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I-1 and I-2 are heterozygous at both the R and B locus - VCE - SSCE Biology - Question 2 - 2002 - Paper 1
Question 2
I-1 and I-2 are heterozygous at both the R and B locus. What evidence from the pedigree supports this conclusion? The evidence from the pedigree that supports the c... show full transcript
Worked Solution & Example Answer:I-1 and I-2 are heterozygous at both the R and B locus - VCE - SSCE Biology - Question 2 - 2002 - Paper 1
Step 1
What evidence from the pedigree supports this conclusion?
Answer
The pedigree illustrates the presence of red (rr) and liver (bb) offspring, indicating that both I-1 and I-2 carry the alleles necessary for these colours. This supports the conclusion that they are heterozygous (RrBb) because their offspring also express traits associated with the homozygous recessive conditions.
Step 2
Step 3
Step 4
Explain how many different phenotypes could be expected in the offspring of a mating between individuals II-4 and III-4. Show all working.
Answer
To determine the expected phenotypes from the crossing of II-4 (RrBb) and III-4 (rrBb), we can set up a Punnett square:
| RB | Rb | rB | rb | |
|---|---|---|---|---|
| rB | RrBb | Rrbb | rrBb | rrbb |
| rb | RrBb | Rrbb | rrBb | rrbb |
From this square, the phenotypes include:
- Black (R_B_): RrBb
- Liver (rrB_): rrBb
- Red (rrbb): rrbb
- Lemon is not possible based on the given genotypes.
Thus, we could expect 4 distinct phenotypes.