Download La génétique - Ms McRae`s Science

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EST
Questions 1–17, A and B
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CHAPTER 11
Date: ___________
ANSWER KEY
Genetics
Checkup
1 FACTORS RESPONSIBLE FOR CHARACTER TRAITS AMONG LIVING ORGANISMS (pp. 350–358)
1. Look at the two cells opposite.
a) What is the form of the DNA in cell 1?
The DNA is in the form of chromosomes.
b) What is the form of the DNA in cell 2?
The DNA is in the form of chromatin.
2. All members of the same species have an
identical number of chromosomes in their
cells.
a) In total, how many chromosomes do humans have in most of their cells?
46 chromosomes
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b) What is the name of a representation of chromosomes in ordered pairs?
A karyotype
c) What is the name of the DNA segment that forms chromosomes and contains information
for making proteins?
A gene
d) Give three examples of character traits that are expressed because of the proteins our
bodies manufacture.
Answers will vary. Example: hair colour, eye colour and nose length.
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CHAPTER 11
Genetics
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3. Look at the illustration opposite representing DNA in a simplified form.
Use the information in the illustration to answer the following questions.
(See the colour illustration in the student book, p. 374.)
a) Name the nitrogenous base represented by the following shape:
(Write its full name.)
Thymine
b) Name the nitrogenous base represented by the following shape:
(Write its full name.)
Guanine
c) Name the nitrogenous base represented by the following shape:
(Write its full name.)
Adenine
d) Name the nitrogenous base represented by the following shape:
(Write its full name.)
Cytosine
e) If
represents a phosphate group, what does
represent?
A sugar, deoxyribose
4. We know that letters are the building blocks for forming words.
a) What are the building blocks for making proteins called?
Amino acids
b) The alphabet contains 26 letters. How many different building blocks can be used to make
proteins?
c) True or false? The building blocks for forming proteins in bacteria and fungi are different
from those we use to make our own proteins. Explain your answer.
False. The same 20 amino acids enter into the composition of proteins in all living species.
5. The growth hormone stimulates growth and metabolism, among other things. This molecule is a
sequence of 191 amino acids.
a) Why can this hormone be identified as a protein?
Because it is a molecule formed by a sequence of amino acids.
b) The growth hormone controls functions and carries messages in our bodies. Name four
other roles proteins can play in the human body.
Support, transport of substances, immunity and catalysis
CHAPTER 11
Genetics
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20
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Date: ___________
6. Protein synthesis occurs as a result of certain processes in a cell. Place the following steps in
the correct order.
A. An mRNA is formed.
B. tRNA bond with the mRNA. Amino acids are joined together.
C. The synthesized protein detaches itself from the ribosome and folds into its final shape.
D. The two strands of DNA separate.
E. An mRNA attaches itself to a ribosome.
D, A, E, B, C
7. Does each of the following statements refer to DNA or RNA?
a) My full name is ribonucleic acid.
RNA
b) The sugar I contain is deoxyribose.
DNA
c) I do not contain any thymine.
RNA
d) Most of the time, I am a molecule made up of two complementary strands.
DNA
e) One of my nitrogenous bases is uracil.
RNA
f) I act as a messenger during protein synthesis.
RNA
2 PRINCIPLES OF HEREDITY (pp. 358–369)
8. Fruit flies are often used for experiments in genetics. To reproduce, sperm from the male flies
fertilize the ova of the female flies, which then lay eggs. Why can fruit flies be said to
reproduce by crossbreeding?
Because to reproduce, a male fruit fly and a female fruit fly exchange gametes. Crossbreeding, by
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definition, is the exchange of gametes between two different individuals.
9. Among the character traits studied in fruit flies is the
length of their wings. Two shapes are possible for this
character trait: normal wings and miniature wings.
If two pure-line individuals with normal wings are
crossbred, what proportion of the offspring will also have
normal wings? Explain your answer.
One hundred percent of the fruit flies obtained will have
1
2
normal wings because when two pure-line individuals are
crossbred, all of their offspring carry the same gene for
1. Fruit fly with miniature wings
2. Fruit fly with normal wings
wing length.
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CHAPTER 11
Genetics
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10. When a fruit fly has an allele for normal wings and an allele for miniature wings, its phenotype
for this character trait is “normal-winged.”
a) Is this individual homozygous or heterozygous for the character trait? Explain your answer.
It is a heterozygous individual because it has two different alleles for the character trait.
b) Which of the two alleles is dominant?
The allele for normal wings
c) Which of the two alleles is recessive?
The allele for miniature wings
d) What would be the possible genotype or genotypes for a fruit fly with normal wings?
NN or Nn
e) What would be the possible genotype or genotypes for a fruit fly with miniature wings?
nn
a) the tendency to tan in the sun
Not hereditary
b) eye colour
Hereditary
c) hair length
Not hereditary
d) the presence of a scar
Not hereditary
e) hand size
Not hereditary
f) occurrence of cystic fibrosis
Hereditary
g) infection with the flu
Not hereditary
12. In guinea pigs, the allele for black-coloured fur (B) is dominant over the allele that produces
white fur (b). A pure-line individual with black fur is crossbred with an individual with white fur.
What is the probability that a black-haired offspring from this cross will be heterozygous for
the character trait? Support your answer with a Punnett square.
The probability that a black-haired offspring is heterozygous for the character trait is 100 percent, as
shown by the Punnett square below.
Parents
Black fur
White fur
BB
bb
Genotype
Possible
gametes
CHAPTER 11
Genetics
B
B
b
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b
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11. Is each of the following character traits hereditary or not?
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Date: ___________
Punnett square
b
b
B
Bb
black
Bb
black
B
Bb
black
Bb
black
13. In rabbits, the allele for black hair (B) is dominant over the allele for tan-coloured hair (b).
Second, the allele for short hair (S) is dominant over the allele for long hair (s). A long-haired
male rabbit that is heterozygous for hair colour is crossbred with a black short-haired female
that is homozygous for both character traits. Using a Punnett square:
a) Specify the possible genotype or genotypes of the offspring from this crossbreeding.
BBSs and BbSs, or SsBB and SsBb
b) Specify the possible phenotype or phenotypes of the offspring from this crossbreeding.
The only possible phenotype is short black hair.
Parents
Long black hair
Short black hair
ssBb
SSBB
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Genotype
Possible
gametes
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sB
sB
SB
SB
sb
sb
SB
SB
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Genetics
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SB
Punnett square
SB
SB
Date: ___________
SB
sB
SsBB
SsBB
SsBB
SsBB
short black short black short black short black
sB
SsBB
SsBB
SsBB
SsBB
short black short black short black short black
sb
SsBb
SsBb
SsBb
SsBb
short black short black short black short black
sb
SsBb
SsBb
SsBb
SsBb
short black short black short black short black
a) a purple stem and yellow fruit
30
b) a purple stem and red fruit
90
c) a green stem and yellow fruit
10
d) a green stem and red fruit
30
Parents
Genotype
CHAPTER 11
Genetics
Purple stem, red fruit
Purple stem, red fruit
PpRr
PpRr
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14. In tomatoes, the allele for purple stems (P) is dominant over the allele for green stems (p).
Second, the allele for red fruit (R) is dominant over the allele for yellow fruit (r). Two tomato
plants that are heterozygous for the two character traits are crossbred. Supposing that 160
new plants are obtained, use a Punnett square to show how many of them, in theory, will
have:
Name: _______________________________________
Possible
gametes
Group: ______________
Date: ___________
PR
Pr
PR
Pr
pR
pr
pR
pr
PR
Pr
pR
pr
PR
PPRR
purple
red
PPRr
purple
red
PpRR
purple
red
PpRr
purple
red
Pr
PPRr
purple
red
PPrr
purple
yellow
PpRr
purple
red
Pprr
purple
yellow
pR
PpRR
purple
red
PpRr
purple
red
ppRR
green
red
ppRr
green
red
pr
PpRr
purple
red
Pprr
purple
yellow
ppRr
green
red
pprr
green
yellow
Punnett square
3 CLONING (pp. 369–373)
15. Why can identical twins be described as clones of each other?
Because identical twins have the same genes, and clones, by definition, are genetic copies of an
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individual.
16. Distinguish between natural cloning and artificial cloning. Give an example of each.
Answers will vary. Example: Natural cloning takes place when individuals reproduce asexually. For
example, a raspberry bush can produce other raspberry bushes by root suckering, a form of asexual
reproduction.
Artificial cloning requires human intervention. For example, Starbuck the bull was cloned to produce
Starbuck II.
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Genetics
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17. Look at the figures below.
Tadpole
Frog spawn
Fertilization
a) Which of the two figures illustrates cloning? Explain your answer.
Figure 1, because the two tadpoles illustrated will be genetically identical.
b) Is this natural or artificial cloning? Explain your answer.
It is artificial cloning because human intervention is required.
A. Read the following text and then answer the questions below.
In Canada, one in 10 000 people suffers from Huntington’s chorea, which causes neurons in
the brain to decay. Patients typically have difficulty controlling their movements; eventually
they become completely immobile and die.
On our fourth pair of chromosomes, we all have a gene called the Huntington gene. It
contains instructions for synthesizing a protein called huntingtin, whose exact function in
our neurons remains unexplained. It is known, however, that a particular amino acid is
repeated in its structure. If this amino acid is repeated fewer than 35 times in a row, the
carrier does not normally suffer from Huntington’s chorea. When there is a sequence with
more than 35 repetitions, the person has the disease.
Unfortunately, people who carry the allele causing Huntington’s chorea in their DNA are
inevitably afflicted with the disease. The first symptoms of this hereditary disease usually appear
between the ages of 30 and 45 years, so affected adults may already be parents before realizing
that they are sick.
a) Which mRNA has the longer nucleotide sequence: the one copied from the mutant allele
associated with Huntington’s chorea or the one copied from the normal allele? Explain your
answer.
The mRNA copied from the allele causing Huntington’s chorea, because the protein synthesized
from this allele contains more amino acids. It therefore takes more nucleotides to copy the entire
chain.
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Genetics
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REVIEW QUESTIONS
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b) Which of the two alleles is dominant: the one that causes the disease or the one that does
not? Explain your answer.
The allele that causes the disease is dominant because people who carry this allele in their DNA
are inevitably afflicted with the disease. The allele is expressed even if a person’s other allele for
the same character trait is different.
c) What are the possible genotypes for a person with this disease?
Hh or HH
d) If the father of a child is heterozygous for this character trait and the mother does not have
Huntington’s chorea, what is the probability that the child will have the disease? You can
use a Punnett square to answer this question.
The probability that the child will have the disease is 50 percent.
Parents
Huntington’s chorea
Unafflicted
Hh
hh
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Genotype
Possible
gametes
H
h
h
h
Punnett square
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h
h
H
Hh
afflicted
Hh
afflicted
h
hh
unafflicted
hh
unafflicted
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CHAPTER 11
Genetics
Name: _______________________________________
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Date: ___________
B. Prepare your own summary of Chapter 11 by building a concept map.
See the Concept maps section in Guide B.
Follow-up
1. Why were researchers interested in the nucleotide sequence of the gene responsible for taxol
synthesis?
Answers will vary. Examples: Because researchers could then introduce the gene into microorganisms
so that they would produce taxol.
– If Pacific yews were to disappear, researchers would be familiar with the gene and could try to use it
to synthesize taxol artificially.
2. In Québec, phytotherapy, which is the treatment of diseases with plants, is becoming
increasingly popular. Explain why protecting genetic diversity is important for this industry.
Answers will vary. Example: The better we protect the genetic heritage of a wide variety of plants, the
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greater the possibilities of developing new plant-based treatments for certain diseases or ailments.
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Genetics
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