GENETIC DIVERSITY

Question 1

whats a gene muatation

Answer 1

-change in the base sequence of DNA on chromosome
-can arise spontaneously during DNA replication (interphase)
-involves base deletion/substitution

Question 2

changes to one or more bases in DNA triplet could result what

Answer 2

change in amino acid sequence of the polypeptide

Question 3

Why might a mutation not lead to a change in the amino acid sequence

Answer 3

-Genetic code is degenerate, so may code for the same amino acid
-may change an intron which is not expressed

Question 4

When does gene mutation by deletion of bases occur

Answer 4

when a nucleotide is lost from the normal DNA sequence

Question 5

what does 1 deleted nucleotide cause

Answer 5

-causes all triplets in a sequence to be read differently
-because each has been shifted to the left by one base

Question 6

two forms chromosome mutation can take

Answer 6

-changes in whole set of chromosome
and
- changes in the number of individual chromosomes

Question 7

describe changes in whole set of chromosomes

Answer 7

-occurs when organisms have 3 or more sets of chromosomes rather than usual 2
-called polyploidy + occurs mostly in plants

Question 8

describe changes in the number of individual chromosomes

Answer 8

-sometimes individual homologous pairs of chromosomes fail to separate during meiosis (non-disjunction)
-usually results in gamete having either 1 more or 1 fewer chromosome
-eg down syndrome

Question 9

What is a mutagenic agent?

Answer 9

a factor that increases the risk of mutations

Question 10

What is a frame shift mutation?

Answer 10

-the mutation results in the rest of the base sequence being impacted,
-therefore causing a greater impact of the codons
-therefore the amino acid sequence that is coded for.

Question 11

mutation can lead to production of non-functional protein/enzyme

Answer 11

-changes in base/ triplet sequence of DNA
-changes sequence of codons on mRNA
-changes sequence of a.a in primary structure of polypeptide
-changes position of H/ ionic /S-S bonds in tertiary structure of protein
-changes tertiary structure and thus shape of protein (and active site if enzyme)
-(if enzyme substrate can’t bind to active site and form enzyme substrate complex)

Question 12

Base deletion process

Answer 12

-one nucleotide / base removed from DNA sequence
-changes triplet/codon from point of mutation (frameshift)
-changes sequence of codons on mRNA after point of mutation
-changes sequence of a.a in primary structure of polypeptide
-changes position of H/ionic/S-S bonds in tertiary structure of protein
-changes tertiary structure, thus shape of protein

Question 13

Base substitution process

Answer 13

-nucleotide /base in DNA replaced with another nucleotide/base
-change in one base = changes one triplet
-changes one mRNA codon and one a.a > sequence of a.a in primary structure of polypeptide changes etc
-OR due to degenerate nature of genetic code , the new triplet may still code for same a.a so sequence of a.a in primary structure of polypeptide remains unchanged

Question 14

products of meiosis

Answer 14

-4 daughter cells
-each with half the number of chromosomes as the parent cell

Question 15

Process of meiosis

Answer 15

-before meiosis starts. DNA replicates so there’s 2 copies of each chromosome (sister chromatids joined by centromere)
-homologous pairs line up randomly and one from each pair move either side of the cell
-independent segregation (increases genetic variation in gametes)
-crossing over - recombination occurs where chromosomes swap genetic material
-homologous chromosomes separate
-4 new daughter cells are formed

Question 16

How does meiosis create genetic variation

Answer 16

1)crossing over between homologous chromosomes
- alleles exchanged between chromosomes
-creates new combination of maternal and paternal alleles on chromosome
2) independent segregation of homologous chromosomes
- random alignment of homologous pairs at equator > random which chromosomes from each pair goes to each daughter cell
-creates different combinations of maternal and paternal chromosomes and alleles in daughter cells
3) random fertilisation when 2 gametes fuse to form zygote

Question 17

Importance of meiosis

Answer 17

-2 divisions > creates haploid gametes (half number of chromosomes)
-diploid number restored at fertilisation
-maintains chromosome number from one generation to the next
-independent segregation and crossing over creates genetic variation

Question 18

Why is meiosis important?

Answer 18

-so that gametes formed are haploid
-therefore fuse to make a cell with a diploid number of chromosomes.
-Without meiosis the number of chromosomes would increase with each generation
-therefore it is needed to keep the number constant/stable

Question 19

What is 2 differences between meiosis and mitosis?

Answer 19

-mitosis; genetically identical daughter cells
-meiosis; genetic variation in daughter cells

-mitosis; 1 nuclear division
-meiosis; 2 nuclear divisions

-mitosis; diploid
-meiosis; haploid

Question 20

genetic recombination by crossing over

Answer 20

-chromatids of each pair become twisted around one another
-during this twisting process, tensions created and portions of chromatids break off
-these broken portions might then rejoin with the chromatids its homologous partner
usually it is the equivalent portions of homologous chromosomes that are exchanged
-in this way new genetic combination of maternal and paternal alleles are produced

Question 21

What is exchanged in crossing over?

Answer 21

equivalent sections of DNA/homologous chromosomes

Question 22

What does crossing over produce?

Answer 22

a new combination of alleles

Question 23

How can you calculate the possible number of chromosome combinations following meiosis?

Answer 23

2^n where n = number of pairs of homologous chromosomes

Question 24

Genetic diversity

Answer 24

the total number of different alleles in a population

Question 25

Define population

Answer 25

group of interbreeding individuals of the same species

Question 26

advantage of a greater number of different alleles that all members of a species possess

Answer 26

the greater the genetic diversity of that species

Question 27

when is genetic diversity reduced

Answer 27

when a species has fewer different alleles

Question 28

What advantage does high genetic diversity provide?

Answer 28

the stability to adapt to a change in the environment, allows natural selection to occur

Question 29

Why does greater genetic diversity mean more likely that some individuals in population survive and environmental change

Answer 29

-because of a wider range of alleles
-therefore a wider range of characteristics
-giving a greater probability that some individuals will possess a characteristic that suits the new environmental conditions
-genetic diversity is a factor that enables natural selection to occur

Question 30

Why are not all alleles of a population are equally likely to be passed to the next generation

Answer 30

-because only certain individuals are reproductively successful and so pass on their alleles

Question 31

reproductive success and allele frequency

Answer 31

-within population of a species there’ll be a gene pool containing a wide variety of alleles
-random mutation of alleles within this gene pool> new allele of a gene that could be harmful
-but in certain environments, new allele of gene might give its possessor an advantage over other individuals in population due to being better adapted > survive in their competition with others
-more likely to obtain available resources > grow more rapidly and live longer > have better chance of breeding successfully and producing more offspring that contain the ‘new allele’
-so they will be more likely to survive and reproduce successfully
-over many generations , the number of individuals with ‘new advantageous allele’ will increase at the expense of individuals with ‘less advantageous’ alleles

Question 32

Explain how natural selection results in the development of new characteristics

Answer 32

-mutations -> new alleles
-some alleles provide a selective advantage, meaning they are more likely to survive and reproduce
-the offspring receive the allele and pass it to next generation, allele frequency increases