9.1 & 2 gene mutations and meiosis Flashcards
What is a mutation?
Change to the quantity or base sequence of DNA
What are the three main causes of mutations?
Substitution of bases, deletion of bases and chromosomes changing structure
What happens when there is a substitution of bases?
A nucleotide is replaced with a different nucleotide which can cause the polypeptide produced to differ and if it is important in forming bonds in the tertiary structure the shape will change so it won’t be able to function properly however the new triplet code could still code for the same amino acid due to the code being degenerate so it could have no effect.
What happens when there is a deletion of bases?
A nucleotide is lost from the DNA sequence which means it is all shifted to the left and due to it being read across all the triplet codes will change which will lead to different amino acids and different polypeptide chains.
What causes chromosome mutations?
Changes in structure to the whole chromosome
What is it called when they have 3 or more sets of chromosomes not 2?
Polyploidy usually occurs in plants
What is it called when the gametes don’t seperate properly during meiosis and what does it cause?
non disjunction gamete when they fail to seperate ends up having fewer or more chromosomes
What causes down syndrome?
One more chromosome 21
What are the 3 main differences between mitosis and meiosis?
Mitosis Meiosis
2 daughter cells 4 daughter cells
Identical Genetically varied
Diploid same Haploid half chromosomes
Why is meiosis so important?
Creates genetic variation increasing survival chance, allows sexual reproduction by producing two gametes with a haploid number so cell has correct number of chromosomes not double.
How many main stages are there is meiosis?
2
What happens in interphase?
DNA replicates, protein synthesis and other organelles synthesise
What happens during prophase 1?
Homologous chromosomes pair up chromatids wrap around eachother called crossing over
What are the points of crossing over called?
chiasma
What happens in metaphase 1?
Bivalents line up the way they are placed creates genetic variation this is called independent segregation
What happens in anaphase 1 ?
Homologous pairs are seperated and move to poles by spindle fibres
What are the last two stages of meiosis 1 and what happens?
Telophase half number of chromosomes in each cell nuclear envelope and cell wall divide
Why must the cells divide again in meiosis 2?
Right number of chromosomes but each have twice the DNA needed
What is the final result of meiosis?
4 haploid daughter cells with one chromosome from each homologous pair
What are the two ways genetic variation occurs?
Independent segregation and crossing over
What is independent segregation and where does it occur?
Occurs in metaphase 1 when the chromosomes of homologous pairs randomly line themselves up which determines what one goes to each daughter cell so alleles will be different
What is crossing over and when does it occur?
Occurs in prophase 1 when the chromatids become twisted and DNA is exchanged also due to the tension some parts break off and recombine so many different cells can now be produced.
Where is the last place where a lot of variation occurs?
Fertilization where two random gametes fertilize to produce a large variety of offspring
How do you calculate the number of combinations?
2 to the power of n all squared
What does the combinations calculation not take into account?
recombination would make even more options
