chapter 4 - mutation Flashcards
(12 cards)
Define gene expression
The translating of a gene into a protein by an organism; the phenotype is directly affected by gene expression.
Name 3 environmental factors that influence the expression of a phenotype
Epigenetics: chemicals that can switch genes on or off
Internal: presence or absence of hormones
External: temperature or light intensity
Define mutation
A permanent change in the DNA sequence of a gene
Name the types of point mutations and explain how they work
Frameshift: when a nitrogenous base has been added or deleted in the dna sequence, altering all amino acids after it
Silent/Synonymous: a nitrogenous base has been changed but does not alter the amino acid coded for
Missense: a nitrogenous base has been changed and alters the amino acid (can cause peptide chain not to form)
Nonsense: a nitrogenous base has been changed in a codon and turned it into a stop codon, if this an exon it will prematurely end the sequence
Explain spontaneous mutations
A spontaneous mutation is a random mutation that occurs in the absence of any mutagens
Explain physical causes of mutations
Physical mutagens consist of nuclear radiation (which cause breaks in a DNA strand), x-rays (cause gene + chromosome abnormalities), and uv light (cross links neighbouring nucleotides causing structural distortion)
Explain chemical causes of mutations
Chemical mutagens consist of mustard gas (causes a substitution mutation in the base guanine), nitric acid (causes adenine to behave like guanine), and colchicine (prevents spindle formation in mitosis resulting in doubled chromosome numbers)
Explain biological causes of mutations
Biological mutagens consist of bacteria which are able to introduce new genes to a host
Explain the four kinds of chromosome mutation in meiosis
Inversion: broken chromosome segment is flipped and order of genes is inverted
Deletion: genetic material breaks off
Translocation: when a fragment from one chromosome breaks off and attaches to another chromosome
Duplication: additional copies of genes are generated
What is monoploidy
Monoploidy is when an organism is 1n and their chromosomes represent a single complete operational set, this is not the same as haploid where the chromosomes represent half of the full set and cannot allow the organism to function this way. An example of monoploidy are insects, where male bees are monoploid and females are diploid, males are produced when a females gametes are not fertilised (males make gametes by mitosis, hence not haploid and females make eggs by meiosis hence monoploid).
If a defective allele arises in a monoploid organism occurs, it is the only allele for a certain gene and the consequences are likely to be deletrious.
What is aneuploidy and how does it occur
Aneuploidy is when there is an addition or loss of a chromosome (2n + 1 or 2n - 1) and is caused by non-disjunction (when homologous chromosomes do not separate in meiosis 1 (resulting in two gametes that are n+1 and two that are n-1) or when sister chromatids do not separate in meiosis 2 (resulting in two gametes that are normal (n), one is n-1 and one is n+1)
The fusion of a diploid and haploid gamete results in a zygote with three of the same chromosomes, this condition is trisomy. The fusion of a haploid gamete and a gamete with neither homologous chromosome results in a condition called monosomy
What is polyploidy and how does it occur
When non-disjunction (specifically when half the gametes get nothing and the others get everything) occurs in meiosis and half the gametes produced are diploid (2n) with a full set of chromosomes and the others have none (0n). If a diploid gamete fuses with a haploid gamete the result is triploid (3n) and if two diploid gametes form the result is tetraploid (4n).
