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 genotype Your phenotype is what you look like, your characteristics
If both the alleles you inherit are the same you are homozygous for that characteristic e.g. NN or nn If you inherit different alleles you are heterozygous e.g Nn
DiseaseWhat it affectsType of allele cystic fibrosis the lungs – sticky mucus – difficulty in breathing recessive haemophiliathe blood can’t clot recessive Huntington’s disease the nervous system – uncontrollable movements dominant sickle cell anaemiathe bloods ability to pick up oxygen co-dominant These are the key ones to remember
inherited Characteristics depend on environment both eg eye coloureg 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.
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 is transferred to an empty unfertilised egg cell;
Spend 10 min writing down everything you can remember about B1