Question 12
HHaemophilia is a sex-linked genetic disorder. It is caused by a recessive allele, XhX^hXh, on the X X\,X chromosome. The dominant allele is XHX^HXH.
The Figure shows a family pedigree for haemophilia.
Figure
a.[1]
Give the genotype of person 3.
b.[2]
Explain why person 2 must be a carrier of haemophilia.
c.[3]
Persons 4 and 6 are expecting another child.
Use a genetic diagram to calculate the probability that this child will be a boy with haemophilia.
d.[1]
State the probability that person 8 is a carrier of haemophilia.
e.[2]
Explain why haemophilia is more common in males than in females.
3.3 Inheritance Questions
43 exam-style questions on Edexcel GCSE Biology 3.3 Inheritance, covering 3.3.1 Gregor Mendel and the basis of genetics, 3.3.2 Alleles and inherited characteristics, 3.3.3 Monohybrid inheritance, 3.3.4 Determination of sex at fertilisation, 3.3.5 Outcomes from monohybrid crosses, 3.3.6 Inheritance of ABO blood groups, 3.3.7 Inheritance of sex-linked disorders, and 3.3.8 Multiple genes and phenotypic features. Each one has a worked solution and a mark scheme showing where the marks go.