2 (a) Sickle cell disease is a recessive genetic disorder in humans. (i) Two parents are heterozygous for sickle cell disease. complete the Punnett square to show the possible genotypes of their children. & D & d D & D & d & & (ii) State the percentage probability that their children could have sickle cell disease. percentage probability = iii) A father with the genotype dd and a mother with the genotype DD plan to have several children. Explain why none of their children will have sickle cell disease.

## Step1: The first part of the question asks to complete the Punnett square for parents heterozygous for sickle cell disease. In genetics, heterozygous refers to having different alleles, one normal and one disease causing, at a specific genetic locus. For people heterozygous for sickle-cell, the alleles can be represented as "D" (for normal) and "d" (for disease).### ### By making a Punnett square out of these genotypes you will be putting each of the 'parental' alleles (one from the Mom and one from the Dad) on top and on the left side of the chart to represent all the possible combinations:##...|Parent1/Parent2 | **D** | **d** ||----------------|------|-------|| **D** | DD | Dd || **d** | dD | dd |## Step2: From these results, we can see that one in four (or 25%) inherited genotypes is 'dd' (recessive) which is the genotype representing sickle cell anemia.## Step3: In the situation where a father with the 'dd' genotype and a mother with the 'DD' genotype plan to have children, none of their children will have sickle cell disease. This is due to the father only being able to contribute a 'd' allele (disease) and the mother only being able to contribute a 'D' allele (healthy), hence their child would have 'Dd' genotype which is a carrier not the sickle cell disease itself.