IGCSE Biology Inheritance topical questions

Define each term.

1. (a)Gene[1]
2. (b)Allele[1]
3. (c)Genotype[1]
4. (d)Phenotype[1]

Complete the sentences about the divisions of the nucleus. (Extended)

1. (a)........................ produces genetically identical cells and is used in growth and repair.[2]
2. (b)........................ produces gametes, halving the chromosome number from .................... to .................... .[2]

In humans, the sex chromosomes determine sex.

1. (a)State the sex chromosomes in a male and in a female.[2]
2. (b)Complete a Punnett square for XX × XY and state the expected ratio of sexes.[2]

In pea plants, the allele for tall (T) is dominant to the allele for short (t). Two heterozygous tall plants are crossed.

1. (a)State the parental genotypes and the gametes each parent produces.[2]
2. (b)Complete a Punnett square to show all possible genotypes.[2]
3. (c)State the genotypic and phenotypic ratios of the offspring.[2]

A couple who are both carriers (heterozygous) for a recessive condition have children.

1. (a)Using A/a, complete a Punnett square for Aa × Aa.[2]
2. (b)State the chance that a child of theirs is affected.[1]
3. (c)Explain why an affected child can be born to parents who are unaffected.[2]

A grower has a red-flowered plant of unknown genotype. Red is dominant to white.

1. (a)Name the type of cross used to find the unknown genotype and state what it is crossed with. (Extended)[2]
2. (b)State the expected results and conclusion if the plant is heterozygous.[2]
3. (c)State the expected result if the plant is homozygous dominant.[1]

DNA controls what a cell does by controlling which proteins it makes. (Supplement)

1. (a)Name the molecule that carries a copy of the gene’s instructions out of the nucleus.[1]
2. (b)Outline how the instructions in a gene result in a protein.[3]
3. (c)Explain why a liver cell and a muscle cell contain the same genes but make different proteins.[2]

A child grazes a knee; within days the wound is covered with new skin. (Supplement)

1. (a)Name the type of nuclear division that produces the new skin cells.[1]
2. (b)State two roles of this type of division in the human body.[2]
3. (c)Name the unspecialised cells that divide to replace damaged tissue, and state what makes them useful for repair.[2]

A human liver cell contains 46 chromosomes. (Supplement)

1. (a)State the term describing a nucleus with 46 chromosomes, and how many pairs of chromosomes this represents.[2]
2. (b)State how many chromosomes a human sperm cell contains.[1]
3. (c)Calculate the number of chromosomes in the zygote formed by fertilisation. Show your working.[1]
4. (d)Name the type of nuclear division that produces gametes.[1]

In snapdragon flowers, the allele CR gives red petals and the allele CW gives white petals. The two alleles are codominant. (Supplement)

1. (a)Explain what codominance means.[2]
2. (b)State the genotype and phenotype of all the offspring of a red-flowered plant crossed with a white-flowered plant.[2]
3. (c)Two of these offspring are crossed. Give the genotypic ratio and the phenotypic ratio of their offspring.[1]
4. (d)Calculate the percentage of offspring with white flowers in the cross in (c).[1]

In a family pedigree, two unaffected parents have an affected daughter and an unaffected son. Another, unrelated affected parent marries into the family and all of that person’s children are unaffected. The condition is controlled by a single gene with two alleles.

1. (a)State whether the condition is caused by a dominant or a recessive allele. Give evidence from the pedigree.[2]
2. (b)Deduce the genotypes of the two unaffected parents, using A for the dominant allele and a for the recessive allele.[2]
3. (c)State the chance that the next child of these parents will be affected.[1]
4. (d)State the term for people who carry the recessive allele without showing the condition.[1]

In humans, the allele for red-green colour blindness (X^n) is recessive and sex-linked. A carrier mother (X^N X^n) and a normal-vision father (X^N Y) have children. (Extended)

1. (a)Complete a Punnett square for this cross.[3]
2. (b)State the expected phenotypes of the daughters and of the sons.[2]
3. (c)Explain why colour blindness is more common in males than females.[2]

A group A mother and a group B father have a group O child. Neither parent is group AB. (Extended)

1. (a)State the genotype of the group O child.[1]
2. (b)Deduce the genotypes of the mother and father, explaining your reasoning.[3]
3. (c)Complete a Punnett square for this cross and state the expected ratio of blood group phenotypes.[3]

A gene is 1500 bases long and codes for a protein of 500 amino acids. A mutation changes one base near the start of the gene. (Supplement)

1. (a)Use the data to calculate how many bases code for one amino acid. Show your working.[1]
2. (b)Calculate how many bases are needed to code for a protein of 240 amino acids.[1]
3. (c)Explain how the changed base can alter the protein’s shape and function.[2]
4. (d)Explain how DNA controls the function of a cell.[2]
5. (e)State the type of nuclear division that replicates this DNA exactly before dividing.[1]