[3.4] Genetic Information, Variation & Relationships Between Organisms Flashcards
1
Q
Compare and contrast DNA in eukaryotic cells with DNA in prokaryotic cells.
A
SIMILARITIES
-
Nucleotide structure is identical.
- Deoxyribose attached to phosphate and a base.
- Adjacent nucleotides joined by phosphodiester bonds.
- Complementary bases joined by hydrogen bonds.
- DNA in mitochondria/chloroplasts have similar structure to DNA in prokaryotes.
- Short, circular, not associated with proteins.
DIFFERENCES
- Eukaryotic DNA is longer.
- Eukaryotic DNA is linear, prokaryotic DNA is circular.
- Eukaryotic DNA is associated with histone proteins, prokaryotic DNA is not.
- Eukaryotic DNA contains introns, prokaryotic DNA does not.
2
Q
What is a chromosome?
A
- Long, linear DNA + its associated with histone proteins.
- In the nucleus of eukaryotic cells.
3
Q
What is a gene?
A
A sequence of DNA (nucleotide) bases that codes for:
- The amino acid sequence of a polypeptide.
- Or a functional RNA (e.g. ribosomal RNA or tRNA).
4
Q
What is a locus?
A
Fixed position a gene occupies on a particular DNA molecule.
5
Q
Describe the nature of the genetic code.
A
- Triplet code.
- A sequence of 3 DNA bases, called a triplet, codes for a specific amino acid.
- Universal.
- The same base triplets code for the same amino acids in all organisms.
- Non-overlapping.
- Each base is part of only one triplet so each triplet is read as a discrete unit.
- Degenerate.
- An amino acid can be coded for by more than one base triplet.
6
Q
What are ‘non-coding base sequences’ and where are they found?
A
-
Non-coding base sequence - DNA that does not code for amino acid sequences/polypeptides. It is found:
- Between genes - e.g. non-coding multiple repeats.
- Within genes - introns.
(In eukaryotes, much of the nuclear DNA do not code for polypeptides)
7
Q
What are introns and exons?
A
EXON
- Base sequence of gene coding for amino acid sequences (in a polypeptide).
INTRON
- Base sequence of a gene that doesn’t code for amino acids, in eukaryotic cells.
8
Q
Define ‘genome’ and ‘proteome’.
A
GENOME
- The complete set of genes in a cell (including those in mitochondria and/or chloroplasts).
PROTEOME
- The full range of proteins that a cell can produce (coded for by the cell’s DNA/genome).
9
Q
Describe the two stages of protein synthesis.
A
TRANSCRIPTION
- Production of messenger RNA (mRNA) from DNA, in the nucleus.
TRANSLATION
- Production of polypeptides from the sequence of codons carried by mRNA, at ribosomes..
10
Q
Compare and contrast the structure of tRNA and mRNA.
A
COMPARISON
- Both single polynucleotide strand.
CONTRAST
- tRNA is folded into a ‘clover leaf shape’, whereas mRNA is linear/straight.
- tRNA has hydrogen bonds between paired bases, mRNA doesn’t.
- tRNA is a shorter, fixed length, whereas mRNA is a longer, variable length (more nucleotides)
- tRNA had an anticodon, mRNA has codons.
- tRNA has an amino acid binding site, mRNA doesn’t.
11
Q
Describe how mRNA is formed by transcription in eukaryotic cells.
A
- Hydrogen bonds between DNA bases break.
- Only one DNA strand acts as a template.
- Free RNA nucleotides align next to their complementary bases on the template strand.
- In RNA, uracil is used in place of thymine (pairing with adenine in DNA).
- RNA polymerase joins adjacent RNA nucleotides.
- This forms phosphodiester bonds via condensation reactions.
- Pre-mRNA is formed and this is spliced to remove introns, forming (mature) mRNA.
12
Q
Describe how the production of messenger RNA (mRNA) in a eukaryotic cell is different from the production of mRNA in a prokaryotic cell.
A
- Pre-mRNA produced in eukaryotic cells whereas mRNA is produced directly in prokaryotic cells.
- Because genes in prokaryotic cells don’t contain introns so no splicing in prokaryotic cells.
13
Q
Describe how translation leads to the production of a polypeptide.
A
- mRNA attaches to a ribosome and the ribosome moves to a start codon.
- tRNA brings a specific amino acid.
- tRNA anticodon binds to complementary mRNA codon.
- Ribosome moves along to next codon and another tRNA binds so 2 amino acids can be joined by a condensation reaction forming a peptide bond.
- Using energy from hydrolysis of ATP.
- tRNA released after amino acid joined polypeptide.
- Ribosome moves along mRNA to form the polypeptide, until a stop codon is reached.
14
Q
Describe the role of ATP, tRNA and ribosomes in translation.
A
ATP
- Hydrolysis of ATP to ADP + Pi releases energy.
- So amino acids join to tRNAs and peptide bonds form between amino acids.
tRNA
- Attaches to/transports a specific amino acid, in relation to its anticodon.
- tRNA anticodon complementary base pairs to mRNA codon, forming hydrogen bonds.
- 2 tRNAs bring amino acids together so peptide bond can form.
RIBOSOMES
- mRNA binds to ribosome, with space for 2 codons.
- Allows tRNA with anticodons to bind.
- Catalyses formation of peptide bond between amino aids (held by tRNA molecules).
- Moves along mRNA to the next codon.
15
Q
Describe how the base sequence of nucleic acids can be related to the amino acid sequence of polypeptides when provided with suitable data
A
- You may be provided with a genetic code to identify which triplets/codons produce which amino acids.
-
tRNA anticodons are complementary to mRNA codons.
- e.g. mRNA codon = ACG
-> tRNA anticodon = UGC
- e.g. mRNA codon = ACG
- Sequence of codons on mRNA are complementary to sequence of triplets on DNA template strand.
- e.g. mRNA base sequence = ACG UAG AAC
-> DNA base sequence = TGC ATC TTG
- e.g. mRNA base sequence = ACG UAG AAC
- In RNA, uracil replaces thymine.
16
Q
What is a gene mutation?
A
- A change in the base sequence of DNA on chromosomes.
- Can arise spontaneously during DNA replication (in interphase).
- Examples include base deletion and substitution.
17
Q
What is a mutagenic agent?
A
A factor that increases rate of gene mutation e.g. ultraviolet (UV) light or alpha particles.
18
Q
Explain how a mutation can lead to the production of a non-functional protein or enzyme.
A
- Changes of base triplets in DNA (in a gene) so changes sequence of codons on mRNA.
- So changes sequence of amino acids in the polypeptide.
- So changes position of hydrogen/ionic/disulphide bonds between amino acids.
- So changes protein tertiary structure of protein.
- Enzymes active site changes shape so substrate can’t bind, enzyme-substrate complex can’t form.
19
Q
Explain the possible effects of a substitution mutation.
A
- Base/nucleotide in DNA replaced by a different base/nucleotide.
- This changes one triplet so changes mRNA codon.
- So one amino acid in polypeptide changes.
-
Tertiary structure may change if position of hydrogen/ionic/disulphide bonds change.
OR amino acid doesn’t change - Due to degenerate nature of genetic code (triplet could code for same amino acid) OR if mutation is in an intron so removed during splicing.
-
Tertiary structure may change if position of hydrogen/ionic/disulphide bonds change.
20
Q
Explain the possible effects of a deletion mutation.
A
- One nucleotide/base removed from DNA sequence.
- Changes sequence of DNA triplets from point of mutation (frameshift).
- Changes sequence of mRNA codons after point of mutation.
- Changes sequence of amino acids in primary structure of polypeptide.
- Changes position of hydrogen/ionic/disulphide bonds in tertiary structure of protein.
- Changes tertiary structure/shape of protein.
21
Q
Describe features of homologous chromosomes.
A
Same length, same genes at same loci, but may have different alleles.
22
Q
Describe the difference between diploid and haploid cells.
A
- Diploid - has 2 complete sets of chromosomes, represented as 2n.
- Haploid - has a single set of unpaired chromosomes, represented as n.
23
Q
Describe how a cell divides by meiosis.
A
In interphase, DNA replicates to form 2 copies of each chromosome (sister chromatids), joined by a centromere.
-
Meiosis I (first nuclear division) separates homologous chromosomes.
- Chromosomes arrange into homologous pairs.
- Crossing over between homologous chromosomes.
- Independent segregation of homologous chromosomes.
-
Meiosis II (second nuclear division) separates chromatids.
- Outcome = 4 genetically varied daughter cells that are haploid.
24
Q
Draw a diagram to show the chromosome content of cells during meiosis.
A
- You should be able to complete diagrams showing the chromosome contents of cells after the first and second meiotic division when given the chromosome content of the parent cell.
- In the example shown below:
- The parent cell has 4 chromosomes = 2 homologous pairs.
25
Explain why the number of chromosomes is halved during meiosis.
**Homologous chromosomes** are separated during **meiosis I** (first division).
26
Explain how crossing over creates genetic variation.
1. **Homologous pairs** of chromosomes associate/form a **bivalent**.
2. **Chiasmata** form.
- Point of contact between non-sister chromatids.
3. **Alleles** exchanges between chromosomes.
4. Creating **new combinations** of maternal and paternal **alleles** on chromosomes.
27
Explain how independent segregation creates genetic variation.
1. Homologous pairs **randomly** align at **equator**.
- So random which chromosome from each pair goes into each daughter cell.
2. Creating **different combinations** of maternal and paternal chromosomes/alleles in daughter cells.
28
Other than mutation and meiosis, explain how genetic variation within a species is increased.
1. **Random fertilisation/fusion of gametes**.
- Creating new **allele combinations**/new maternal and paternal **chromosome combinations**.
29
Explain the different outcomes of mitosis and meiosis.
1. Mitosis produces **2 daughter cells**, whereas **meiosis** produces **4 daughter cells**.
- As **1 divison** in mitosis, where as **2 divisions** in meiosis.
2. **Mitosis maintains** the chromosome number (e.g. **diploid** -> **diploid** or **haploid** -> **haploid**) whereas **meiosis halves** the chromosome number (e.g. **diploid** -> **haploid**)
- As **homologous chromosomes separate** in meiosis but not mitosis.
3. **Mitosis** produces **genetically identical** daughter cells, whereas **meiosis** produces **genetically varied** daughter cells.
- As **crossing over** and **independant segregation** happen in meiosis but not mitosis.
30
Explain the importance of meiosis.
- **Two divison** creates **haploid** gametes (halves number of chromosomes).
- So **diploid** number is restored at **fertilisation**.
- **Chromosome number maintained** between generations.
- **Independant segregation** and **crossing over** creates **genetic variation**.
31
How can you recognise where meiosis and mitosis occur in a life cycle?
- **Mitosis** occurs between stages where chromosome number is **maintained** (e.g. diploid (2n) -> diploid (2n) OR haploid (n) -> haploid (n)).
- **Meiosis** occurs between stages where chromosome number **halves** (e.g. diploid (2n) -> haploid (n)).
32
Describe how mutations in the number of chromosomes arise.
- **Spontaneously** by **chromosomes non-disjunction** during **meiosis**.
- **Homologous chromosomes** (meiosis I) or **sister chromatids** (meiosis II) **fail to separate** during meiosis.
- So some gametes have an extra copy (n+1) of a particular chromosome and others have none (n-1).
33
Suggest how the number of possible combinations of chromosomes in daughter cells following meiosis without crossing over can be calculated.
**2ⁿ** where n = number of pairs of homologous chromosomes (half the diploid number).
34
Suggest how the number of possible combinations of chromosomes following random fertilisation of two gametes can be calculated.
**(2ⁿ)²** where n = number of pairs of homologous chromosomes (half the diploid number).
35
What is genetic diversity?
Number of different **alleles** of genes in a **population**.
36
What are alleles and how do they arise?
- **Variations** of a particular **gene** due to different DNA **base sequence**.
- Arises by **mutation**.
37
What is a population?
- A group of organisms of the **same species** in a particular **space** at a particular time.
- That can potentially **interbreed** to produce fertile offspring.
38
Explain the importance of genetic diversity.
1. Enables **natural selection** to occur.
2. As in certain environments, a new **allele** of a gene might **benefit** its possessor.
3. Benefit due to **positive changes in polypeptide's properties** which are coded for by that new allele.
4. Giving possessor a **selective advantage**.
- Such as increased chances of survival or reproductive success.
39
What is evolution?
- **Change** in **allele frequency** over **many generations** in a population.
- Occurring through the process of **natural selection**.
(**Adaptation** and **selection** are major factors in evolution and contribute to the **diversity** of living organisms)
40
Explain the principles of natural selection in the evolution of populations.
1. _**M**utation_
- **Random gene mutations** can result in **new alleles** of a gene.
2. _**A**dvantage_
- In certain **environments**, the new allele might **benefit** its possessor [explain why].
- Organism has a **selective advantage**.
3. _**R**eproductive_
- Possessors are more likely to **survive** and have **increased reproductive success**.
4. _**I**nheritance_
- Advantageous allele is **inherited** by members of the next generation (**offspring**).
5. _**A**llele frequency_
- Over **many generations**, allele **increases** in **frequency** in the population.
(**Natural selection** results in species that are better adapted to their environment)
41
Describe 3 types of adaptations.
**_ANATOMICAL_**
- Structural/physical features that increase chance of survival.
**_PHYSIOLOGICAL_**
- Processes/chemical reactions that increase chance of survival.
**_BEHAVIOURAL_**
- Ways in which the organism acts that increase chance of survival.
42
Explain directional selection using an example.
_Example_
- **Antibiotic resistance** in bacteria.
_Key feature - who has a selective advantage?_
- Organisms with an **extreme variation of a trait**.
- e.g. Bacteria with high level of resistance to a particular antibiotic.
_Change in environment?_
- **Yes**, usually.
- e.g. antibiotic introduced.
_Effect on population over many generations_
- **Increased** frequency of organisms with/alleles for extreme trait.
- Normal distribution curve **shifts** towards extreme trait.
43
Explain stabilising selection using an example.
_Example_
- Human **birth weight**.
_Key feature - who has a selective advantage?_
- Organisms with an **average/modal variation of a trait**.
- e.g. babies with an average weight.
_Change in environment?_
- **No**, usually **stable**.
_Effect on population over many generations_
- **Increased** frequency of organisms with/alles for **average trait**.
- Normal distribution curve similar, **less variation** around mean.
44
What is a species?
A group of organisms that can interbreed to produce **fertile offspring**.
45
Suggest why 2 different species are unable to produce fertile offspring.
- Different species have **different chromosome numbers** -> offspring may have **odd chromosome number**.
- So **homologous pairs** cannot form -> **meiosis** cannot occur to produce gametes.
46
Explain why courtship behaviour is a necessary precursor to successful mating.
1. Allows **recognition** of members of **same species** so **fertile offspring** produced.
2. Allows recognition/attraction of **opposite sex**.
3. Stimulates/**synchronises mating**/production/release of **gametes**.
4. Indicates **sexual maturity**/fertility.
5. Establishes a **pair bond** to raise young.
47
Describe a phylogenetic classification system.
- Species arranged into **groups**, called **taxa**, based on their **evolutionary origins** and **relationships**.
- Uses a **hierarchy**:
- **Smaller groups** are placed within larger groups.
- **No overlap** between groups.
48
Name the taxa in the hierarchy of classification.
**Domain** (largest/broadest) -> **Kingdom** -> **Phylum** -> **Class** -> **Order** -> **Family** -> **Genus** -> **Species** (smallest)
49
How is each species universally identified?
- A **binomial** consisting of the name of its **genus** and **species**.
- e.g. Homo sapiens.
50
Suggest an advantage to binomial naming.
**Universal** so no **confusion** as many organisms have more than one common name.
51
How can phylogenic trees be interpreted?
- Branch point = **common ancestor**.
- Branch = **evolutionary** path.
- If two species have a more recent common ancestor, they are **more closely related**.
- e.g. C & D in the diagram below.
52
Describe two advances that have helped to clarify evolutionary relationships between organisms.
1. Advances in **genome** sequencing allow for comparison of **DNA base sequences**.
- More **differences** in DNA sequences, **more distantly related/earlier common ancestor**.
- As **mutations build up over time**.
2. Advances in **immunology** allow for comparison of **protein tertiary structure**.
- **Higher amount** of protein from one species **binds** to **antibody** against the same protein from another species, **more closely related/more recent common ancestor**.
- As indicates a similar **amino acid sequence** and **tertiary structure**.
- So less time for **mutations** to build up.
53
What is biodiversity?
- **Variety** of living organisms (species, genetic & ecosystem diversity).
- Can relate to a range of **habitats**, from a small **local** habitat to the **Earth**.
54
What is a community?
All **populations** of different species that live in an area.
55
What is species richness?
A measure of the **number** of **different species** in a **community**.
56
What does an index of diversity do?
_Describes the **relationship** between:_
1. The **number of species** in a community (species richness).
2. The number of **individuals in each species** (population size).
57
Suggest why index of diversity is more useful than species richness.
- Also takes into account **number of individuals in each species**
- So takes into account that some species may be present in **small** or **high numbers**.
58
What is the formula for index of diversity?
59
List the steps involved in calculating an index of diversity.
1. Calculate the total number of organims (**N**), if not given.
2. Multiply **N** by **(N-1)**.
3. For **each species**, multiply the number of organisms (**n**) by **(n-1)**.
4. Add up all the values of **n(n-1)** to get **∑n(n-1)**.
5. Divide N(N-1) by ∑n(n-1).
60
Describe how index of diversity values can be interpreted.
_HIGH_
- **Many species** present (high species richness) and species **evenly represented**.
_LOW_
- Habitat **dominated** by one/a few species.
61
Explain how some farming techniques reduce biodiversity.
_FARMING TECHNIQUES AND HOW THEY REDUCE BIODIVERSITY_
1. Removal of **woodland** and **hedgerows**.
2. **Monoculture** (growing one type of crop).
3. Use of **herbicides** to **kill weeds**.
- Reduces **variety of plants**
- So fewer **habitats** and niches.
- And less **variety of food sources**.
4. Use of **pesticides** to kill pests.
- **Predator** population of pests decreases.
62
Explain the balance between conservation and farming.
- Conservation required to **increase biodiversity**.
- But when implemented on farms, **yields** can be reduced, reducing **profit/income** for farmers.
- e.g. by reducing land area for crop growth, increasing competition, increasing pest population.
- To offset loss, **financial incentives/grants** are offered.
63
Give examples of how biodiversity can be increased in areas of agriculture.
- Reintroduction of **field margins** and **hedgerows**.
- Reduce use of **pesticides**.
- Growing **different crops** in the same area (intercropping).
- Using **crop rotation** of nitrogen-fixing crops instead of fertilisers.
64
How can genetic diversity within or between species be measured?
- Comparing **frequency** of **measurable or observable characterisitcs**.
- Comparing **base sequence** of **DNA**.
- Comparing **base sequence** of **mRNA**.
- Comparing **amino acid sequence** of a specific **potein** encoded by DNA or mRNA.
65
Explain how comparing DNA, mRNA and amino acid sequences can indicate relationships between organisms within a species and between species.
1. More **differences** in sequence, **more distantly related/earlier common ancestor**.
2. As **mutations build up overtime**.
3. More mutations cause more changes in **amino acid sequences**.
66
Explain the change in methods of investigating genetic diversity over time.
1. Early estimates made by inferring DNA differences from **measurable or observable characteristics**.
- Many **coded for by more than one gene**.
- Difficult to distinguish one from another.
- Many influenced by **environment**.
- Differences due to environment, not genes.
2. Gene technologies allowed this to be replaced by direct investigation of **DNA sequences**.
67
Explain how data should be collected when investigating variation within a species quantitatively
1. **Collect data** from **random** samples (use random number generator) to **remove bias**.
- Use a **grid** /divide area into squares.
- Use a **random number generator** to obtain random **coordinates**.
2. Use **same method** of **measurement** each time.
3. Use **large** sample size / measure a **large number** of organisms so **representative** of whole population.
4. Calculate a **running mean** and sample until number becomes fairly **constant**.
5. Ensure **ethical** sampling so to **not harm** organism/allow release **unchanged**.
68
Explain how data should be processed and analysed when investigating variation within a species quantitatively.
1. **Calculate** a **mean** value of collected data and **standard deviation** of that mean.
2. **Interpret** mean values and their standard deviations.
- Standard deviations shows **spread of values about the mean**.
- Higher standard deviation = higher variation.
- If standard deviations **overlap**, causing values of two sets of data to be **shared**, any difference between the two may be **due to chance/not significant**.
3. Use [named] **statistical test** to analyse whether there is a **significant difference** between populations.
