9.1 & 2 gene mutations and meiosis

Question 1

What is a mutation?

Answer 1

Change to the quantity or base sequence of DNA

Question 2

What are the three main causes of mutations?

Answer 2

Substitution of bases, deletion of bases and chromosomes changing structure

Question 3

What happens when there is a substitution of bases?

Answer 3

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.

Question 4

What happens when there is a deletion of bases?

Answer 4

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.

Question 5

What causes chromosome mutations?

Answer 5

Changes in structure to the whole chromosome

Question 6

What is it called when they have 3 or more sets of chromosomes not 2?

Answer 6

Polyploidy usually occurs in plants

Question 7

What is it called when the gametes don’t seperate properly during meiosis and what does it cause?

Answer 7

non disjunction gamete when they fail to seperate ends up having fewer or more chromosomes

Question 8

What causes down syndrome?

Answer 8

One more chromosome 21

Question 9

What are the 3 main differences between mitosis and meiosis?

Answer 9

Mitosis Meiosis
2 daughter cells 4 daughter cells
Identical Genetically varied
Diploid same Haploid half chromosomes

Question 10

Why is meiosis so important?

Answer 10

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.

Question 11

How many main stages are there is meiosis?

Answer 11

2

Question 12

What happens in interphase?

Answer 12

DNA replicates, protein synthesis and other organelles synthesise

Question 13

What happens during prophase 1?

Answer 13

Homologous chromosomes pair up chromatids wrap around eachother called crossing over

Question 14

What are the points of crossing over called?

Answer 14

chiasma

Question 15

What happens in metaphase 1?

Answer 15

Bivalents line up the way they are placed creates genetic variation this is called independent segregation

Question 16

What happens in anaphase 1 ?

Answer 16

Homologous pairs are seperated and move to poles by spindle fibres

Question 17

What are the last two stages of meiosis 1 and what happens?

Answer 17

Telophase half number of chromosomes in each cell nuclear envelope and cell wall divide

Question 18

Why must the cells divide again in meiosis 2?

Answer 18

Right number of chromosomes but each have twice the DNA needed

Question 19

What is the final result of meiosis?

Answer 19

4 haploid daughter cells with one chromosome from each homologous pair

Question 20

What are the two ways genetic variation occurs?

Answer 20

Independent segregation and crossing over

Question 21

What is independent segregation and where does it occur?

Answer 21

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

Question 22

What is crossing over and when does it occur?

Answer 22

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.

Question 23

Where is the last place where a lot of variation occurs?

Answer 23

Fertilization where two random gametes fertilize to produce a large variety of offspring

Question 24

How do you calculate the number of combinations?

Answer 24

2 to the power of n all squared

Question 25

What does the combinations calculation not take into account?

Answer 25

recombination would make even more options