genes

chromosomes are found in the nucleus of the cell. during fertilisation chromosomes from our mother pair up with chromosomes from our father. this means that we have two copies of every chromosome and two copies of every gene (or a gene pair), one on each chromosome. chromosomes are made up of a molecule called DNA. short sections of DNA on a chromosome represents genes. genes hold information about all of our features. for example, our genes determine characteristics such as eye and hair colour. the two genes in a gene pair are known as alleles. they are alternative forms of the same gene. one allele in a gene pair may be dominant an the other may be recessive. a dominant allele will determine what characteristics are shown in the individual, even f a recessive allele is present. to develop a characteristic that is determined by recessive alleles, you must have two recessive alleles present in a gene pair.

definitions

gene: a piece of DNA with the instructions for a particular characteristic, e.g. eye colour.

allele: alternative forms of the same gene e.g. the flower colour gene in peas has alleles for white and yellow.

organisms that are produced by asexual reproduction have only one parent. asexual reproduction produces clones which are genetically identical to the parent. sexual reproduction produces offspring that are a variation of the two parents as genes from one parent mix with genes from the other parent during fertilisation. not all of our characteristics are determined by genes alone - some features such as the rate at which we grow, our weight, or our intelligence are also influenced by environmental factors.

definitions

variation: differences shown in a group of organisms e.g. flower colour.

sexual rproduction: half the genes are inherited from each of the two parents

asexual reproduction: only one parent passes on genes.

some disorders, such as cystic fibrosis can be inherited from our parents. CF is a recessive disorder, which means that the offspring must have two recessive alleles, one from each parent. CF causes certain cells in the lungs and digestive systems to produce large amounts of thick, sticky mucus. huntingtons disease affects the brain and nervous system. huntingtons disease is caused by a dominant allele so only one parent needs to carry the faulty gene.

gene therapy is a process that involves repairing faulty genes or replacing them with healthy ones. genetic disorders such as cystic fibrosis and some types of breast cancer could soon be prevented or cured using gene therapy. viruses or tiny lipid droplets can carry the healthy genes into certain cells that make up the lungs of CF sufferers. a DNA fingerprint is your unique barcode that distinguishes you from everyone else. a DNA fingerprint can be used to determine whether an individual has an inherited disease or is at a greater risk of developing a disease. individuals at a greater risk of developing diseases such as breast cancer can be monitored more closely. forensic scientists can use DNA fingerprints in many ways including identifying criminals or crime victims.

definitions

cancer: rapid uncontrolled growth of cells to form tumors which may spread.

forensic: using scientific knowledge to help detect crime.

DNA i made up of smaller units called bases. there are 4 different types of bases in DNA. they are given the letters A,G,C,T. many millions of these bases line up to form a chromosome, and short stretches of these bases make up the codes for our genes. the human genome project (HGP) has worked out the order of these bases on all of our chromosomes. using the information gained from the HGP, scientists have been able to work out the codes for certain genes including some that cause disease. eventually, the codes for all our genes will be known and some people are very concerned about the effects hat this might have on their lives.

human genome project: a project that worked out the sequence of genes in human DNA

genes can be transferred from one organism to another to produce a transgenic organism. transgenic organisms have new or altered characteristics. some transgenic organisms have human genes inserted into their cells. these organisms can produce milk containing human antibodies or other useful substances to treat diseases, for example cystic fibrosis.

cloning mammals

scientists are able to create clones of mammals and other organisms artifically. clones may also be made of human organs for transplants. cloning mammals has raised concern amongst the general public and some scientists.

defintion

transgenic organism: an organism containing genes taken from anoher species.