Section 4 - Genetic Information, Variation and Relationships Between Organisms Flashcards
What is a Gene?
a gene is a section of DNA that codes for the sequences of amino acids in a polypeptide and functional RNA
What is the locus?
The location of the gene on the strand of DNA or chromosome. its called the loci if there are multiple genes.
How many different types of amino acids are there?
20 different types
What is the triplet code?
The standard version of the genetic code, in which a sequence of three nucleotides on a DNA or RNA molecule codes for a specific amino acid in protein synthesis.
Why is the triplet code often described as degenerate?
Because some amino acids are coded for by more than one triplet. (lacking an expected pattern)
What is the benefit of Triplet / genetic code being degenerate?
provides protection against mutations in the DNA sequence, as changes to one or two nucleotides in a codon can still result in the same amino acid being produced.
What are the features of the genetic code?
- code is degenerate
- each triplet is read in the same direction 5’ to 3’
- three triplets cause for no amino acids. these are called stop codons. they signify the end of a gene
- the genetic code is non overlapping and each base can only be read once
- the genetic code is universal - each triplet codes for the same amino acid in every organism , this is indirect evidence for evolution.
What are the coding and non-coding regions of DNA called?
Exons are the coding sequences of bases while introns are the non coding sequences of bases.
What are Introns used for?
They are not used or read by ribosomes but are removed in a process called splicing.
what are exons used for?
these are the coding sequences of bases
what is the difference in eukaryotic vs prokaryotic DNA?
- vey long in eukaryotes vas shorter in prokaryotes
- many molecules of DNA in eukaryotes vs one main piece of DNA in prokaryotes
- no plasmids vs plasmids in prokaryotes
- linear in eukaryotes vs ring structure in prokaryotes
- associated with proteins (histones) in eukaryotes.
what is a chromosome?
an entire chain of DNA along with a group of stabilizing proteins
what is the structure of a chromosome?
- DNA molecule
- DNA combined with histones
- DNA histone complex is coiled
- Coils fold to form loops
- Loops coil and pack together to form the chromosome.
what are homologous chromosomes?
- one of each pair of chromosomes comes from each parent
- corresponding pairs are called chromosomes.
What is a haploid cell? (n) and what do they do?
- a cell with half the number of chromosomes
- they join together to restore the chromosome number at fertilisation
what is sexual reproduction?
- a process where the cells of reproductive organs undergo meiosis after interphase
- this is necessary to maintain a species diploid number after fertilization,.
- this creates genetically unique offspring
What is the process of meiosis 1?
- homologous chromosomes pair up.
- chromatids from each pair wrap around each other then crossing over and recombination of portions of chromatids occur
- one of each pair of chromosomes is randomly separated into 2 daughter cells. - this is independent segregation
what is the process of meiosis 2?
- sister chromatids are pulled apart at the centromere and separated into 4 haploid daughter cells
- resulting gametes have varying combinations of alleles.
what is involved in the process of protein synthesis?
- transcription of a gene
- splicing to remove introns
- translation of mRNA into amino acid sequence
What is involved in transcription?
- the DNA strands separate by breaking the h bonds using DNA helicase
- only the template strand is used to make mRNA
- complimentary base pairing occurs between free RNA nucleotides and the template strand
- RNA polymerase joins nucleotides together (phosphodiester bonds)
- Pre- mRNA formed
- splicing occurs and introns are removed to form mRNA
What happens in translation?
- a ribosome attaches to mRNA
- ribosomes moves to find the start codon
- tRNA brings a specific amino acid
- anticodon on tRNA is complimentary to codon on mRNA
- ribosome moves along to next codon
- this process is repeated and amino acids join by peptides bonds to form polypeptide bonds using energy form atp.
What is tRNA
- transfer RNA works with the ribosome to translate mRNA
-tRNA transfers free amino acids from the cytoplasm to the ribosomes to begin protein synthesis. - polynucleotide
- folded by h bonds
- anticodon is specific to the amino acid it carries
what are the differences between the structure of mRNA and the structure of tRNA?
- miRNA is longer and has more nucleotides
- mRNA is a straight molecule but trna is clover leaf shaped
- ## mRNA contains no paired bases
what is a mutation?
- a random change in the base sequence of DNA
where in the cell cycle are mutations most likely to occur?
- interphase because DNA replication is happening
what are some examples of mutagenic agents?
- high energy radiation
- x rays / cosmic rays
- uv light
- carcinogens
mustard gas
what are the three types of mutations?
- substitution
- insertion
- deletion
why are insertion and deletion such bad mutations to have?
- all bases after the the mutated base are shifted and so a frame shift occurs. this means that all subsequent codons change
what is non- disjunction?
the failure of chromones to separate properly during anaphase 1 or 2 or meiosis
- this causes an uneven number of chromosomes in the gametes
- this can cause genetic diseases such as down syndrome
what does it mean when we say DNA is universal , non overlapping and degenerate?
-universal: the genetic molecule is in all living organisms
- non overlapping: each DNS triplet and gene is separate from each other
- Degenerate: the same amino acid can be coded for by more that one triplet
what is a genome?
the complete set of genes in a cell / organism
what is a proteome?
- the full range of proteins that a cell can make.
what is DNA like in eukaryotes?
- long linear and double helix
- found in nucleus
- folded around proteins called histones.
- folded into chromosomes
- have introns
what is DNA lie in prokaryotes?
- DNA is shorter and circular
- no proteins / histones
- have plasmids.
- no introns`
what is mitochondrial and chromosomal DNA look like?
- have their own DNA
- no nucleus
- circular
- no plasmids.
what does transcription look like prokaryotes?
- no splicing occurs because there are no intron in prokaryotes so DNA goes straight to mRNA
what is an anticodon?
- triplet of bases on tRNA that is complimentary to codon on mRNA
what is a codon?
- triplet of bases on mRNA that codes for a specific amino acid
what is the difference between meiosis and mitosis?
- meiosis as 2 divisions while mitosis only has 1
- meiosis creates 4 daughter cells while mitosis creates 2
- cells created from meiosis are genetically different due to crossing over and independent segregation while cells from mitosis are genetically identical
- cells in meiosis have half the amount of genetic info while mitotic cells have all
what is crossing over?
chromatids of homologous pairs cross over and swap alleles during prophase 1
What is independent segregation?
Independent segregation occurs in metaphase I and anaphase I, and is where the homologous chromosomes are randomly shuffled into the two daughter cells.
What is genetic diversity?
- the number of different alleles within a population
What is a population?
A population is a group of the same species in the same place that can interbreed
What is the advantage of more genetic diversity?
- More genetic diversity + more alleles means a wider range of characteristics/variation( bigger gene pool), which leads to a greater chance of individuals surviving environmental change.
What is the model paragraph for mutations and selection pressures
- A change in environment causes a selection pressure
- Random mutations produce genetic diversity
- Some alleles provide an advantage to gaining resources
- Those individuals with the alleles survive and reproduce
- Advantageous alleles are passed on
- The frequency of advantageous alleles in the population increases
- The frequency of mutation increases.
What decides if a mutation is advantageous?
- nature
- natural selection
What are the features of variation between species?
- different species have different genes
- they may also have a different number of chromosomes
- they cannot breed to produce fertile offspring and have different features.
What is selection?
- the process by which organisms that are better adapted to their environment survive and reproduce, while those who are less well adapted do not.
What is selection pressure?
- an environmental change that leads to selection
What is continuous variation?
- a characteristic that can have a wide range of values and shows continuous variation.
- Producing a histogram of continuous variation in a population produces a ‘bell shaped’ normal distribution curve
What is discontinuous variation?
- a characteristic with few possible values shows discontinuous variation.
- The graph does not show a bell curve.
What are polygenic traits?
- Most characteristics are controlled by multiple genes/alleles; these are polygenic traits.
- Polygenic traits are more influenced by the environment than monogenic traits.
What is direction selection
- favouring individuals whose characteristics vary from the mean
- phenotypes are selected for genotypes are indirectly selected.
- changes characteristics
What is stabilising selection
- if conditions remain stable, individuals with average characteristics are favoured
- phenotypes at the extremes are selected against
- preserves characteristics
Why do organisms reproduce?
- organisms reproduce to ensure they survive over time
- the females of most species produce eggs at specific times
This places a selection pressure on courtship behaviours
What are the features of courtship behaviour?
- allows individuals to:
1. recognise members of the same species
2. identify a sexually mature mate
3. Form a pair bond that will lead to successful mating and raising of offspring
4. synchronise mating so that it takes place at a time where egg and sperm are most likely to meet
5. become able to breed by bringing a member of the opposite sex into a state that allows breeding to occur.
What is artificial classification?
- grouping organisms based on features that are useful at the time, e.g. colour wings. the evolutionary origin of these features may not be taken into account.
What is phylogenetic classification?
- based on evolutionary relationships determined from fossils, DNA analysis
- based on shared homologous features
What are hierarchies?
- Groups within groups that do not overlap
What are the different taxonomic ranks?
- Domains (divine)
- kingdom (kings)
- phylum (play)
- class (chess)
- order (on)
- family (fat)
- genus (green)
- species (stools)
What are the benefits of classification?
- universal
What is species diversity?
- the number of different species in a community and their proportions
What is genetic diversity?
- the frequency of different alleles within a population
What is ecosystem diversity?
- the number of different habitats that make up an ecosystem
What is species richness?
- the number of different species in a community
It only tells you the number of species in an area and not the proportions of individuals
What is the index of diversity?
a quantitative measure of biodiversity.
How do you calculate the index of diversity?
- d= N(N-1)/En(n-1)
- where d = species diversity index
- N total is the number of individuals of all species
- n = no. of individuals of each species
What is a natural ecosystem?
- an ecosystem consists of a community of organisms and the habitats in which they live
What is an artificial ecosystem?
- an ecosystem that is controlled by humans farmers select which species are allowed to grow there
- they have a low genetic diversity, species richness and index of diversity
What impact do artificial ecosystems have on biodiversity?
=- By reducing competition, few species dominate
- genetic diversity decreases
– species richness decreases
- index of diversity decreases
- fewer habitats
- variety of plants /insects/animals decrease
- Variety of food decreases
How can we determine evolutionary relationships?
- comparing physical characteristics
- comparing proteins/enzymes
- compare amino acids
- compare mRNA sequences
- Compare DNA sequences
How are mutations linked to DNA sequencing?
- organisms accumulate random mutations over time
- More closely related species show more DNA similarities. This allows for phylogenetic classification
How do you compare mRNA sequences?
- mRNA is complimentary to DNA from which it is transcribed
Therefore, species that share similar mRNA sequences are more closely related.
How do you compare Amino acid sequences?
- amino acid sequences are determined by mRNA sequences, which are determined by DNA sequence
More closely related species will have more similarities in amino acid sequences
How can you compare species using immunological comparisons?
- antibodies of one species will respond to specific antigens on proteins in the blood serum of another
- serum containing the antigen from species a is injected into species b
- species b produces antibodies specific to all the antigen sites on the antigen from species a
- The serum is extracted from species b This serum contains antibodies specific to the antigens on the antigens in serum a
- serum from species b is mixed with serum from the blood of a third species c
- The antibodies respond to their corresponding antigens in the serum of species c
The response is a formation of a precipitate
-the greater the number of similar antigens, the more precipitate and vice versa - Higher precipitate = a more closely related species
How do you measure variation?
Most characteristics show continuous variation; this makes it impossible to give them a definitive measurement value
- You can get around this by sampling
What is sampling?
- looking at smaller groups of organisms and using them to represent the whole population
What are the errors that can be made when sampling?
- may show bias like choosing where to collect samples
What is random sampling?
- draw a grid over a map of the land
- Use a random number generator to generate coordinates
- place the quadrant at coordinates
- This eliminates sampling bias
How can you do random sampling with leaves?
Number the leaves
- place numbered balls in a bag
- Select balls at random
What are the downsides of sampling?
- chance
Even without bias, the measured value may be down to chance - e.g. 50 chosen buttercups may all happen to be tall ones.
How can you reduce the impact of chance?
- increase sample size or more / bigger quadrats
How do you display variation?
- If you measured a characteristic of a population that showed continuous variation under stable conditions, it would present a normal distribution
- symmetrical
- mean, median and mode values are the same
Why may a distribution curve be skewed?
This may be because of insufficient sampling
- an external factor/selection pressure favouring a characteristic
What is the standard deviation?
- the spread of data about the mean
The bigger the standard deviation, the greater the variation.8
How do you calculate the standard deviation on a calculator?
- press mode
- Select STAT
- Select 1–VAR
- Enter the first measurement and press = to enter it
- Continue to enter other measurements, pressing enter each time
- When done, press M+ to add values to memory
- Clear screen and press shift
- Press STAT button
- Select ‘sx’ if calculating s.d for a sample or press ‘OX’ if calculating s.d for a whole population
- Press M+
- The number given is the standard deviation
- What does it mean if the standard deviation in two sets of data overlaps?
The results are not significant and are due to chance
What is interspecific variation?
- variation in characteristics between species.
What is intrspecific variation?
- Variation in characteristics between members of the same species.
How can you reduce the impact of chance in sampling?
- carry out statistical test - this tells you exactly how confidently you can be that the result is not due to chance
- we usually aim to be 95% confident.
