Meiosis and genetic variation

Question 1

what can mutations be caused by?

Answer 1

-errors in replication
-mutagenic agents (e.g. chemicals, radiation, smoking)

Question 2

what is the definition of mutation?

Answer 2

any change to the quantity or base sequence of DNA of an organism

Question 3

what is a gene mutation?

Answer 3

any change to the nucleotide bases or sequence of bases in DNA

Question 4

what are the 3 types of gene mutation?

Answer 4

-addition (one base added)
-deletion (one base removed)
-substitution (one base swapped for another)

Question 5

which gene mutations lead to frameshift mutations?

Answer 5

deletion and addition

Question 6

why are frameshift mutations more harmful?

Answer 6

they cause a shift in all other triplet bases, changing the way other bases are read, causing the mutated protein to be different to the original protein.

Question 7

why may the protein coded for change in gene mutations?

Answer 7

if the amino acid sequence is altered then the tertiary structure changes, affecting the functioning of the protein

Question 8

what is a chromosome mutation?

Answer 8

a change in the structure or number of whole chromosomes

Question 9

what are the 2 forms of chromosome mutation?

Answer 9

-changes in the whole set of chromosomes
-changes in the number of individual chromosomes

Question 10

what happens when there are changes in the whole set of chromosomes?

Answer 10

this is when an organism has 3 sets of chromosomes instead of 2, called polyploidy (mostly in plants)

Question 11

what happens when there are changes in the number of individual chromosomes?

Answer 11

this may be due to failure to separate properly in meiosis 1- called nondisjunction and it usually results in the gamete having 1 extra or less chromosome

Question 12

what is non-disjunction?

Answer 12

when chromosomes fail to separate in meiosis 1, resulting in a gamete having one extra or less chromosome, leading to inherited diseases

Question 13

what is a disease that is an example of non-disjunction?

Answer 13

down’s syndrome, which is 1 extra chromosome

Question 14

what does diploid mean?

Answer 14

full set of chromosomes (46)

Question 15

what does haploid mean?

Answer 15

half the full set of chromosomes (23)

Question 16

what are gametes?

Answer 16

sex cells

Question 17

what is a homologous pair of chromosomes?

Answer 17

2 chromosomes in a pair, one maternal, one paternal, with the same genes

Question 18

what is independent segregation in meiosis 1?

Answer 18

the mechanism by which each chromatid goes into which cell (random)

Question 19

describe the process of crossing over

Answer 19

when the non-sister chromatids twist around each other at the chiasmata in meiosis 1 and then break to exchange pieces of DNA. this allows new combinations of genetic information to form. they then re-join, forming recombinant chromosomes.

Question 20

what happens in meiosis 1?

Answer 20

homologous chromosomes pair up and their chromatids wrap around each other. crossing over occurs. by the end of the division, homologous pairs have separated, with one chromosome from each pair going into one of the 2 daughter cells

Question 21

what happens in meiosis 2?

Answer 21

chromosomes move apart. at the end of the division, 4 haploid daughter cells are formed, genetically different. this leads to adaptations which increase survival chances.

Question 22

when do you start referring to chromatids as chromosomes?

Answer 22

meiosis 2

Question 23

what is random fertilisation?

Answer 23

the process of which male gamete fertilises a female gamete being random, creating a specific offspring

Question 24

how is genetic variation added?

Answer 24

-independent segregation
-crossing over
-random fertilisation

Question 25

describe independent segregation

Answer 25

during anaphase in meiosis 1, the process by which the chromosomes migrate is random. chromosomes from each pair line up at random and move to either pole, giving many different combinations.