Unit 4: Genetic Information, Variation and Relationships between Organisms

Question 1

describe the difference between DNA in prokaryotes and eukaryotes

Answer 1

in Pk, it is short, circular, not wound around histones and not found in the nucleus. in Eu it is long, linear, wound around histones and in the nucleus.

Question 2

define a gene

Answer 2

a section of DNA which codes for the amino acid sequence of a polypeptide and functional RNA

Question 3

define locus

Answer 3

the particular points on a DNA where the genes are found

Question 4

how many pairs of chromosomes are present in the human body

Answer 4

23 pairs, 46 individuals

Question 5

describe 3 features of the genetic code

Answer 5

universal - the same triplets code for the same amino acids in all living organisms
degenerate - the same amino acid is coded for by more than one triplet
non-overlapping - each base is only read once in its triplet, each is only part of one triplet

Question 6

define genome and proteome

Answer 6

the genome is the complete set of genes in a cell and the proteome is the full range of proteins that a cell can produce

Question 7

define exons and introns

Answer 7

exons code for amino acids and introns don’t code for anything, they are remove during protein synthesis to prevent disruption to the order of amino acids

Question 8

define non-coding multiple repeats

Answer 8

areas in the genome between genes which repeat over and over but do not code for any amino acids, used in DNA fingerprinting

Question 9

where does transcription occur

Answer 9

in the nucleus in eukaryotes and in the cytoplasm in prokaryotes

Question 10

why does prokaryotic mRNA not require splicing

Answer 10

it contains no introns so there is no threat to the primary structure

Question 11

describe splicing

Answer 11

when the base sequences corresponding to the introns are removed and functional exons are joined together to make mRNA, which happens in the nucleus

Question 12

describe the role of a ribosome in the production of a polypeptide

Answer 12

the ribosomes has two codons which allow the tRNA anticodons to bind
also catalyses the peptide bonds between amino acids

Question 13

define diploid

Answer 13

2 of each chromosomes in pairs

Question 14

where are gametes in plants and animals

Answer 14

in the ovule + pollen in plants
the sperm + egg in animals

Question 15

where are gametes made in animals and plants

Answer 15

the ovary + anther in plants
the testes + ovary in animals

Question 16

are gametes haploid or diploid

Answer 16

haploid (n), they have one copy of a homologous pair. the haploid number for humans is 23.

Question 17

what are the products of meiosis

Answer 17

4 genetically different daughter cells which are haploid

Question 18

what happens in meiosis 1 and 2

Answer 18

in 1, homologous chromosomes pair up and the chromatids wrap around each other (crossing over)
in 2, the chromatids move apart

Question 19

describe crossing over

Answer 19

when homologous pairs line up next to each other and their chromatids wind around each other

Question 20

define independent segregation/assortment

Answer 20

the daughter cells have different combinations of chromosomes because the pairs line up in a random order

Question 21

define alleles

Answer 21

different forms of the same gene

Question 22

what does an increased genetic diversity mean positively

Answer 22

that the organisms are more blé to adapt and cope with disease

Question 23

two factors that increase genetic diversity

Answer 23

mutations and migration (causes a gene flow as alleles from other populations are introduced)

Question 24

define a genetic bottleneck

Answer 24

when there is a reduction in population so the gene pool decreases which in turn decreases genetic diversity as there are less alleles

Question 25

define the founder effect

Answer 25

when a small number of individuals start a new population and there is a small gene pool as a result due to a small number of alleles

Question 26

define behavioural, anatomical and physiological adaptations

Answer 26

behavioural - changes in behaviour to increase chances of survival
anatomical - changes in the structure of the organism
physiological - biochemical processes inside

Question 27

what is recombination

Answer 27

when the portions of chromatids that broke off during crossing over recombine

Question 28

which type of mutation doesn’t always cause a change and which does

Answer 28

not all substitutions produce different amino acids because the code is degenerate
all deletions cause a change because they cause a shift in the triplets read

Question 29

define mutagenic agents and their way of working

Answer 29

mutagenic agents increase the chance of mutations, they can act as a base or alter the bases and change the DNA structure

Question 30

define chromosome non-dysjunction

Answer 30

when chromosomes don’t separate properly during independent assortment

Question 31

define directional and stabilising selection

Answer 31

directional is when an individual in the population has alleles for an extreme characteristic, the selection favours those outside of the mean. in response to an environnement change.
stabilising is when alleles for characteristics are in the middle range and so are more likely to survive and reproduce, the mean is favoured and the environnement isn’t changing

Question 32

define normal distribution and standard deviation

Answer 32

when values are spread about the mean symmetrically and how much a set of data points range around the mean

Question 33

define phylogeny and taxonomy

Answer 33

the study of evolutionary relationships between organisms and their ancestors, and taxonomy is the putting of those organisms into groups within a hierarchy

Question 34

define genetic diversity

Answer 34

the total number of different alleles in a population

Question 35

how does courtship benefit species

Answer 35

means they can recognise members of their own species
can identify a mate capable of breeding/sexually mature

Question 36

define artificial classification

Answer 36

classifying species based on the characteristics useful at the time e.g wings, not very accurate as doesn’t prove evolutionary connections

Question 37

which factors affect the representation of a sample

Answer 37

sampling bias and chance

Question 38

how can samples be made more representative

Answer 38

increase the sample size so chance is less likely to influence the result
analysis of data to understand how much influence chance has had

Question 39

define hierarchy

Answer 39

smaller groups within larger groups with no overlap at each levels

Question 40

how do you calculate standard deviation

Answer 40

calculate the mean and for each value subtract the mean and square the answer.
add all these numbers together and divide by the total number of values.
square root this number and round to 2 significant figures.

Question 41

explain the steps of transcription

Answer 41

DNA polymerase breaks the hydrogen bonds between DNA strands causing them to separate
free complementary nucleotides pair up to the exposed nucleotide bases on the template strand via complementary base pairing rules
RNA polymerase joins the nucleotides together to form a pre-mRNA molecule
when the RNA polymerase reaches the stop codon it detaches and completes the production of pre-mRNA

Question 42

explain the steps of translation

Answer 42

a ribosomes attaches to the start codon at the end of an mRNA molecule
the tRNA with the complementary anti codon sequence pairs with the next codon on the mRNA, this t carries a specific amino acid
a t molecule that is complementary then pairs to the next mRNA codon, carrying another amino acid
the ribosome moves along the mRNA, bringing together two t molecules
the 2 amino acids on the tRNA are joined by a peptide bond and ATP which is hydrolysed to provide the energy
the ribosome moves along to the next codon, linking the amino acids on the second and third tRNA molecules.
as this happens, the first tRNA is released from its amino acid and is free to collect another amino acid from the pool
the process continues until a polypeptide chain is built up and the ribosome reaches the stop codon where all 3 molecules involved separate.