Section 3: Reproduction and inheritance

a) Reproduction b) Inheritance

Before we start try this Key stage 3 revision quiz, how much do you know?

A good BBC video by with Robert Winston can be found here:

a) Reproduction
Students will be assessed on their ability to:

3.1 describe the differences between sexual and asexual reproduction
3.2 understand that fertilisation involves the fusion of a male and female gamete to produce a zygote that undergoes cell division and develops into an embryo

Flowering plants

3.3 describe the structures of an insect-pollinated and a wind-pollinated flower and explain how each is adapted for pollination
3.4 understand that the growth of the pollen tube followed by fertilisation leads to seed and fruit formation
3.6 recall the conditions needed for seed germination
3.7 understand how germinating seeds utilise food reserves until the seedling can carry out photosynthesis
3.8 understand that plants can reproduce asexually by natural methods (illustrated by runners) and by artificial methods (illustrated by cuttings).

3.9 recall the structure and function of the male and female reproductive systems

3.10 understand the roles of oestrogen and progesterone in the menstrual cycle


3.11 describe the role of the placenta in the nutrition of the developing embryo

3.12 understand how the developing embryo is protected by amniotic fluid

3.13 recall the roles of oestrogen and testosterone in the development of secondary sexual characteristics

b) Inheritance
3.14 recall that the nucleus of a cell contains chromosomes on which genes are located

3.15 understand that a gene is a section of a molecule of DNA

3.16 describe a DNA molecule as two strands coiled to form a double helix, the strands being linked by a series of paired bases: adenine (A) with thymine (T), and cytosine (C) with guanine (G)

3.17 understand that genes exist in alternative forms called alleles which give rise to differences in inherited characteristics

Mendelian Inheritance

3.18 recall the meaning of the terms: dominant, recessive, homozygous, heterozygous, phenotype, genotype and codominance

There are 46 chromosomes in the human genome, that is 23 pairs of homologous chromosomes.
This means that for any gene we will have two different versions of it, one on each homologous chromosome.
There are normally many different versions of each gene so it is possible that each of the two homologous chromosomes has a different version of the gene, if this is the case the persons is said to be heterozygous for this gene (e.g. Ff).
Someone who has two alleles which are the same is homozygous for that gene (e.g. FF).

3.19 describe patterns of monohybrid inheritance using a genetic diagram

3.20 understand how to interpret family pedigrees

3.21 predict probabilities of outcomes from monohybrid crosses

Predicting inheritance
If we know the genotype of the mother and the father then we can predict the possible genotype of the offspring by using a punnett square.
For cystic fibrosis the normal gene (F) is dominant over the cystic fibrosis gene (f) which is recessive.
In this first example both the parents are heterozygous (Ff) for the cystic fibrosis gene
By drawing a punnett square we can predict the likelihood of a child acquiring CF.
Predict the likelihood of the child having cystic fibrosis?
What is the likelihood of the child being a carrier of cystic fibrosis?

Read p 119-125 and answer the following questions

1) What is codominance?
2) How is blood group inherited?
3) Draw a diagram to show inheritance of dwarfism in plants
4) What do we mean by the first and second filial generations
5) What is a test cross?

Try these
1) Sickle cell anaemia is caused by a recessive allele of the gene that codes for Haemoglobin.
The normal, dominant allele is H, and the faulty recessive allele is h.
What would be the result of a man with a genotype Hh having a child with a woman with sickle cell anaemia?

2) Wing length in flies is controlled by one gene. The allele for normal wings is dominant to the allele for short wings. Using the symbol W=normal wing and w=short wing, answer the following questions:
a. What is the genotype for a fly that is heterozygous for this character?
b. What are the possible genotypes of its gametes?
c. Draw a genetic diagram to show the offspring that would be produced if a heterozygous fly mated with one that was homozygous for normal wing
3) If a red tulip was crossed with a white tulip and all the tulips produced were pink what can you say about the dominant allele?

3.22 recall that the sex of a person is controlled by one pair of chromosomes, XX in a female and XY in a male

3.23 describe the determination of the sex of offspring at fertilisation, using a genetic diagram

3.24 understand that division of a diploid cell by mitosis produces two cells which contain identical sets of chromosomes

3.25 understand that mitosis occurs during growth, repair, cloning and asexual reproduction

3.26 understand that division of a cell by meiosis produces four cells, each with half the number of chromosomes, and that this results in the formation of genetically different haploid gametes

3.27 understand that random fertilisation produces genetic variation of offspring

3.28 recall that in human cells the diploid number of chromosomes is 46 and the haploid number is 23

3.29 understand that variation within a species can be genetic, environmental, or a combination of both

3.30 recall that mutation is a rare, random change in genetic material that can be inherited

3.31 describe the process of evolution by means of natural selection

3.32 understand that many mutations are harmful but some are neutral and a few are beneficial

3.33 understand how resistance to antibiotics can increase in bacterial populations

3.34 understand that the incidence of mutations can be increased by exposure to ionising radiation (for example gamma rays, X-rays and ultraviolet rays) and some chemical mutagens (for example chemicals in tobacco)