4 - Genetics Flashcards
(46 cards)
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
