3.4 Genetic information, variation and relationships between organisms Flashcards
(92 cards)
1
Q
Gene
A
- a section of DNA that contains a code for making a polypeptide and functional RNA
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2
Q
Locus
A
- the location of a particular gene on a chromosome
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3
Q
Allele
A
- a different version of the same gene
4
Q
Chromosome
A
- threadlike structure
- composed of tightly coiled DNA wrapped around histones (if it is a eukaryotic cell)
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5
Q
Homologous chromosome
A
- a pair of chromosomes that have the same genes
- ∴ they are the same size
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6
Q
Eukaryotic DNA
A
- DNA is stored as chromosomes inside the nucleus
- linear chromosomes
- DNA is tightly coiled and wrapped around proteins called histones
7
Q
Prokaryotic DNA
A
- DNA molecules are shorter and circular
- DNA is not wound around histones. Instead, it supercoils to fit in the cell.
8
Q
Codon
A
- 3 bases on mRNA that code for an amino acid
9
Q
Start codon
A
- 3 bases at the start of an mRNA sequence which help to initiate translation
10
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 ∴ stops translation
11
Q
Genetic code
A
- an amino acid is coded for by 3 DNA bases which are described as the “triplet code”
12
Q
What is meant by ‘the genetic code is degenerate’?
A
- each amino acid is coded for by
more than one triplet of bases
13
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
- ∴ the mutation will have no impact on the final protein produced
14
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
15
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 ∴ one amino acid
16
Q
Triplet code
A
- an amino acid is coded for by 3 bases
17
Q
Mutation
A
- a change in the DNA
- can be a gene or chromosome mutation
18
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
19
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
- ∴ each codon is read as a discrete unit
20
Q
Introns
A
- non-coding sequence of DNA
21
Q
Exons
A
- sequences of DNA that code for amino acids
22
Q
What is splicing?
A
- post-transcription modification
- removing introns
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23
Q
Genome
A
- the complete set of genes in a cell
24
Q
Proteome
A
- The full range of proteins that a cell is able to produce
25
Anticodon
* 3 bases on the tRNA which are **complementary to the codon** on mRNA
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mRNA structure
* single-stranded
* made up of **codons**
* a copy of one gene
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tRNA structure
* single-stranded, folded to create a **cloverleaf shape**
* held in place by **hydrogen bonds**
* has an **anticodon** and **amino acid binding site**
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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
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tRNA function
* a **specific amino attaches** at the binding site
* **transfers this amino acid** to the ribosome to create the polypeptide chain
30
Transcription
* the **first stage** in protein synthesis
* one gene in DNA is copied into **mRNA**
* occurs in the **nucleus**
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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
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Which enzymes are involved in transcription?
* DNA helicase
* RNA polymerase
33
DNA helicase
* catalyses the **breaking of hydrogen bonds** between the two strands of DNA
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RNA polymerase
* **joins adjacent RNA nucleotides**
together
* forming a **phosphodiester bond**
35
pre-mRNA
* mRNA in eukaryotes that still
**contains the introns**
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How is pre-mRNA modified?
* the **introns are removed** by a protein called a spliceosome
* this leaves just the exons
37
What is ATP used for in translation?
* forming the **peptide bond** between amino acids
38
Haploid
* **one** copy of each chromosome in a cell
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Diploid
* **two** copies of each chromosome in a cell
40
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 (sperm and egg)
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How does meiosis introduce variation?
* crossing over
* independent segregation
45
Types of gene mutations
* deletion
* substitution
46
What is a frameshift?
* the removal of one base
**changes all of the subsequent codons**
* all the bases shift back one position
47
Chromosome mutation
* change in the **number of chromosomes**
* occurs during meiosis
48
Deletion mutation
* a **gene** mutation
* a base is removed from a sequence
* causes a **frameshift**
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Substitution mutation
* a **gene** mutation
* a base is **swapped** for a different one
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Non-disjunction
* the chromosomes or chromatids **do not split equally** during anaphase
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Polyploidy
* changes in **whole sets of chromosomes**
* e.g. when organisms have three or more sets of chromosomes
* mainly occurs in plants
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Aneuploidy
* a change in the **number of individual chromosomes**
* e.g. 3 copies of chromosome 21
53
Down's syndrome
* caused by a **chromosome mutation**
* an example of **aneuploidy**
* e.g. 3 copies of chromosome 21
54
Genetic diversity
* the number of **different alleles** in a population
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Natural selection
* the **process** that leads to evolution in populations
* results in species **becoming better adapted** to their environment
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Gene pool
* all the **genes** and **alleles** in a **population** at a particular time
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Allele frequency
* the **proportion** of organisms within the population carrying a particular allele
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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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Types of selection
* stabilising
* directional
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Directional selection
* **one of the extreme traits** has a selective advantage
* occurs when there is a **change in the environment**
* the modal trait changes
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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
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An example of directional selection
* antibiotic resistance
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An example of stabilising selection
* human birth weight
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Definition of a species
* a group of similar organisms that can **breed to make fertile offspring**
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Binomial system
* a universal naming system
* individuals are named after their **genus** and **species**
* e.g. Homo sapiens
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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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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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What is meant by a hierarchy?
* **smaller groups** arranged within **larger groups**
* there is also **no overlap** between groups
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Phylogenetics
* the study of species' **evolutionary origins** and **relationships**
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Common ancestor
* the species from which another species evolved
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Taxon
* the term for each group in classification
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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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Species diversity
* 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**
80
Which farming techniques reduce biodiversity?
* destruction of hedgerows
* selective breeding
* monocultures
* over-grazing
* filling in ponds and draining wetlands
81
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**
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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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83
How do you make sure your sampling is representative of the population?
* take a **large sample** (at least 30)
* **randomly sample** to avoid bias
84
How can you measure genetic diversity?
* by comparing the **base sequence of DNA**, **mRNA** and the **amino acid sequence** of the proteins
85
Genetic diversity
* the measure of **how many different alleles** there are for each **gene**
86
Formula for Index of Diversity
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87
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**
88
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**
89
What is the role of ribosomes in translation?
* it holds **two tRNA molecules**
* to **enable peptide bonds** to form between the amino acids
90
What is the role of tRNA in translation?
* it carries a **specific amino acid**
* **anticodons** align opposite **complementary codons** on the mRNA
91
Gene mutations
* a **change in the base sequence** of DNA
* **substitution** or **deletion**
92
When in the cell cycle do gene mutations occur?
* **interphase** (S phase)
* this is when DNA is replicated
