Models of single-gene inheritance: family tree diagrams | Starter Quiz | Oak National Academy

Starting with the smallest, put these in order of increasing size.

• nucleotide

• nucleus

• chromosome

• gene

• cell

Answer explanation

DNA is a polymer of nucleotides. Chromosomes are long DNA molecules, and sections of these molecules which code for proteins are called genes. In eukaryotic cells the chromosomes are in the nucleus which is part of a cell.

Which is the correct end for the sentence? All humans have the same ...

• alleles.

• genes.

• genotype.

• phenotype.

Answer explanation

Although all humans have the same genes, they do not have the same alleles for these genes. The amino acid sequence of the proteins coded for by different alleles are not the same and so individual humans differ in genotype and phenotype.

A single gene with two alleles controls the wetness of earwax. The E allele is dominant and causes wet ear wax. The e allele is recessive. What is the genotype of a person with dry earwax?

• Ee

• ee

• EE

Answer explanation

All people with dry earwax are homozygous recessive. If they had even a single E allele they would have wet earwax.

The shape of peas is controlled by a single gene with two alleles: R for round and r for wrinkled. R is dominant. Which of the numbered boxes in the Punnett square contains a mistake?

• 1

• 2

• 3

• 4

Answer explanation

Box 2 should be Rr (or rR).

PKU is a disorder in humans caused by a recessive allele, p. Two carriers of PKU are shown this Punnett square. What can they learn from the Punnett square?

• The probability that they will have a child with PKU is 0.

• Only if they have four children, will one inherit PKU.

• The probability that they will have a child who carries PKU is 0.75.

• The probability that any child they have will inherit PKU is 0.25

Answer explanation

Each child the couple have has a probability of 0.25 of inheriting PKU.

A dominant allele R codes for red flower colour, and the allele r codes for white flowers. A RR plant is crossed with a rr plant. What colour flowers will their offspring have?

Answer explanation

The offspring will all be heterozygous, Rr, so will have one dominant R allele and will have red flowers.