Genetics - 3.1 Genes Flashcards
Understandings:
- A gene is a heritable factor that consists of a length of DNA and influences a specific characteristic
- A gene occupies a specific position on a chromosome
- The various specific forms of a gene are alleles
- Alleles differ from each other by one or only a few bases
- New alleles are formed by mutation
- The genome is the whole of the genetic information of an organism
- The entire base sequence of human genes was sequenced in the Human Genome Project
DNA
codes for/determines characteristics of an organism (eg. physical, behavioural, physiological)
Genes =
lengths of DNA that code to make a proteins (ie sequence of DNA that encloses a specific trait)
Chromosoms =
DNA packaged and organisen into
Locus / Loci
= position on a chromosome where a gene for a particular trait is located
Homologous chromosome =
- same gene
- each homologous pair = same size has the centromere in the same place, has the same gene loci in the same sequence and has the same pattern of banding.
Alleles
alternative forms of a gene that codes for the different variations of a specific trait
= possess very similar gene sequences
= only differ by one or two bases
(“homologous pair carry alternative forms of a gene called alleles)
Homologous chromosomes carry the same sequence of genes but not necessarily the same alleles of those genes
Mutations (definition, causes, types of mutations, locations)
Mutations = alternations in the DNA of the chromosomes that is not immediately and properly repaired (changed in nucleotide sequence of a sections of DNA for a specific trait)
Mutations may be:
- neutral
- harmful
- Beneficial
Causes:
- randomly/spontaneously
- induced
locations:
- somatic cells (are not inherited)
- Gametic (occur in the cells of the gonads (which produce sperm/eggs) and may be inherited)
neutral - mutations
neutral/silent (ie they have no observable effect on the organism) - no effect on the functioning of the specific feature
harmful - mutations
harmful (detrimental) evident because they may alter the survival capacity of the organism = + truncate the gene sequence to abrogate the normal function of a trait (eg. sickle cell anaemia)
beneficial - mutations
beneficial mutations form the bases for evolution - any mutation that improves survival of an organism will be passed on = change the gene sequence to create new variations of a trait
spontaneous mutations
arise from errors in DNA replication - different genes mutate at different rates
Induced mutations (eg by environmental factors)
induced mutations can be induced by mutagens (environmental factors that cause a change in DNA)
eg.
- radiation
- viruses
- microorganisms
- alcohol / diet
Gene mutation vs chromosome mutations (ie the two main types of mutations)
gene mutation = which is the change in the DNA base sequence
chromosome mutations = which can affect the number of chromosomes
Gene mutations
gene mutations = change the sequence of bases in DNA for a single gene (they may produce a new allele of a gene)
Gene mutations involving a single nucleotide = usually called POINT MUTATIONS
((
1. the new DNA sequence may result in a new sequence of the amino acids constituting a protein
2. Because of the DEGENERACY in the genetic code, not all changes in a DNA sequence will result in a new sequence of amino acids
3. even with a change in amino acid sequence, protein function may be unaffected (the mutation is neutral)
4. A change that forms the ‘stop’ codon would stop production of the polypeptide at the wrong place
5. A change in a ‘stop’ codon would chase the polypeptide to go on and on
6. Adding or taking away a nucleotide causes a READING FRAME SHIFT. They continue to read mRNA nucleotides 3 at a time (frame shift mutations are usually lethal)
))
