You + Your Genes

B1 Revision Notes

Individual Characteristics Features determined either owing to

environment or inheritance. Examples? Variation amongst individuals

Organisms made of cells. Cells controlled by a nucleus containing

chromosomes. Each chromosome is made of thousands of

genes which control how you develop. Genes tell the cell how to make proteins (50,000

types in human body).

Chromosomes Put in correct order, largest 1st

Chromosome, gene, cell, nucleus

Each body cell contains 46 (23 pairs) chromosomes. 23 from each parent.

Only sex cells (gametes) contain only 23 chromosomes.

Genes and Alleles

Chromosomes pair up and genes for the same feature align next to each other.

Different versions of the same gene are called alleles, e.g. eye colour (brown and blue alleles, but gene for the same feature).

One allele is always dominant and means this feature shows up. The other allele is recessive.

Genetic Crosses

Mum has 2 alleles, A and a for hair colour.

Dad has the same ones. A is brown hair a is blond hair. Both parents have brown hair. What is chance of offspring having blond?

X and Y

XX is female. XY is male. Y dominates. 50:50 chance of either sex

Sex-linked diseases; Haemophilia Colour-blindness Muscular dystrophy

Inherited Diseases

Cystic Fibrosis. Caused by recessive allele. Mainly people are carriers. Causes cells to produce sticky mucus. Results in

lengthy physio and higher infections rates.

Huntington’s Disease. Attacks the nervous system. Symptoms include

loss of muscle control and memory loss and commence later in life.

Caused by dominant allele.

Ethical Decisions

Amniocentesis is a test on an unborn baby to detect if it has cystic fibrosis.

It is not 100% reliable with a 0.5% miscarriage risk, small chance of infection, and results only between 15-18 weeks.

Information could be used to decide on a termination (abortion). This is an ethical decision based on genetic testing

Reliability of Genetic Tests

False-negative; Wrong result which says a person does not have a

medical condition but they do.

False-positive; Wrong result which says a person has a medical

condition but they do not (this could have been aborted so ethics again!)

Designer babies

Embryo selection (form of IVF);

Gametes fertilised in labs, and then the embryo’s tested for genetic disease/s (checking the alleles). Healthy ones used for mothers womb. What about the others??

Gene therapy; Curing an inherited disease by

putting correctly working alleles into a person.

Had limited success. Currently illegal for sex cells. People worried it could lead to control features like eye colour, etc.

Cloning

Clone is genetically identical to the organism it was made from.

Happens naturally with identical twins and also asexual reproduction (one parents such as bacteria).

Early embryos are made of stem cells which can develop into any specialised cell. Scientists want to clone using cloned embryos. Ethical decisions?

Arguments

In favour; Scientific progress Organ transplants Legal up to 14 days Your relation/friend?

Against; Human rights Lowers value of life ‘Murder’ of embryos