7.3: mutations + their effects

Question 1

three types of mutation effects

Answer 1

1. cellular
2. individual
3. population

Question 2

cellular mutations

Answer 2

type of cell affected determines effects
i.e. germline cell = passed to every cell in offspring, somatic cell = localized tumour

Question 3

individual mutations

Answer 3

differing phenotypic effects; can be beneficial, harmful, or neutral

Question 4

population mutations

Answer 4

direct source of new alleles + genetic variation in population; are inheritable, may be acted upon by natural selection

Question 5

how are mutations inherited

Answer 5

somatic cells: not inherited by descendants
germline cells: may be inherited

Question 6

somatic mutations

Answer 6

occurs in somatic cells, usually due to replication errors prior to mitosis
- may result in phenotypic difference in tissue, a tumor, or other form of disease observable in an organ
- does not always result in phenotypic changes; may occur as physiological changes; depends on how early in development mutation occurs

Question 7

spontaneous mutations

Answer 7

occurs during S phase of cell cycle, when DNA is vulnerable to replication
- if not ‘proofread’ in G2 phase, passed onto daughter cells
- if error continues replication, amplifies issue

Question 8

germline mutations

Answer 8

occurs in sexual reproductive cells, passed off to offspring
- when gamete carrying mutation becomes embryo, mutation is replicated in embryo and affects all cells in resulting offspring

Question 9

coding vs non-coding DNA

Answer 9

coding: codes for proteins, reflected in phenotype of individual
non-coding: does not code for proteins, may affect gene expression

Question 10

mutations in coding DNA

Answer 10

usually affects type/sequence of amino acids in protein
- eukaryotes: can also affect gene splicing, and therefore function/levels of protein product
- prokaryotes: contains most coding DNA, mostly for repair enzymes; maintaining integrity of DNA = survival for prokaryotes

Question 11

mutations in non-coding DNA

Answer 11

may effect coding for end-products other than DNA, such as rRNA + nuclear RNA
- affects gene expression and cell functioning
- non-coding genes may also be linked to birth defects, important during embryonic development; hence mutations may = abortion/congenital abnormalities
- may be associated with predisposition to specific disease in adults

Question 12

junk DNA

Answer 12

no one knows what it does
- may be inserted copies of DNA from viruses, are ‘transposable’; both types considered mutations if inserted where they change gene expression/functioning
- transposons: transposed DNA
- retrotransposons: inserted viral RNA that has been reverse-transcribed back into DNA

Question 13

variability

Answer 13

increased as a result of:
1. recombination of genetic material; meiosis + fertilisation
2. an increased number of alleles for a particular gene; mutation

Question 14

meiosis in increasing variability

Answer 14

crossing over: exchange of genes between homologous pair, results in mixed parental genetics in offspring
random segregation: two alleles of single trait will separate randomly; 50% chance either allele will end up in either gamete

Question 15

chromosomal errors

Answer 15

occurs when crossing over goes wrong, results in chromosomal aberrations

Question 16

chromosomal aberrations

Answer 16

chromosomal abnormalities
- i.e. having none(deletion) or two centromeres(duplication)

Question 17

nondisjunction

Answer 17

change in chromosomal numbers: when one/more pairs of homologous chromosomes/sister chromatids do not separate, resulting in abnormal distribution of chromosomes in daughter cells