Using the pedigree chart, deduce the type of allele that causes hypophosphatemia.

The pedigree chart shows a family affected by cystic fibrosis.

[Source: © International Baccalaureate Organization 2019]

What is the genotype of the affected boy’s father?

A. AA only

B. Either AA or Aa

C. Aa only

D. aa only

Distinguish between sex-linked genes and genes with linked loci.

Which pedigree chart is consistent with the inheritance of red-green colour blindness?

[Source: © International Baccalaureate Organization 2019]

A pair of alleles controls the secretion of antigens corresponding to blood group in saliva. Examine the pedigree chart.

[Source: © International Baccalaureate Organization 2019]

Based on this pedigree chart, which best describes the allele conferring antigen secretion in saliva?

A. Dominant

B. Recessive

C. Sex-linked

D. Co-dominant

Nail patella syndrome is a rare disease that causes abnormalities of the nails and some bones. Its alleles are linked to the blood group alleles on the same chromosome. The pedigree chart shows the inheritance of these two characteristics over three generations.

[Source: Copyright © 1998. Phillip McClean]

Which descendant represents a recombinant phenotype?

Outline how it can be shown that the genes for shell base colour (Cc) and presence or absence of bands (Bb) are linked.

Explain the reasons for none of the females in the pedigree chart having hemophilia.

A family has a history of hemophilia that is caused by a sex-linked recessive allele. A woman from this family is a carrier and marries a man who does not have the allele. Showing your working, determine the probability of their children having the disease.

Outline how sperm are produced from diploid cells in the testis and how this production can be sustained over many decades of adult life.

Creeper in chickens is a condition in which the chickens are born with very short legs. The creeper allele (C) is dominant over the normal allele (c). Embryos which are homozygous for the dominant allele fail to develop into viable chickens and die before they hatch. What phenotypic ratio would you expect in the live offspring of a cross between two creeper chickens?

A. All creeper

B. 1 creeper; 2 normal

C. 2 creeper; 1 normal

D. 3 creeper; 1 normal

The pedigree chart shows the inheritance of hemophilia in some of the descendants of Queen Victoria. Which letter points to a family member certain to be heterozygous?

[Source: © International Baccalaureate Organization 2019]

Draw a Punnett square to show all the possible genotypes of Queen Victoria’s children.

Outline the inheritance of blood types in the ABO blood system in humans.

The genes for cystic fibrosis and blood group are not linked. Two parents are heterozygous for cystic fibrosis. One parent has blood group O and the other has blood group AB. Using a Punnett square, determine the probability that their child will have both cystic fibrosis and blood group A.