B1 (Biology): You and your genes

This section shows links to revision materials Biology B1 - You and your genes.

Overview of Module

The inheritance of detailed information from each generation to the next is a fundamental story in science. For each of us, inheritance also raises questions about our own development. In this module, candidates learn basic concepts of inheritance: genes as units of inheritance, the interplay between genes and environment and sexual reproduction as a source of variation. 

These concepts are sufficiently detailed for candidates to make sense of related ideas in other GCSE Science modules. More complex ideas, such as mechanisms for protein synthesis and cell division, are not required; these are covered in GCSE Additional Science A.

Throughout the module, candidates are introduced to genetic technologies that open up new possibilities for individuals and society. In doing so, they present significant ethical issues for citizens. Candidates explore some of the ideas people use to make ethical decisions. This enables them to engage with issues which regularly appear in the media, such as genetic testing and cloning research.

Biology 

B1 - You and your genes (click on the links below for general headings or look below for more detail on what you may be tested on)

• B1.1 - Genes,
• B1.2 - Inheritance,
• B1.3 - Testing and treating genetic diseases,
• B1.4 - Cloning and stem cells

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

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

2. recall that genes are instructions for a cell that describe how to make proteins

3. recall that proteins may be structural (e.g. collagen) or functional (e.g. enzymes such as amylase)

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

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

6. understand that many characteristics are determined by several genes working together (e.g.eye colour).

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

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

2. understand that chromosomes in a pair carry the same genes in the same place, but that there may be different versions of genes called alleles

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

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

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

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

7. 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. 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. recall that human males have XY sex chromosomes and females have XX sex chromosomes

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

2. recall that disorders may be caused by dominant alleles (e.g. Huntington’s disease) or recessive alleles (e.g. cystic fibrosis)

3. recall 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. 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. 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. describe uses of genetic testing for screening adults, children and embryos, limited to:

• a. testing embryos for embryo selection (pre-implantation genetic diagnosis)
• b. predictive testing for genetic diseases
• c. testing an individual before prescribing drugs

7. understand that testing adults and fetuses 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. understand the implications of testing embryos for embryo selection prior to implantation

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

B1.4 How is a clone made?

1. understand that bacteria, plants and some animals can reproduce asexually to form clones (individuals with identical genes)

2. understand that any differences between clones are likely to be due only to environmental factors

3. understand that clones of plants occur naturally when plants produce bulbs or runners

4. understand that clones of animals occur:

• a. naturally, when cells of an embryo separate (identical twins)
• b. artificially, when the nucleus from an adult body cell is transferred to an empty unfertilised egg cell

5. understand that there are different types of stem cells:

• a. adult stem cells which are unspecialised cells that can develop into many, but not all, types of cells
• b. embryonic stem cells which are unspecialised cells that can develop into any type of cell

6. understand that, as a result of being unspecialised, stem cells from embryos and adults offer the potential to treat some illnesses

7. understand that the majority of cells of multicellular organisms become specialised during the early development of the organism.