Genetic information, variation and relationships between organisms Flashcards
what is the genetic code?
the sequence of base triplets/codons in mRNA that code for specific amino acids
what are the features of the genetic code?
- 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
define gene
a sequence of bases on a DNA molecule that codes for a specific sequence of amino acids to make a polypeptide chain
define proteome
the full range of proteins that a cell is able to produce at a given time
define locus
the fixed position on a DNA molecule occupied by a gene
define allele
different version of the same gene found on the same locus of a chromosome
describe transcription
-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
describe splicing
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
describe translation
-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
what is tRNA?
-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
compare and contrast structure of mRNA and tRNA
-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
define population
-all of the organisms of a particular species that live in the same place
define community
-all of the populations of various species that live in a habitat
define genetic diversity
the number of different alleles of genes in a population
what are the sources of diversity in meiosis?
-crossing over
-independent segregation of homologous chromosomes
outline the steps of crossing over
- 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
explain independent segregation in meiosis
-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
describe stages in meiosis briefly
-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
what are homologous chromosomes
a pair of chromosomes that carry the same genes, but not necessarily the same alleles of the genes
why is meiosis required
-production of gametes and therefore sexual reproduction
-provides genetic diversity
what are the differences between meiosis and mitosis
-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
explain the advantage of variation to the species
-causes individuals to have different adaptations making some better adapted
-better adapted to survive
-allows for changing environment
-allows for them to reproduce
what is non-disjunction?
-chromosomes do not separate properly during meiosis
-gametes have the incorrect number of chromosomes
-can arise spontaneously
what is polyploidy?
-changes in the whole set of chromosomes
-organism have 3 or more sets rather than 2
describe how natural selection produces genetic diversity
-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
describe stabilising selection
-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
describe directional selection
-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.
explain how selection will affect the genetic diversity of a species
-diversity is reduced as there are fewer different alleles present which creates a smaller gene pool as alleles have been chosen or rejected
define species
-groups of similar organism
-that can produce offspring which are fertile
what two measurements are needed to calculate an index of diversity?
-number of individuals of each species
-total number of individuals
hows does removing hedgerows reduce biodiversity
-smaller fields are made into one larger field
-this destroys habitats
-biodiversity is reduced as habitats and food sources are removed
what agricultural practices reduce biodiversity
-removing hedgerows
-clearing large woodlands
-use of pesticides
-use of herbicides
-monocultures
define species richness
the number of different species that are in a community
how can species richness be determined
-random samples are taken from a community
-the number of different species are counted
how can we calculate the number of gametes with different chromosome combinations?
2n
n= the number of pairs of homologous chromosomes
what is courtship behaviour
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
give five ways in which courtship behaviour increases the probability of successful mating
-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
how do we minimise the effect of chance from the sampling process
-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
what is phylogenetic classification
-division of organisms
-based on evolutionary relationships
-based on shared characteristics which have been taken from ancestors
-hierarchy of groups formed
how have we used immunological methods to clarify phylogenetics relationships
-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
in taxonomy we can compare organisms through…
-similarities in DNA base sequence
-similarities in mRNA base sequence
-similarities in amino acid sequence
