4 - Genetics Flashcards
Why do not all mutations cause a change in the structure of a polypeptide?
- triplets code for same amino acid
- occurs in introns
What is an exon?
Base sequence coding for sequence of amino acids
What are non-coding base sequences, and where are they positioned
- DNA that does not code for protein
- positioned between genes
How is DNA in a chloroplast different from DNA in the nucleus
chloroplast DNA is shorter and has fewer genes, and is circular not linear
Compare and contrast tRNA and mRNA
S - both single polynucleotide strand
D - tRNA is ‘clover leaf shape’, mRNA is linear
D - tRNA has hydrogen bonds, mRNA does not
D - tRNA is shorter but mRNA is longer
Give a difference between mRNA and pre-mRNA
mRNA has fewer nucleotides because of splicing
Describe how one amino acid is added to a polypeptide that is being formed at a ribosome during translation
- tRNA brings specific amino acid to ribosome
- Anticodon (on tRNA) binds to codon (on mRNA)
- Amino acids join by condensation reaction
Describe how mRNA is produced from an exposed template strand of DNA
- Free RNA nucleotides form complementary base pairs
- Phosphodiester bonds form
- by RNA polymerase
Describe transcription (5 marks)
- helicase breaks Hydrogen bonds (between DNA bases)
- Free RNA nucleotides align by complementary base pairing
- Uracil base pairs with adenine
- RNA polymerase joins nucleotides forming phosphodiester bonds
- pre-mRNA is spliced to remove introns
Describe translation (6 marks)
- mRNA attaches to ribosomes
- anti codons bind to complementary codons
- tRNA brings a specific amino acid
- amino acids join by peptide bonds using ATP
- tRNA released
- ribosome moves along the mRNA to form the next polypeptide
What is a mutation?
A change in the base sequence of DNA resulting in the formation of a new allele
How can a mutation have no effect on an individual?
- Genetic code is degenerate so amino acid sequence may not change
- new allele is recessive so doesn’t effect phenotype
How can a mutation have a positive effect on an individual?
- Results in change in polypeptide that positively changes the properties of the protein
- may result in increased survival chances
Give two differences between mitosis and meiosis
- in mitosis there is 1 division, in meiosis there is 2
- in mitosis daughter cells are genetically identical, but in meiosis they are different
Describe the process of crossing over and explain how it increases variation (4m)
- homologous pairs of chromosomes form a bivalent
- chiasmata form
- equal lengths of non sister chromatids are exchanged
- producing new combinations of alleles
Give two ways meiosis produces genetic variation
- independent segregation
- crossing over
What happens during prophase 1 of meiosis? (4m)
- nuclear membrane dissolves
- crossing over between non sister chromatids
- homologous pair associate through synapsis
- bivalent forms
What happens during metaphase 1 in meiosis?
- random orientation occurs
- bivalents line up at equator
What’s the definition of genetic diversity?
the number of different alleles of genes in a
population
What does natural selection cause?
- beneficial alleles increase in frequency
- negative alleles decrease in frequency
Describe the process of evolution by natural selection (4m)
- genetic variation is caused by mutation
- overproduction of offspring leads to competition for survival
- individuals with beneficial adaptations are more likely to survive
- over many generations there is a change in allele frequency (evolution)
How does variation occur?
- random mutation in meiosis
- sexual reproduction (crossing over in meiosis or random fertilisation)
What’s the definition of phenotype?
The physical expression of a genotype
What’s the definition of codominant alleles
Both alleles expressed in the phenotype
What is a gene pool
All the alleles in a population
What is a species?
Similar organisms that can reproduce to produce fertile offspring
What are courtship behaviours?
Behaviours that animals exhibit to attract a mate (essential for successful mating)
- species specific
- indicate sexual maturity
- establishes a pair bond to raise young
- prevents interbreeding
How can mating success and offspring survival be increased
- attract same species
- stimulates release of gametes
- attraction of opposite sex
What is the order of the taxon system?
- domain
- kingdom
- phylum
- class
- order
- family
- genus
- species
What is the genus and species of this name : Homosapiens
Genus: Homo
Species name: Sapiens
What are the different measures of biodiversity
- Species richness: measure of no. of different species in a community
- index of diversity: relationship between no. Of species in a community and no. of individuals in each species
What are farming agriculture techniques that decrease biodiversity
- monoculture (only 1 type of crop grown) limits food and habitats for other species
- removal of woodland and hedges - destroys habitats forcing species to migrate/die
- ploughing
- herbicides - kills weeds so removes a food source for other organisms
- spray crops with pesticides - kills pests which removes a food source for organisms
Describe phylogenetic classification
- there is a hierarchy
- no overlap between groups at the same level
- smaller groups within larger groups
What are ways to compare genetic diversity?
- order of amino acids sequence
- base sequence of DNA
- base sequence of mRNA
- frequency of observable characteristics
How could breeding experiments determine if 2 organisms belong to the same species
- breed them together
- if they produce fertile offspring they are from the same species
Explain how the chromosome number is halved during meiosis
- homologous chromosomes
- one of each pair goes to each daughter cell
What is the proteome?
The number of different proteins DNA is able to code for
What is the genome
The complete set of genes in a cell
What does it mean that the genetic code is universal
The same specific DNA base triplets code for the same amino acids in all living organisms
What does it mean that the genetic code is non-overlapping
Discrete, each base can only be used once and in only one triplet
What does it mean that the genetic code is degenerate
The same amino acid can be coded for by more than one base triplet
What is a mutagenic agent?
Increases the rate of gene mutation
Describe what is meant by non-disjunction
- failure of chromosome pairs to separate
- failure of chromatids to separate
- During anaphase
- So both chromatids go to one pole of spindle
How do you calculate the number of possible chromosome combinations from the diploid number?
(2^n)^2.
- n = half the diploid number
Eg if diploid number is 12 then-> (2^6)^2
What is a gene
A sequence of DNA bases that codes for the amino acid sequence of a polypeptide or a functional RNA
What is a chromosome
Long linear DNA and its associated histone proteins in the nucleus of eukaryotic cells
