paper 1 - genetic code and genetic variation

Question 1

what is a gene

Answer 1

base sequence of DNA that codes for amino acid sequence or a functional RNA
located at a particular site on a DNA molecule called its locus

Question 2

what does the base sequence of each gene carry

Answer 2

the coded genetic info that determines the sequence of amino acids during protien sythesis

Question 3

what is meant by universal

Answer 3

the same triplets always code for the same amino acids in all species
as the genetic code used is the same in all organisms, this provides indirect evidence for evolution

Question 4

what is meant by degenerate

Answer 4

more than one triplet codes for each amino acid

Question 5

what is meant by non overlapping

Answer 5

each base is only part of one triplet, they do not overlap

Question 6

prokaryotic DNA

Answer 6

• DNA molecules are short, circular and not associated with protiens

Question 7

eukaryotic DNA

Answer 7

• longer, linear and associated with histones
• the nuclear DNA does not code for polypeptides

Question 8

what is an exon

Answer 8

codes for amino acd sequences

Question 9

what is an intron

Answer 9

non coding region

Question 10

what is a genome

Answer 10

complete set of all genes in a cell

Question 11

what is a proteome

Answer 11

full range of different protiens that a cell can produce, as coded for by ts DNA ( genome )

Question 12

how can variation within a species be measured

Answer 12

using differences in the base sequence of DNA or in the amino acid sequence of protiens

Question 13

comparison of mRNA and tRNA

Answer 13

• mRNA is longer than tRNA
• mRNA is a straight molecule whereas tRNA is clover leaf shaped
• mRNA contains no paired bases ( no H bonds ), whereas tRNA has some paired bases and H bonds

Question 14

what is transcription

Answer 14

• production of mRNA from DNA
• the dna strands sepearte by breaking the H bonds using dna helicase
• only one of the dna strands is used as a t emplare strand to synthesise mrna againts
• free rna nucleotides align next to the exposed bases via complemenatry base pairing
• rna polymerase joins adjacent mrna nucleotides together via condensation reactions, forming phoshphodiester bonds

Question 15

what is splicing

Answer 15

• transcription prodices a pre - mrna which musyt be spliced to remove any introns before leaving the nucleus to form mrna
• in prokaryotes transcription results directly in the production of mrna from dna as they do not have spliceosomes required for splicng

Question 16

what is translation

Answer 16

the production of polypeptides at a ribosome from the sequence of codons carried by mrna
the ribosome has two binding sites for trna moleucles

Question 17

what occurs during translation

Answer 17

• mrna assocaites with a ribosome
• the ribosome moves to the start codon AUG
• the trna brings a specific amino acid to the ribososme
• the anticodon on the trna binds to the complementary codon on the mrna
• the ribosome moves along one codon and a second trna binds via complementary base pairing between the second codon and anticodon
• the amino acids join togetehr via condensation reaction using ATP to provide energy forming a peptide bond
• the ribosome moves along one codon, the first trna is recycled back to the cytoplasm and the process repeats until a stop codon is reached, forming a polypeptide which detatches from the ribosome

Question 18

what could differeces between a species be a result of

Answer 18

genetic factors, environmental factors, or a combo of both

Question 19

how can mutations arise

Answer 19

mutations in the number of chromosomes can arise spontaneously by chromosome non disjunction during meiosis

Question 20

substitution mutations

Answer 20

• due to degenerate code not all substitutions cause a change in sequence of amino acids
• if different bonds form in different places due to a change in the r group on the amino acids this could change the tertairy structure of the protien

Question 21

insertion/deletion mutations

Answer 21

• deletion mutations would cause a frame shift
• if the mutation occurs early this could alter all the codons so the protien would be different

Question 22

mutagenic agents

Answer 22

• increase rate of gene mutation
• include high energy radiation which damage the dna molecule and chemicals that later the dna structure

Question 23

what is genetic diversity

Answer 23

the number of different alleles of genes in a population

Question 24

how does the genetic diversity arise

Answer 24

• mutation - produces new allelels
• independant segregation of homologous chromosomes pairs on equator during meiosis
• crossing over of tips of non sister chromatids during meiosis
• random fusion of haploid gametes to produce ziploid zygote

Question 25

what is discontinous data

Answer 25

only controlled by a few genes, this or that, distinct categories

Question 26

what is continous data

Answer 26

numerically can continue, quantative, no distinct catgegories, can be affected by the environment

Question 27

what does a sample need to be

Answer 27

random to remove bias large enough to represent the population

Question 28

standard deviation

Answer 28

a meausre of dispersion of the values around the sample mean, it is less effected by outliers and gives a better measure of the overall variation if the sds overlap there is no significant difference

Question 29

what does p=0.05

Answer 29

less than 5% probability the difference between the 2 means is due to chance reject the null hypothesis

Question 30

what is a t test

Answer 30

investigates differences between 2 means

Question 31

what is natural selection

Answer 31

- random mutation produces a new allele of a gene - many mutations are harmful but in certain environmnets the new allele of a gene is benefit its possessor in this environment leading to increased reproductive success - the advantageous allele is inherited by memebrs of the next generation - as a result over many generations the new allele increases in frequency in the population

Question 32

what is stabilising selection

Answer 32

- occurs in all populations where environment is stable - selective pressure at both ends of the distribution - favouors the average - tends to eliminate extremes - reduces variability, the size of the range within the population , SD will increase over time - reduces oppertunity for evolutionary change

Question 33

what is an example of stabalising selection

Answer 33

birth mass in humans babies who are heavy or very light show higher neonatal mortality rates than those of medium mass over time selection operates to reduce the number of heavy and light babies

Question 34

what is directional selection

Answer 34

- mean in population represents optimum for exisiting conditions - environmental change may produce new selection pressure that favours an extreme characteristic - when conditions change optimum necessary for survival changes - some organisms will possess the new optimum - over time selection means these will predominate and the mean will shift

Question 35

what is an example of directional selection

Answer 35

thicker fur in mice is an advantage in a cold climate over time selection operates against the disadvantaged extreme and in favour of other extremes. the mean values and range shift towards the favoured extreme the frequency of the alleles causing long hair will increase

Question 36

what is antibiotic resistance

Answer 36

- example of directional selection - a chance mutation results in an allele that gives resistance to an antibiotic to bacteria that posses it, so when the antbiotic is presnt they are at an advantage - in the presence of this antiobiotic bacteria with the resistance allele are able to survive and reproduce more successfully than those with the orginal allele - bacteria with resistant allele reproduce - the resistance allel is passed on to offspring - the allele frequency is said to have increased