Principles of Inheritance and Variation: Questions and Answers (Evaluation)

Evaluation

1. Haemophilia is more common in males because it is a

a) Recessive character carried by Y-chromosome

b) Dominant character carried by Y-chromosome

c) Dominant trait carried by X-chromosome

d) Recessive trait carried by X-chromosome

Answer: d) Recessive trait carried by X - chromosome

2. ABO blood group in man is controlled by

a) Multiple alleles

b) Lethal genes

c) Sex linked genes

d) Y-linked genes

Answer: a) Multiple alleles

3. Three children of a family have blood groups A, AB and B. What could be the genotypes of their parents?

a) IA IB and ii

b) IA Io and IBIo

c) IB IB and IA IA

d) IA IA and ii

Answer: b) I^A I^o and I^BI° 

4. Which of the following is not correct?

a) Three or more alleles of a trait in the population are called multiple alleles.

b) A normal gene undergoes mutations to form many alleles

c) Multiple alleles map at different loci of a chromosome

d) A diploid organism has only two alleles out of many in the population

Answer: c) Multiple alleles map at different loci of a chromosome

5. Which of the following phenotypes in the progeny are possible from the parental combination AxB?

a) A and B only

b) A,B and AB only

c) AB only

d) A,B,AB and O

Answer: d) A,B,AB and O

6. Which of the following phenotypes is not possible in the progeny of the parental genotypic combination IAIO X IAIB?

a) AB

b) O

c) A

d) B

Answer: b) O

7. Which of the following is true about Rh factor in the offspring of a parental combination DdXDd (both Rh positive)?

a) All will be Rh-positive

b) Half will be Rh positive

c) About ¾ will be Rh negative

d) About one fourth will be Rh negative

Answer: d) About one fourth will be Rh negative

8. What can be the blood group of offspring when both parents have AB blood group?

a) AB only

b) A, B and AB

c) A, B, AB and O

d) A and B only

Answer: b) A,B and AB

9. If the childs blood group is ‘O’ and fathers blood group is ‘A’ and mother’s blood group is ‘B’ the genotype of the parents will be

a) IA IA and IB Io

b) IA Io and IB Io

c) IA Io and IoIo

d) IoIo and IB IB

Answer: b) I^AI° and I^BI°

10. XO type of sex determination and XY type of sex determination are examples of

a) Male heterogamety

b) Female heterogamety

c) Male homogamety

d) Both (b) and (c)

Ans. a) male heterogamety

11. In an accident there is great loss of blood and there is no time to analyse the blood group which blood can be safely transferred?

a) ‘O’ and Rh negative

b) ‘O’ and Rh positive

c)’B’ and Rh negative

d) ‘AB’ and Rh positive

Answer: a) 'O' and Rh negative

12. Father of a child is colourblind and mother is carrier for colourblindness, the probability of the child being colourblind is

a) 25%

b) 50%

c) 100%

d) 75%

Answer: b) 50%

13. A marriage between a colourblind man and a normal woman produces

a) All carrier daughters and normal sons

b) 50% carrier daughters, 50% normal daughters

c) 50% colourblind sons, 50% normal sons

d) All carrier offsprings

Answer: a) All carrier daughters and normal sons

14. Mangolism is a genetic disorder which is caused by the presence of an extra chromosome number

a) 20

b) 21

c) 4

d) 23

Answer: b) 21

15. Klinefelters’ syndrome is characterized by a karyotype of

a) XYY

b) XO

c) XXX

d) XXY

Answer: d) XXY

16. Females with Turners’ syndrome have

a) Small uterus

b) Rudimentary ovaries

c) Underdeveloped breasts

d) All of these

Answer: d) All of these

17. Pataus’ syndrome is also referred to as

a) 13-Trisomy

b) 18-Trisormy

c) 21-Trisormy

d) None of these

Answer: a) 13 - Trisomy

18. Who is the founder of Modern Eugenics movement?

a) Mendel

b) Darwin

c) Francis Galton

d) Karl pearson

Answer: c) Fransis Galton

19. Improvement of human race by encouraging the healthy persons to marry early and produce large number of children is called

a) Positive eugenics

b) Negative eugenics

c) Positive euthenics

d) Positive euphenics

Answer: a) Positive eugenics

20. The _______deals with the control of several inherited human diseases especially inborn errors of metabolism

a) Euphenics

b) Eugenics

c) Euthenics

d) All of these

Answer: a) Euphenics

21. “Universal Donor” and “Universal Recipients” blood group are _____ and_______respectively

a) AB, O

b) O, AB

c) A, B

d) B, A

Answer: b) O, AB

22. ZW-ZZ system of sex determination occurs in

a) Fishes

b) Reptiles

c) Birds

d) All of these

Answer: d) All of these

23. Co-dominant blood group is

a) A

b) AB

c) B

d) O

Answer: b) AB

24. Which of the following is incorrect regarding ZW-ZZ type of sex determination?

a) It occurs in birds and some reptiles

b) Females are homogametic and males are heterogametic

c) Male produce two types of gametes

d) It occurs in gypsy moth

Answer: b) Females are homogametic and males are heterogametic

25. What is haplodiploidy?

Haplodiploidy (Ex. Honey bee, wasp, Ants)

• The sex of the off spring is determind by the numbers of sets of chromosomes

• Fertilized egg develops into females. (Queen / worker honeybee)

• Unfertilised eggs develop into males (or) drones. This is called parthenogenesis.

• So males have half the number of chromosomes (haploid).

• Females have double the number (diploid)

This system of sex determination is called haplodiploidy. It is seen in hymenopterans.

26. Distinguish between heterogametic and homogametic sex determination systems.

Homogametic

i. Individuals with homomorphic sex chromosomes (Similar chromosomes) produce only one type of gamete. So they are said to be homogametic

ii. Example In human the females are homogametic. They produce only one kind of egg (with X chromosome)

Heterogametic

i. Heteromorphic individuals (dissimilar sex chromosomes) produce two types of gametes, so they are said to be heterogametic.

ii. In human males produce 2 kinds of sperms. Some with X chromosome and some with Y chromosome.

27. What is Lyonisation?

Lyonisation (X - Inactivation) (Lyon's hypothesis)

• In the XY Chromosomal system of sex determination, males have only one X Chromosome.

• The females have two X Chromosomes.

• This dosage differences between the sexes (male, female) are compensated.

• This is done by the inactivation of one of the X Chromosomes in females.

• Now both males and females have only one functional X chromosome per cell.

• Mary Lyon suggested that Barr bodies represent the inactive chromosome.

• Mary Lyon suggested that Barr bodies represent the inactive chromosome.

• In females, these X Chromosome becomes tightly coiled into a heterochromatin (Heterochromation என்பது Protein Synthesis நிகழ்ச்சியில் Tanscription நடக்காத குரோமோசோம் பகுதி)

• Heterochromatin is a condensed and visible form of chromatin. (chromatin என்பது Eukaryotic செல்களில், குரோமோசோமும் அதிலுள்ள DNA வும் கெட்டியாகச் சேர்ந்திருப்பது) (அடைப்புக்குறியில் உள்ளவற்றை தேர்வில் எழுத வேண்டாம். புரிந்து கொள்ள மட்டுமே).

28. What is criss-cross inheritance?

In Criss - Cross inheritance a trait is inherited from the male parent to the grandson through the carrier daughter. (ஒரு Character or disease க்குரிய ஜீனை உடலில் கொண்டவர்கள் ஆனால் அந்த நோய் அல்லது பண்பினால் பாதிக்கப்படாதவர்கள் 'Carrier' எனப்படுவர்)

The inheritance of colour blindness is an example. Haemophilia is another example.

29. Why are sex linked recessive characters more common in the male human beings?

• Males are hemizygous.

• Therefore they express the trait when they inherit one mutant allele.

• So, sex linked traits are more common in males than females.

30. What are holandric genes?

• Genes in the differential region of 'Y' chromosome are called Y. linked or holandric genes.

• The Y linked genes have no corresponding allele in X chromosome.

• The Y linked genes inherit along with Y chromosome.

• These genes phenotypically express only in the male sex.

31. Mention the symptoms of Phenylketonuria.

• Mental Retardation

• Light pigmentation of skin and hair

• Phenylpyruvic acid is excreted in urine.

32. Mention the symptoms of Downs syndrome.

• Mental Retardation

• Increased separation between eyes.

• Malformed ears.

• Tongue Protrudes

• Defective development of Central Nervous system.

• Flattened nose.

• Mouth is constantly open.

33. Differentiate Intersexes from Supersexes.

Intersex

1. Combination of chromosomal genotype and sexual phenotype other than XY male and XX female

2. Variations in Sex characteristics like chromosomes, gonads, sex hormones or genitals. They do not fit into typical male or female

3. Previously they were called as hermaphrodites

4. They have one extra X and Y chromosome

5. They have both ovarian and testicular tissues.

6. External genitalia is not well defined.

Supersex

1. Super females

They are Poly X females

2. They have 47 autosomes and 3x chromosomes.

3. It is called triple X syndrome

4. They are mentally retarded and sterile. Supermales (XYY males)

5. They have an extra'Y' chromosome

6. This is called xyy syndrome.

They show mental retardation and criminal attitude.

34. Explain the genetic basis of ABO blood grouping man.

Genetic basis of blood grouping in man :

• Three autosomal alleles are on chromosome 9.

• These alleles determine the blood group.

• The gene for blood group is labeled as 'L' (L - Landsteiner, the discover) or ‘I’

(I - Isoagglutinogen, another word for antigen)

• I gene has 3 allelic forms I^A, I^B, 1°

• I^A specifies A antigen

• I^B for B antigen

• I° allele specifies no antigen.

• Each allele produces a transferase enzyme (These enzyme catalyse the transfer of sugar from one molecule to another)

• I^A allele produces N - acetyl galactose transferase. It can add N - acetyl galactosamine.

• I^B allele produces the enzyme galactose transferase. This adds galactose to the precursor (H substance)

• I° allele produce no enzyme. So it is called 'null' allele. It cannot add NAG (N-acetyl glucosamine) or galactose to the precursor. 

35. How is sex determined in human beings?

Sex determination in human beings :

• Gene determining sex in human beings are located in sex chromosomes (allosomes)

• Sex determination is based on chromosomal differences between male and female.

• Females have XX chromosomes. Males have XY chromosomes.

• Females are homogametic. They produce only one type gamete (Each egg has one X chromosome)

• Males are heterogametic. They produce 2 types of sperms. (One type with X and another type with Y chromosome)

• This XY system or sex determination is also seen in Drosophila.

• The sex of the embryo depends on the fertilising sperm.

• The egg fertilised by X sperm produce female.

• The egg fertilised by Y sperm produce male. 

36. Explain male heterogamety.

Male heterogamety :

• In this method of sex determination, males are heterogametic. They produce dissimilar gametes.

XX-XO Type :

• It is in bugs, insects, cockroaches, grasshoppers.

• The males are heterogametic. They have only one X chromosome (XO)

• They produce 2 types of sperms. One with X chromosome. The other half without X chromosomes.

• The sex of the off spring depends on the sperm which fertilises the ovum (X sperm or O sperm)

XX - XY Type (Lygaeus type) (Ex. Man and Drosophila) :

• Here the males are heterogametic.

• They produce 2 types of sperms. Some with X chromosome. Some with Y chromosome.

• The sex of the embryo depends on the fertilising sperm.

• The egg fertilised by X sperm produce female.

• The egg fertilised by Y sperm produce male.

37. Brief about female heterogamety.

Female Heterogamety :

In vertebrates like fishes, reptiles and birds, the females produce dissimilar gametes.

ZO - ZZ Type :

• It is seen in moths, butterflies, domestic chickens.

• The female is heterogametic (ZO)

• The female produces 2 kinds of eggs

• Some with Z chromosome. Some without Z chromosome.

• The male is homogametic (ZZ).

ZW-ZZ Type :

• It is in gypsy moth (insects) and vertebrates like fishes, reptiles and birds.

• The female produces 2 kinds of eggs.

• Some with Z chromosomes. Some with W chromosome. The male is homogametic (ZZ).

38. Give an account of genetic control of Rh factor.

• 3 different pairs of alleles are located in 3 different close loci on the homologous chromosomal pair -1 (Cc, Dd, Ee)

• This system uses Cde' nomenclature

• The possible genotypes are

One C or c

One D or d

One E or e

• For example

CDE / cde

CdE / cDe

cde / cde

CDe / CdE

• All genotypes with dominant D produce Rh⁺ Phenotype

• Double recessive genotype 'dd' produce Rh^- phenotype

Wiener Hypothesis:

• Eight alleles (R¹, R², R°, R^z, r, r¹, r¹¹, r^y) are at a single Rh locus.

• Genotype with dominant 'R allele' (R¹, R², R°, R^z) produce Rh⁺ positive phenotype.

• Double recessive genotypes (rr, rr¹, rr¹¹, rr^y) produce Rh^- negative phenotype.

39. Explain the mode of sex determination in honeybees.

Haplodiploidy (Ex. Honey bee, wasp, Ants)

• The sex of the off spring is determind by the numbers of sets of chromosomes

• Fertilized egg develops into females. (Queen / worker honeybee)

• Unfertilised eggs develop into males (or) drones. This is called parthenogenesis.

• So males have half the number of chromosomes (haploid).

• Females have double the number (diploid)

This system of sex determination is called haplodiploidy. It is seen in hymenopterans.

40. Discuss the genic balance mechanism of sex determination with reference to Drosophila.

Genic Balance Mechanism :

• It was first described by C.B. Bridges in 1921.

• The sex of the individual depends on the ratio of X chromosomes to the autosomes.

• Each X chromosome carries female determining factors. Their value in 1.5.

• Autosomes carry male determining factors. Their value is 1.0.

• Normale male is AAXY. So, the male, female determinants are in the ratio of 2:1.5 (A = Haploid set of autosomes). Here the genic balance favours maleness.

• Normal female has male, female determinants in the ratio of 2:3 (AAXX = 2:3) Here the genic balance favours femaleness.

41. What are the applications of Karyotyping?

• Gender identification

• To defect chromosomal aberrations like

 • Debetion  • Duplication  • Translocation  • Nondisjunction

• To identify chromosomal abnormalities (Ex. Aneuplidy)

• To predict evolutionary relationship between species.

• Genetic diseases can be detected.

42. Explain the inheritance of sex linked characters in human being.

Sex linked characters in human being:

• Inheritance of traits by genes located in sex chromosomes. It is called sex linked Inheritance.

• Genes in the differential region of X chromosome are called X linked genes.

• Genes in the differential region of Y chromosome are called Y linked genes (or) Holandric genes.

Inheritance of X - linked genes:

Examples for X - linked inheritance are

• Red - green colour blindness or daltonism.

• Haemophila

• Duchenne's muscular dystrophy.

• Let's see one example in detail.

1. Haemophila:

It is caused by X - linked gene.

• Persons with recessive gene for haemophilia lack clotting substance (thromboplastin) in blood.

• Minor injuries lead to continous bleeding and death.

• Females are carriers of this disease. They transmit the disease to 50% of their sons.

• Haemophilia follows criss cross inheritance (Father → daugher → grandson)

2. Colour blindness :

• A dominant X - linked genes is needed for the formation of colour sensitive cones.

• Recessive form of these genes are incapable of producing cone cells.

• So, homozygous recessive females (X^c, X^c) and hemizygous recessive males (X^c Y) are colour blind. They cannot distinguish red and green colour.

43. What is extra chromosomal inheritance? Explain with an example.

Extra chromosomal inheritance:

• Normally genes are in chromosomes of the nucleus.

• Genes may be in cytoplasm also. In cytoplasm these genes are in mitochontria (or) chloroplast.

• So, the pattern of inheritance by extra nuclear genes is different from the genes of nuclear chromosomes. This is called extra chromosomal inheritance.

• This extra chromosomal inheritance is of Non - Mendelian pattern of inheritance.

• Only females transmit cytoplasmic characters, because the ovum or egg contributes most of the cytoplasm to the zygote. So this is called maternal inheritance or uniparental inheritance.

• Example: Plastid inheritance in 4'o' clock plant.

44. Comment on the methods of Eugenics.

Methods of Eugenics:

• Eugenics (Greek : Well bom) aims at improving the genetic quality of human population. This is done by excluding less desirable genetic groups and promoting superior genetic groups.

Negative Eugenics of Methods:

• Sexual abstinence of genetically less desirable.

• Sex education

• Use of contraception.

• Voluntary sterilization, abortion.

• Incentives for volunttary co - operation.

Positive Methods of Eugenics :

• Financial incentives to have children.

• Eugenic immigration.

New Methods of Eugencis:

• Artificial insemination by donor.

• Egg donation.

• Gene therapy.

• Cloning.

• Genetic engineering.