Genes And Diversity ( Year 12 content ) Flashcards
What are the three components of nucleotides?
A pentose sugar, a phosphate group, and a nitrogenous base
Describe the structure of DNA
Made up of deoxyribose sugar, a phosphate group, and one of 4 bases (A,T,C,G). Its 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 ribose sugar, a phosphate group, and one of four bases(A,U,C,G). It is single-stranded
Describe the role of RNA
Transfers genetic information from DNA to ribosomes for protein synthesis
Which bases are purine and which are pyrimidine?
Purine(double ring)= adenine, Guanine
Pyrimidine(Single ring)= Cytosine, thymine,Uracil
How Is DNA in eukaryotic cells different from in prokaryotic cell?
●Eukaryotic cells=found in the nucleus,long and linear. Associated with histone proteins to form chromosomes
●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-overlappinh=each triplet is only read once
●Degenerate= more than one codon can code for the same amino acid
●Universal= one codon codes for the same amino acid in most organisms
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
What is a locus?
The fixed postion on a DNA molecule occupied by a gene
What is an allele?
A different version of the same gene, found at the same locus on a chromosome
What are exons and introns?
●Exons=region of DNA that code for amino acid sequence, 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 entire 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 advantage of using mRNA rather than DNA for translation
●shorter and contain uracil=breaks down quickly, so no excess polypeptide forms
●single-stranded and linear=ribosomes move along strands, and 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, it is an anti-codon. On the opposite end is an amino acid bnding site
What is produced by transcription?
mRNA
Where does transcription take place?
Nucleus
Outline the process of transcription
●DNA helicase breaks the weak hydrogen bonds between bases, causing DNA to unzip, forming 2 template strands
●free nucleotides line up next to their commentary bases on the template strand
●RNA polymerase joins the adjacent RNA nucleotides by forming phosphodiester bonds in a condensation reaction
●pre-mRNA is formed, and introns are spliced using enzymes forming m-RNA
Outline the process of translation
●mRNA leaves the nucleus via nuclear pores and attaches to ribosomes
●ribosomes read the mRNA base sequence
●this causes tRNA to bring an anti-codon on one side that’s complementary to the codon on mRNA and a specific amino acid on the other side
●amino acids join together in a condensation reaction forming peptide bond
●this process requires ATP
Where does translation take place?
Ribosomes
What is a mutation?
A random change to the DNA base sequence
Why might a mutation not lead to change in the amino acid sequence?
●genetic code is degenerate, so mutations 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 base sequence is replaced by another
What is a deletion mutation?
When a nucleotide in the DNA base 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?
Factors that increase the rate of gene mutations
X-rays
UV Light
What is meiosis?
A form of cell division that produces four genetically haploid cells( cells with half the number 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 cell
●mitosis produces two genetically identical cells with the same number of chromosomes as the parent cell
What happens during meiosis I?
1) Homologous chromosomes pair to from bivalents
2) crossing over(exchange of alleles between sisters chromatids) occurs at chiasmata
3) Cell divides into two. Homologous chromosomes separate randomly
What happens during meiosis II?
1) independent segregation of sister chromatids
2) Each cell divides again, producing 4 haploid cells
In which two ways does meiosis produce genetic variation?
1) crossing over
2) Independent assortment
Define population
All the organisms of a particular species that live in the same place
Define genetic diversity
The total number of different alleles in a population
What advantage does a high genetic diversity provide?
The ability to adapt to a change in the environment allows natural selection to occur
Explain how natural selection results in the 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 alleles, and the frequency of advantageous allele increases
What is directional selection?
Occur when phenotype of the extreme is favoured. Individuals with phenotype suited to the new condition will survive and pass on their genes
Give an example of directional selection
Antibiotic resistance
What stabilising selection?
Occurs when the environment is constant. Phenotypes closest to the mean are favoured, and phenotype of the extreme is favoured against
Give an example of stabilising selection
Baby Birth weight
Heavy babies= problem in delivery
Light babies= complications
What are the three types of adaptation?
1) chemical
2) physical
3) behavioural
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 opposite sex
●synchronises mating
●forms a pair bond
Define classification
The process of arranging organisms into groups
Name the eight groups in the classification hierarchy, 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
Specific name= the species the organism belongs to
What is phylogenetic classification?
The process of arranging organisms into groups based on their evolutionary origins and relationship
How can we clarify evolutionary relationships between organisms?
Analyse their molecular differences
Advances in immunology sequencing
Explain hierarchical classification
Smaller groups within larger groups with no overlap between the groups
What is biodiversity?
The variety of living organisms
Define community
All the different species that live in one area and interact with each other
How do you calculate the index of diversity?
D= N(N-1) / Σn(n-1)
n = total number of organisms for a single species in the community
N = total number of organisms in the community
Σ = sum of
What impact does agriculture
(Farming) have on species diversity?
Decreases species richness
●farmland is typically used for 1 species
● use of pesticides/ herbicides
● removal of hedgerows
What impact does farming have on genetic diversity?
Decreases
●farmers select for certain characteristics, which reduces the number of different alleles in the population
How can biodiversity be increased in areas of agriculture?
1) use of hedgerows instead of fences
2) rotate crops around after a season
3) Limit the use of pesticides and herbicides
Name four ways we can measure genetic diversity
1) observable characteristics
2) base sequence of DNA
3) base sequence of mRNA
4) amino acid sequence
Why do scientists prefer to use gene technology instead of observation?
Simply Inferring DNA differences by observing an organisms 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 random sampling be achieved?
Create a grid for the sample area, and then randomly generate coordinates where a quadrat can be placed. Repeat until the required sample size is reached
