SF3 answers

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Answers to Science Focus 4 second edition Student Book questions

3.1 Answers

Remembering

1 heredity (potential height), environment (nutrition)

2 characteristics inherited from parents

3 plants that consistently produce offspring the same as the parents

4 a recessive

b dominant

c dominant

d dominant

e recessive

5 deoxyribonucleic acid (DNA)

6 a 46 (2 pairs)

b 2

c 46

7

P1

P2

R W

R RR RW

W WR WW

Understanding

8 a A gene that is not !mas"ed#, it appears in the $%generation& 't is the gene that mas"s a

recessive gene&

b hen both alleles are the same for example, gg or **&

c +he form different genes come in&

d +he physical appearance produced by the genotype&e +he first ne cell formed hen sperm and ova -oin during fertilisation&

9 A gene is a hereditary unit that controls a particular characteristic& *enes determine the physical

features of an organism&

10 .perm and ova contain only one of each type of chromosome (only half of the necessary

chromosomes) therefore, they cannot ma"e a ne organism by themselves&

11 hen a dominant allele is present in a genotype (GGhomo/ygous and *g hetero/ygous) it ill

alays be displayed in the phenotype&

Copyright Pearson Australia 2010 (a division of Pearson Australia Group Pty td! "#$% &' 1 ))2* 1*)1 +


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12 a hen the hetero/ygous genotype displays a patchor" of the homo/ygous parents& hen a

red (RR) co mates ith a hite (WW) co it produces a hetero/ygous (RW) roan (patches of

red and hite) co&

b hen hetero/ygous genes in an offspring blend to produce a different colour to the parents& 'nthe case of snap dragons, a red and hite parent ill produce a pin" offspring&

Applying

13 a haploid

b diploid

c diploid

d haploid

14 a meiosis

b mitosisc mitosis

d mitosis

e meiosis

15

Symbol Description

gg 0omo/ygous genotype

green pods 1henotype

G Dominant allele

Gg 0etero/ygous genotype

g ecessive allele

16 a blac"

b bron

c blac"

d blac"

17 a red

b hite

c parent 2

d 35

e 35



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18 a Hh

b HH,Hh, hH,hh

c long hair, short hair

d 35 long hair, 235 short hair

19 a incomplete dominance

b complete dominance

c complete dominance

Analysing

20 eight

,valuating

21 a

b



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c

d

Creating

22 a

P1

P2

W w

w Ww ww

w Ww ww

b i Ww(hetero/ygous),

ww(homo/ygous recessive)

ii 35 hetero/ygous,

35 homo/ygous recessive

iii 35



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23 a

P1

P2

L L

l Ll Ll

l Ll Ll

b

P1P2

L l

L LL Ll

l Ll ll

c 7%

d 8es, because there is one homo/ygous dominant (LL) and to hetero/ygous dominant (Ll,Ll)

to give offspring ith the long9stem phenotype, and one homo/ygous recessive (ll) to giveoffspring ith the short9stem phenotype& +his means there are three chances out of four of

producing an offspring ith the long9stem phenotype&

24 a blac" (BB), hite (WW), blue (BW)

b

P1

P2

B W

B BB BW

W BW WW

c 235 blac", 35 blue, 235 hite

d +he blue Andalusian fol carries the alleles for both the hite and the blac", so henever it

is crossed ith another blue fol it has a 35 chance of producing a colour other than blue&



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3.1 Practical activities

Pra- 1. /bserving mitosis

Common mistakes

'ncorrect focusing techni:ues may result in bro"en cover slips and slides& 'nstruct students on the use

and care of microscopes and slides&

A videoflex or a digital microscope camera ould be useful for this activity&

Possible results

;sing prepared slides and images of mitosis, students observe the se:uence changes in the nucleus of

an onion root tip cell undergoing mitosis&

Suggested answers

1 Results will vary, but should be similar to Figure 3.1.6.

2 The seo!d stage o" ell divisio! i! mitosis does !ot i!volve hromosomes li!i!g u# i!homologous #airs.

Pra- 2. odelling meiosis

Common mistakes

.oft malleable plasticine ill assist this exercise& 'f the plasticine is too hard, place on paper toel and

microave for a very brief time (too long and it melts)&

Possible results

.tudents construct models to demonstrate the process of meiosis&

Suggested answers1 $eiosis #rodues "our gametes i! males a!d o!e i! "emales. %ight ombi!atio!s o" hromosomes

are #ossible.

2 Whe! li!i!g u# i! homologous #airs, the hromosomes "rom the mother do !ot gather together.

Li&ewise, the hromosomes "rom the "ather do !ot gather together. This mea!s that whe! the

hromosomes se#arate a!d move to the e!ds o" the ell, there is !o way o" #rediti!g whih

hromosomes e!d u# with whih gamete' it is o!ly ertai! that eah hromosome will be

re#rese!ted.

3 $eiosis e""etively #rodues ells with hal" the !umber o" hromosomes.

4 The rossi!g over o" homologous hromosomes was !ot demo!strated i! this model.

Pra- +. odelling inheritan-e

Common mistakes


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Suggested answers

1 (Hetero)ygous* mea!s that the ge!oty#e is made u# o" two di""ere!t alleles.

2 The three ge!oty#es that should be see! are +- RG, +- RR a!d +- GG.

3 /tatistial #atter!s beome more obvious whe! the sam#le is large, so may !ot be see! a"ter seletio!s.

4 /tatistial #atter!s beome more obvious whe! the sam#le is large, so should be see! a"ter 1

seletio!s.

5 a homo)ygous 0 homo)ygous RR 0 GG

b homo)ygous 0 hetero)ygous RR 0 RG or GG 0 RG

3.2 Answers

Remembering1 tongue rolling, right9 or left9 handed, hairline, ear lobe attached or free, albinism, cleft chin,

colour blindness

2

Male

Female

XH Y

XH 2H2H 2H

Xh 2H2h 2h

3 a RRorRr

b rr

4 a green and grey

b ha/el and blac"

5 a height, eye, hair or s"in colour

b albinism, ear lobe attachment or left=right handed



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6

7 a 2

b 22

Understanding

8 a +o2chromosomes are responsible for female characteristics&

b >ales have the genotype ?8&

c +he2chromosome carries more genetic coding than the chromosome&

d .ex9lin"ed diseases occur because the chromosome doesn#t have a matching gene on the2chromosome&

e Diseases such as haemophilia are inherited through females in a family&

9 @oth parents carry a !mas"ed# gene, hich is then passed onto their child&

10 Due to the presence of the dominant allele, a carrier !hides# or mas"s the recessive gene, hich

re:uires to copies to cause the disorder&

11 >ales have only one2chromosome, so it solely determines hether or not the disorder is

present, unli"e females ho can mas" a recessive gene causing a disorder ith its dominant allele

on the other2chromosome&

Applying12 a A

b A

c A@

d @

e @



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13 'f @@ B AA, children are all A@&

'f @ B AA, children are A@ and A&

'f @ B A, children are A@, @, A, &

'f @@ B A, children are A@, @&

14 a @, @@, A@

b @ or A@

15 a 235

b 35

c 'n each of the three affected children, the male gamete (sperm) carried the recessive trait and

fertilised an ovum that also carried the recessive trait&


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Creating

20

Donor

#ecipient

$% $& '% '& $'% $'& (% (&

$%

$&

'%

'&

$'%

$'&

(%

(&

21 a E tongue roller

r E non9tongue roller

P1

P2

r r

r rr rr

r rr rr

b none



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22 a

P1

P2

a a

a aa aa

a aa aa

%5

b

P1P2

a a

A 4a 4a

a aa aa

35

23


Pra- 1. ominant or re-essive

Common mistakes

.tudents may mista"enly believe that -ust because a characteristic is more fre:uent in a population

that it is the dominant characteristic&



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Possible results

Dominant characteristics are usually free ear lobes, no bump on the outer rim of the ear, no gap

beteen the front teeth and little finger bent inards&

Suggested answers1 4!swers will vary de#e!di!g o! whether the stude!ts themselves have these harateristis.

2 4!swers will vary.

Pra- 2. Continuous variation

Common mistakes

>easurement errors&

Possible results

esults sho that height is a continuous variation&

Suggested answers1 The results obtai!ed should show o!ti!uous variatio! withi! the heights !ormal "or this age

grou#.

2 The results obtai!ed are !ot re#rese!tative o" the e!tire #o#ulatio! beause they sam#le o!ly a

!arrow ba!d o" ages. 5e#e!di!g o! the shool, they may also be re#rese!tative o" o!e #artiular

ge!der or eth!iity o!ly.

3 The average height o" boys i! ear will ge!erally be greater tha! that o" girls. 7! ear 8,

however, the results may be o##osite, as girls te!d to go through #uberty be"ore boys.

Pra- +. 3egetable babies

Common mistakes

+he vegetables in this activity ill ma"e better appendages if the vegetables are crisp& Fut the

vegetables -ust before starting the activity&

Possible results

.tudents construct different phenotype vegetable babies based on dominant and recessive alleles&

Suggested answers

1

Feet F f

f F" ""

f F" ""

$rms a a

A 4a 4a

A 4a 4a

)yes E e

e %e ee

e %e ee

2 "eet9 +- arrot, +- #ars!i#'

arms9 1- short elery sti&'

eyes9 +- #eas, +- sulta!as



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3 +-

4 Results will vary.



3.3 Answers

Remembering

1 a double helix

b sugar, phosphate

c nitrogen bases (adenine, thymine, cytosine, guanine)

2 A7 adenine, +7 thymine, F7 cytosine, *7 guanine

3 a cytosine

b adenine

4 atson and Fric" (Games atson and $rancis Fric") and they shared the Nobel 1ri/e ith

>aurice il"ins&

5 H&35

6 hen it produces a change in the gene or chromosome that leads to a ne species, such as the

*ranny .mith apple&

7 a sic"le9cell anaemia

b Don syndrome

Understanding

8 a A set of three bases is called a codon&

b A mutation is a spontaneous change in a gene or chromosome that may alter a characteristic

for hich it codes&

c A mutation9causing agent&

9 A codon is a set of three bases that contains the instructions to form an amino acid& +hese amino

acids -oin to form chains that ma"e proteins& +hese proteins, in turn, determine the characteristics

of individuals&

10 nitrogen base, codon, DNA strand, cell

11 hen genes become active and are expressed that is, the characteristic they code for appears, it

is referred to as gene expression&

12 +he mutation must be present in the sex cells (gametes7 ova and sperm) to be inherited by the

next generation&



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13

14 >utations allo for genetic variation, hich means that individuals may possess desirable traits

that are advantageous& +his increases their chances of survival&

Applying

15 ;I radiation, ben/ene, asbestos

16 a *FF+A++F*A+

b .tudent responses ill vary& An example is7 *FFAA++F*A+

c 't changes the amino acid produced and, in turn, the protein and the gene it codes for&

Analysing

17 2 B E 6 bases

18 a 2%

b girl

,valuating

19 ;I radiation is a mutagen& hen cells, such as s"in cells, are exposed to mutagens they cause a

mutation (alteration) in the genetic ma"e9up of an individual&20 DNA needs to undergo replication so that it is able to ma"e copies of cells undergoing mitosis

during groth and repair& 'f DNA cannot replicate, the organism dies&



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Creating

21


Pra- 1. odelling %A

Common mistakes

.tudent9designed experiments should be assessed by the teacher for feasibility before they are carried

out&

Possible results.tudents construct a model of DNA&

Suggested answers

/tude!t desig!.

Pra- 2. ,4tra-ting %A

Common mistakes

+o achieve impressive strands of DNA it is essential to stir very gently&

Possible results

+hin strands of DNA are extracted from a sample of heatgerm&Suggested answers

1 4!swers will vary, but the 5:4 should a##ear as thi! threads.

2 a 5eterge!t brea&s dow! ell walls a!d !ulear membra!es to e;#ose the 5:4.

b %tha!ol #rei#itates the 5:4, ma&i!g it visible.

3 $ai!tai!i!g the tem#erature betwee! + a!d 6


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3.4 Answers

Remembering

1 "eeping the seeds from only the best plants for next year#s crop crossing ith a related plantgenus to produce a ne plant that possesses desirable traits from both parent plants

2 +he protein "ills the ma-or pest of cotton (Heliothiscaterpillar) hen the caterpillar eats the

leaves&

3 en/ymes

4 sic"le9cell anaemia, cystic fibrosis

5 DNA fingerprinting to solve criminal cases therapeutic cloning to gro cells for repair of

damaged cells

6 a HH&H5

b 2 genesc 26 proteins

Understanding

7 a >anipulating DNA to change the genes ithin an organism& $or example, insulin for use by

diabetics is produced in large :uantities by bacteria& +he DNA se:uence of insulin is inserted

into plasmids that have been removed from bacteria& +he altered plasmids are then put bac"

into the bacteria& n reproduction, these bacteria :uic"ly produce multiple copies of the

!foreign# DNA that as spliced into them, in this case, insulin&

b +he altering of a plant#s gene se:uence& $or example, genetically modified cotton has the

bacteria @acillus thuringiensis inserted to help the cotton produce a protein that "ills its ma-orpest, 0eliothis caterpillar&

c 'nsertion of modified genes directly into animal cells& $or example, insertion of the -elly fish

gene into mice to code for *$1 (green fluorescent protein)&

8 a 1lasmids are circular pieces of DNA that occur naturally in bacterial cells&

b


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10 DNA fingerprinting relies on the fact that everyone has a uni:ue se:uence of bases in their DNA

found in every cell of their body&

Applying

11 ice that produces more seeds dairy cattle that produce more mil"&

12 .tudents# responses ill vary&

Analysing

13 Floning is the process in hich a single cell is gron to produce a ne individual, hereas

therapeutic cloning is the insertion of an individual#s DNA into eggs to produce stem cells& +hese

stem cells are then manipulated to produce any type of cell re:uired by the patient to repair

damaged tissue&

,valuating14 .tem cells have the same DNA as the rest of the cells in the body, so the heart ill not be re-ected

and the patient may have a faster and easier recovery&

15 a plan a healthier lifestyle (food and exercise)

b 'f you are prone to illness, a prospective employer might not hire you or may not promote

you& 8our medical bills and insurance premiums could be higher or you could be refused

medical insurance because you could become costly to the insurer&

c .tudents# responses ill vary&

16 a *ene cell therapy involves removing the genetic material from some body cells, manipulating

it and reinserting it into the same person&

b +o overcome diseases, such as cancer, and to prevent the inheritance of diseases such as

haemophilia&

17 +he protein may "ill other insects that feed on the cotton& 1redators of the caterpillar may also be

affected&



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18

Creating


20 a .tudents# responses ill vary&

b .tudents# responses ill vary&



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Chapter answers

Remembering

1

*erm Description

>eiosis Fell division producing gametes

>itosis Fell division producing daughter cells identical to the parent cell

Diploid A cell having to of each type of chromosome

0aploid A cell having one of each type of chromosome

*ene A hereditary unit

DNA +he chemical that carries the genetic code&

2 double helix

3 uprights7 alternating sugar and phosphate units

rungs7 nitrogen bases (adenine, thymine, guanine, cytosine)



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4

*erm Description

Fodon A se:uence of three bases that codes for an amino acid

*enetic map .hos positions of genes on chromosomes

1lasmid A circular piece of DNA

*ene probe A small piece of DNA that recognises a gene

ecombinant DNA A molecule containing DNA from to organisms

+ransgenic organism An organism ith a ne gene

>utagen Fauses a spontaneous change in a gene or chromosome

Understanding

5 0eredity7 the set of characteristics inherited from your parents the environment7 a diverse set of

factors that act on the organism throughout its life, such as pollutants and :uality of food&

6 A gene is a hereditary unit that controls a particular characteristic& *enes are made of a chemical

called DNA& *enes are located on chromosomes&

7 DNA un/ips and ma"es an exact copy of each strand by matching each base ith its

complementary base&

8 a >utations can cause cells to mutate, forming cancerous tumours in an individual, but have no

effect on the species, unless they occur in the sex cells (sperm or egg cells) or in the /ygote

that forms on fertilisation&

b A change in the base se:uence of DNA ithin sex cells (sperm or ova) ill not affect the

individual& 0oever, if this change is passed onto their offspring, the ne base se:uence

could code for a dysfunctional=harmful gene that could lead to a disease or a non9desirable

trait&

c .ometimes, mutations can lead to the creation of a different species e&g& *ranny smith apples&

9 a *ene technology is the manipulation of DNA to change the genes ithin an organism&

b Floning is the process in hich a single cell is gron to produce a ne individual ithout the

need for fertilisation&

c *ene cell therapy involves removing the genetic material from some body cells, manipulating

it and reinserting it into the same person&

Applying




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11 a *enes come in different forms& 'n this example, there are to alleles for stem lengthJone

allele codes for long stem (L) and the other codes for short stem (l)&

b +he possible combinations of to alleles together determine a genotype e&g& to long stem

alleles (LL), to short stem alleles (ll) or one of each allele (Ll)&c +he appearance produced by the genotype is the phenotype e&g& the plant ill have long (Ll

orLL) or short (ll) stems&

d 0omo/ygous is hen both alleles are the same e&g&LLor ll&

e 0etero/ygous is hen both alleles are different e&g& (Ll)&

Analysing

12 a both

b mitosis

c meiosisd meiosis

e mitosis

13 a RrBrr

b

R r

r Rr rr

r Rr rr

c 35 hetero/ygous, 35 homo/ygous recessive

d red eyes, hite eyes

e 35 red eyes, 35 hite eyes

14 Fharacteristics that are clearly defined, such as ear lobe attachment and albinism, are

discontinuous& Fontinuous variation refers to characteristics that have a range of possible

outcomes, such as eye colour and height&

15 a 't is not possible for to non9tasters to have three children ho are tasters, because both

parents must each have a recessive gene&

b @oth parents must be hetero/ygous (Tt) tasters for them to produce one non9taster and three

taster children&

16

$ '

( A @



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( A @

+he child ill either be blood group A or @&

17 a i 2$

ii 2m2m

iii 2m

b recessive

c

XM Xm

XM 2$2$ 2m2$

Y 2$ 2m

+here is a 35 chance of the boy having the disease&

,valuating

18 a HH&H 5

b 8es, identical tins come from the same fertilised egg and so ill have the same total DNA

base se:uence&19 a *> foods may be more nutritious and "eep better than conventional foods, may be pest

resistant and tolerate harsher environmental conditions&

b *> foods that contain pesticide9resistant genes don#t necessarily solve the orld#s food

shortage problems, they may pass on the resistant gene to other plants creating !supereeds#,

and insects that are not pests may be "illed&

Creating

20 a

R W

R RR RW

R RR RW

2 red7 hite7 2 pin"

b



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R W

R RR RW

W RW WW

% red7 % hite7 2 pin"

21 a RrB rr

b

R r

r Rr rr

r Rr rr

c Rr, rr

d 35Rr, 35 rr

e tongue rolling and non9tongue rolling 35 tongue rolling and 35 non9tongue rolling

22 a No, they are not albino&

b

A a

A 44 4a

a 4a aa

c K

23 a

Xn Xn

XN 2:2! 2:2!



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Y 2! 2!

b +he husband carries the dominant gene because he isn#t colour blind, therefore !mas"ing# the

colour9blind gene in the daughters ho are carriers&

c All their sons ill be affected&

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