3.4 Genetic information, variation and relationships between organisms Flashcards
What are the features of DNA molecules in prokaryotic cells
Short, circular and not associated with proteins
What are the features of DNA molecules in eukaryotic cells?
Long, linear, found in the nucleus and associated with proteins called histones
DNA molecule and its histones form a chromosome
What eukaryotic cell organelles apart from the nucleus contain DNA and how does this differ from the DNA in the nucleus?
Mitochondria/chloroplasts
It’s similar to the DNA of prokaryotes: short, circular and not associated with proteins
A gene is a base sequence that codes for:
- the amino acid sequence of a polypeptide
- a functional RNA (including rRNA and tRNAs).
Define locus
Define proteome
The fixed position that a gene occupies on a particular DNA molecule
Complete set of proteins that a cell can code for
What is a triplet?
A sequence of 3 DNA bases that code for a specific amino acid
Explain how the genetic code is universal, non-overlapping and degenerate
Universal because:
code is the same in almost all organisms
acts as evidence for evolution.
Non-overlapping because:
the first three bases are read as one codon, then the next three as the second etc
therefore each base is read only once and the bases do not overlap.
Degenerate because:
more than one triplet can code for a particular amino acid.
Define genetic diversity
Benefit of it?
What can lower it?
number of different alleles of genes in a population
factor that allows natural selection to occur
Benefit:
-species able to adapt with changes in the environment
-e.g. if a new disease arises, some individuals will have characteristics to survive, and will reproduce passing on their alleles, so the species does not become extinct
Can be lowered by:
-small population size
-e.g. founder effect (the numbers start low)
-or genetic bottleneck (where the numbers decrease)
Define species richness
Number of species in a community
Define species diversity
What is the benefit of it?
How is it measured?
How does deforestation lower species diversity?
How does agriculture/farming lower species diversity?
-number of different species
-number of individuals for each species
-Stable ecosystem
-each species is less likely to become extinct (due to high genetic diversity)
-if a species does become extinct it will not affect the food chain as there are other species available
-Species Diversity Index
-takes into account the number of different species and how many individuals there are for each species
-the larger the species diversity index, the larger the species diversity
Deforestation:
-decreases plant species diversity
-less variety of habitats
-less variety of food sources
-decreases animal species diversity
Farming:
-deforestation to make space
-only a few plant and animal species kept
-selectively breed plants & animals
-use pesticides to kill other species
Define ecosystem diversity
Variety of ecosystems
Define taxonomy
the science of identifying, describing, and classifying organisms based on their characteristics and evolutionary relationships.
Outline the principles of natural selection in the evolution of populations
-population of species has variation
-random mutation can result in new alleles of a gene
-many mutations are harmful but, in certain environments, the new allele of a gene might benefit its possessor
-leads to increased reproductive success
-people with the mutation are more likely to survive and reproduce
-advantageous allele is inherited by members of the next generation
-over many generations, the new allele increases in frequency in the population
Outline the difference between directional and stabilising selection using an example
Directional selection:
-occurs when environmental conditions change, so phenotypes best suited to the new conditions are more likely to survive
-hence these individuals will breed and produce offspring
-overtime the mean population will move in the direction of these individuals
-e.g. bacteria being resistant to antibiotics
-a single bacteria will have had a mutation to prevent being killed by penicillin, e.g. producing the enzyme penicillinase
-allows it to grow and populate
-frequency of the allele that enabled penicillinase production increased alongside the population
-hence population moved to have greater penicillin resistance
Stabilising selection:
-phenotypes with successful characteristics are preserved
-phenotypes with greater diversity are reduced
-this selection doesn’t occur due to changes in environment
-if the environment stays the same then the individuals closest to the mean are favoured because they have the alleles that have given them the survival advantage
-the furthest from the mean are selected against
-e.g. new born babies weights
-those that have a birth weight of around 3kg are more likely to survive than those at the extremes
Define biodiversity
Variety of habitats and species in an ecosystem
What is classification and the two types?
What is the naming system used?
-places organisms into groups
Hierarchical/Linnean classification:
-large groups divided into smaller groups with no overlap
-domain, kingdom, phylum, class, order, family, genus, species
Phylogenetic classification:
-based on evolutionary relationships – how closely related different species are and how recent a common ancestor they have
Binomial naming system:
-using Genus name and Species name to name organism
-Genus name first in capital, Species name second in lower case
-e.g. tiger = Felix tigris
Why are the offspring from 2 different species mating infertile?
-offspring will have a odd number of chromosomes
-therefore, cannot perform meiosis, cannot produce gametes
-example: horse + donkey = mule,
Outline 3 ways of comparing relationship between different species
Why is one method better?
1) DNA Hybridisation: comparing DNA base sequence
-take DNA from 2 species to be compared
-radioactively label one of the DNA
-heat both sets so double strand separates
-cool so single strands join together
-look for Hybrid DNA (one strand from species A, one strand from species B)
-identify Hybrid DNA by 50% radioactivity
-heat Hybrid DNA to measure similarity
results = higher temperature required, as:
more hydrogen bonds present
more complementary base pairing
more similar the base sequence
more similar the species
more closely related
more recent a common ancestor
2) Amino Acid Sequence: comparing AA sequence for the same protein (e.g. haemoglobin in mammals)
results = more similar the AA sequence
more similar the DNA base sequence
more similar the species
more closely related
more recent a common ancestor
(comparing DNA sequence better then comparing AA sequence:
DNA sequence provides information on INTRONS and triplet code is DEGENERATE)
Protein Shape: comparing shape of the same protein (e.g. albumin) using immunological technique
- comparing species A and species B
- take albumin from species A
- place in a blood of rabbit
- rabbit will make antibodies against albumin of species A
- takes these antibodies and place in blood from species B
- if the albumin in species B has a similar shape to species A, the antibodies will bind to form antigen-antibody complexes, which will then form a precipitate
results = more precipitate
more complexes
more similar shape
more similar the species
more closely related
more common recent ancestor
Define variation
Types of variation and causes
difference in characteristics between organisms
intraspecific = differences between organisms of the same species
Causes: genetic factors (same genes but different alleles) and environmental factors
interspecific = differences between organisms of different species
Causes: genetic factors (different genes and different alleles) and environmental factors
What are the two types of characteristics and their properties
Discontinuous:
-characteristics fall into certain groups with no overlap (e.g. blood group) – determined by genetics only (a single gene)
Continuous:
-characteristics show a range (e.g. height) – determined by genetics (a few genes, polygenes) and environment
What is a gene and how does it code for a protein?
-a section of DNA that codes for a protein
-made out of intron and exon
-intron = non-coding DNA (function e.g. turns gene on or off)
-exon = coding DNA (codes for protein)
-made out of a sequence of bases
-each 3 bases code for 1 amino acid (called triplet code)
-therefore sequence of bases
-determines sequence of triplet codes
-which determine the sequence of AAs
-hence the polypeptide chain/primary structure (folds to secondary, then to tertiary/quaternary)
How does a mutation lead to a non-functional enzyme?
-change in base sequence
-change in sequence of triplet codes
-change in sequence of AAs
-change in primary structure
-change in hydrogen/ionic/disulfide bonds
-change in tertiary structure (3D shape)
-change in active site shape
-substrate no longer complementary
-can no longer form enzyme-substrate complex
What is mRNA?
-messenger RNA
-single stranded complementary copy of a gene
-carries the code for assembling protein (on DNA called triplet code, on mRNA called codon)
What is tRNA?
-transfer RNA
single stranded RNA folded over into a ‘clover leaf’ shape (held by hydrogen bonds between the bases)
-has an AA attachment site on the top
-has 3 specific bases on the bottom (anticodon)
-anticodon binds to complementary codons on mRNA
Outline protein synthesis
Transcription:
-occurs in nucleolus of nucleus
-produces single stranded complementary copy of a gene (mRNA) from template strand of DNA
Process:
-DNA helicase hydrolyses hydrogen bonds between complementary bases in the gene
-gene unwinds and leaves 2 separate strands (1 coding strand and 1 template strand)
-only 1 strand acts as a template
-complementary RNA nucleotides bind to exposed bases on the template strand
-uracil is used instead of thymine
-RNA polymerase joins the sugar-phosphate backbone of the RNA strand by forming phosphodiester bonds between nucleotides
-forms pre-mRNA (contains introns and exons)
-the copies of the introns are removed by splicing
-mRNA leaves via nuclear pore
Translation:
-takes place on ribosomes
-uses sequence of codons on mRNA to assemble the protein (tRNA brings in AAs)
Process:
-mRNA attaches to a ribosome
-complementary tRNA carrying specific AAs bind to the codons on mRNA via their anticodon
-the AAs on the tRNA are joined by peptide bonds
-stop codon reached, so no more AAs
-primary structure polypeptide chain formed, which can fold into secondary/tertiary
What does meiosis produce?
Benefits of meiosis?
Stages?
How is variation produced by meiosis?
-produces 4 genetically different cells, haploid (half the amount of chromosome/DNA)
Benefits:
-produces gametes which will be used in sexual reproduction in animals & plants
-(2 gametes fuse to form a zygote, zygote develops into organisms)
Interphase:
-G1: protein synthesis
-S: DNA replication (doubles set of DNA)
-G2: organelle synthesis
Meiosis I:
Prophase I: DNA coils to form chromosomes, nucleus breaksdown, spindle fibres form, crossing over occurs
Metaphase I: homologous pair of chromosomes line up in middle of cell and attach to spindle fibre via centromere
Anaphase I: spindle fibres pull, homologous pair of chromosomes separate to opposite sides by independent assortment
Telophase I: chromosomes uncoil, nucleus reforms (left with 2 nuclei)
Meiosis II:
Prophase II: DNA coils to form chromosomes, nucleus breaksdown, spindle fibres form
Metaphase II: chromosomes line up in middle of cell and attach to spindle fibre via centromere
Anaphase II: spindle fibres pull, centromere splits, sister chromatids move to opposite sides by independent assortment
Telophase II: chromatids uncoil, nucleus reforms (left with 4 genetically different nuclei)
Cytokinesis:
separating cell into 4 (each receives a nucleus and organelles/cytoplasm)
Crossing over:
-occurs in Prophase I of Meiosis I
-homologous pairs of chromosomes wrap around each other and swap equivalent sections of chromatids
-produces new combination of alleles
Independent assortment:
-in Anaphase I of Meiosis I – the homologous pairs of chromosomes separate
-in Anaphase II of Meiosis II – the chromatids separate
-independent assortment produces a mix of alleles from paternal and maternal
What happens to DNA mass in meiosis?
What happens to chromosome number in meiosis?
Quarters
Halves
What is mutation and what causes it?
Outline two types of mutations
-Change in DNA
-causes: random or due to mutagens (e.g. radiation, chemicals)
Chromosome mutation:
-polyploidy in plants = inherit more than one diploid set of chromosomes
-non-disjunction in animals = homologous pair of chromosomes don’t separate in meiosis, so inherit one extra or one less chromosome
Gene mutation:
-a change in the base sequence of DNA
-2 types = substitution and insertion/deletion
-substitution = replace one base for another, changes one triplet code, can be:
-silent (new triplet code codes for same AA)
-mis-sense (codes for a different AA, so protein shape changes slightly),
-non-sense (codes for a stop codon, so polypeptide chain not produced)
-insertion = adding a base, deletion = removing a base
-both insertion/deletion causes frameshift, all the triplet codes after the mutation changes, so normal polypeptide chain/protein not produced
If two organisms can produce fertile offspring, they….
belong to the same species
Outline courtship behaviour and its importance
-behaviour that leads to successful mating
-enables organisms to identify members of their own species
-courtship behaviour leads to the formation of a pair bond
-which results in better reproductive success, due to increased survival probability of offspring
Order of Linnaean classification system
Domain
Kingdom
Phylum
Class
Order
Family
Genus
Species
difference between stabilising and directional selection
Stabilizing selection results in a decrease of a population ‘s genetic variance when natural selection favors an average phenotype and selects against extreme variations. In directional selection, a population’s genetic variance shifts toward a new phenotype when exposed to environmental changes
