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1516 –  Biology

Term 2 Week 10

Week 10 (Feb. 28 –  Mar. 03)

AMS : 11019

11019 AMS SQ answers

1. The gene controlling blood group has multiple alleles. What three alleles control the ABO

blood groups?

IA

, IB

, and IO

or (i)

2. Define codominance and give an example.

Codominance is a condition in which two alleles are equally expressed in the phenotype of a

heterozygous individual. An example is the ABO blood groups, where human beings with

 blood group AB (genotype IAIB) have A and B antigens on their RBC’s, equally expressed by

the two alleles IA (produces antigen A) and I

B (produces antigen B).

3*. Define incomplete dominance and give an example.

Incomplete dominance is a condition in which a recessive allele is not completely masked by a

dominant allele. Both alleles are expressed to some degree. Sickle cell anemia is an example of

incomplete dominance because the heterozygote (HbAHB

S) shows mild signs of the disease.

4*. a) Complete the diagram below, showing inheritance of sex in human with reference

to XX and XY, the sex chromosomes in humans.

Parents’ phenotype male   female

Parents’ genotype __  _XY___   XX

Gametes _X__ , _Y__ X , X

F1 genotypes __XX__ __XX__ _XY__ _XY_

Ratio of male to female in F1 generation is: 1 male: 1 female

b) Do boys inherit their Y chromosome from their mother or their father? Explain.

Boys inherit their Y chromosome from their father, because the father can give his child

either an X or a Y chromosome while the mother can only give an X chromosome.

5*. a) What is a sex-linked characteristic? An example is colour blindness in humans.

A sex-linked characteristic is a trait in which the gene responsible is located on the sex

chromosome. This makes its more common in one sex than in the other.

b) Draw a genetic diagram to show the transmission of colour blindness in humans.

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Let C = normal vision c = colour blind

Male is colour blind with one recessive allele eg. XcY

Female is a carrier i.e., XCX

c with one recessive allele

Female is colour blind, only if she has 2 recessive alleles XcX

c 

Parent phenotype Normal male   Carrier female

Parent genotype XCY X

CX

c 

Gametes XC  Y X

CX

c 

Fertilization

Offspring genotype XCX

C  X

CX

c  X

CY X

cY

Offspring phenotype: normal vision female-normal vision female -normal vision male-colour blind

male

5*. Explain mutations and their characteristics.

A mutation is a spontaneous change in the genetic material (gene or chromosome) of a cell,

resulting sometimes in the disruption of the function of genes or chromosomes. Mutations can

occur during chromosomal replication. May be detected in the fetus by amniocentesis. They

cause varying genetic and chromosomal disorders.

6*. How does Down’s syndrome arise in humans? 

Down’s syndrome is an example of chromosome mutation which occurs when there is one

extra copy of chromosome 21. The extra chromosome is usually present in an ovum (due to

errors in meiosis) and after fertilization is passed into every cell of the developing child. This is

more common in older women.

7. Give one example of a gene mutation. Explain.

Sickle cell anemia occurs when a single gene involved in hemoglobin synthesis is defective.

 Normal haemoglobin protein and defective haemoglobin protein differs only in one of theiramino acid component.

8. Give one example of a human chromosome mutation.

Down’s syndrome . An extra chromosome 21 making up the total to be 47.

9. a) How is it possible for two healthy adults to produce a child with a genetic defect?

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It is possible for two healthy adults who are heterozygous (carriers) for the same

mutation which is recessive to produce a child with a genetic defect.

 b) Probability of two carriers producing a child with a genetic defect is ¼ or 25%

10. a) Give examples of mutagens.

Ultra violet light , X-rays, chlorine, atomic radiation are factors that increase the chanceof mutation. 

b) Is use of sound waves in early pregnancy a risk for mutation?

 No, ultrasound waves used to monitor the growth of the fetus in mother’s uterus is safe. 

11. What is the function of restriction enzymes in genetic engineering?

Restriction enzymes are specific enzymes used to cut genes out of chromosomes.

12. What is recombinant DNA?

Recombinant DNA is the DNA that is formed from more than one species.

13. Name two types of vectors that are used to transmit DNA into a host cell.

Virus or plasmid (present in bacteria)

14*. Name four applications of genetic engineering. Refer to HQ SQ 9(a & b) as well.

Gene therapy (treatment of inherited disorders), genetically modified plants (improved crops),

manufacture of hormones eg. insulin, genetically modified animals (production of vaccines)

15. In a table form, summarize the different blood group genotypes and their corresponding

phenotypes.

Genotype Phenotype (blood group)

I I or I i A

I I or I i B

I I AB

ii O

16. a) Explain what sickle cell trait is.

It is a condition in which a person has one normal allele of the hemoglobin gene (Hb

A

)and one abnormal (sickle) hemoglobin allele (Hb

S). A person heterozygous for this

condition is referred to as a carrier (HbAHb

S).

b) State the genotype for the condition, sickle cell trait.

HbAHb

S 

NB: phenotype is sickle cell trait

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c) What is one advantage of sickle cell trait?

It gives immunity to malaria.

d) State the genotype for normal hemoglobin.

HbAHb

A 

17. Explain what genetic engineering is.

Scientists are able to cut a single gene from a chromosome from one species and insert it in the

chromosome in another species. This is termed genetic engineering.

18. a) What are the symptoms of sickle cell anemia?

  Distortion of red blood cells (sickle-shaped RBCs)

  Blockage of capillaries by abnormal shaped red blood cells, causing severe pain

and anemia

b) What causes sickle cell anemia / disease?

The recessive allele (HbS) in the homozygous state Hb

SHb

S causes sickle cell anemia in

the blood.

19. What is a karyotype? How is it prepared?

A karyotype is a photograph of the human chromosomes. The chromosomes in an actively

dividing cell are photographed and then the photograph is cut up so that homologous pairs

could be aligned. Text pg.134

20. Is it possible for parents., both of blood group B to have a child with blood group O?Explain your answer with the help of a genetic diagram.

Blood group B has two possible genotypes IBIB or I

Bi. If both the parents have genotype I

Bi,

then both can contribute an i allele and produce a child with blood group O (genotype ii)

Parents’ phenotype Blood group B × Blood group B

Parents’ genotype  IBi × I

Bi

Gametes IB  i I

B  i

F1 genotype IB I

B  I

Bi I

Bi ii

F1 phenotype 75% blood group B, 25% blood group O

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21. How are ligase enzymes used in genetic engineering?

The desired gene isolated from one species, is inserted into the DNA of a vector (plasmid) with

the help of ligase enzymes to form recombinant DNA. Both the DNA of the gene and the

vector have complementary sticky ends which enable them to come together. Ligase enzymesare used to seal the opened up plasmid and isolated gene.

22. Explain the significance of human insulin gene being put into bacteria using process of

genetic engineering?

-Genes tell cells to make proteins.

-Human insulin gene tells the human pancreatic cells (Islets of Langerhans) to make the

hormone insulin (Gene code is universal)

-Most insulin used to treat diabetics comes from bacteria that have been genetically engineered

to contain the human gene for insulin

-Genetically modified bacteria multiply rapidly, producing insulin identical to human insulin.

23*. What are some of the concerns about the use of genetic engineering technology?

  Risk of native species becoming endangered if genetically modified species are allowed

to escape.

  Risk of some species becoming extinct if vectors escape and transmit genes into wild

species that outcompete competitor species (species extinction)

  Difficulty treating contagious diseases if vectors carrying antibiotic resistance genes

escape and passing it onto pathogens.

  Danger posed by foreign genes in food (health risks)

  Moral issues created by transferring genes from one species to another and going

against nature.

  Ethical issues when dealing with larger animals or humans

24. 2 heterozygous individuals for a certain trait gives what sort of a genotypic ratio?

1 homozygous dominant : 2 heterozygous dominant : 1 homozygous recessive, i.e. 1:2:1

Eg. Tt  Tt (T = tall, t = dwarf)

1 TT : 2Tt : 1 tt

25. List the correct sequence for manufacturing insulin by genetic engineering.

1. The gene is identified

2. The gene is cut out of the chromosome using restriction enzymes

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3. The gene is inserted into the DNA of a vector eg. plasmid

4. The vector carries the gene into a new host cell.

5. The host cell expresses the new gene in its phenotype

26. Genetic counselling can assist in regulating the spread of harmful genes. When is a

genetic counselor consulted?

Before starting / increasing a family, the following people are advised to seek counselling.

i)  Anyone suffering from a genetic disorder

ii)  Anyone has a family history of genetic disorder

iii)  Anyone marrying a relative

iv)  Anyone already has a child with genetic disorder

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Homework : BMH29-WRCC

BMH29 HW SQ-answers

1. What does the term codominance mean? Give an example.

It means that two alleles are equally expressed in the phenotype of a heterozygous individual.

Eg. ABO blood groups

2. Identify the type of inheritance where a recessive allele is not completely masked by a 

dominant allele, resulting in three phenotypes. Give an example. 

Incomplete dominance. Eg. sickle-cell anemia

3. a) Identify the type of antigens found on the RBCs of people with genotypes:

i) IAI

Oantigen A

ii) IBI

Oantigen B

 

iii) I

O

I

O

no antigenb) Name the alleles in blood group inheritance and indicate the dominant and

recessive alleles.

IA, I

B and i

IA and I

B are alleles codominant and the i allele is recessive to both I

A and I

B 

4. a) Determine the blood groups of parents having children with blood A and Blood

group O.

Blood groups A and O

b) Is it possible for parents having blood groups AB and O to have a child with blood

group O? Explain.

 No, because the parent with blood group AB will either give an IA allele or I

B allele (not

IO allele).

c) What are the possible genotypes for blood groups A, B and O?

Phenotype (blood group) Genotype

A I I or I I

B I I I I

O ii

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5. a) Why does the mother not determine the gender of her children?

Gender in humans is determined by sex chromosomes. The mother (genotype : XX)

gives her children X chromosomes only while the father (genotype: XY) gives either an

X or Y chromosome.b)* Which sex chromosome is only inherited from the father?

Y chromosome. X chromosome can come from the mother or father.

6. What are mutations?

Spontaneous changes in the genetic material (gene or chromosome) of a cell. Mutations

occurring during mitosis may affect individual, not his offspring, while mutations occurring

during meiosis (in gametes) are passed on to the offspring.

7. What is the effect of X-rays, Ultra violet rays, ionizing radiation, atomic radiation,

gamma rays and chemicals, eg. chlorine on cell?

They all increase the chance of mutations they are all mutagens

8. What type of mutations cause Down’s syndrome and sickle cell anemia? 

Down’s syndrome is caused by a chromosome mutation, while sickle cell anemia is caused by a

gene mutation.

9. a) Define genetic engineering.

The process of changing the genetic material of an organism by removing, changing or

inserting individual genes into the organism.

b) State examples of genetic engineering.

i. the insertion of human genes into bacteria to produce human insulin

ii. the insertion of genes into crop plants to produce plants resistance to herbicides

(weed killers)

iii. the insertion of genes into crop plants to produce plants resistant to insect pests

iv. the insertion of genes into crop plants to produce additional vitamins.

10. a) Why are resistance to malaria and inheritance of sickle cell trait notapplications of genetic engineering?

Genetic engineering involves inserting a gene from one species into the chromosome of

another species, which does not apply to sickle cell trait or malaria. The inheritance of

sickle cell trait is caused by a spontaneous change in the genetic material of the cell,

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resulting in the formation of a mutant allele HBS. This trait gives rise to a defective

hemoglobin protein.

 b) List ways in which genetically engineered bacteria have been used.

-Producing insulin for treating diabetics

-Manufacturing blood clotting factor VIII for treating hemophiliacs who otherwise can bleed to death.

11. Give an example of a hereditary condition that is caused by a change in the structure of

the gene that is involved in hemoglobin synthesis, leading to the production of an

abnormal hemoglobin protein.

Sickle cell anemia

12*. Describe the process of inserting human insulin genes into bacteria using genetic

engineering. Refer to Text pg. 150-151 Q.4

  DNA making up human gene is identified

  The gene is cut out of the chromosome using restriction enzymes, resulting in a segment

with sticky ends

  Bacterial plasmid (DNA) are opened using the same restriction enzymes used to cut

desired gene and this action produces complementary sticky ends

  The gene is inserted into the opened up plasmid and sealed using ligase enzyme. A

recombinant plasmid (recombinant DNA) forms.

  Recombinant plasmid (vector) is reinserted into bacterial cells (host cells)

  Bacteria containing desired gene are selected and cultured in a fermenter under

optimum pH, temperature and nutrient levels to provide a large population that

 produces the desired gene product, insulin.

13. a)* Why are bacteria useful for genetic engineering?

They can make complex molecules and they reproduce rapidly, thus enabling useful

 products eg. insulin and blood clotting factor VIII, to be made in large quantities

quickly.

b)* State reasons why bacteria are useful and are accepted for use in genetic

engineering.

i. Cheap, easily available to culture

ii. Lack of ethical concerns for their manipulation and growth

iii. Genetic code is shared with all other organisms

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iv. Plasmids are available to serve as vectors

14*. See Text pg.142-143 Level M Biology 2

a) What is DNA?

Deoxyribonucleic acid. Chromosomes and genes are made of DNA.

b) Name the subunit of DNA. Nucleotide

c) i. How many different DNA nucleotides are there?

There are 4 different nucleotides because there are four different bases.

ii. Name the four bases

Adenine (A), Guanine (G), Cytosine (C), Thymine (T)

15*. DNA molecules consist of several different bases which are connected in a long sequence. 

What is the significance of this segment of DNA with the different nucleotides in a sequence?

The sequence in DNA carries the message of a gene. Different genes are comprised of different

sequences of bases.

16*. What is a gene with reference to a DNA?

A gene is a section of DNA that codes for one protein.( Protein may be structural eg. collagen

or functional eg. enzyme or hormone.)

17*. There are about 20 amino acids and hundreds or thousands may be present in one

protein. Proteins are made by linking amino acid molecules at the site of the ribosomes in

the cell.

a) What controls the synthesis of proteins?

Proteins are made according to instructions present in the DNA molecule in the nucleus

of a cell.

b) In what form are the instructions in the nucleus of the cell?

Instructions are in the form of a sequence of bases in the DNA segment. A row of 3

 bases codes for one amino acid. This means a row of 30 bases will code for 10 amino

acids.

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18. The table shows the codes for some of the amino acids found in human proteins.

ALANINE GCC

CYSTEINE ACA

GLYCINE CCC

HISTIDINE GTA

ISOLEUCINE TAA

LYSINE TTT

METHIONINE TAC

PHENYLALANINE AAA

PROLINE CCG

TYROSINE ATG

VALINE CAT

The following is a sequence of bases in a section of DNA.

TAC –  ATG –  CCC –  GCC –  GTA

a) If the DNA is read from left to right, write out the sequence of amino acids coded

by this DNA by referring to the table.

Methionine, tyrosine, glycine, alanine, histidine

b) Sometimes a base letter is lost, perhaps as a result of exposure to radiation. Write

out the new code sequence if the ninth letter(C) is lost in this way.

TAC –  ATG –  CCG –  CCG –  TA

c) Write out the sequence of amino acids if this altered DNA sequence is used. (You

need 3 bases in a row to specify an amino acid)

Methionine –  tyrosine –  proline –  proline

d) What name is given to the changes in DNA (such as in (b)) that can affect the

production of proteins?

Gene mutation

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Homework : BMH29-WRCC

Concepts Description 

No GRID Description Book / Chapter / Section

1 Definition of codominance B2.19.001 Both alleles can have aneffect on the phenotype

2 Definition of incomplete dominance B2.19.001 Both alleles can have aneffect on the phenotype

3 Know blood group alleles / antigens B2.19.001 Both alleles can have aneffect on the phenotype

4 Blood group resulting from B/A and O. B2.19.001 Both alleles can have aneffect on the phenotype

5 G Father determines gender of his children B2.19.002 Sex determination inhumans

6 G Definition of mutation B2.19.003 Genetic disorders andcounseling

7 Examples of mutagens. B2.19.003 Genetic disorders andcounseling

8 Know gene, chromosome mutations withexamples

B2.19.003 Genetic disorders andcounseling

9  Applications of genetic engineering B2.19.004 Genetic engineeringmakes genes work for people

10 Father determines the gender of a child, not themother

B2.19.002 Sex determination inhumans

11 Cause of sickle cell anemia B2.19.004 Genetic engineering

makes genes work for people12 The principles of genetic engineering B2.19.004 Genetic engineering

makes genes work for people

13 Blood group O is homozygous B2.19.001 Both alleles can have aneffect on the phenotype

14 G How blood groups A × B gives O B2.19.001 Both alleles can have aneffect on the phenotype

15 Example of 2 products for humans produced bygenetic engineering

B2.19.004 Genetic engineeringmakes genes work for people

16 Manufacture of human insulin B2.19.004 Genetic engineering

makes genes work for people17 Structure of DNA and its link to gene B2.19.004 Genetic engineering

makes genes work for people

18 Interpret codes for amino acids in a protein, givendata

B2.19.004 Genetic engineeringmakes genes work for people