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The diagram shows crosses in a breeding programme involving different breeds of sheep - Scottish Highers Biology - Question 9 - 2018
Question 9
The diagram shows crosses in a breeding programme involving different breeds of sheep. (P) Scottish Blackface female X Border Leicester male Gre... show full transcript
Worked Solution & Example Answer:The diagram shows crosses in a breeding programme involving different breeds of sheep - Scottish Highers Biology - Question 9 - 2018
Step 1
Suggest a reason why breeding programmes such as this include crossbreeding.
Answer
Crossbreeding allows for the introduction of new and desirable traits from different breeds. This can improve the overall characteristics of the offspring, ultimately producing lambs that may have enhanced traits such as growth rate, disease resistance, or wool quality.
Step 2
Explain why Greyface sheep are produced by crossbreeding Scottish Blackfaces with Border Leicesters instead of breeding F1 Greyface sheep together.
Answer
Crossbreeding the Scottish Blackfaces with Border Leicesters produces F1 Greyface sheep that exhibit increased genetic variation and hybrid vigor. These traits enhance the potential for improved characteristics in the offspring when compared to breeding F1 Greyface sheep together, which may lead to a reduction in genetic diversity and undesirable traits.
Step 3
To produce commercial lambs which show a desired dominant characteristic, Suffolk males homozygous for that characteristic are used.
Answer
(i) Test cross.
(ii) Selecting a Suffolk male that is homozygous for the desired dominant trait is important because it ensures that all offspring will express that trait, thereby maintaining the desired characteristics in the commercial lambs produced.
Step 4
State why inbreeding could cause an increase in the number of lambs born with this condition.
Answer
Inbreeding can lead to an accumulation of recessive deleterious alleles within the population. As genetically similar individuals are paired, the likelihood of offspring inheriting two copies of a recessive allele increases, resulting in a higher occurrence of conditions such as spider lamb syndrome.