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KS4 Genes & Inheritance
6.1.4 DNA and the genome
- Know that the genetic material in the nucleus of a cell is composed of a chemical called DNA.
- Know that DNA is a polymer made up of two strands forming a double helix.
- Know that DNA is contained in structures called chromosomes.
- Know that a gene is a small section of DNA on a chromosome that codes for a particular sequence of amino acids, to make a specific protein.
- Know that the genome of an organism is the entire genetic material of that organism.
- Know that the whole human genome has now been studied and this will have great importance for medicine in the future.
- Be able to discuss the importance of understanding the human genome, limited to the:
- search for genes linked to different types of disease
- understanding and treatment of inherited disorders
- use in tracing human migration patterns from the past.
6.1.5 DNA structure
- Know that DNA contains four bases, A, C, G and T.
- Know that a sequence of three bases is the code for a particular amino acid and that the order of bases controls the order in which amino acids are assembled to produce a particular protein.
- Know that the long strands of DNA consist of alternating sugar and phosphate sections and that attached to each sugar is one of four bases; A, C, G or T.
- Know that the DNA polymer is made up of repeating nucleotide units each consisting of a common sugar, a phosphate group and one of the four different bases attached to the sugar.
- Be able to interpret a diagram of DNA structure but will not be required to reproduce it.
- be able to:
- recall a simple description of protein synthesis
- explain simply how the structure of DNA affects the protein made
- describe how genetic variants may influence phenotype: a) in coding DNA by altering the activity of a protein: and b) in noncoding DNA by altering how genes are expressed. (HT only)
- Know that in the complementary strands a C is always linked to a G on the opposite strand and a T to an A. (HT only)
(NB: Students are not expected to know or understand the structure of mRNA, tRNA, amino acids, or proteins).
- Be able to explain how a change in DNA structure may result in a change in the protein synthesised by a gene. (HT only)
- Know that proteins are synthesised on ribosomes, according to a template, and that carrier molecules bring specific amino acids to add to the growing protein chain in the correct order. (HT only)
- Know that when the protein chain is complete it folds up to form a specific shape. This specific shape enables the proteins to do their job as enzymes, hormones or forming structures in the body such as collagen. (HT only)
- Know that mutations occur continuously and that most do not alter the protein, or only alter it slightly so that its appearance or function is not changed. (HT only)
- Know that a few mutations code for an altered protein with a different shape, for example an enzyme may no longer fit the substrate binding site or a structural protein may lose its strength. (HT only)
- Know that not all parts of DNA code for proteins: Non-coding parts of DNA can switch genes on and off, so variations in these areas of DNA may affect how genes are expressed. (HT only)
- Be able to model insertions and deletions in chromosomes to illustrate mutations.
6.1.6 Genetic inheritance
- Be able to explain the terms: gamete, chromosome, gene, allele, dominant, recessive, homozygous, heterozygous, genotype, phenotype.
- Know that some characteristics are controlled by a single gene, such as: fur colour in mice; and red-green colour blindness in humans.
- Know that each gene may have different forms called alleles.
- Know that the alleles present, or genotype, operate at a molecular level to develop characteristics that can be expressed as a phenotype.
- Know that a dominant allele is always expressed, even if only one copy is present.
- Know that a recessive allele is only expressed if two copies are present (therefore no dominant allele present).
- Know that if the two alleles present are the same the person is homozygous for that trait, but if the alleles are different they are heterozygous.
- Know that most characteristics are a result of multiple genes interacting, rather than a single gene.
- Be able to understand the concept of probability in predicting the results of a single gene cross, but recall that most phenotype features are the result of multiple genes rather than single gene inheritance.
- Be able to use direct proportion and simple ratios to express the outcome of a genetic cross.
- Be able to complete a Punnett square diagram and extract and interpret information from genetic crosses and family trees.
- Be able to construct a genetic cross by Punnett square diagram and use it to make predictions using the theory of probability. (HT only)
6.1.7 Inherited disorders Knowledge of embryo screening is not included.
- Know that some disorders are inherited and that these disorders are caused by the inheritance of certain alleles.
- Know that Polydactyly (having extra fingers or toes) is caused by a dominant allele.
- Know that Cystic fibrosis (a disorder of cell membranes) is caused by a recessive allele.
- Be able to make informed judgements about the economic, social and ethical issues concerning embryo screening, given appropriate information.
- Appreciate that embryo screening and gene therapy may alleviate suffering but consider the ethical issues which arise.
6.1.8 Sex determination
- Know that an ordinary human body cells contain 23 pairs of chromosomes, 22 pairs control characteristics only, but one of the pairs carries the genes that determine sex: females the sex chromosomes are the same (XX) and in males the chromosomes are different (XY).
- Be able to carry out a genetic cross to show sex inheritance.
- Understand and use direct proportion and simple ratios in genetic crosses
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