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Coat colour in cocker spaniel dogs varies - VCE - SSCE Biology - Question 2 - 2002 - Paper 1
Question 2
Coat colour in cocker spaniel dogs varies. Four of these colours are black, liver, red and lemon. These four colours result from the interaction of two particular au... show full transcript
Worked Solution & Example Answer:Coat colour in cocker spaniel dogs varies - VCE - SSCE Biology - Question 2 - 2002 - Paper 1
Step 1
I-1 and I-2 are heterozygous at both the R and B locus. What evidence from the pedigree supports this conclusion?
Answer
The evidence from the pedigree indicates that both red and liver are present in the offspring, suggesting that dogs that are either rr-bb or Rr-bb must be produced. Since I-1 and I-2 have offspring that display these phenotypes, it can be concluded that both parents must be heterozygous, leading to the conclusion that I-1 must be Rr and I-2 must also be Rr.
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 find out the different phenotypes, we need to set up a Punnett square using the genotypes RrBb (II-4) and rrbb (III-4).
- The gametes from II-4 (RrBb) are RB, Rb, rB, rb.
- The gametes from III-4 (rrbb) are rb.
The possible combinations are:
| RB | Rb | rB | rb | |
|---|---|---|---|---|
| rb | RrBb | Rrbb | rrBb | rrbb |
From this Punnett square, the phenotypes that can be expected are:
- RrBb - Black
- Rrbb - Red
- rrBb - Liver
- rrbb - Lemon
Thus, there are four distinct phenotypes expected among the offspring.