genetic info, variation and relationships between organisms Flashcards
(93 cards)
1
Q
Gene
A
a section of DNA that contains a code for making a polypeptide and functional RNA
2
Q
Locus
A
the location of a particular gene on a chromosome
2
Q
Allele
A
a different version of the same gene
3
Q
Eukaryotic DNA
A
- DNA is stored as chromosomes inside the nucleus
- linear chromosomes
- DNA is tightly coiled and wrapped around proteins called histones
4
Q
Chromosome
A
composed of tightly coiled DNA wrapped around histones (if it is a eukaryotic cell)
5
Q
Homologous chromosome
A
a pair of chromosomes that have the same genes therefore, they are the same size
6
Q
Prokaryotic DNA
A
- DNA molecules are shorter and circular
- DNA is not wound around histones. Instead, it supercoils to fit in the cell
7
Q
Codon
A
3 bases on mRNA that code for an amino acid
7
Q
Start codon
A
3 bases at the start of an mRNA sequence which help to initiate translation
8
Q
Stop codon
A
- 3 bases at the end of every gene that do not code for an amino acid
- this causes ribosomes to detach
- and therefore stops translation
9
Q
What is meant by ‘the genetic code is degenerate?
A
each amino acid is coded for by more than one triplet of bases
9
Q
Mutation
A
a change in the DNA
can be a gene or chromosome mutation
9
Q
What is the advantage of the genetic code being non- overlapping?
A
if a point mutation occurs, it will only affect one codon and therefore one amino acid
10
Q
What is the advantage of the genetic code being universal?
A
- genetic engineering is possible
- a human gene can be inserted into another organism
e.g human gene for insulin inserted into bacteria to make insulin
10
Q
Genetic code
A
an amino acid is coded for by 3 DNA bases which are described as the “triplet code”
10
Q
What is meant by ‘the genetic code is non-overlapping?
A
each base in a gene is only part of one triplet of bases that codes for one amino acid
therefore each codon is read as a discrete unit
11
Q
What is the advantage of the genetic code being degenerate?
A
- if a substitution mutation occurs, the new triplet of bases may still code for the same amino acid
- therefore the mutation will have no impact on the final protein produced
12
Q
Triplet code
A
an amino acid is coded for by 3 bases
13
Q
What is meant by ‘the genetic code is universal?
A
the same triplet of bases codes for the same amino acid in all organisms
14
Q
Introns
A
non-coding sequence of DNA
15
Q
Exons
A
sequences of DNA that code for amino acids
15
Q
What is splicing?
A
post-transcription modification
removing introns
16
Q
Genome
A
the complete set of genes in a cell
16
Q
Proteome
A
The full range of proteins that a cell is able to produce
17
Anticodon
3 bases on the tRNA which are complementary to the codon on mRNA.
17
mRNA structure
single-stranded
made up of codons a copy of one gene
18
tRNA structure
-single-stranded, folded to create a cloverleaf shape
-held in place by hydrogen bonds has an anticodon and amino acid binding site
18
mRNA function
- a copy of a gene from DNA
- created in the nucleus, and it
then leaves the nucleus
- to carry the copy of the genetic code of one gene to a ribosome in the cytoplasm
19
tRNA function
- a specific amino attaches at the binding site
- transfers this amino acid to the ribosome to create the polypeptide chain
19
Transcription
the first stage in protein synthesis
- one gene in DNA is copied into mRNA
- occurs in the nucleus
20
Translation
the second stage in protein synthesis
- the polypeptide chain is created using both the mRNA base sequence and the tRNA
- occurs on ribosomes in the cytoplasm
21
Which enzymes are involved in transcription?
DNA helicase
RNA polymerase
22
DNA helicase
catalyses the breaking of hydrogen bonds between the two strands of DNA
23
RNA polymerase
joins adjacent RNA nucleotides
together
forming a phosphodiester bond
24
pre-mRNA
mRNA in eukaryotes that still
contains the introns
25
How is pre- mRNA modified?
the introns are removed by a protein
- this leaves just the exons
26
What is ATP used for in translation?
forming the peptide bond between amino acids
27
Haploid
one copy of each chromosome in a cell
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Diploid
two copies of each chromosome in a cell
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Meiosis
- cell division that creates genetically different gametes
- there are two nuclear divisions in this process
- results in four haploid daughter cells
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Independent segregation
- homologous pairs of chromosomes randomly line up opposite each other at the equator of the cell
- when they separate it creates a large number of possible combinations of chromosomes in the daughter cells produced
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Crossing over
- homologous pairs of chromosomes line up opposite each other at the equator in meiosis 1
- parts of the chromatids twist, break and recombine with another chromatid
- results in new combinations of alleles in the gametes
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Gametes
sex cells
33
How does meiosis introduce variation?
crossing over independent segregation
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Types of gene mutations
deletion
substitution
35
What is a frameshift?
the removal of one base changes all of the subsequent codons
- all the bases shift back one position
36
Chromosome mutation
change in the number of chromosomes
occurs during meiosis
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Deletion mutation
a gene mutation
a base is removed from a sequence
causes a frameshift
38
# *
Substitution mutation
a gene mutation
a base is swapped for a different one
39
Non-disjunction
the chromosomes or chromatids do not split equally during anaphase
40
Polyploidy
changes in whole sets of chromosomes
e.g. when organisms have three or more sets of chromosomes
- mainly occurs in plants
41
Down's syndrome
causes by a chromosome mutation
an example of aneuploidy
- 3 copies of chromosome 21
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Aneuploidy
a change in the number of individual chromosomes
e.g 3 copies of chromosome 21
43
Genetic diversity
the number of different alleles in a population
44
Natural selection
the process that leads to evolution in populations
- results in species becoming better adapted to their environment
45
Allele frequency
the proportion of organisms within the population carrying a particular allele
45
Gene pool
all the genes and alleles in a population at a particular time
46
Evolution
the change in allele frequency over many generations in a population
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Selection pressure
factors that affect the survival of an organism
the driving force of natural selection
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Stabilising selection
- the middle (median) trait has a selective advantage and continues to be the most frequent in the population
- represented by a normal distribution graph
- range decreases as the extreme traits are lost over time
49
Directional selection
one of the extreme traits has a selective advantage
- occurs when there is a change in the environment
- the modal trait changes
49
Types of selection
stabilising, directional
50
An example of directional selection
antibiotic resistance
51
Binomial system
a universal naming system individuals are named after their genus and species
e.g. Homo sapiens
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Phylogenetics
the study of species' evolutionary origins and relationships
52
What is meant by a hierarchy?
smaller groups arranged within larger groups
there is also no overlap between groups
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Importance of courtship
- helps to synchronise mating behaviour so that the animals are more likely to mate when the female is releasing eggs
- increases the likelihood of successful mating
- enables individuals to recognise members of the same species and opposite sex
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Courtship behaviour
- different sequences of behaviours that animals demonstrate to attract a mate
- each species demonstrates its own unique behaviour
- essential for successful mating
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species
a group of similar organisms that can breed to make fertile offspring
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An example of stabilising selection
human birth weight
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What are the taxa in the Linnaeus classification system?
domain kingdom phylum class order family genus species
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Taxon
the term for each group in classification
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Common ancestor
the species from which another species evolved
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Species diverstity
the number of different species and the number of individuals within each species in a community
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Species richness
the number of different species in a particular area at the same time
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Index of diversity
- a measure of species diversity
- a calculation to measure the relationship between the number of species in a community and the number of individuals in each species
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Community
all the species in a particular area at a particular time
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Environment
the abiotic (non-living) factors in an area
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Habitat
The range of physical, biological and environmental factors in which a species can live
61
How do you make sure your sampling is representative of the population?
take a large sample (at least 30)
randomly sample to avoid bias
61
Which farming techniques reduce biodiversity?
* destruction of hedgerows
* selective breeding
* monocultures
* over-grazing
* filling in ponds and draining wetlands
62
Biodiversity
* a measure of the **range of habitats**
* from a small local habitat to the entire Earth
* a measure of **species diversity**
* a measure of **genetic diversity**
63
How is standard deviation more useful than a mean?
it gives you the spread of data (variance) around the mean\
- overlaps in standard deviation indicate no significant difference in the means
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How can you measure genetic diversity?
by comparing the base sequence of DNA, mRNA and the amino acid sequence of the proteins
65
Genetic diversity
the mesure of how many different alleles there are for each gene
66
Formula for Index of Diversity
D = N(N-1) / sum of n(n-1)
67
Compare the DNA in chloroplast/ mitochondria to prokaryotic DNA
the DNA is similar to prokaryotic DNA, in that it is:
* short
* circular
* not histone bound
68
How does transcription differ between prokaryotes and eukaryotes
- Transcription in prokaryotic organisms results in mRNA that requires no modification
- because prokaryotic DNA does not contain any introns
- eukaryotic transcription results in pre-mRNA that needs introns removed
69
What is the role of ribosomes in translation?
it holds two tRNA molecules to enable peptide bonds to form between the amino acids
70
What is the role of tRNA in translation?
it carries a specific amino acid anticodons align opposite complementary codons on the mRNA
71
Gene mutations
a change in the base sequence of DNA
substitution or deletion
72
When in the cell cycle do gene mutations occur?
interphase (s phase)
this is when DNA is replicated
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