Genetic Diversity Flashcards
What is the definition of genetic diversity?
Measure of the number of different alleles of genes in a population
What is genetic diversity caused by?
1) gene mutations
2) chromosome mutations
3) crossing over
4) random assortment
5) random fusion of gametes
What is a gene mutation?
• Involves a change in the base sequence of a chromosome
• mutations usually occur when the DNA molecule is replicated (mitosis)
What could happen if a gene mutation occurs in the exon?
• if a mutation occurs within an exon of a gene, the polypeptide coded for may be changed in structure and consequently be non-functional
What is a neutral mutation?
When the change in amino acid sequence does not affect the function of the protein
What are the 3 types of gene mutations?
1) substitution
2) addition
3) deletion
What is substitution?
• When one or more bases in the gene sequence are exchanged for others, this results in a change in a base triplet
• many substitutions result in a change in only one triplet and consequently only one amino acid in the polypeptide coded for.
• the DNA code is degenerate so some substitutions may not result in any change in the polypeptide because the new triplet may code for the same amino acid as the original did, especially if the substitution occurs at the last base in the triplet.
• these mutations that cause no change in the polypeptide are called silent mutations
• if the new triplet is a stop triplet the polypeptide coded for will be shorter
What is an addition mutation?
One or more bases are added to the base sequence of the gene, this results in a frame shift
What is a deletion mutation?
One or more bases are deleted from the base sequence of a gene, this results in a frame shift
What does a frame shift in the base sequence of the gene result in?
Each triplet following either the deletion or addition is altered with the consequence that an entirely new sequence of amino acids is coded for and the protein will have a completely different structure and probably be non functional
What are mutagenic agents?
Things that can increase the rate at which mutations occur despite them normally occurring spontaneously and at random DNA replication
Such as:
• high energy radiation eg UV light
• ionising radiation eg gamma and X rays
• chemicals eg tar in cigarette smoke, bromine, peroxide or benzene
• viruses eg human papilloma virus infection can cause cancer of the cervix
What are carcinogens?
Substances which cause mutations in oncogenes cause a cell to become cancerous (uncontrolled cell division)
What are oncogenes?
Genes that control the rate of cell division
How do chromosome mutations occur?
Spontaneously and random during meiosis.
• During meiosis homologous chromosomes are separated to give gametes with only one set of chromosomes (haploid), when two gametes fuse the resulting zygote is diploid
• sometimes the homologous chromosomes do not separate (non-disjunction) and a gamete will have two chromosomes of the same type. When the gamete fuses with another the zygote will have 3 chromosomes instead of just a pair
What is an example of chromosome mutations?
• Down syndromes result from non-disjunction of chromosome 21
• either the egg or sperm cell from this persons parents would have had an extra chromosome 21 in it so the child has an extra chromosome 21
