5

Q1. The recessive genes located on the X-chromosome in humans are always

• Sub-lethal
• Expressed in males
• Expressed in females
• Lethal

Solution

Females have genetic constitution (XX), while males have genetic constitution (XY). So, if the recessive gene is located on the X chromosome, then it would always be expressed in females as they have a double dose of the X chromosome in contrast to males who have one Y chromosome as well.

Q2. Which of the following is not a Mendelian disorder?

• Haemophilia
• Cystic fibrosis
• Colour blindness
• Turner's syndrome

Solution

A Mendelian disorder is an inherited disease caused by a single-gene mutation. The mutation can either occur on a single chromosome or on a pair of homologous chromosomes. Turner’s syndrome is caused by XO genotype. This genotype results from the union of an abnormal O egg with a normal X sperm or a normal X egg and abnormal O sperm.

Q3. Lack of independent assortment of two genes A and B in fruit fly Drosophila is due to

• Recombination
• Linkage
• Crossing over
• Repulsion

Solution

The genes located on the same chromosome (linked genes) usually do not assort independently but remain together in the gametes and the offspring.

Q4. Colchicine is a mutagen which results in 

• Deletion
• Point mutation
• Polyploidy cells
• Haploid cells

Solution

Colchicine is a chemical mutagen which prevents the formation of spindle fibres during cell division and results in the lack of splitting up of chromosomes, resulting in the formation of polyploids.

Q5. The gene which controls many characters is called

• Co-dominant gene
• Polygene
• Pleiotropic gene
• Multiple gene

Solution

A gene having multiple phenotypic effects is called a pleiotropic gene. The alleles which, when present together in a heterozygous individual, express their traits independently instead of showing a dominant-recessive relationship are called co-dominant alleles. Two or more pairs of non-allelic genes, which produce a cumulative effect on the same phenotypic quantitative character, are called multiple genes or cumulative genes or polygenes.

Q6. Cytoplasmic inheritance is due to (1) Mitochondria (2) Cilia (3) Cytoplasmic particles (4) Cell wall

• 1, 2 and 3 are correct.
• 1 and 2 are correct.
• 2 and 4 are correct.
• 1 and 3 are correct.

Solution

Cytoplasmic inheritance is the inheritance of characteristics coded for by genes found in the cytoplasm, typically from the mitochondria or chloroplasts. Cilia and cell wall are extracellular organelles, and so, their inheritance is not cytoplasmic.

Q7. The theory of pangenesis proposed by Charles Darwin was disapproved by? 

• G.J. Mendel 
• Weismann 
• Swammerdam 
• B.C. Greek 

Solution

The theory of pangenesis proposed by Charles Darwin was disapproved by Weismann in 1892 and proposed the theory of continuity of germplasm. 

Q8. Down's syndrome is due to

• Linkage
• Sex-linked inheritance
• Crossing over
• Non-disjunction of chromosome

Solution

Down's syndrome is caused by the presence of an extra chromosome no. 21. Both the chromosomes of the pair 21 pass into a single egg due to non-disjunction during oogenesis in the mother’s ovary.

Q9. Which of the following factors increases the strength of linkage between genes?

• Temperature
• X-rays
• Age
• Rapid mitosis

Solution

The chance of crossing over between genes reduces as the age of an individual increases, thus increasing the strength of linkage between them.

Q10. Point mutation involves

• Insertion
• Change in single base pair
• Duplication
• Deletion

Solution

Gene mutations which involve the substitution, deletion or insertion of a single nitrogenous base are called point mutations.

Q11. An allele which is dominant and widespread in the population is known as a

• Mutant allele
• Allelomorph
• Wild allele
• Mendelian allele

Solution

An allele which is dominant and is widespread in the population is known as a wild allele.

Q12. Mating of an organism to a double recessive in order to determine whether it is homozygous or heterozygous for a character under consideration is called

• Reciprocal cross
• Test cross
• Dihybrid cross
• Back cross

Solution

A reciprocal cross involves same traits but is carried by sexes opposite to those in the original or first cross. A back cross is a genetic cross between a hybrid organism and one of the original parental types. A dihybrid cross is a cross which deals with two pairs of contrasting characters at the same time.

Q13. Muscular dystrophy is caused by

• Frameshift mutation
• Transversion
• Point mutation
• Substitution

Solution

Muscular dystrophy is a disease in humans which is caused by a frameshift mutation in the gene responsible for the production of the protein dystrophin. In this disease, the mutation leads to premature termination of translation of the protein.

Q14. Haemophilia is due to

• Factor-VI
• Factor-VII
• Factor-VIII
• Factor-IX

Solution

Haemophilia is a sex-linked trait caused by a recessive gene located in the X-chromosome. This gene controls the synthesis of a coagulation protein called factor VIII needed for clotting of blood. 

Q15. In which of the following organisms are sperms formed by the process of mitosis?

• Ants
• Fruit flies
• Cockroaches
• Round worms

Solution

In certain organisms, the unfertilised egg develops into a male, while the fertilised egg develops into a female. This is the haploid-diploid system of sex determination. It is observed in ants, bees, wasps and saw flies.

Q16. Which one of the following conditions of a zygotic cell would lead to the birth of a normal human female child?

• Only one X chromosome
• One X and one Y chromosome
• Two X chromosomes
• Only one Y chromosome

Solution

In case of human beings, if the ovum of a female fertilises with the sperm having X chromosome, then the zygote develops into a female (XX). If it fertilises with Y, then the zygote develops into a male (XY).

Q17. All genes located on the same chromosome

• Form different groups depending upon their relative distance
• Form one linkage group
• Will not form any linkage groups
• Form interactive groups which affect the phenotype

Solution

All the genes in a particular chromosome form a linkage group. Because the genes in a particular chromosome have their alleles in the corresponding homologous chromosome, a pair of homologous chromosomes is said to form a single linkage group.

Q18. Crossing over is the exchange of genetic material between

• Non-sister chromatids of homologous chromosomes
• Sister chromatids of homologous chromosomes
• Chromatids of non-homologous chromosomes
• Genes which are completely linked

Solution

Crossing over is the mutual exchange of the corresponding segments of the adjacent paternal and maternal chromatids of the synapsed homologous chromosomes in the pachytene stage of meiosis-I, producing new combinations of genes. In crossing over, adjacent non-sister chromatids break at homologous sites, mutually exchange small corresponding segments and rejoin.

Q19. Complete linkage is observed in

• Male Drosophila sp.
• Female Drosophila sp.
• Female silkworm
• None of these

Solution

In complete linkage, the genes closely located in the chromosome show complete linkage as they have no chance of separating by crossing over and are always transmitted together to the same gamete and the same offspring. Thus, the parental combination of traits is inherited as such by the young one in case of complete linkage. In female Drosophila sp., no recombinant types are formed because linkage is complete and no crossing over occurs.

Q20. A pure tall and a pure dwarf plant were crossed to produce offspring. Offspring were self-crossed. Find out the ratio between true breeding tall to true breeding dwarf.

• 1:1
• 3:1
• 2:1
• 1:2:1

Solution

A cross between pure tall (TT) and a pure dwarf plant (tt) produces heterozygous tall (Tt) offspring. When the offspring are self-crossed, we obtain four offspring - 2 heterozygous tall (Tt), 1 pure tall (TT) and 1 pure dwarf (tt). So, the ratio between true breeding tall to true breeding dwarf is 1:1.

Q21. ‘XO’ type of sex determination is seen in

• Man
• Grasshopper
• Horses
• Drosophila

Solution

Grasshoppers show XX-XO type of sex determination. The Y chromosome is missing, and so, the male has only one sex chromosome. The condition is XO in male and XX in female. Human beings, horses and Drosophila show XX-XY type of sex determination. Birds show ZZ-ZW type of sex determination.

Q22. Which of the following individuals is a genetically pure individual for the given trait?

• RrYY
• RRyy
• RRYY
• Both RRYY and RRyy

Solution

Individuals in which both the alleles of a character at the corresponding loci of the homologous chromosome are identical are known as homozygous or pure individuals for that trait. 

Q23. Individuals with sickle cell anaemia have a less chance of suffering from which of the following diseases?

• Malaria
• Jaundice
• AIDS
• Herpes

Solution

Individuals with sickle cell anaemia possess sickle-shaped RBCs. The malaria parasite reproduces in the RBCs of the affected individual. Due to the abnormal shape of the RBCs in individuals with sickle cell anaemia, the parasite fails to reproduce and hence has a less chance of affecting the individual.

Q24. Mutations which arise suddenly in nature are called

• Chromosomal mutations
• Induced mutations
• Gene mutations
• Spontaneous mutations

Solution

Spontaneous mutations occur at random. They may arise by the errors in the process of replication and from failure to repair damaged DNA properly. Chromosomal mutations affect large portions of the chromosomes and involve morphological modifications in the chromosomes. Induced mutation is a mutation which has been artificially engineered in an effort to change the DNA sequence that is passed from the parent to offspring. Gene mutation is a sudden, stable, inheritable alteration in the base sequence of a gene capable of changing the phenotype of an organism.

Q25. The frequency of crossing over between two genes is directly proportional to

• Strength of linkage
• Distance of the genes
• Type of genes
• Number of alleles

Solution

The frequency of crossing over between two genes is directly proportional to the distance between them. This is the Morgan and Sturtevant’s hypothesis.

Q26. Which of the following diseases is also known as bleeder’s disease?

• Sickle cell anaemia
• Haemolytic anaemia
• Haemophilia
• PKU

Solution

Haemophilia is an X-linked recessive disease. In this case, the affected individuals carry a defect due to which the blood fails to clot and the person may bleed to death even with minor injuries.

Q27. Gene for colour blindness is located on

• Y chromosome
• 13^th chromosome
• X chromosome
• 21^st chromosome

Solution

Red-green colour blindness is produced by an X-linked recessive gene by causing lack of one of the primary cone pigments of the retina. Normal eyesight is dominant to colour blindness.

Q28. Turner syndrome is

• XO
• XXY
• XXX
• XYY

Solution

Turner’s syndrome is an aneuploid condition with a single set of chromosomes. It is caused by XO genotype which results from the union of an abnormal O egg with a normal X sperm or a normal X egg and abnormal O sperm.

Q29. The term ‘Genetics’ was proposed by

• Mendel
• Bateson
• Morgan
• Johannsen

Solution

Mendel is regarded as the Father of Genetics. Thomas Hunt Morgan elucidated the role of chromosomes in heredity. Johannsen coined the term gene.

Q30. Which of the following conditions is called monosomic?

• 2n + 1
• 2n + 2
• n + 1
• 2n − 1

Solution

The presence of a single copy of a chromosome indicates monosomy (2n − 1). The presence of three copies of a particular chromosome indicates trisomy (2n + 1). An aneuploid having four copies of one chromosome is known as tetrasomic (2n + 2).

Q31. Which of the following characters was not considered by Mendel in his inheritance studies?

• Type of pod
• Colour of cotyledon
• Position of flower
• Type of petiole

Solution

In his inheritance studies on garden pea, Mendel considered 7 different characters—type of stem (tall/dwarf), position of flowers (axial/terminal), pod colour (green/yellow), pod type (inflated/constricted), flower colour (coloured/white), colour of cotyledons (yellow/green) and seed shape (round/wrinkled).

Q32. Which of the blood groups can be given to any person?

• A
• B
• AB
• O

Solution

There are four blood groups in the human population - A, B, AB and O depending on the type of glycoprotein (antigen) present on the surface of the blood corpuscles. People with blood group A produce A antigen, those with blood group B form B antigen, those with blood group AB produce both the antigens and those with blood group O form no antigen. As people with blood group O have no antigen on the surface of their red blood cells, they act as universal donors. Their blood type is compatible with any blood type.

Q33. In sickle cell anaemia, glutamic acid is replaced by valine. Which one of the following triplets codes valine?

• A A G
• G U G
• G G G
• G A A

Solution

In sickle cell anaemia, base substitution from glutamic acid to valine occurs at the relevant portion of the beta chain of the haemoglobin molecule. This substitution occurs due to the single base substitution at the sixth codon of the beta globin gene from GAG to GUG.

Q34. Klinefelter's syndrome is due to

• One X and two Y
• Two X and one Y
• One X only
• One Y only

Solution

Klinefelter's syndrome is an aneuploid condition with three sex chromosomes. It is caused by XXY genotype. This genotype results from the union of a non-disjunct XX egg and a normal Y sperm or a normal X egg and an abnormal XY sperm. The individual has 47 chromosomes (2n + 1).

Q35. Genes present in the cytoplasm of eukaryotic cells are found in

• Mitochondria and inherited via egg cytoplasm
• Lysosomes and peroxisomes
• Golgi bodies and smooth endoplasmic reticulum
• Plastids and inherited via male gamete

Solution

Cytoplasmic inheritance is the inheritance of characteristics coded for by genes found in the cytoplasm, typically from the mitochondria or chloroplasts. The cytoplasmic genes are inherited via the egg cytoplasm.  

Q36. In F₁ and F₂, the 'F' stands for 

• Fusion 
• Father 
• Filial 
• Foster 

Solution

In F₁ and F₂, the 'F' stands for filial. 

Q37. The enzyme tyrosinase is linked to which disease?

• Phenylketonuria
• Alkaptonuria
• Albinism
• Colour blindness

Solution

In albinism, the individual lacks the enzyme tyrosinase, which is necessary for the synthesis of the dark pigment melanin.

Q38. The blood group antigens found on the surface of RBCs are

• Lipoproteins
• Glycoproteins
• Phospholipids
• Glycolipids

Solution

Human blood group is governed by the gene ‘I’. This gene is responsible for the production of a glycoprotein antigen which is found on the surface of the RBCs. The type of sugar found in these glycoprotein molecules determines the blood group of the individual (A, B, AB or O).

Q39. Heterozygous purple flower is crossed with recessive white flower. The progeny has the ratio:

• 75% purple and 25% white
• 50% purple and 50% white
• All purple
• All white

Solution

When a heterozygous purple flower (Rr) is crossed with a recessive white flower (rr), the progeny obtained are with the genotype (Rr), (Rr), (rr) and (rr). So, 50% of the progeny are with purple flowers (Rr) and 50% are with white flowers (rr).

Q40. The phenotypic ratio in the F₂ generation of a dihybrid cross is

• 9:3:3:1
• 1:2:2:4:1:2:1:2:1
• 7:1:1:7
• 12:3:4