Genetic information, variation and relationships between organisms

Question 1

what is the genetic code?

Answer 1

the sequence of base triplets/codons in mRNA that code for specific amino acids

Question 2

what are the features of the genetic code?

Answer 2

• it is non-overlapping so each triplet is only read once
  -it is degenerate so more than one triplet can code for the same amino acid
  -it is universal so same bases and same sequences used by all the same species
  -it is one direction so triplets always read in one direction

Question 3

define gene

Answer 3

a sequence of bases on a DNA molecule that codes for a specific sequence of amino acids to make a polypeptide chain

Question 4

define proteome

Answer 4

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

Question 5

define locus

Answer 5

the fixed position on a DNA molecule occupied by a gene

Question 6

define allele

Answer 6

different version of the same gene found on the same locus of a chromosome

Question 7

describe transcription

Answer 7

-dna helicase breaks hydrogen bonds between the complimentary bases so the double DNA double helix is unwound
-RNA nucleotides align next to their complementary bases on the template strand
-RNA polymerase joins adjacent nucleotides through condensation reactions foring phosphodiester bonds
-when RNA polymerase reaches the stop codon the pre-mRNA detaches from the DNA
-mRNA leaves the nucleus through the nuclear pores

Question 8

describe splicing

Answer 8

in eukaryotic cells, pre-mRNA must undergo splicing in order to remove introns (Non coding regions) and leave only the exons (coding regions) which are joined back together through condensation reactions

Question 9

describe translation

Answer 9

-after the mRNA is transcribed it travels through nuclear pores to a ribosome
-the ribosome attaches the start codon of mRNA
-tRNA with the complimentary anti-codon pairs with the codon on the mRNA . this tRNA has a specific amino acid attached
-the ribosome moves along the mRNA, allowing another tRNA to attach to the next codon along.
-the two amino acids which are attached to the tRNA molecules are joined by peptide bonds using an enzyme to catalyse the reaction and ATP which is hydrolysed to supply energy
-the tRNa detaches without its amino acid and the ribosome moves along the mRNA to the next codon
-it continues until a stop codon is reached

Question 10

what is tRNA?

Answer 10

-tRNA is involved in translation as it carries amino acids to the ribosomes which are then used to make polypeptides
-tRNA is a single polynucleotide
-tRNA is folded into a clover shape
-there are hydrogen bonds between specific base pairs
-it has a specific sequence of three bases at the end called an anticodon and an amino acid binding site at the other end

Question 11

compare and contrast structure of mRNA and tRNA

Answer 11

-mRNA does not have hydrogen bonds but tRNA does
-mRNA is a linear chain whilst tRNA has a coverleaf shape
-mRNA does not have an amino acid binding site but tRNA does
-mRNa has codons and tRNA has anticodons

Question 12

define population

Answer 12

-all of the organisms of a particular species that live in the same place

Question 13

define community

Answer 13

-all of the populations of various species that live in a habitat

Question 14

define genetic diversity

Answer 14

the number of different alleles of genes in a population

Question 15

what are the sources of diversity in meiosis?

Answer 15

-crossing over
-independent segregation of homologous chromosomes

Question 16

outline the steps of crossing over

Answer 16

• non-sister chromatids wrap around each other and join up at the chiasmata
  -chromosomes break up at the chiasmata and sections of the chromosomes are exchanged
  -final chromatids have the same genes but a different combination of alleles

Question 17

explain independent segregation in meiosis

Answer 17

-provides genetic variation
-one chromosomes in a homologous pair comes from the father and one from the mother
-separation in meiosis 1 is random and the combinations of chromosomes in the daughter cells are random

Question 18

describe stages in meiosis briefly

Answer 18

-interphase the DNA replicates
-meiosis 1 produces two haploid daughter cells and crossing over occurs
-meiosis 2 is when the two haploid daughter cells divide to produce a total of four haploid daughter cells, each with a single copy of every chromosome

Question 19

what are homologous chromosomes

Answer 19

a pair of chromosomes that carry the same genes, but not necessarily the same alleles of the genes

Question 20

why is meiosis required

Answer 20

-production of gametes and therefore sexual reproduction
-provides genetic diversity

Question 21

what are the differences between meiosis and mitosis

Answer 21

-mitosis produces two daughter cells and meiosis produced 4 daughter cells
-mitosis produces two genetically identical daughter cells and meiosis produces two genetically different daughter cells
-mitosis produces diploid daughter cells so they have the full number of chromosomes and meiosis produces haploid daughter cells so they have the number of chromosomes

Question 22

explain the advantage of variation to the species

Answer 22

-causes individuals to have different adaptations making some better adapted
-better adapted to survive
-allows for changing environment
-allows for them to reproduce

Question 23

what is non-disjunction?

Answer 23

-chromosomes do not separate properly during meiosis
-gametes have the incorrect number of chromosomes
-can arise spontaneously

Question 24

what is polyploidy?

Answer 24

-changes in the whole set of chromosomes
-organism have 3 or more sets rather than 2

Question 25

describe how natural selection produces genetic diversity

Answer 25

-there is genetic variety of different phenotypes within a population due to random mutation resulting in new alleles
-an environmental change occurs causing the selection pressure to change
-some individuals possess advantageous alleles which give them a selective advantage which allows them to survive and reproduce
-the advantageous alleles are passed to the offspring
-overtime the frequency of the alleles in a population changes

Question 26

describe stabilising selection

Answer 26

-environmental conditions remain the same so individuals with mean/average traits are favoured . this results in low diversity
-the birth weight of babies is an example of stabilising selection as babies born around 3 kg will have a higher chance of survival than those at either extremes of that

Question 27

describe directional selection

Answer 27

-environmental conditions change so selection favours one of the extremes in a range of phenotypes leading to one phenotype becoming rare and the other common
-for example antibiotic resistance is a type of directional selection. within a population of bacteria there will be a mutation which allows them to survive and reproduce by binary fission in the presence of antibiotics. thus the frequency of this allele will increase and population will shift to having greater antibiotic resistance.

Question 28

explain how selection will affect the genetic diversity of a species

Answer 28

-diversity is reduced as there are fewer different alleles present which creates a smaller gene pool as alleles have been chosen or rejected

Question 29

define species

Answer 29

-groups of similar organism
-that can produce offspring which are fertile

Question 30

what two measurements are needed to calculate an index of diversity?

Answer 30

-number of individuals of each species
-total number of individuals

Question 31

hows does removing hedgerows reduce biodiversity

Answer 31

-smaller fields are made into one larger field
-this destroys habitats
-biodiversity is reduced as habitats and food sources are removed

Question 32

what agricultural practices reduce biodiversity

Answer 32

-removing hedgerows
-clearing large woodlands
-use of pesticides
-use of herbicides
-monocultures

Question 33

define species richness

Answer 33

the number of different species that are in a community

Question 34

how can species richness be determined

Answer 34

-random samples are taken from a community
-the number of different species are counted

Question 35

how can we calculate the number of gametes with different chromosome combinations?

Answer 35

2n
n= the number of pairs of homologous chromosomes

Question 36

what is courtship behaviour

Answer 36

behaviour carried out by organisms with the aim of attracting a mate of the correct species
this may involve secreting chemicals, a dance or colour changing

Question 37

give five ways in which courtship behaviour increases the probability of successful mating

Answer 37

-can recognise and attract the same species
-stimulates the release of gametes
-attracts opposite sex
-indicates sexual maturity
-can form a bond so the pair can reproduce several times

Question 38

how do we minimise the effect of chance from the sampling process

Answer 38

-use a large sample size as this lessens the influence of anomalies
-analysis of the data collected as statistical tests can determine how much of the results were influenced by chance

Question 39

what is phylogenetic classification

Answer 39

-division of organisms
-based on evolutionary relationships
-based on shared characteristics which have been taken from ancestors
-hierarchy of groups formed

Question 40

how have we used immunological methods to clarify phylogenetics relationships

Answer 40

-proteins of different species can be compared using immunological techniques
-antibodies of one species will respond to specific antigens on proteins in the blood serum of another
-forms a precipitate - a greater amount shows closer evolutionary relationship

Question 41

in taxonomy we can compare organisms through…

Answer 41

-similarities in DNA base sequence
-similarities in mRNA base sequence
-similarities in amino acid sequence