B1-You And Your Genes

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B1.1 What are genes and how do they affect the way that organisms develop?

1. Know that instructions to control how an organism develops and functions are found in the nucleus of its cells and are called genes.

2. Know that genes consist of molecular instructions for a cell that describe how to make proteins.

3. Know that proteins may be structural (eg collagen) or functional (eg enzymes such as amylase)

4. Know that genes are sections of very long DNA molecules that make up chromosomes in the nuclei of cells

5. You need to understand that some characteristics are determined by genes (eg dimples), some are determined by environmental factors (eg scars), and some are determined by a combination of genes and the environment (eg weight)

6. You need to understand that many characteristics are determined by several genes working together (eg eye colour).

B1.2 Why can people look like their parents, brothers and sisters, but not be identical to them?

1. Know that body cells contain pairs of chromosomes and that sex cells contain only one chromosome from each pair.

2. You must know and understand that chromosomes in a pair carry the same genes in the same place, but that there may be different versions of genes calledalleles.

3. Know that an individual usually has two alleles for each gene

4. Know that in an individual the two alleles of each gene can be the same (HT, homozygous) or different (HT, heterozygous)

5. You must know and understand that during sexual reproduction genes from both parents come together and produce variation in the offspring

6. You must know and understand that offspring have some similarities to their parents because of the combination of maternal and paternal alleles in the fertilised egg

7. You must know and understand that different offspring from the same parents can differ from each other because they inherit a different combination of maternal and paternal alleles.

8. You must know and understand that an allele can be dominant or recessive, and that ...

a) an individual with one or both dominant alleles (in a pair of alleles) will show the associated dominant characteristic

b) an individual with one recessive allele (in a pair of alleles) will not show the associated recessive characteristic

c) an individual with both recessive alleles (in a pair of alleles) will show the associated recessive characteristic

9. Know that human males have XY sex chromosomes and females have XX sex chromosomes.

10. HT only: You must know and understand that the sex-determining gene on the Y chromosome triggers the development of testes, and that in the absence of a Y chromosome ovaries develop

11. You need to be able to use and interpret genetic diagrams (family trees and Punnett squares) showing ...

a) the inheritance of single gene characteristics with a dominant and recessive allele

b) the inheritance of sex chromosomes

12. HT only: You must know and understand that the term genotype describes the genetic make-up of an organism (the combination of alleles), and the term phenotype describes the observable characteristics that the organism has.

B1.3 How can and should genetic information be used? How can we use our knowledge of genes to prevent disease?

1. Be able to understand that a small number of disorders are caused by faulty alleles of a single gene, including Huntington’s disease and cystic fibrosis.

2. Know and understand that disorders may be caused by dominant alleles (eg Huntington’s disease) or recessive alleles (eg cystic fibrosis)

3. Know the symptoms of Huntington’s disease and cystic fibrosis, to include:

a) Huntington’s disease – late onset, tremor, clumsiness, memory loss, inability to concentrate, mood changes

b) cystic fibrosis – thick mucus, difficulty breathing, chest infections, difficulty in digesting food

4. Know and understand that a person with one recessive allele (in a pair of alleles) will not show the symptoms of the disorder, but is a carrier and can pass the recessive allele to their children.

5. Be able to interpret through genetic diagrams (family trees and Punnett squares) the inheritance of a single gene disorder, including the risk of a child being a carrier.

6. Be able to describe uses of genetic testing for screening adults, children and embryos, limited to:

a) testing embryos for embryo selection (HT only: pre-implantation genetic diagnosis)

b) predictive testing for genetic diseases

c) testing an individual before prescribing drugs

7. Be able to understand that testing adults and fetuses (foetuses) for alleles that cause genetic disorders has implications that need to be considered, including:

a) risk of miscarriage as a result of cell sampling for the genetic test

b) using results that may not be accurate, including false positives and false negatives

c) whether or not to have children at all

d) whether or not a pregnancy should be terminated

e) whether other members of the family should be informed

8. HT only: Know and understand the implications of testing embryos for embryo selection prior to implantation.

9. Know and understand the implications of the use of genetic testing by others (for example, for genetic screening programmes by employers and insurance companies).

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