B1 Specification

Module B1: You and your genes

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 (eg collagen) or functional (eg 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 (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. 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. 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  brosis

2. recall that disorders may be caused by dominant alleles (eg Huntington’s disease) or

recessive alleles (eg 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, dif culty 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.

© OCR 2012 GCSE Additional Science