3.13 – Understand that the nucleus of a cell contains chromosomes on which genes are
located.
– The nucleus of a cell contains chromosomes on which genes are located.
3.14 – Understand that a gene is a section of a molecule of DNA and that a gene codes
for a specific protein.
– Gene: A section of a molecule of DNA that codes for a specific protein.
3.15 – 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).
– A DNA molecule consists of two coiled strands to form a double helix.
– The strands consists of paired bases:
• Adenine (A) – Thymine (T)
• Cytosine (C) – Guanine (G)
3.16 – Understand that genes exist in alternative forms called alleles which give rise to
differences in inherited characteristics.
– Allele: Alternate form of a gene.
– Alleles give rise to differences in inherited characteristics.
3.17 – Understand the meaning of the terms: dominant, recessive, homozygous,
heterozygous, phenotype, genotype and codominance.
– Dominant: Gene allele that expresses over another allele.
• Present in both homozygous pairs and heterozygous pairs.
• Represented by a capital letter.
– Recessive: Gene allele that is only expressed when paired with another recessive
allele.
• Present in homozygous recessive pairs only. In heterozygous pairs, the dominant
allele is expressed over the recessive allele.
• Represented by a lowercase letter.
– Homozygous: Same pair of genes.
• Homozygous dominant: Two dominant gene alleles.
• Homozygous recessive: Two recessive gene alleles.
– Heterozygous: Different pair of genes (i.e. one dominant and recessive gene).
– Phenotype: The characteristic that the gene displays.
– Genotype: The actual nature of the gene.
– Codominance: When both alleles are expressed in a heterozygous pair.
3.18 – Describe patterns of monohybrid inheritance using a genetic diagram.
– Monohybrid inheritance: The inheritance of one gene (see 3.20).
3.19 – Understand how to interpret family pedigrees.
3.20 – Predict probabilities of outcomes from monohybrid crosses.
– Probabilities (where A is the dominant allele and a is the recessive allele):
• 25% AA • 50% Aa • 25% aa
3.21 – Understand that the sex of a person is controlled by one pair of chromosomes, XX
in a female and XY in a male.
– The sex of a person is controlled by one pair of chromosomes.
– XX in a female, XY in a male.
3.22 – Describe the determination of the sex of offspring at fertilisation, using a genetic
diagram.
– The sperm contains the XY chromosome.
– The ovum contains the XX chromosome.
3.23 – Understand that division of a diploid cell by mitosis produces two cells which
contain identical sets of chromosomes.
– Division of a diploid cell by mitosis produces two cells which contain identical sets of
chromosomes.
3.24 – Understand that mitosis occurs during growth, repair, cloning and asexual
reproduction.
– Mitosis occurs during growth, repair, cloning and asexual reproduction.
3.25 – 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.
– Division of a cell by meiosis produces four cells, each with half the number of
chromosomes.
– This results in the formation of genetically-different haploid gametes.
3.26 – Understand that random fertilisation produces genetic variation of offspring.
– Random fertilisation produces genetic variation of offspring.
3.27 – Know that in human cells the diploid number of chromosomes is 46 and the
haploid number is 23.
– In human cells, the diploid number of chromosomes is 46.
– In human cells, the haploid number of chromosomes is 23.
3.28 – Understand that variation within a species can be genetic, environmental, or a
combination of both.
– Variation within a species can be genetic, environmental, or a combination of both.
3.29 – Understand that mutation is a rare, random change in genetic material that can be
inherited.
– Mutation: A rare, random change in genetic material that can be inherited.
3.30 – Describe the process of evolution by means of natural selection.
– Variation within a species is caused by a rare, random mutation.
– The mutation of a gene means that the animal survives and is not killed.
– The survived animals reproduce and pass on the gene.
– This is repeated over time and many generations.
3.31 – Understand that many mutations are harmful but some are neutral and a few are
beneficial.
– Many mutations are harmful.
– Some mutations are neutral.
– Few mutations are beneficial.
3.32 – Understand that resistance to antibiotics can increase in bacterial populations,
and appreciate how such an increase can lead to infections being difficult to control.
– Resistance to antibiotics can increase in bacterial populations.
– The increase of resistance to antibiotics can lead to bacterial infections being difficult
to control.
3.33 – 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).
– The incidence of mutations can be increased by exposure to ionising radiation.
• E.g. Gamma rays, X-rays and ultraviolet rays.
– The incidence of mutations can be increased by some chemical mutagens.
• E.g. Chemicals in tobacco