10 Jun Describe the control of gene expression
Question
Describe the control of gene expression.
Question 1.
In the Andalusian fowl, the allele for black feathers (B) is incompletely dominant to that for white feathers (b) and the phenotype of the heterozygote is described as blue. The texture of the feathers is controlled by a second gene locus, silky feathers (f) being recessive to normal (F).
What phenotypic ratio would be expected for the offspring? Show your working clearly. Please do the punnett square for a dihybrid cross and then work out the phenotypes.
Question 2. Please note that this is the most important question, it must be accurate and answered in full, take your time answering this.
The table below shows the effect of two genes in providing resistance to powdery mildew disease in peach trees.
Note that the observed phenotypic ratio did not agree with the expected phenotypic ratio.
F2 Classes
F2 Expected Phenotypic ratio
Reaction to powdery mildew disease
T_H_
9
Highly resistant (HR)
T_hh
3
Highly resistant (HR)
ttH
3
Fairly resistant (FR)
tthh
1
Susceptible (S)
Observed phenotypic ratio
12 HR : 3 FR : 1S
a) If plants with the genotypes TThh and ttHH were crossed, what proportion of their offspring would be expected to be fairly resistant to powdery mildew disease? (Show your working clearly).
b) Proportion fairly resistant to powdery mildew:
Question 3.
This is a diagrammatic representation of the biochemical process of translation.
Here is a list of some of the molecules shown in the diagram:
(i) mRNA
(ii) nascent polypeptide chain
(iii) uncharged tRNA
What is molecule (iv) in full answer? I know it is an anti-codon, but what does the “u” stand for? (Note: the answer “anti-codon” is not sufficient here).
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