Chapter 4: Variation & Mutation

Question 1

when is a gene expressed

Answer 1

when a gene is read, transcribed and translated into a protein

Question 2

what is the phenotype

Answer 2

by coding for proteins, genes determkine important facts of biological structure and function. these observable traits are known as the phenotype

Question 3

what is variation

Answer 3

the diversity of genetic and phenotypic traits within and between populations

Question 4

what are the mechanisms behind variation

Answer 4

environmental factors, mutation, and sexual reproduction

Question 5

what are the types of environmental factors

Answer 5

external = temperature, ph, avaliability of food.

internal = action of hormones

Question 6

what is epigenetics

Answer 6

the study of inheritable (but reversable changes in gene expression without a change in DNA sequence.

epigenetics can also influence phenotype by controlling gene expression,, and can effect growth and developement of organisms

Question 7

when can spontaneous mutations occur

Answer 7

during cell division or DNA replication

Question 8

what are mutagens

Answer 8

physical or chemical environmental factors that induce mutations

Question 9

when do spontaneous mutations occur

Answer 9

during the S phase of the cell cycle, when dna is exposed during replication is vulnerable to damage.

Question 10

what are the main ideas scientists have formed about mutations

Answer 10

mutations arise spontaneously and are not directed by the environment. mutations are persistent. majority of mutations confer disadvantages on the organisms that inherit them.

Question 11

how do mutations occur during meiosis

Answer 11

unequal corssing over, if non-sister chromatids misalign during crossing over, one gamete may gain extra nucleotides (leading to an insertion mutation), and one may lose some nucleotides (leading to a deletion mutation).

Question 12

name three physical mutagens

Answer 12

x-rays, UV light, nuclear radiation

Question 13

what do x-rays do

Answer 13

gene and chromosome aberrations

Question 14

what does uv light do

Answer 14

stuctural distortion by cross-linking neighbouring nucleotides

Question 15

what does nuclear radiation

Answer 15

breaks in DNA strands

Question 16

give an example of a chemical mutagen

Answer 16

mustard gas , affects the base guanine , resulting in a substitution mutation

Question 17

what are point mutations

Answer 17

the simplest form of a mutation, just a single nucleotide within the original DNA sequence is affected by a substitution, addition or deletion.

Question 18

what is substitution

Answer 18

occurs when one nucleotide is replaced by another, they have number of affects on the translated protein, they are the source for new SNPs

Question 19

what are SNPs

Answer 19

single nucleotide polymorphisms, if it occurs in a gene, the mutated gene sequence can be transcribed and translated into a protein that is the same as that encoded by the original form of the gene.

Question 20

what are the types of point mutations

Answer 20

synonymous mutation, missense mutation, nonsense mutation

Question 21

what are synonymous mutations

Answer 21

also called silent mutations, occurs when the substituted base results in a codon that codes for the same amino acid as the original codon. this happens because there is a level of redundancy in the genetic code.

Question 22

what are missense mutations

Answer 22

when a SNP changes the amino acid.

Question 23

what are nonsense mutations

Answer 23

occurs when a SNP creates a new stop codon within the original gene sequence, this leads to early termination of translation of the transcribed gene sequence. results in the production of an incomplete polypeptide

Question 23

what is a frameshift mutation

Answer 23

the reading frame for the corresponding amino acid has been nudged away from the original, can be from a gene insertion or deletion, has a profound effect on the corresponding protein

Question 24

what are the three effects of mutations on survival

Answer 24

neutral mutations, deleterious mutations, beneficial mutations.

Question 25

what are neutral mutations

Answer 25

the protein product is unchanged compared to the original, organisms survival is unaffected. missense substitutions are sometimes also neutral mutations, if the amino acid is swapped with one with similar properties.

Question 26

what are deleterious mutation

Answer 26

mutations may disrupt the function of an encoded protein, undermining the organism’s overall abilirty to carry out its basic processes and survive, nonsense mutations are typically deleterious.

Question 27

what are beneficial mutation

Answer 27

gene mutation produce a new allele that benefits the survival of the organism. it could be a missense mutation that changes the function of the original protein, or a nonsense mutation that eliminates a protein that may have been harmful to the organism in some circumstances.

Question 28

what are the types of chromosomal mutations

Answer 28

variations in chromosome number and variations in chromosome stucture

Question 29

what is monoploidy

Answer 29

they are n, have more than one set of chromosomes

Question 30

what is polyploidy

Answer 30

have many sets of chromosomes

Question 31

what is aneuploidy

Answer 31

the condition in which there is an addition or loss of one chromosome from a cell (e.g. 2n + 1 or 2n - 1).

Question 32

what are the types of variations in chromosome number

Answer 32

monoploidy, polyploidy, aneuploidy

Question 33

what are the types of variation in chromosome structural

Answer 33

deletions, inversions, duplications, translocations

Question 34

what are deletions

Answer 34

a region of a chromosome is lost, resulting in the absence of all the genes in that area.

Question 35

what are inversions

Answer 35

one region of a chromosome is flipped and reinserted.

Question 36

what are duplications

Answer 36

a region of a chromosome is repeated, resulting in an increase in copies of the genes in that region.

Question 37

what are translocations

Answer 37

a region from one chromosome is aberrantly attached to another chromosome.

Question 38

what is independent assortment

Answer 38

during meiosis, homologous chromosome pair and then randomly move to different daughter cells.

Question 39

what are the causes of variation is sexual reproduction

Answer 39

crossing over, independent assortment and random segregation, crossing over, random fertilisation.

Question 40

what is crossing over

Answer 40

the swapping of alleles that occurs in meiosis during prophase I only. during the formation of off and sperm cells in meiosis, paired maternal and paternal homologous chromosomes align so that corresponding DNA sequences from the paired chromosomes are able to cross over one another.

Question 41

what is random segregation

Answer 41

during anaphase I, the randomly lined up maternal and paternal homologous chromosomes move to opposite poles of the cell

Question 42

what is random fertilisation

Answer 42

the random union of gametes. because a male gamete can fertilise any of the females gametes, resulting in a unique combination of the maternal and paternal genes

Question 43

what is non-disjunction

Answer 43

the two identical chromosomes do not separate, but go into the same cell. it results in the formation of two types of gametes in equal proportions, but one type has two copies of a particular chromosome, and the other has none.

Question 44

define mutation

Answer 44

a mutation refers to a change in the base sequence of an organisms DNA.

Question 45

causes of mutations

Answer 45

mutagens:

• chemicals
• radiation
• toxins

cellular error

• chromosomal
• point

Question 46

when can a mutagen not arise

Answer 46

during cell divison

Question 47

Explain why insertion and deletion mutations can have a profound effect on the protein produced by a gene.

Answer 47

• Insertion- additional bases added to sequence (1)
• Deletion- bases removed from sequence (1)
• May cause a FRAMESHIFT (1),
• the ‘reading frame’ has shifted/moved, every codon after the mutation is read incorrectly. (1)

Question 48

identify three factors that increase genetic diversity and explain each one

Answer 48

Random Assortment (1)

During metaphase I, the homologous chromosomes line up in a random order at the equator of the cell (1)
therefore the chromosomes that sort into the new cells is a chance event (1).

Fertilisation (1)

Any two gametes combine to form a diploid zygote (1) so any egg or sperm has the same chance to be fertilised (1).

Crossing Over (1)

Non-sister chromosomes (of homologous pairs) tangle during Prophase I (1)
Two non-sister chromatids exchange DNA material (1)
and new allele combinations are created (1).