Sec 4 Combined Science (Biology) Inheritance topical questions

Distinguish between a gene and an allele.

Classify as continuous or discontinuous variation: (a) height, (b) blood group, (c) body mass, (d) tongue-rolling.

Define genotype and phenotype.

State the sex chromosomes of (a) a human female and (b) a human male.

State the phenotype of each genotype, where T = tall (dominant) and t = short: (a) TT, (b) Tt, (c) tt. Name the term for each genotype (homozygous/heterozygous).

Draw a genetic diagram for the cross Tt × Tt. Show parent genotypes, gametes, offspring genotypes and the phenotype ratio.

A heterozygous tall plant is crossed with a short plant. (a) Write the cross. (b) Predict the offspring genotypes and phenotype ratio.

Explain, using a genetic grid, why a couple's children are equally likely to be boys or girls.

A student counts 37 tall and 13 short plants in an F2 population and claims the 3:1 ratio "failed". (a) Calculate the expected numbers at 3:1. (b) Comment on the claim using the idea of chance. (c) State what sample size would make the claim testable.

Explain how ionising radiation and chemical mutagens affect mutation rate, and describe the two kinds of mutation with a named example each.

In humans, the allele for free earlobes (E) is dominant over attached earlobes (e). A heterozygous man marries a heterozygous woman. (a) Draw the genetic diagram. (b) State the genotype and phenotype ratios. (c) The couple have four children and all have free earlobes. Explain why this does not disprove your prediction.

Link this chapter back to Chapter 4: explain how a gene mutation in the haemoglobin gene leads to sickle cell anaemia, using the chain base sequence → polypeptide → protein → trait.