Think about the following statementsbook to get rid of any misconceptions

carefully, Are they true or false? Check the answers at the back of the

1 A dominant trait is expressed when both alleles are recessive.

2 An allele is a gene on a homologous chromosome.EUJ

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3 A male somatic cell contains 22 pairs of autosomes and a pair of X chromosomes.

4 Discontinuous variation is caused by genetic and environmental factors.

5 A person with Down's Syndrome has 47 chromosomes, with one extra sex chromosome.

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Review'Exercise 14PAPER 1 Multiple Choice Auestions

lnstruction: Answer all questions. For each questionthere are four possible answers, A, B, C and D.

Choose the one you consider correct and record yourchoice in the bracket.

1 A tall stem is a dominant trait in a plant while a

short stem is the recessive trait. lf thephenotype of the plant is tall, what are thepossible genotypes of the plant?

I Homozygous dominantll Heterozygous for tall plantlll Homozygous recessivelV Heterozygous for dwarf plant

A I and ll only B I and lll onlyC ll and lV only D lll and lV only ( )

2 The diagram shows the apparatus used in anexperiment. A student closed both of his eyesand selected one bead from each container.This step was carried out 200 times.

allele, how many individuals would display thedominant (red) phenotype?

A54 B10ic146 D153 ( )

3 The allele for red flowers and the allele forwhite flowers in a plant show codominance,the heterozygous being pink. Which phenotypicratio could be expected in the offspring from a

cross between heterozygous pink-floweredplants?

A lred:lwhiteB lred:1pink:lwhiteC lred:2pink:lwhiteD lwhite:3red (

l

4 The genetic diagram below is used todetermine the sex of offspring.

Parents Mother Father

Meiosis

Fertilisation

Male baby Female baby

What are the genotypes of cells R, S and T?

44+X 44 +Y 44 +Y

44+XX44+XY22+X 22+X

MM.100 white beads 100 white beads100 red beads 100 red beads

The table showed the result of selecting 200pairs of beads.

54,9947lf each red bead represents a dominant alleleand each white bead represents the recessive

A

B

cD

44

22 +Y

22+X

RWhite pairsRed pairs,

22+X 22 +Y

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Mixed pairs

)(

s T

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5 P represents the dominant allele for browneyes and p represents the recessive allele forblue eyes. Which of the following statementsare true?

I The genotype for homozygous brown eyes isPP

ll The phenotype for Pp is brown eyes.lll The genotype for heterozygous blue eyes is

pp.lV The dominant allele will express its trait when

it is heterozygous.

A l, ll and lll onlyB l, ll and lV onlyC ll, lll and lV onlyD l, ll, lll and lV ( )

6 Some long-winged fruit flies were self-mated.Out of the 520 offspring, 130 had short wingswhile the remainder had long wings.The allelefor long wings is dominant (W).The allele (w)represents short wings. Which are thegenotypes of the parents?

A Wwxww B \y'y'WxwwC WwxWw D V/WxWw ( )

7 The table shows a Punnett square for a crossbetween heterozygous parents. T represents thedominant allele.

A student made the following statements in hissummary of the Punnett square.

X -The phenotypic ratio of offspring is 3 : 1.

Y -The genotypic ratio of offspring is 1 : 2 : 1

Z -The phenotypes displayed by the allelesTT andTt are similar.

Which of the above statements are true?

What is the probability of producing offspringwith heterozygous genotypes for tongue-rolling?

A 25% B 50%c 75% D 100% (

9 The pedigree for the inheritance of bloodgroups in a family is shown on the next pageJ, K, L, M, N, P O, R and S are the immediatemembers of the family.

Generation I J

Generation llP

Generalion lll

G,UJ

o-

()K

LMN

OR S

Key:

Blood group A

Blood group B

Blood group AB

Blood group O

@@@@

Male

EEE

Female

U

What are the genotypes of individuals K and P

respectively?

TT:TtTt tt

A

B

cD

AA

AA

AO

AO

BB

BO

BO

BB

AXCY

andYonly B XandZonlyand Z only D X,Y and Z

10 Three babies, P, O and R, have the bloodgroups A, AB and O respectively.Three coupleshave the following blood groups:

Couple 1: A and B

Couple 2: B and OCouple 3: AB and O

Which of the following shows the correctcombination of the couples and their respectivebabies?

R

P

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8 The genotypes of a couple are given below

Husband Wife

Parents: Gg x Gg

Key:

G: Ability to roll the tongue, dominant alleleg: lnability to roll the tongue, recessive allele

P

oR

P

oR

P

R

A

B

cD

T

gamete

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K PT t

t

, Couple 1 Couple 2 Couple 3

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( )

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11 Which of the following is a result of genemutation?

A Changes in the chromatidsB Changes in the structure of genesC Changes in the length of chromosomesD Changes in the number of chromosomes

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12 Which of the following is/are the characteristicsof continuous variation?

I lt is controlled by several genes.ll lt is a quantitative variation.lll lt does not have distinct differences.lV lt can be inherited.

A lV onlyB ll and lll onlyC l, ll and lll onlyD ll, lll and lV only

13 The bar charts below show the percentage of a

human population with each type of blood groupand the percentage of a cattle population that arewith or without horns.

% populationo

14 The graph below shows the distribution ofbody mass of a group of students in a school.

Number of students

160

120

40

Mass (kg)30 35

What conclusions can be made from the graph?

I Every individual shows a distinct differencein body mass.

ll Body mass is a continuous variation.lll There are intermediates in the body mass of

the students.IV Body mass is influenced by the

environment.

A I and lll onlyB ll and lV onlyC l, lll and lV onlyD ll, lll and lV only

15 S,I U and V are characteristics in a pair ofidentical twins.

EEUJ

cro

60

50

2010

0 human blood group

% population

without horns

with horns

cattle horns

Which type of variation is shown in eachpopulation?

S - Body weightT - lntelligenceU - Tongue rollingV - Skin colour

60

5040

302010

0

B AB

Continuous

Continuous

Discontinuous

Continuous

Discontinuous

Which characteristics may be different whenthey grow up?

A TandUonlyB S,T and U onlyC S,T and V onlyD S,T, U andV (

A

B

cD

Continuous

uous :

(

Discontinuous Discontin

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'1, l{uman 1""t"" cattle

)

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PAPER 2 Structured and Free-response Auestions

Section A Structured Ouestions

A farmer has three types of plants, O, P and S. Plants O and P produce red flowers while plant S

produces white flowers.The farmer carried out cross-pollination between plant O and plant S. Plants

with red flowers were produced.The farmer also cross-pollinated plant S and plant P in which plants

with both white and red flowers were produced.

(a) Which plant has a heterozygous genotype?(b) (i) Draw a genetic diagram to show the cross between plant S and plant P

(ii) What is the phenotypic ratio of the F, generation?(c) What is the genotype of Plant S?

(d)(i) lf the offspring from the cross between plant O and plant S were self-pollinated, whatwould be the genotypic ratio and phenotypic ratio of the offspring produced?

(ii) Draw a Punnett square to show the results of the cross in (dXi).

(e) What is the name of the inheritance for the genetic cross between the plants O, P and S?

2 The diagram below shows the karyotype of a woman with a genetic disease

lill lill lffi ilt tl,t123

20 21

45

ill flll )ltt l(ll 8l{ lfitilltilt6 7 I 9 10 11 12 13

,lll llt{ t{ll }lll till l{}{14 15 16 17 18 19

8r( ,{r{r{ xx )|l{22 XX

(a) (i) Name the genetic disease.(ii) Give a reason for your answer.

(b) How many autosomes are there in the karyotype of the woman?(c) Describe the karyotype of a woman without a genetic disease.(d) Draw a genetic diagram to show how the sex of an offspring is determined in a family with normal

parents.(e) Explain how the sex of a baby is determined.(f) The diagram below shows a genetic cross between Parent I (heterozygous maize for the seed colour

and seed texture) and Parent ll (homozygous maize which is recessive for both characteristics).Coloured seeds (Y) and smooth seeds (S) are dominant traits while white seeds (y) and wrinkledseeds (s) are recessive traits.

v

S

Parent I Parent ll

v v

X

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Complete the table below by drawing the possible gametes for Parent I and Parent ll. Write thegenotypes and phenotypes of the offspring from the first generation.

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Gamete of Parent I Genotype of firstge4eration

3 Couple X and CoupleY both had their newborn babies on the same day, in the same hospital.The bloodgroups of the parents and the babies are shown in the table below. One day later, couple X made a

report to the hospital claiming that baby X was not their baby.

AB

A o B

0

With the help of a genetic diagram, explain whether the babies were accidentally exchanged.

4 A group of science students collected thirty snails from a garden.The length of each snailb shell wasmeasured and recorded in the table below.

48

39

53

42

23

32

26

44

36

38

54

41

34

37

45

39

44

34

58

40

47

42

35

37

43

49

30

(a) Use the data to complete the table below

21-25 26-30 31-35 36-40 4'.t45 46-50 51-55 56-60

(b) Based on the results in the table, draw a bar chart to show the number of snails against the length ofthe shell.

(c) On the graph, join the midpoints of the bars and name the type of graph obtained.(d) (i) What type of variation is shown by these snails?

(ii) Explain briefly your answer in (d)(i).(iii) Give two other examples of this type of variation.

(e) (i) Suggest one type of factor that can influence this type of variation.(ii) Besides the factor given in (eXi), genetic factors can also cause variation. Give two examples of

genetic factors that can cause variation.

Blood groupBabyYWifeY

Baby XHusband X ,

Length,of,shell {mm)

261

Gamete of Par6nt ll Phenotype ol lirst, generation

B

31

38

50

Number oI snails

Wife X

Husband Y

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5 The graphs below show height variation in a human population and a population of pea plants

Number of Number olindividualstall

short

Heightshort

Graph B

tallHeight

Graph A

(a) (i) Which graph shows the height variation in human?(ii) What types of variation are shown by the two graphs?

(b) Explain briefly what causes the two types of variation to occur.(c) Name three examples of variations in humans that are caused by

(i) genetic factors only.(ii) both genetic and environmental factors.

(d) State three differences between the types of variation in both graphs.

Section B Free-response Ouestions

6 (a) Distinguish the difference between the following terms:(i) phenotype and genotype(ii) homozygote and heterozygote(iii) dominant and recessive alleles

(b)State Mendel's First Law.(c) Explain how the following occurs by using Mendel's First Law.

A farmer has two plants, O and R. Both plants are pure-breeds for red-flowered plants and white-flowered plants respectively. When the alleles are heterozygous, pink-flowered plants are produced.Plant O and plant R are cross-pollinated.The offspring are then self-pollinated to produce the secondgeneration. Using a genetic diagram, explain the inheritance of flower colour for plants O and R.

State the genotype, genotypic ratio and phenotypic ratio in the diagram.

7 (a) A pure-breeding, tall pea plant is crossed with a pure-breeding, dwarf pea plant. All theoffspring produced are tall. Use a genetic diagram to describe the above cross based onMendel's First Law.

(b) The presence of hairs on the stems of a ceftain species of plant is controlled by a pair of alleles.When a pure-breeding plant with hairy stems is crossed with a pure-breeding plant with smoothstems, all the offspring produced have hairy stems. Use a genetic diagram to show a cross thatwould produce offspring with hairy stems and smooth stems in the ratio1 : 1.

(c) Siti has a blood group O. Her father, Ahmad suspects that Siti is not his biological daughterAhmad's blood group is A while his wife's blood group is B.

Study the above case. State your opinion and explain your answer.

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8 (a)A student conducted a survey to study the variation in two characteristics among thestudents in his class.The following observations were obtained.

Based on the information above, write a report to explain the characteristics studied in the survey.(b) Both environmental and genetic factors are responsible for the variations in an organism. Explain

each factor.(c) An identity card has a thumbprint and a photograph of an individual. Explain why this type of identity

card is more effective than one that has either only the thumbprint or the photograph.

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I All the students in the class have different fingerprint patterns - whorl, composite, archand loop. Each pattern can be distinguished easily.

ll All the students show a wide range of heights.The difference in heights between thestudents are not distinct.

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