3.2. Gene and Chromosomal Mutations

Question 1

an alteration in DNA sequence; any base-pair change in any part of a dna molecule

Answer 1

gene mutation

Question 2

basis of classifying gene mutation

Answer 2

(1) cause
(2) location
(3) molecular change
(4) phenotypic effects

Question 3

types of mutation based on the cause

Answer 3

(1) spontaneous
(2) induced

Question 4

differentiate spontaneous mutation vs induced mutation; also describe their mutation rates.

Answer 4

(1) spontaneous mutation : type of mutation that occurs without external intervention. these mutations arise as a result of occasional errors during DNA replication. it has a very low mutation rate
(2) induced mutation : type of mutation caused by mutagens, which are biological, chemical, or physical agents in the environment, such as transposons, base analogs, and UV radiation. these mutation are made deliberately bu humans. it has a higher mutation rate.

Question 5

types of mutation based on location

Answer 5

(1) somatic
(2) germ-line
(3) autosomal
(4) sex chromosome
(5) noncoding region of the gene
(6) coding region of the gene

Question 6

describe somatic mutation

Answer 6

somatic mutation occurs in somatic cells; may lead to altered cellular function of tumors

Question 7

true or false : somatic mutation is transmitted to the next generation.

Answer 7

false. somatic mutation is not transmitted to the next generation

Question 8

describe germ-line mutation; it is heritable?

Answer 8

occurs in germ cells; heritable

Question 9

type of mutation within located on the autosomes

Answer 9

autosomal mutation

Question 10

x- or y-linked mutations

Answer 10

sex chromosome mutation

Question 11

types of mutation based on molecular change

Answer 11

(1) base substitution
(2) frameshift
(3) rearrangement

Question 12

what is base substitution?

Answer 12

also known as point mutation; change of one base pair to another in a DNA molecule

Question 13

two terms are used to describe base substitutions: transition and trasversion. differentiate them.

Answer 13

(1) a transition has occurred if a pyrimidine replaces a pyrimidine or a purine replaces a purine
(2) a transversion has occurred if a purine replaces a pyrimidine or vice versa

Question 14

effects of base substitutions

Answer 14

(1) missense mutation : creation of a new triplet that codes for a different amino acid in the protein product
(2) nonsense mutation : triplet may be changed into a stop codon; translation is prematurely stopped
(3) silent mutation : mutation alters a codon but does not result in a change in the amino acid at that position in the protein (wobble concept)

because eukaryotic genomes consist of so much more noncoding DNA than coding DNA, the vast majority of mutations are likely to occur in noncoding regions. these mutations may be considered neutral mutations if they do not affect gene products or gene expression. most silent
mutations, which do not change the amino acid sequence of the encoded protein, can also be considered neutral mutations.

Question 15

type of mutation based on molecular change that involves the addition/deletion of one or small fragments of nucleotides; may lead to premature translation termination if nonsense codon is created

Answer 15

frameshift mutation

Question 16

where is frameshift mutation most prevalent?

Answer 16

repeated sequence units

repeated sequences are more prone to forming secondary structures like hairpins, which can cause the DNA polymerase to lose its place. when the DNA polymerase realigns itself, it may add or omit nucleotides, leading to insertions or deletions.

Question 17

true or false : there is no profound effect observed if nucleotides added or deleted are in multiple of 3s

Answer 17

true

Question 18

type of mutation based on molecular change involving the deletion/insertion of large numbers of nucleotides

Answer 18

rearrangement mutation

Question 19

consequence of sequence deletion in rearrangement mutation

Answer 19

leads to a truncated protein, which is often inactive

this is because essential parts of the protein, necessary for its function, are missing

Question 20

consequence of sequence insertion in rearrangement mutation

Answer 20

protein may have partial activity or may become completely non-functional depending on the site of insertion

the addition of large segments can disrupt the normal structure and function of the protein

Question 21

types of mutation based on phenotypic effects

Answer 21

(1) loss-of-function : reduces or eliminates the function of the gene product
(2) null : complete loss of function
(3) visible : altered morphological trait
(4) nutritional : inability to synthesize an amino acid or vitamin
(5) biochemical : altered metabolic abilities
(6) behavioral : altered behavioral patterns
(7) regulatory : inappropriately activate or inactivate gene expression
(8) lethal : affects organism survival
(9) conditional : phenotype expressed only under certain environmental conditions; env’t-dependent
(10) neutral : negligible effects

Question 22

are chromosome mutations passed to offspring?

Answer 22

yes, these mutations/chromosome abberations are passed to offsprings in a predictable manner; they have phenotypic consequences on the offspring

Question 23

two general classes of chromosome aberrations

Answer 23

(1) variation in chromosome number
(2) variation in chromosome structure and arrangement

Question 24

types of variation in chromosome number

Answer 24

(1) aneuploidy
(2) euploidy

Question 25

differentiate aneuploidy from euploidy

Answer 25

in aneuploidy, an organism gains or loses one or more chromosomes but not a complete set, leading to an imbalance in the number of chromosomes; in euploidy, complete haploid sets of chromosomes are present

monosomy : loss of a single chromosome from an otherwise diploid genome
trisomy : gain of one chromosome
tetrasomy, pentasomy, etc. : 2n + 2, 2n + 3, etc.

Question 26

why does aneuploidy occur?

Answer 26

aneuploidy is a result of an error in meiosis called nondisjunction, wherein paired homologs fail to disjoin during segregation. this process disrupts the normal distribution of chromosomes into gametes