Inheritance

What the syllabus asks of you

• Describe inheritance as the transmission of genetic information from generation to generation
• Define an allele as an alternative form of a gene
• Understand and use the terms: dominant, recessive, phenotype, genotype, homozygous and heterozygous
• Use genetic diagrams, including Punnett squares, to predict the results of monohybrid crosses and calculate phenotypic ratios, limited to 1 : 1 and 3 : 1 ratios
• Explain why observed ratios often differ from expected ratios, especially when there are small numbers of offspring
• State that two identical homozygous individuals that breed together will be pure-breeding
• Explain codominance by reference to the inheritance of the ABO blood groups (phenotypes A, B, AB, O, gene alleles IA, IB and Io)
• Describe the determination of sex in humans (XX and XY chromosomes)
• Describe a gene mutation as a random change in the base sequence of DNA, using sickle cell anaemia as an example
• Describe a chromosome mutation as a change in the chromosome number or structure, using Down’s syndrome as an example (47 chromosomes instead of 46)
• State that mutation, meiosis, random mating and random fertilisation are sources of genetic variation in populations
• Understand that ionising radiation and some chemicals increase the rate of mutation