Genetics, Biodiversity and Classification Flashcards
What are the three components of nucleotides?
A pentose sugar, a phosphate group, an organic base.
Describe the structure of DNA.
Made up of a deoxyribose sugar, a phosphate group, and one of four organic bases (A,C,G,T). It is double stranded, and hydrogen bonds between the bases form a helix shape.
Describe the role of DNA.
Carries genetic information, determines our inherited characteristics.
Describe the structure of RNA.
Made up of a ribose sugar, a phosphate group, and one of four organic bases (A,C,G,U). It is single stranded.
Describe the role of RNA.
Transfers genetic information from DNA to ribosomes for protein synthesis.
How is DNA in eukaryotic cells different from in prokaryotic cells?
● Eukaryotic cells = found in nucleus, long and linear. Associated with histone proteins to form chromosomes. Mitochondria and chloroplasts contain prokaryotic-like DNA.
● Prokaryotic cells = short and circular. Not
associated with proteins.
What is the genetic code?
The order of bases on DNA. Consists of codons (triplets of bases that code for a particular amino acid).
Identify features of the genetic code.
● Non-overlapping = each triplet is only read once.
● Degenerate = more than one triplet codes for the same amino acid (64 possible triplets for 20 amino acids).
● Universal = same bases and sequences used by all species.
What is a gene?
A sequence of bases on a DNA molecule that codes for a specific sequence of amino acids to make a polypeptide. Can also code for functional RNA.
What is a locus?
The fixed position on a DNA molecule occupied by a gene.
What is an allele?
Different versions of the same gene, found at the same locus on a chromosome.
What are exons and introns?
Exons = regions of DNA that code for amino acid sequences. Separated by one or more introns.
Introns = regions of DNA that do not code for anything.
Where are introns found?
between exons
within genes
What is the genome?
The complete set of genetic information contained in the cells of an organism.
What is the proteome?
The complete set of proteins that can be produced by a cell.
Describe the structure of mRNA.
A long, single strand. Its base sequence is complementary to the DNA it was transcribed from.
Suggest advantages of using mRNA rather than DNA for translation.
● shorter & contains uracil = breaks down quickly so no excess polypeptide forms
● single-stranded & linear = ribosome moves along strand & tRNA binds to exposed bases
● contains no introns
Describe the structure of tRNA.
A single strand of around 80 nucleotides that is folded over into a clover leaf shape. On one end is an anti-codon, on the opposite end is an amino acid binding site.
What is produced by transcription?
mRNA.
Where does transcription take place?
In the nucleus
Outline the process of transcription.
● DNA uncoils into two strands with exposed bases. One used as a template.
● Free nucleotides line up next to their complementary bases, and are joined together by RNA polymerase.
What happens to mRNA after transcription?
In eukaryotic cells, pre-mRNA must be spliced to remove introns, leaving only the coding regions. Then it moves out of the nucleus and attaches to a ribosome.
What is produced by translation?
Proteins
Where does translation take place?
In the cytoplasm (on ribosomes).
Outline the process of translation.
● The anti-codon of tRNA attaches to complementary bases on the mRNA.
● Amino acids bonded to tRNA form peptide
bonds, continuing to form a polypeptide chain until a stop codon is reached.
● This process requires ATP.
What is a mutation?
An alteration to the DNA base sequence. Often arise spontaneously during DNA replication.
Why might a mutation not lead to change in the amino acid sequence?
● Genetic code is degenerate so mutation may end up coding for same amino acid as the original triplet.
● Mutation may occur in intron.
What is a substitution mutation?
When a nucleotide in the DNA sequence is replaced by another. This is more likely to be a quiet mutation, meaning no change occurs in the amino acid sequence.
What is a deletion mutation?
When a nucleotide in the DNA sequence is lost. This is more likely to be harmful and significant, as it leads to a frame shift which means the entire amino acid sequence will be different.
What is a mutagenic agent? Give examples of this.
Factors that increase the rate of gene mutation. X-rays, UV light, gamma rays, certain chemicals e.g. in alcohol and tobacco.
What is a polyploidy chromosome mutation?
Where an individual has three or more sets of chromosomes instead of two.
What is chromosome non-disjunction?
When chromosomes fail to separate correctly in meiosis, resulting in gametes with one more or less chromosome than normal.
What is meiosis?
A form of cell division that produces four genetically different haploid cells (cells with half the number of chromosomes found in the parent cell) known as gametes.
How does meiosis differ from mitosis?
● Meiosis produces four genetically different cells with half the number of chromosomes as the parent cells.
● Mitosis produces two genetically identical cells with the same number of chromosomes as the parent cells.
What happens during meiosis Ⅰ?
- Homologous chromosomes pair to form bivalents.
- Crossing over (exchange of sections of genetic material) occurs at chiasmata.
- Cell divides into two. Homologous chromosomes separate randomly. Each cell contains either maternal or paternal copy.
What happens during meiosis Ⅱ?
- Independent segregation of sister chromatids.
- Each cell divides again, producing 4 haploid cells.
Give 2 ways meiosis produces genetic variation?
- Crossing over during meiosis Ⅰ
- Independent assortment (random segregation) of homologous chromosomes & sister chromatids
Result in new combinations of alleles.
Define population.
All the organisms of a particular species that live in the same place.
What is an allele?
Different forms of a particular gene, found at the same locus (position) on a chromosome. A single gene could have many alleles.
Define genetic diversity.
The total number of different alleles in a population.
What advantage does a high genetic diversity provide?
Ability to adapt to a change in environment; allows natural selection to occur.
Explain how natural selection results in development of new characteristics.
● Random mutations result in new alleles.
● Some alleles provide an advantage, making an individual more likely to survive and reproduce.
● Their offspring receive the new allele, and frequency continues to increase over many generations.
What is directional selection?
Occurs when environmental conditions change. Individuals with phenotypes suited to the new conditions will survive and pass on their genes. Over time the mean of the population will move towards these characteristics.
Give an example of directional selection.
Antibiotic resistance. Bacteria with a mutation allowing them to survive in the presence of antibiotics will reproduce. Therefore frequency of this allele will increase and the population will shift to have greater antibiotic resistance.
What is stabilising selection?
Occurs when environmental conditions stay the same. Individuals closest to the mean are favoured, and any new characteristics are selected against.
Results in low diversity.
Give an example of stabilising selection.
Birth weight; babies that weigh around 3kg are more likely to survive than those at lower or higher weights.
Define a niche.
The role of a species within its environment. Species sharing the same niche will compete with each other.
What are the three types of adaptation? Give examples of each.
● Anatomical (changes to body structure) e.g. oily fur.
● Physiological (changes to bodily processes) e.g. venom production.
● Behavioural (changes to actions) e.g. hibernation.
Define species.
A group of organisms that can interbreed to produce fertile offspring.
What are the advantages of courtship behaviour?
Individuals can recognise sexually mature members of their own species of the opposite sex, synchronise mating, form a pair bond, and successfully breed.
Define classification.
The process of arranging organisms into groups.
Name the eight groups an organism can be classified into, from largest to smallest.
domain → kingdom → phylum → class → order → family → genus → species
What system is used to give species a universal name?
Binomial naming system.
What are the two components to a binomial name?
Generic name= the genus the organism belongs to. Two closely related species will share the same genus.
Specific name= the species the organism belongs to.
How are binomial names handwritten?
The first letter of the generic name should be capitalised, with the rest in lowercase. The whole name should be underlined.
What is phylogenetic classification?
The process of arranging organisms into groups based on their evolutionary origins and relationships.
How can we clarify evolutionary relationships between organisms?
Analyse their molecular differences. Advances in immunology/genome sequencing provide clear pictures of how related two organisms are.
Explain hierarchical classification.
● groups within groups
● no overlap between groups
What is biodiversity?
The variety of living organisms. It can be measured in terms of species diversity (number of species in a community), ecosystem diversity (range of different habitats) and genetic diversity.
Define community.
All the different species that live in one area and interact with each other.
What impact does farming have on species diversity?
decreases species richness
● farmland is typically used for only 1 species (monoculture)
● use of pesticides/ herbicides
What impact does farming have on genetic diversity?
decreases
● farmers select for certain characteristics, which reduces number of different alleles in the population
How can biodiversity be increased in areas of agriculture?
- Use hedgerows instead of fences.
- Grow different crops in the same area, or rotate crops around after a season.
- Limit use of pesticides and herbicides.
Name four ways we can compare genetic diversity between organisms.
- Frequency of observable characteristics.
- Base sequence of DNA.
- Base sequence of mRNA.
- Amino acid sequence.
What is meant by gene technology?
Sampling DNA or mRNA in order to read and compare the base sequence of organisms.
Alternatively the amino acid sequence can be studied as this will also provide information on the organism’s mRNA and DNA sequences.
Why do scientists prefer to use gene technology instead of observation?
Simply inferring DNA differences by observing an organism’s characteristics is not reliable; the characteristics could be coded for by more than one gene, or could be influenced by the environment.
What is meant by interspecific and intraspecific variation?
Interspecific = differences between individuals of different species.
Intraspecific = differences between individuals of the same species.
What is sampling?
Selecting a group of individuals to measure that will represent the whole target population.
How can a random sample be achieved?
Create a grid for your sample area, and then randomly generate coordinates where a quadrat or transect can be placed. Repeat until required sample size is reached.
