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neurologyYou need to know

• Mitosis is cell division that produces two genetically identical diploid daughter cells for growth, repair and asexual reproduction.
• Asexual reproduction involves one parent and produces offspring that are genetically identical clones, except where mutations occur.
• Sexual reproduction involves the fusion of male and female gametes, produces genetically different offspring, and requires meiosis to make haploid gametes.
• Meiosis is cell division in reproductive organs that produces four genetically different haploid gametes from one diploid cell.
• Mitosis involves one cell division and produces two identical diploid cells, whereas meiosis involves two cell divisions and produces four different haploid gametes.
• Sexual reproduction causes variation because gametes contain different combinations of alleles and fertilisation combines alleles from two parents at random.
• DNA is a polymer made from two strands coiled into a double helix, with each strand made of nucleotides containing a sugar, phosphate group and one of four bases: A, T, C or G.
• A gene is a section of DNA that codes for a specific sequence of amino acids, and the order of amino acids determines the shape and function of a protein.
• Chromosomes are long molecules of DNA found in the nucleus, a genome is the entire genetic material of an organism, and genes are sections of chromosomes.
• The human genome is important because it helps scientists identify genes linked to disease, understand inherited disorders, trace human migration and develop personalised medicine.
• Protein synthesis involves transcription of a gene into messenger RNA in the nucleus and translation of messenger RNA at a ribosome into a chain of amino acids.
• A mutation is a change in the DNA base sequence that can alter the amino acid sequence of a protein, although some mutations have no effect on the protein produced.
• An allele is a version of a gene; a dominant allele is expressed if one copy is present, and a recessive allele is expressed only if two copies are present.
• A genotype is the combination of alleles an organism has, while a phenotype is the observable characteristic caused by the genotype and the environment.
• Human biological sex is usually inherited through sex chromosomes: females are XX, males are XY, and the sperm determines the sex of the offspring.
• Cystic fibrosis is caused by a recessive allele and can cause thick sticky mucus, breathing difficulties and digestive problems; polydactyly is usually caused by a dominant allele and causes extra fingers or toes.
• Genetic screening tests DNA, embryos or individuals for particular alleles, and embryo screening can raise economic, social and ethical issues about cost, access, disability and selection of embryos.
• Variation between organisms can be caused by genetic factors, environmental factors, or a combination of both, and mutation is a source of new alleles.
• Natural selection occurs when individuals with advantageous characteristics are more likely to survive, reproduce and pass on alleles, causing the frequency of those alleles to increase over generations.
• Selective breeding is when humans choose organisms with desirable characteristics to breed, but it can reduce genetic variation and increase the risk of inherited disorders.

• Compare asexual and sexual reproduction by referring to number of parents, type of cell division, genetic similarity of offspring, production of gametes and effect on variation.
• Compare mitosis and meiosis by stating the number of divisions, number of cells produced, chromosome number of daughter cells and whether the cells are genetically identical or different.
• Construct and complete a Punnett square using parental genotypes, gametes and allele combinations, then calculate predicted genotype and phenotype ratios or probabilities.
• Interpret a family tree by using affected and unaffected individuals to infer whether an allele is dominant or recessive and to identify possible genotypes.
• Represent variation data from a population using an appropriate graph, such as a bar chart for discontinuous variation or a histogram/line graph for continuous variation.
• Explain evolution by natural selection as a sequence involving mutation or variation, selection pressure, differential survival, reproduction and inheritance of advantageous alleles.
• Describe genetic engineering by identifying a useful gene, cutting it out using enzymes, inserting it into a vector such as a plasmid, and transferring it into a host organism.
• Evaluate genetic engineering or embryo screening by giving balanced benefits and risks, including medical or agricultural uses, ethical concerns, economic cost and possible environmental effects.
• Interpret evolutionary trees by identifying common ancestors, branching points, closest relatives and patterns of evolutionary relatedness.
• Name species using the binomial system by writing the genus with a capital letter followed by the species with a lower-case letter, such as Homo sapiens.