B3: Variation, inheritance and evolution

• Variation
• Inheritance
• Evolution

Variation

Candidates will be assessed on their ability to:

• recall that the nucleus of a cell contains chromosomes on which genes (units of inherited information) are located (B3.01)
• understand that each gene is a section of a molecule of DNA (B3.02)
• describe a DNA molecule as two strands coiled to form a double helix, the strands being linked by a series of paired bases (adenine with thymine and cytosine with guanine) (B3.03)
• understand that:
  - variation between individuals arises from genetic and environmental causes and from a combination of both
  - environmental conditions during growth and development cause variation between genetically identical individuals (B3.04)
• understand:
  - that genes exist in alternative forms (alleles) which cause variation in inherited characteristics
  - the terms dominant and recessive
  - that some alleles cause diseases which can be inherited (B3.05)
• recall that:
  - chromosomes are present as pairs in body cells and singly in gametes
  - 46 and 23 are the diploid and haploid numbers of chromosomes in human cells (B3.06)
• understand that division of a cell by mitosis produces two cells which contain identical sets of chromosomes for growth and replacement; interpret diagrams showing the overall behaviour of chromosomes during mitosis (technical terms not required) (B3.07)
• understand that division of a cell by meiosis produces four cells, each with half the number of chromosomes for the formation of genetically different haploid gametes during sexual reproduction; interpret simple diagrams and photographs showing stages in meiosis (technical terms not required) (B3.08)
• define fertilisation as the fusion of haploid male and female gametes, restoring the diploid number of chromosomes in the zygote; explain the resulting genetic variation in the new generation of individuals (B3.09)
• explain that asexual reproduction involves only one parent and gives rise to genetically identical offspring (clones) (B3.10)
• recall that a mutation is a change in a gene or the number of chromosomes in a cell, which leads to genetic variation (B3.11)
• understand that many mutations are harmful, some are neutral and a few are beneficial and can increase in the population by natural selection (B3.12)
• understand that exposure to ionising radiation (including gamma rays, ultraviolet rays and X- rays) and some chemical mutagens (including chemicals in tobacco) increases the incidence of
  mutations (B3.13)

Inheritance

Candidates will be assessed on their ability to:

• recall that the sex of a person is controlled by one pair of chromosomes, XX in a female or XY in a male, and describe the determination of the sex of offspring at fertilisation, using a genetic diagram (B3.14)
• describe the mechanism of monohyhrid inheritance using a crossing diagram (B3.15)
• understand how individuals can be homozygous or heterozygous for particular alleles; distinguish between genotype and phenotype (B3.16)
• predict probabilities of inheritance from parents using genetic diagrams (B3.17)
• explain family trees showing the inheritance of polydactyly (dominant allele) and cystic fibrosis (recessive allele) (B3.18)
• describe some of the implications of the outcome of the Human Genome Project (B3.19)
• describe how selective breeding is used to develop crop plants and agricultural animals with desirable characteristics such as resistance to disease and production of high yields (B3.20)
• understand that cloning is used to produce large numbers of identical individuals with desirable characteristics eg plant cuttings (B3.21)
• describe the ethical implications of selective breeding and cloning (B3.22)


In order to meet statutory requirements, candidates following the Northern Ireland National Curriculum should be taught how proteins can be obtained from genetically engineered bacteria.


• describe how the transfer of a required gene from a donor to a recipient, including the use of restriction enzymes and ligase, can produce genetically modified organisms (B3.23)
• evaluate the ethical implications of genetic modification (B3.24)

Evolution

Candidates will be assessed on their ability to:

• understand that fossils provide evidence of evolution (B3 25)
• describe how inherited variation can lead to evolution or extinction by the process of natural selection (B3.26)

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