 1/2
= 1/32
II. Required progeny =
aabbccddee
Probability = 1/4 X 1/2 X 1/4 X 1/2 X 1/4
= 1/256
III. The probability for true
breeding recessive homozygote = 1/256
i.e. one in 256
~4 in 1000 (or 3 in 1000)