Chapter 9 - Genetic diversity and mutation Flashcards
What is a gene mutation?
Any change to the quantity or the base sequence of the DNA of an organism
What is a substitution mutation?
When one base is substituted for another
Why are mutations bad?
The order of DNA bases in a gene determines the amino acid sequence which codes for a certain protein. If this is altered, it may lead to the protein lacking characteristics that are important for its role
What is a deletion mutation?
One base is deleted from the DNA sequence
Why do deletion mutations normally cause a large change to the organism?
Every base after the one that has been deleted experiences a frameshift and moves one to the left. Because bases are read in triplets, the codons aren’t read correctly
What will adding a base result in?
A frame-shift to the right
What is a silent mutation?
Because the DNA code is degenerate, a substitution mutation may result in the same amino acid being coded for and so have no effect on the organism
What is a mutagenic agent?
Something that increases the likelihood of a mutation, e.g. UV radiation and ionising radiation
What are chromosome mutations?
Spontaneous changes in the number of or structure of whole chromosomes
What are the two forms of chromosome mutations?
Changes in whole sets of chromosomes
Changes in the number of individual chromosomes
When will changes to whole sets of chromosomes occur?
When organisms have three or more sets of chromosomes rather than the normal two
What is a change to a whole set of chromosomes called?
Polyploidy and it occurs mainly in plants
What is non-disjunction?
When homologous pairs of chromosomes fail to separate during meiosis. This leads to changes in the number of individual chromosomes and sometimes syndromes like Down’s
What causes Down’s syndrome?
An extra copy of chromosome 21
How many daughter cells are produced from meiosis?
4
How many divisions take place during meiosis?
2
*What is a haploid number?
The number of chromosomes gametes have - half of the normal amount
*What is the diploid number?
The full set of 46 chromosomes
*What happens during the first division of meiosis?
Homologous chromosomes pair up and their chromatids wrap around each other
One chromosome from each pair goes into one of the daughter cells
*What happens during the second division of mitosis?
The centromere is divided and the sister chromatids move to each end of the cell
*What is a gene?
A length of DNA that codes for a polypeptide
*What is the locus?
The position of a gene on a chromosome or DNA molecule
*What is an allele?
Different forms of a gene
*What are homologous chromosomes?
One maternal and one paternal chromosome which have the same gene loci