Unit 4 - Genetic Information and Variation Flashcards
(80 cards)
1
Q
Gene
A
- A section of DNA that codes for a specific sequence of amino acids which makes up the primary structure of a protein
- Alternatively codes for functional RNA (rRNA or tRNA)
2
Q
Allele
A
- An alternative form of a gene
- Occupies the same locus as a gene
3
Q
Locus
A
The position on a gene where a chromosome is situated
4
Q
4 Features of the Genetic Code
A
- Triplet Code
- Degenerate
- Non -Overlapping
- Universal Code
5
Q
Features: Triplet Code
A
- 3 bases code for 1 amino acid
- 3 bases are known as a codon
6
Q
Feature: Degenerate
A
- Most amino acids are coded for by more than 1 triplet code
- This minimises the risk of substitution mutations having an impact on the sequence of amino acids
7
Q
Feature: Non-Overlapping
A
- Each base is read only once in each triplet
- E.g CACGGACAGGCCATGGGT is read as [CAC] [GGA] [CAG], etc
8
Q
Feature: Universal Code
A
- A triplet code will always code for the same amino acid
- E.g ATG will never not code for methionine (Met)
9
Q
Transcription
A
The process by which an mRNA copy of a gene is formed
10
Q
Messenger RNA (mRNA)
A
A transcript copy of a gene used to encode a polypeptide
11
Q
Transfer RNA (tRNA)
A
A clover leaf shaped sequence that carries an amino acid (involved in translation)
12
Q
Ribosomal RNA (rRNA)
A
A primary component of ribosomes
13
Q
Transcription Process
A
- DNA in the nucleus
- RNA polymerase binds to the start of a gene
- RNA polymerase unwinds the helix and makes a copy of the template strand
- Copy is made by matching complementary RNA nucleotides to the DNA nucleotides on the template (antisense) strand
- RNA nucleotides covalently bond, forming pre-mRNA
- DNA behind the RNA polymerase rejoins into a double helix
- When the RNA polymerase reaches a terminator, the chain is terminated and pre-mRNA detaches; the the double helix reforms
- mRNA goes to the ribosomes (in prokaryotes for translation
14
Q
Pre-mRNA
A
- Product of transcription
- Contains exons (coding regions) and introns (non-coding regions)
- Before leaving the nucleus and and undergoing translation, introns are removed to form mature mRNA
- Process only occurs in eukaryotes
- Prokaryotic RNA doesn’t contain introns
15
Q
What happens to introns once they are removed?
A
Introns are broken down back into nucleotides ready for use
16
Q
Spliceosome
A
Forms and causes the introns to form loops which allows exons to be joined and introns to be removed
17
Q
Differences between Prokaryotic DNA and Eukaryotic DNA
A
- DNA molecules are short, circular and aren’t associated with proteins (histones) in prokaryotes
- DNA molecules are very long, linear and associated with proteins (histones) in eukaryotes
- DNA is found in a membrane-bound nucleus in eukaryotes
- Mitochondria and chloroplast DNA can be found in eukaryotes (it is short, circular and not associated with proteins)
18
Q
Translation
A
- mRNA attaches to ribosome
- tRNA anticodons bind to complementary codons on mRNA
- tRNA brings specific amino acid to the codon
- tRNA detaches from mRNA
- the amino acids join by peptide bonds and ribosome moves along the mRNA until a stop codon is reached
19
Q
Mutation
A
- Any change to one or more nucleotide bases or a change in the sequence of bases in the DNA
- Gene Mutations arise spontaneously during DNA replications
20
Q
Locations of Genetic Mutations
A
- Germline (happens in gametes)
- Somatic (happens in body cells)
21
Q
Point Mutation
A
Changes in a nucleotide base
22
Q
Frameshift Mutation
A
Addition or deletion of a nucleotide base, causing all the bases to be read differently
23
Q
Types of Point Mutations
A
- Silent point mutations
- Missense point mutations
- Nonsense point mutations
24
Q
Silent Point Mutations
A
- There is no change to the primary structure of the polypeptide despite the change in a nucleotide base
- Occurs when the substituted base still codes for the same amino acid
- Possible as genetic code is degenerate
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Missense Point Mutation
- There is a change to a single amino acids at the point of mutation
- The effect of this mutation will be determined by the role of the amino acid in the final polypeptide
-
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Nonsense Point Mutation
The new codon is now a stop codon so translation stops at the point of mutation
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Reading Frame
A way of dividing the sequence of nucleotides on a DNA or RNA molecule into conservative, non-overlapping triplets
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Types of Frameshift Mutations
- Deletion
- Insertion
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Deletion
- Occurs when a base is removed from the DNA sequence
- Leads to codons not being read properly
- All the bases would be shifted forward one (a frameshift)
- The new amino acid sequence is entirely different from the original
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Insertion
- The insertion of a single base into the DNA sequence
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Homologous Chromosome
A pair of chromosomes (one maternal and one paternal) that have the same gene locus (position on a gene) and carry the same genes
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Haploid
- A single set of chromosomes in an organisms cells
- In a human this would be 23 single chromosomes
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Diploid
- Two complete sets of chromosomes in an organism's cells with each parent contributing a chromosome to each pair
- In humans this would be 46 chromosomes (23 pairs)
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Meiosis
- Homologous pairs of chromosomes separate so only 1 chromosome from each pair enters a daughter cell
- Stages in meiosis and mitosis are the same but in meiosis the stages happen twice
- 2N to 4N to 2N (diploid) again to N (haploid)
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Prophase 1
- Non-sister chromatids crossover and allow for the exchange of genetic material
- A chiasma randomly forms and creates a point of contact between chromatids
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Why do chiasmas form?
Allows for recombinants (new combinations of alleles that weren't in the parents)
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Metaphase 1
- Homologous chromosomes align at the equator at a completely random nature
- Sometimes the paternal chromosomes could face left and the maternal chromosomes could face right (and vice versa)
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Anaphase 1
- The spindles contract and the chromosomes are pulled apart
- The way the pairs are lined up randomly so when they're pulled apart a random selection of paternal and maternal chromosomes will end up in the gametes (AKA independent segregation)
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Telophase1
- Exact same as mitosis telophase
- Nuclear envelope reforms
- Nucleolus reappears
- Cytokinesis
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Prophase 2
Same as prophase 1 but no crossover or formation of chiasma
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Metaphase 2
Same as metaphase 1 but sister chromatids line up at the equator instead of homologous pairs
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Anaphase 2
Sister chromatids are pulled apart instead of homologous chromosomes
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Telophase 2
Same as telophase 1 (nucleolus, nuclear envelope, cytokinesis)
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Chromosome Mutations
Changes in the structure or number of whole chromosomes
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Aneuploidy
Changes in the number of individual chromosomes (n+1 or n-1)
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Polyploidy
Changes in the number of whole sets of chromosomes (when organisms end up with more than 1 chromosome in each daughter cell at the end of meiosis)
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Non-Disjunction
When the homologous pair of chromosomes (or chromatids depending on the stage of meiosis) fail to separate leading to the production of gametes with one too many or one too few chromosomes
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Mutagenic Agents
- Increase the rate of developing a mutation
- UV Lights
- Ionising Particles (alpha, beta, gamma)
- Carcinogens
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Genetic Diversity
Total number of different alleles in a population
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Population
A group of individuals of the same species that live in the same area and can interbreed
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Gene Pool
The number of different alleles across all the genes in a population at a given time
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What is the consequence of a decrease in genetic diversity?
- The gene pool of the species is reduced
- The phenotypes of the organisms are all very similar
- If there were a sudden change in environment the chance of the population being wiped out is greater
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Natural Selection Process
- In a given population there is a gene pool of various alleles
- A random mutation of alleles within the gene pool creates a new phenotype that is advantageous
- The individuals with the mutation will be more likely to survive and reproduce
- They pass on their alleles to their offspring
- Over time the frequency of that alleles increases
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Structural Adaptations
Changes to the physical features of an organism
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Functional Adaptations
Changes to the biological processes of an organism
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Behavioural Adaptations
Changes to the behaviour of a species
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Directional Selection
- Selection that favours individuals that vary in one direction from the mean of the population
- E.g. Having thinner or thicker fur
- Happens when environmental conditions change
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Stabilising Selelction
Preserves the average characteristics of a population
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How does stabilising selection work?
- Environmental conditions remain stable, individuals with the phenotypes closest to the mean are favoured
- They're more likely to survive and reproduce
- Stabilising selection eliminates phenotypes at the extremes
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Species
A group of organisms that are able to interbreed to produce fertile offspring
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Order of Taxonomies
- Domain
- Kingdom
- Phylum
- Class
- Order
- Family
- Genus
- Species
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How should a species name be written?
- Genus written with an uppercase letter
- Species written with a lowercase letter
- All of it written in italics
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Benefits of Mating
- Helps animals of the same species recognise one another
- Helps identify a mate that is capable of breeding
- Can form pair bonds
- Helps synchronise mating
- Enables copulation (intercourse)
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Artificial Classification
- Organisms are divided into groups based on physical characteristics (size, shape, colour, etc)
- These are known as analogous characteristics and they have the same function but not the same evolutionary origins
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What is the issue with Artificial Classification?
It doesn't show the origins of a species so you can't tell how closely related different species actually are
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Homologous Characteristics
- Characteristics in multiple species that all have similar evolutionary origins, regardless of the function in adult life
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Biodiversity
The number and variety of living organisms in a particular area
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3 Components of Biodiversity
- Species Diversity
- Genetic Diversity
- Ecosystem Diversity
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Species Diversity
The number of different species and the number of individuals of each species within a community
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Genetic Diversity
The variety of genes possessed by the individuals that make up a population of a population
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Ecosystem Diversity
The range of different habitats from a small local habitat to the whole Earth
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Individual
1 organism of a single species
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Population
More than 1 organism of the same species that are in a given area
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Community
A group of different organisms made up of a range of species living within the same habitat
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Ecosystem
The abiotic and biotic factors of a habitat that support each other (interdependence)
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Biome
A large, naturally occurring community of flora and fauna occupying a major habitat
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Biosphere
The regions of the surface and the atmosphere of Earth or another planet occupied by living organisms
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Species Richness
- The number of different species in a particular area at a given time
- The different species must live as a community
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Species Diversity Index
N(N-1)/∑n(n-1)
