Genetics, Biodiversity and Classification

Question 1

Describe how a gene is a code for the production of a polypeptide. Do not
include information about transcription or translation in your answer.

Answer 1

Because DNA base sequence
In triplets
Codes for primary sequence of a polypeptide

Question 2

Define the term exon.

Answer 2

DNA base sequence that codes for a polypeptide

Question 3

Describe how a phosphodiester bond is formed between two nucleotides within a DNA molecule

Answer 3

Condensation reaction
Between deoxyribose and phosphate
Catalysed by DNA Polymerase

Question 4

Scientists investigated the genetic diversity between several species of sweet potato. They studied non-coding multiple repeats of base sequences.
Define ‘non-coding base sequences’ and describe where the non-coding multiple repeats are positioned in the genome

Answer 4

DNA base sequence that does not code for a polypeptide
Located between genes

Question 5

Give three ways in which the DNA in a chloroplast is different from DNA in
the nucleus

Answer 5

Circular in chloroplast linear in nucleus
Histones in nucleus none in chloroplast
No introns in chloroplast
Shorter in chloroplast

Question 6

Not all mutations in the nucleotide sequence of a gene cause a change in the structure of a polypeptide.
Give two reasons why

Answer 6

DNA code is degenerate
Mutation may occur in an intron

Question 7

Compare and contrast the DNA in eukaryotic cells with the DNA in prokaryotic cells.

Answer 7

DNA nucleotide structure the same
Nucleotides joined by phosphodiester bonds
Shorter in prokaryotic
Circular in prokaryotic + linear in eukaryotic
Eukaryotic DNA associated with histones
Eukaryotic DNA contains introns

Question 8

Describe two differences between the structure of a tRNA molecule and the structure of an mRNA molecule

Answer 8

mRNA is a straight chain whereas tRNA is a clover shape
tRNA contains an amino acid binding site but mRNA does not
tRNA has hydrogen bonds, mRNA does not
tRNA has anticodon, mRNA has codon

Question 9

Describe how one amino acid is added to a polypeptide that is being formed at a ribosome during translation

Answer 9

tRNA brings specific amino acid
tRNA anticodon binds to complementary mRNA codon
Amino acids join by condensation reaction using ATP

Question 10

Describe how mRNA is produced from an exposed template strand of DNA.

Answer 10

Free RNA nucleotides line up by complementary base pairing
Phosphodiester bonds form
By action of RNA polymerase

Question 11

Describe how mRNA is formed by transcription in eukaryotes

Answer 11

Hydrogen bonds between DNA
One DNA strand acts as a template
Free RNA nucleotides line up by complementary base pairing
Uracil pairs with Adenine
RNA polymerase forms phosphodiester bonds between nucleotides
Introns are removed to form mRNA

Question 12

Describe how a polypeptide is formed by translation of mRNA

Answer 12

mRNA binds to a ribosome
Ribosome reads in triplet codons until it reaches a start codon
Ribosome reads mRNA triplet codon and tRNA with complementary anticodon binds to it, carrying a specific amino acid
Next mRNA codon is read and another complementary tRNA enters with another amino acid
Amino acids undergo a condensation reaction using energy from ATP to form a peptide bond
tRNA carrying first amino acid leaves ribosome
Ribosome moves along mRNA until it reaches a stop codon
Polypeptide leaves ribosome and folds into its final shape

Question 13

What is the proteome of a cell?

Answer 13

The full range of proteins a cell is able to produce at a given time

Question 14

In a eukaryotic cell, the base sequence of the mRNA might be different from the sequence of the pre-mRNA

Answer 14

pre-mRNA still contains introns
Which are removed when mRNA is spliced

Question 15

Define the term mutagenic agent

Answer 15

A factor that effects the rate of mutation

Question 16

Name the type of mutation that changed the number of chromosomes in S. townsendii to produce S. anglica. Explain your answer.

Answer 16

Non-disjunction
In meiosis
Chromosomes are not separated/ chromosomes do not form homologous pairs

Question 17

Apart from mutation, explain one other way genetic variation within a species is increased.

Answer 17

Random fertilisation
Produces new allele combinations

Question 18

Farmed trout produce diploid egg cells. The offspring produced from farmed trout are sterile. Suggest and explain why

Answer 18

Homologous pairs cannot line up in meiosis
So meiosis cannot occur

Question 19

Define ‘gene mutation’ and explain how a gene mutation can have:
* no effect on an individual
* a positive effect on an individual

Answer 19

A gene mutation is a change in DNA base sequence within a gene
It can have no effect as DNA code is degenerate so it may code for the same amino acid
It can have no effect as the mutation can occur in an intron so it is spliced out
Results in change in polypeptide that positively effects its function
It can have a positive impact if it increases chance of survival

Question 20

Give two differences between mitosis and meiosis.

Answer 20

Meiosis involves two divisions mitosis only has one
Mitosis produces genetically identical cells, meiosis produces genetically different cells
Two cells produced in mitosis 4 in meiosis
Meiosis produces haploid
Crossing over + independent segregation only in meiosis

Question 21

Explain how the chromosome number is halved during meiosis

Answer 21

Homologous chromosomes line up in meiosis 1
One of each chromosome goes to each daughter cell

Question 22

Describe the process of crossing over and explain how it increases genetic
diversity

Answer 22

Crossing over occurs in prophase of meiosis 1
When homologous chromosomes line up, they wrap around each other and create tension
This causes some sections of DNA to break off and attach to the other chromosome this is called a chiasmata
This chromosome then exchanges the equivalent length of its allele
It increases diversity as it creates new combinations of alleles within gametes

Question 23

Describe how the change in chromosome number in Patau syndrome was
produced

Answer 23

Non-disjunction
Homologous chromosomes did not separate at meiosis

Question 24

The enzyme encoded by the ADF allele catalyses the breakdown of alcohol
faster than the enzyme encoded by the ADS allele. Suggest why

Answer 24

Change in primary structure
Causes change in tertiary structure
Means ADF is more likely to form enzyme-substrate complexes

Question 25

Alcohol is toxic to fruit flies. Suggest and explain why the frequency of the
ADF allele changed during the 45 generations

Answer 25

ADF gives flies selective advantage
The flies with the ADF allele are therefore more likely to survive and reproduce, passing on the allele
This means over many generations the frequency of the ADF allele will increase as it provides a competitive advantage

Question 26

One hypothesis for LP in humans suggests that the selective pressure was related to some human populations farming cattle as a source of milk. Describe how farming cattle as a source of milk could have led to an
increase in LP.

Answer 26

LP exists due to random mutation
Those who continue to produce lactase can break down lactose into glucose which is useful
This provides a selective advantage
These people are therefore more likely to survive and reproduce and pass on the LP allele
Directional selection
Over many generations the allele frequency of LP will increase

Question 27

Lactase persistence is caused by a mutation in DNA. This mutation does not occur in the gene coding for lactase.
Suggest and explain how this mutation causes LP.

Answer 27

Mutation occurs in promoter region or in transcription factor
So lactase gene continues to be transcribed

Question 28

State three comparisons of genetic diversity that the scientists used in
order to generate genetic classification

Answer 28

DNA base sequence
Amino acid sequence
mRNA base sequence

Question 29

Some populations of animals that have never been hunted show very low levels of genetic diversity.
Other than hunting, suggest two reasons why populations might show very low levels of genetic diversity

Answer 29

Genetic bottleneck event such as an infection wiping out most of a population
Founder effect, all arise from the same organism
Inbreeding

Question 30

Explain why it is more useful to calculate an index of diversity than to record species richness

Answer 30

It shows the size of each species
So useful because there may be many of some species and few of others

Question 31

Give two ways the students would have ensured their index of diversity
was representative of each habitat

Answer 31

Take samples from random coordinates to avoid bias
Take a large number of samples

Question 32

Farmers are now being encouraged to replant hedges on their land. Suggest and explain one advantage and one disadvantage to a farmer of replanting hedges on her farmland

Answer 32

Advantage- increase biodiversity so increases predation of pests + increases number of pollinators
Disadvantage- may increase pest population

Question 33

Outline a method the ecologists could have used to determine the plant
species richness at one site

Answer 33

Lay out a grid on the site and randomly generate coordinates to sample from
Place a quadrat at the coordinate
Count the number of species present within the quadrat

Question 34

The index of diversity of the insects was higher in the hedge than in the barley field.
Suggest why

Answer 34

Greater number of plant species
Greater variety of habitats/niches so more insects can survive
Greater variety of food sources so more insects can survive

Question 35

In this investigation, what is meant by genetic diversity?

Answer 35

Number of different alleles of each gene