B1 – You and your Genes

Locating genes

Genes are located in chromosomes which are in the nucleus of cells

cell nucleus

23 pairs = 46 chromosomes altogether

Sperm cells can have an X or Y sex chromosome

Egg cells can only have an X sex chromosome

Most characteristics are determined by genes called alleles

An allele can be dominant, recessive (or co-dominant)

Alleles mostly come in pairs

The alleles you inherit is called your genotypeYour phenotype is what you look like, your characteristics

Punnettsquare

If both the alleles you inherit are thesame you are homozygous for that characteristic e.g. NN or nn

If you inherit different alleles you are heterozygous e.g Nn

Disease What it affects Type of allele

cystic fibrosisthe lungs – sticky mucus – difficulty in breathing recessive

haemophilia the blood can’t clot recessive

Huntington’s diseasethe nervous system – uncontrollable movements

dominant

sickle cell anaemia the bloods ability to pick up oxygen

co-dominant

These are the key ones to remember

inherited

Characteristics depend on

environment

both

eg eye colour eg dyeing your hair

eg weight

Identical twins (formed when a fertilised egg starts to divide and splits to form 2 babies instead of one).

Natural clones

Asexual reproduction (eg bacteria)

Clones have got identical genes

Plant cuttings can be grown into clones of the original plant.

Stem cells are unspecialised cells

Shows stem cells being extracted from a blastocyst

early embryo

Making stem cells using the DNA from a patient means the cells wont be rejected when they are transplanted into the patient

This means that the patient’s immune system wont attack the transplanted stem cells

foreign cell with antigen

White blood cells recognise it as a

foreign cell and make antibodies

The antibodies help to kill the

foreign cell

X

With this technique the white blood cells do not recognise the

transplanted stem cells as foreign and therefore don’t attack them

IVF – In Vitro Fertilisation

Embryos left over from IVF treatment can be used to obtain stem cells

The fertilised egg can now be implanted into the uterus of the mother

The fertilised egg can now be tested for genetic diseases if desired.

controversial

The right decision is the one which leads to the best outcome for the majority of people involved

Some things are considered to be unnatural or wrong

Opinion. Against cloning and against

using embryos.

Opinion. Seems to be against using stem cells. Points out possible risks. Uses exaggerated

language. No mention of embryos.

Seems to be for using stem cells. Hasn’t said anything

about using embryos.For using stem cells and using embryos.

These people could be biased.

Gordon is supposed to be impartial, ie he should give a balanced view.The other people could have a vested interest, ie they could have a direct benefit or are campaigners for a cause.

Go to HigherContinue with Foundation

Spend 10 min writing down everything you can remember about B1

a gene

recessive

chromosomes

John

Reshma

Kate

Lucy

46

XY

Higher material

understand that genes are instructions for a cell that describe how to make proteins, which may be structural or enzymes;

recall that the sex of a human embryo is determined by a gene on the Y chromosome;

understand the link between this gene and the development of sex organs into either ovaries or testes.

understand the implications of testing embryos for embryo selection (pre-implantation genetic diagnosis);

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

in the context of use of genetic testing by others can:• distinguish what can be done (technical feasibility), from what should be done (values);• explain why different courses of action may be taken in different social and environmental contexts.

understand how clones of animals occur:• naturally, when cells of an embryo separate (identical twins);• artificially, when the nucleus from an adult body cell istransferred to an empty unfertilised egg cell;

Spend 10 min writing down everything you can remember about B1

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