Understanding Inherited Variation: Exploring Genetic Differences in Organisms

1. AO11.6 – Inherited Variation Pass: Candidates demonstrate a basic competence when carrying out an investigation that demonstrates a variation in an organism caused by a gene and give a basic comment using qualitative data on the outcome of the investigation. Candidates produce a basic spreadsheet containing variation data and briefly comment on the reliability of the data collection method that they used. Merit: Candidates demonstrate competence when carrying out an investigation that demonstrates a variation in an organism caused by a gene and gives a detailed account using quantitative data on the outcome of the investigation. Candidates produce a spreadsheet containing variation data and comment in detail on the reliability and validity of the data collection method that they used. Distinction: Candidates demonstrate a high level of competence when carrying out an investigation that demonstrates a variation in an organism caused by a gene. They give a very detailed account, using a range of quantitative data, on the outcome of the investigation. Candidates produce a spreadsheet containing variation data. They evaluate the data collection method that they used, in terms of validity and reliability.

2. Inherited characteristics The members of this family tree are related and so they share certain similar characteristics, such as hair colour and eye colour. Shared family characteristics are inherited from parents. So why don’t all family members look exactly alike? Why are identical twins more similar than brothers and sisters?

3. What is variation? People are similar, but not identical, to their parents and siblings. The differences within a species are called variation. Variation can come about for two reasons. What are they? People inherit characteristics from both parents and each person gets a different combination of features. This is called inherited variation. Other characteristics are affected by a person’s surroundings. This called environmental variation.

4. Which type of variation?

5. Inherited or environmental? Deciding if a characteristic is inherited or environmental can cause a lot of discussion. Scientists have now decided that only four features are truly inherited and not affected by the environment at all. What are the four truly inherited characteristics? • natural eye colour • natural hair colour • blood group • certain inherited diseases.

6. Inherited characteristics What makes this baby human? What determines its gender? In all living things, characteristics are passed on in the chromosomes that offspring inherit from their parents. So all human characteristics, including gender, must be something to do with chromosomes. Where are chromosomes found?

7. What are chromosomes?

8. What are chromosomes? Chromosomes are long strands of genetic information located in the nuclei of cells. Chromosomes are most visible during cell division when they replicate and look like this… You will see chromosomes represented bothways.

9. Homologous chromosomes In most cells chromosomes are matched in pairs based on their sizeand shape. chromosome from male parent chromosome from female parent homologous chromosomes Matching pairs of chromosomes are called homologous chromosomes. Where do homologous chromosomes come from? Each pair of homologous chromosomescontains one chromosome that has been inherited from each parent.

10. Human chromosomes In human body cells there are a total of 46 chromosomes. How many pairs of homologous chromosomes are there in human body cells? 23 pairs of chromosomes You inherit half your chromosomes from your mother and half from your father. How many chromosomes do you inherit from each parent? 23 unpaired chromosomes

11. Inherited or environmental? Nose shape is inherited, but over time may be affected by the environment. For instance, someone might have a nose that looks just like their mum’s. But if they were in an accident, they might break their nose and put a kink in it. Apart from eye colour, natural hair colour, blood group and some inherited diseases, all other features are caused by a mixture of inheritance and environmentalfactors. What environmental factor might affect skin colour?

12. Genes and Alleles • Sections of chromosomes that code for a particular characteristic are called genes, for example there is a gene for eye colour. • Alleles are alternative forms for genes. • Consider the eye colour gene. It has different alleles such as… • Blue • Brown • Green

13. Alleles can be dominant or recessive. Dominant alleles always take over recessive alleles Example… Eye Colour You inherit one allele from your mother and one from your father. The brown allele is dominant whereas the blue allele is recessive. So.. Two brown alleles = brown eyes Two blue alleles = blue eyes One brown allele and one blue allele = brown eyes Dominant and Recessive alleles