SOLUTIONS FOR MEIOSIS AND GENETICS EXAM
1.
(a)
A2 BIO
RICHARD LLOPIS-GARCIA
(i)
Meiosis as number of chromosomes halved;
1
(ii)
Mitosis as number of chromosomes stays the same;
1
(b)
Feature
Female offspring
Male offspring
Crossing over
Independent segregation
of chromosomes
x
Random fusion of
gametes
2
(c)
Offspring will contain a single b allele only;
1
[5]
2.
(a)
Homozygous (for alleles concerned);
1
(b)
24 – 26cm;
1
(c)
(i)
Single characteristic controlled by many genes/more than one gene;
1
(ii)
Many lengths/wide range of lengths/phenotypes;
in F2 generation;
2
(i)
Two different groups/produce intermediate offspring;
1
(ii)
Each parent shows variation although genotype the same;
1
(i)
A piece of DNA which codes for a single protein/polypeptide;
1
(ii)
A particular form of a gene;
1
(i)
w;
1
(ii)
Ww;
1
(i)
The same/0.7 and 0.3;
1
(ii)
Hardy-Weinberg equation given correctly as p2 + 2pq + q2 (= 1);
understands p = 0.7 and q = 0.3;
percentage of heterozygotes = 42
3
(d)
(e)
(f)
(g)
[15]
3.
(a)
mitosis
meiosis
neither
All four answers correct, 2 marks
At least two answers correct 1 mark
(b)
Four haploid cells, each with two chromosomes;
Correct combinations of chromosomes;
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2
2
1
SOLUTIONS FOR MEIOSIS AND GENETICS EXAM
(c)
A2 BIO
RICHARD LLOPIS-GARCIA
8 chromosomes/4 pairs;
1
[5]
p 44. (a)
(b)
(i)
DNA will be halved / less / DNA doubles / increases / there are 2 groups of
nuclei;
1
(ii)
Group with most DNA is before division;
in first division amount of DNA halved;
second division halves this again;
three different amounts of DNA / quoted figures;
3
Random segregation / independent assortment;
allows different combinations DNA / chromosomes;
OR
(c)
(d)
(e)
crossing over / chiasmata;
allows mixing of / swapping / recombination of DNA / mixing alleles / genes
/ exchange of parts of chromatids / chromosomes;
2
(i)
Phosphate / phosphoric acid / P ;
1
(ii)
Hydrogen (bond);
1
(i)
5;
1
(ii)
3;
1
Fragment 14 / 13;
single base represents smallest / lightest piece of DNA;
smallest piece moves furthest / fastest;
3
[13]
5.
x
x
;
1
;
1
x
;
1
x
;
1
x
x
x
x
[4]
6.
(a)
(i)
Alike
both have phosphate/phosphoric acid/PO4;
bases/named bases/accept letters;
nucleotides;
pentose sugar;
Different
DNA deoxyribose;
DNA thymine;
DNA double stranded;
DNA larger/longer;
DNA one form RNA 3 types;
City of Bath College
MAX. 5
2
SOLUTIONS FOR MEIOSIS AND GENETICS EXAM
(ii)
A2 BIO
RICHARD LLOPIS-GARCIA
Alike
H bonds break/DNA unwinds/DNA unzips;
between (complementary) bases;
complementary nucleotides/bases added/DNA acts as template;
same, correctly named, enzymes e.g. polymerase;
Different
uracil/thymine used;
all copied or only section copied respectively;
one strand used transcription, two in replication;
DNA/mRNA produced;
enzymes that are different, correctly named;
(b)
(c)
Only some genes transcribed;
only one strand transcribed;
different protein/enzyme required by different cells;
intron ref/some DNA does not code/non sense codes/junk DNA;
stutter sequences/repeat DNA;
MAX. 6
MAX.2
Crossing over/chiasmata; new combinations of genes/alleles on
chromosome/chromatid;
independent assortment/alignment/clear description;
new chromosome combinations;
4
[17]
7.
(a)
Event
Division I / II
1
2
3
4
I
I
II
I
Phase (anaphase, metaphase,
prophase or telophase)
telophase
prophase
anaphase
metaphase
One mark per row;;;;
(b)
3;
4
1
[5]
8.
(a)
One form of a / the same gene;
1
(b)
Probability (girl with cystic fibrosis) = 1 in 8 / 1/8 / 0.125 / 12.5%;; = 2 marks
Prob. Of cystic fibrosis = ¼ / 0.25 / 25% and P girl = ½ / 0.5/ 50%; = 1 mark
2
Chiasma formation / crossing over;
Random / independent assortment / segregation;
[Ignore: Ref to stages] [ Reject: Mutation]
2
(c)
[5]
City of Bath College
3
SOLUTIONS FOR MEIOSIS AND GENETICS EXAM
9.
(a)
A2 BIO
RICHARD LLOPIS-GARCIA
1. Chromosomes shorten/thicken/condense;
2. Chromosomes associate in homologous/(described) pairs /
formation of bivalents / tetrads;
3. Crossing-over / chiasma formation;
4. Join to spindle (fibres) / moved by spindle;(*)
5. (At) equator/middle of cell;(*)
6. (join via) centromere / kinetochore;(*)
7. (Homologous) chromosomes move to opposite poles /
chromosomes separate/move apart; (ALLOW ‘are pulled apart’)
8. (Pairs of) chromatids separated in 2nd division;
(*) OR “ independent assortment”
unqualified = 1 mark
max 6
(b)
1. Crossing-over; [IGNORE any wrong ref. to timing]
2. Independent/random assortment/orientation/segregation of
(homologous) chromosomes in meiosis I;
3. Independent/random assortment/orientation/segregation of
chromatids in meiosis II;
+
Any three from:
4. Different adaptations / some better adapted;
5. Some survive / example described;
6. To reproduce;
7. Pass on gene/allele;
8. Allows for changing environment/different environment/example described;max 5
(c)
(i)
21;
(ii)
1. T. aestivum has 2 copies of each type of chromosome/is diploid;
2. T. aestivum’s chromosomes can form bivalents/can assort in meiosis/
can produce haploid gametes;
3. T. aestivum’s gametes receive a copy of every chromosome/
receive all the genetic information;
[ACCEPT converse argument for hybrid plants]
1
3
[15]
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4