paper 1: Meiosis and Mutation

Question 1

what is a mutation

Answer 1

a chnage in DNA base sequence of a chromosome

Question 2

how do mutations arise

Answer 2

• base deletion
• base substitution

Question 3

what is a substitution mutation

Answer 3

one base is replaced by a different base

Question 4

what is a deletion mutation

Answer 4

one DNA base is removed from the DNA base sequence

Question 5

what does deletion mutation cause

Answer 5

a frameshift in the DNA base sequence which chnages the triplets from the point of mutation

Question 6

describe and explain the possible effects of a substitution mutation on a protein

Answer 6

the substitution may cause a change in the sequence of encoded amino acids so the tertiary structure of a protein may chnage

Question 7

describe and explain the effect of a deletion mutation on a protein

Answer 7

• causes a frameshift in DNA base sequence so different amino acids would be coded for
• affects position of the ionic, disulfide and hydrogen bonds which would chnage the tertiary structure of the protein meaning the shape of the protein may change
• can become non-functional

Question 8

name some possible mutagenic agents

Answer 8

• UV radiation
• ionising radiation
• carginogens
• chemicals such as benzene and caffine

Question 9

what is menat by haploid

Answer 9

• cells containing one type of each chromosome

(contains n number of chromosomes)

Question 10

what is meant by diploid

Answer 10

cells containing 2 types of each chromosome

(contains 2n number of chromosomes)

Question 11

what are homologous chromosomes

Answer 11

one chromosome from each pair come from the mother and one from the father, each pair has the same gene loci but different alleles

Question 12

what is an allele

Answer 12

different versions of the same gene

Question 13

draw a digram of a pair of homologous chromosomes and label centromere and sister chromatids

Answer 13

Question 14

decsribe what happens during crossing over and explain how it increases genetic variation

Answer 14

• before first division bivalents form and homologous chromosomes form chiasmata and exchange DNA between non-sister chromatids
• creates new combinations of allels resulting in gentic variation

Question 15

describe what ahppens during independent segregation and explain how it increases genetic variation

Answer 15

• during 1st meiosis division homologous pars line up at the equator of the cell and maternal and paternal chromosomes can line up in any random orientation.
• this prodyces different combinations of maternal and paternal chromosomes and therefre alleles in the gametes

Question 16

describe and explain how random fertilisation can increase genetic diversity

Answer 16

• during sexual reproduction, any sperm can fertilise any egg
• fertilisation of gametes is random
• produces zygotes with different combinations of chromosomes and alleles from both parents
• further increasing genetic diversity within a species

Question 17

describe chtomsome non-disjunction

Answer 17

• after meiosis in humans, all 4 daughter cells should contain 23 whole chromsomes, one form each homologous pair
• sometimes chromsomes dont separate properly and any one cell may end up with 2 copies of a chromsome
• is the cause of downs dyndrome

Question 18

decsribe the process of meiosis

Answer 18

• DNA replicates in interphase
• 1st division= spindle fibres atatch to centromeres separating homologous chromsomes
• 2nd division= sister chromatids separate producing 4 haploid daughter cells which are genetically different

Question 19

compare and contrast mitosis and meiosis

Answer 19

mitosis meiosis

number of divisons 1 2

number of daughter cells produced 2 4

haploid or diploid? diplod to diplod or diploid to haploid

haploid to haploid

genetically identical or different? intentical different

Question 20

how do you calculate the possible chromosome combinations following meiosis

Answer 20

2^n

n = number of pairs of homologous chromsomes