Answers to AQA GCSE Pedigree diagrams(Biology)
Practice Questions
1.Describe what a pedigree diagram shows us.
A pedigree diagram is a chart showing how a trait is inherited through generations of a family.
2.Huntingdon’s disorder is caused by a dominant allele H. People with two copies of the recessive alleles (hh) are unaffected. Below is a pedigree diagram for huntingdon’s disease.
Both individuals 1 and 2 have Huntingdon’s disease. Explain how it is possible for them to have children that will not suffer from the disorder.
Both 1 and 2 could be either HH or Hh.
If both parents are Hh, then it is possible to produce a child that is hh.
Look at the punnett square at the bottom.
3. Tay Sachs disease is caused by a recessive allele t. People with T are unaffected by the disease. Below is a pedigree diagram for Tay Sachs disease.
Parents 6 and 7 have two children. Child 9 has Tay sachs. Explain how this is possible.
For an individual to suffer from tay sachs disease, they need to inherit two recessive alleles, one from each parent. So, their genotype is tt.
As neither 6 or 7 suffer from the disease, then they are both heterozygous Tt.
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