Reproduction and Inheritance
Reproduction and inheritance is the topic covering how organisms produce offspring and how characteristics pass from parents to their children through genes. It covers the human and plant reproductive systems, DNA and genes, genetic cross diagrams for predicting inherited characteristics, and the difference between inherited and environmental variation.
Method
- Learn the structures and functions of the male and female reproductive systems in humans.
- Learn the structures of a flower and how pollination and fertilisation differ.
- Understand key vocabulary: gamete, fertilisation, zygote, gene, chromosome and allele.
- Practise completing genetic cross diagrams for monohybrid crosses.
- Convert cross results into genotype ratios, phenotype ratios and percentage probabilities.
- Distinguish between continuous and discontinuous variation, and between inherited and environmental causes of variation.
Worked example
In pea plants, the allele for round seeds (R) is dominant over the allele for wrinkled seeds (r). A heterozygous round-seeded plant (Rr) is crossed with a wrinkled-seeded plant (rr). Complete a genetic cross diagram and state the percentage probability that an offspring will have wrinkled seeds.
- Write down the parents' genotypes: Rr x rr.
- List the possible gametes each parent can produce: R and r from the Rr parent; r and r from the rr parent.
- Combine the gametes in a cross diagram to find the offspring genotypes: Rr, Rr, rr, rr.
- Count the offspring genotypes: 2 Rr (round) to 2 rr (wrinkled), a ratio of 1:1.
- Convert to a percentage: 2 out of 4 offspring are rr, so 2/4 x 100 = 50%.
- State the final answer: 50% probability of wrinkled seeds.
Practice questions
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Q1State the function of the testis in the human male reproductive system.Show answer
Answer: It produces sperm (and the hormone testosterone).
Q2Define the term gamete.Show answer
Answer: A sex cell, such as a sperm cell or an egg cell.
Q3In pea plants, tall (T) is dominant over short (t). State the phenotype of a plant with the genotype Tt.Show answer
Answer: Tall
Q4Classify height as showing continuous or discontinuous variation.Show answer
Answer: Continuous variation
Q5Two heterozygous tall pea plants (Tt) are crossed. State the ratio of tall to short offspring expected.Show answer
Answer: 3 tall : 1 short
Q6In guinea pigs, black fur (B) is dominant over white fur (b). A black guinea pig that is a carrier (Bb) is crossed with a white guinea pig (bb). Calculate the percentage of offspring expected to have white fur.Show answer
Answer: 50% (Bb x bb gives Bb, Bb, bb, bb; 2 out of 4 are bb)
Exam-style questions
Written in the style of a KS3 Science exam paper, with a full mark scheme.
Describe the difference between pollination and fertilisation in a flowering plant.
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In hamsters, the allele for short fur (F) is dominant over the allele for long fur (f). A short-furred hamster with the genotype Ff is crossed with a long-furred hamster. Complete a genetic cross diagram, state the genotype and phenotype ratios of the offspring, and calculate the percentage of offspring expected to have long fur.
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A population of head lice is treated with an insecticide shampoo. Almost all of the lice are killed, but a very small number happen to carry a gene that makes them resistant to the insecticide. Explain how, over time, repeated use of the same insecticide could lead to most head lice in the population becoming resistant to it.
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Free printable worksheet
Want more practice on paper? Download the reproduction and inheritance worksheet pack - 17 pages of exam-style questions with a full mark scheme. One email opens every download in this browser for 14 days - no account, no card. Print it for personal and classroom use.
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