genetic diversity and mutation Flashcards
What is a gene mutation? [3]
- A change in the base sequence of DNA
- Can arise spontaneously during DNA replication
- Involves base deletion / substitution
How can a mutation lead to the production of a non-functional protein / enzyme? [7]
- Change in base sequence of DNA
- Changes sequence of codons on mRNA
- Changes sequence of amino acids in the primary structure of the polypeptide
- Changes position of hydrogen / ionic / disulphide bonds in tertiary structure of protein
- Changes tertiary structure / shape of the protein
(if enzyme) - Changing the shape of the active site
- Substrate can’t bind to active site and form an enzyme-substrate complex
Describe base deletion [6]
- One base removed from DNA sequence
- Changes codon sequence from the point of mutation (frameshift)
- Changes sequence of codons on mRNA 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
i.e. non-functional or new and superior
Describe base substitution [7]
- Base in DNA replaced with another base
- Change in one base → changes one codon
- Changes one mRNA codon and one amino acid
- Sequence of amino acids in primary structure of polypeptide changes etc.
OR - Due to the degenerate nature of the genetic code
- New triplet may still code for the same amino acid
- Sequence of amino acids in the primary structure of the polypeptide remains unchanged
Effect of a mutation in different areas of the DNA
(intron / exon / promoter region)
Intron > no effect as introns are removed by splicing are non-coding regions of the DNA
Exon > mRNA could be altered, change in shape, ineffective
Promoter Region > Gene may not be transcribed
Give 4 examples of a mutagen
ultraviolet light
x-rays
alpha particles
beta particles
What are mutagenic agents?
Increase the rate of gene mutation
What is a homologous chromosome?
an identical chromosome with same genes but different alleles
Meiosis [10]
- 46 chromosomes in normal human cell
- DNA replicates, forming x-shaped chromosomes
- Chromosomes line up in PAIRS in middle of nucleus (M1)
- Whole replicated chromosomes pulled to opposite poles of nucleus by spindle fibres (A1)
- Cell divides into two daughter cells, with 23 x-shaped chromosomes in each (T1)
- Chromosomes line up in middle of nucleus (M1)
- Centromere splits
- Chromatids pulled to opposite poles of nucleus by spindle fibres (A1)
- Each cell divides into two daughter cells, with 23 single chromatids in each (T1)
- Now 4 gamete cells
Give 3 ways meiosis creates genetic variation?
- Crossing over between homologous chromosomes
- Independent segregation of homologous chromosomes
- Random fertilisation when two gametes fuse to form a zygote
What is Crossing Over? [2]
- alleles exchanged between sister chromatids of x-shaped chromosomes
- creating new combinations of maternal and paternal alleles on chromosomes
What is Independent Segregation? [2]
- random alignment of homologous pairs of chromsomes at equator
- random which chromosome from each pair goes to each daughter cell
Why might there be a mutation in the number of chromosomes in each cell? [2]
homologous chromosomes fail to separate during meiosis I
OR
sister chromatids fail to separate during meiosis II
What effect might a differing number of chromosomes have on an organism? [3]
- If zygote has one fewer chromosome upon fertilization it dies
- If zygote has one extra chromosome upon fertilization it survives, causing genetic diseases
- arises spontaneously
How to calculate the number of possible different combinations of chromosomes in daughter cells following meiosis (assuming no crossing over)
2n^
n = the number of pairs of homologous chromosomes
