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Q1. With respect to the trait for dwarfness of a plant, the trait for tallness of a plant is

• 1) All of the above
• 2) Dominant
• 3) Present on the same loci of homologous chromosomes
• 4) Always expressed when present with its other allelomorphs

Solution

In pea plant as per the Mendelian inheritance pattern, the trait for tallness of a plant is dominant, present on the same loci of homologous chromosomes as the trait for dwarfness of the plant and is always expressed when present with its other allelomorphs.

Q2. ZZ/ZW type of sex determination is seen in

• 1) Platypus
• 2) Cockroach
• 3) Peacock
• 4) Snails

Solution

ZZ/ZW type of sex determination is seen in fish, reptiles, birds, butterflies and moths. ZZ/ZO type of sex determination is seen in some butterflies and moths. XX/XO type of sex determination is seen in cockroach and some roundworms. XX/XY type of sex determination is seen in mammals and most insects.

Q3. The blood group antigens found on the surface of RBCs are

• 1) Glycolipids
• 2) Glycoproteins
• 3) Lipoproteins
• 4) Phospholipids

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).

Q4. The enzyme tyrosinase is linked to which disease?

• 1) Alkaptonuria
• 2) Colour blindness
• 3) Albinism
• 4) Phenylketonuria

Solution

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

Q5. Which of the following diseases is also known as bleeder’s disease?

• 1) PKU
• 2) Sickle cell anaemia
• 3) Haemolytic anaemia
• 4) Haemophilia

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.

Q6. An individual with Klinefelter’s syndrome possess how many chromosomes?

• 1) 2n
• 2) n
• 3) 2n − 1
• 4) 2n + 1

Solution

Klinefelter’s syndrome is an aneuploid condition wherein the individual possesses three sex chromosomes. Hence, the individual has one extra chromosome than normal (represented by 2n + 1).

Q7. The term ‘Genetics’ was proposed by

• 1) Johannsen
• 2) Mendel
• 3) Bateson
• 4) Morgan

Solution

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

Q8. 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

• 1) Reciprocal cross
• 2) Test cross
• 3) Back cross
• 4) Dihybrid 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.

Q9. How does a test cross help in identifying the genotype of the organism? Explain.

Solution

In a typical test cross, an organism showing a dominant phenotype (whose genotype is to be determined) is crossed with the recessive parent. The progeny of the cross are analysed to predict the genotype of the test organism. Given below is a test-cross where the violet colour flower of pea (W) is dominant over the white colour flower (w).        

Q10. An allele which is dominant and widespread in the population is known as a

• 1) Mendelian allele
• 2) Wild allele
• 3) Allelomorph
• 4) Mutant allele

Solution

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

Q11. A mutation in which the codon ATC changes to GTC is classified as which type of a mutation?

• 1) Transversion
• 2) Insertion
• 3) Deletion
• 4) Transition

Solution

When the codon ATC changes to GTC, the nitrogen base in the codon is changed from A to G, while the rest of the nitrogen bases remain the same. Because both A and G are purines, the mutation is a transition mutation.

Q12. Klinefelter's syndrome is due to

• 1) One Y only
• 2) One X only
• 3) Two X and one Y
• 4) One X and two Y

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).

Q13. Name one autosomal dominant and one autosomal recessive Mendelian disorder in humans.

Solution

Huntington's disease is an autosomal dominant disorder and haemophilia is an autosomal recessive disorder.

Q14. In one family, each of the four children has a different blood group. The mother is group A and the father is group B. Explain this pattern of inheritance with the help of a cross along with their genotypes.

Solution

A cross is carried out between the heterozygous father (for blood group B) and the heterozygous mother (for blood group A) to get four children with different blood groups.         All the four blood groups are controlled by three allelic genes I^A, I^B, i which exhibit an instance of multiple allelism.  Both I^A and I^B are dominant over i. However, when together, both are dominant and show the phenomena of co-dominance, forming the blood group AB. Six genotypes are possible with the combination of these three alleles.  

Q15. The presence of pink-coloured flowers in snapdragon is due to

• 1) Mendelian inheritance
• 2) Incomplete dominance
• 3) Codominance
• 4) Complete dominance

Solution

In snapdragon, the true parental types are white- and red-coloured flowers. When a pure white flower parent is crossed with a true breeding red-coloured flower parent, the progeny show the presence of pink-coloured flowers. This is because the alleles for the red and white trait are both dominant and when present together are expressed as a mixture of the two traits. This phenomenon deviates from the Mendelian inheritance pattern and is known as incomplete dominance.

Q16. Which of the following individuals is a genetically pure individual for the given trait?

• 1) RRyy
• 2) Both RRYY and RRyy
• 3) RrYY
• 4) 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. 

Q17. Work out F₁ and F₂ generation to explain the inheritance of flower colour in Pisum sativum. Give the phenotypic and genotypic ratios (start with pure breeding).

Solution

This is a case of Mendel's monohybrid cross.                                          

Q18. Which of the following characters was not considered by Mendel in his inheritance studies?

• 1) Colour of cotyledon
• 2) Type of pod
• 3) Position of flower
• 4) 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).

Q19. Turner syndrome is

• 1) XYY
• 2) XXX
• 3) XXY
• 4) XO

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.

Q20. Colchicine is a mutagen which results in 

• 1) Deletion
• 2) Point mutation
• 3) Polyploidy cells
• 4) 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.

Q21. In which of the following organisms are sperms formed by the process of mitosis?

• 1) Fruit flies
• 2) Cockroaches
• 3) Round worms
• 4) Ants

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.

Q22. Lack of independent assortment of two genes A and B in fruit fly Drosophila is due to

• 1) Recombination
• 2) Repulsion
• 3) Crossing over
• 4) Linkage

Solution

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

Q23. The frequency of crossing over between two genes is directly proportional to

• 1) Number of alleles
• 2) Strength of linkage
• 3) Type of genes
• 4) Distance of the genes

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.

Q24. Which of the blood groups can be given to any person?

• 1) A
• 2) B
• 3) AB
• 4) 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.

Q25. Down's syndrome is due to

• 1) Linkage
• 2) Crossing over
• 3) Non-disjunction of chromosome
• 4) Sex-linked inheritance

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.

Q26. Individuals with sickle cell anaemia have a less chance of suffering from which of the following diseases?

• 1) AIDS
• 2) Malaria
• 3) Jaundice
• 4) 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.

Q27. When a tall pea plant was self-pollinated, one-fourth of the progeny was dwarf. Give the genotype of the parent and dwarf progeny.

Solution

The genotype of the parent is Tt and the genotype of the dwarf progeny is tt.

Q28. What is gene locus?

Solution

Gene locus is the particular location or position where a gene is located on a chromosome.

Q29. Haemophilia is due to

• 1) Factor-VII
• 2) Factor-IX
• 3) Factor-VI
• 4) Factor-VIII

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. 

Q30. Which of the following factors increases the strength of linkage between genes?

• 1) Temperature
• 2) Rapid mitosis
• 3) Age
• 4) X-rays

Solution

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

Q31. Mendel referred to genes as

• 1) Alleles
• 2) Traits
• 3) Factors
• 4) Gametes

Solution

Mendel referred to genes as factors before the word gene was introduced by Johannsen in 1909.

Q32. Inheritance pattern of ABO blood group in humans shows dominance, co-dominance and multiple allelism. Explain each concept with the help of blood group genotypes.

Solution

Dominance: The alleles I^A and I^B are dominant over allele i as I^A and I^B form antigens A and B, respectively, but i does not form any antigen. Co-dominance: Both the alleles I^A and I^B are co-dominant as both of them are able to express themselves in the presence of each other in blood group AB (I^AI^B) by forming antigens A and B. Multiple allelism: It is the phenomenon of occurrence of a gene in more than two allelic forms on the same locus.  The ABO blood group in humans is determined by three different allelic forms I^A, I^B and i. The above three explanations prove that the inheritance of ABO blood group in humans shows dominance, co-dominance and multiple allelism.   Genotype Surface antigen Blood group I^Ai A A I^AI^A A A I^Bi B B I^BI^B B B I^AI^B AB AB ii - O    

Q33. Muscular dystrophy is caused by

• 1) Transversion
• 2) Frameshift mutation
• 3) Substitution
• 4) Point mutation

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.

Q34. During his studies on genes in Drosophila which were sex-linked, T. H. Morgan found that the population phenotypic ratios deviated from  the expected 9:3:3:1 ratio. Explain the conclusion he arrived at.

Solution

(i) T. H. Morgan observed that  when  the  two genes  in a dihybrid cross are  located  on  the  same chromosome, the  proportion of parental gene  combinations in  the  progeny was much  higher than  the non-parental or recombination of genes. (ii) Morgan and his colleagues found that when genes were grouped on the same chromosome, some genes are tightly linked and show less recombination. (iii) When the genes are loosely linked, they show higher recombination.

Q35. A human being suffering from Down's syndrome shows trisomy of 21^st chromosome. Mention the cause of this chromosomal abnormality.

Solution

In Down’ syndrome, due to non-disjunction, the 21^st pair of chromosome fails to separate during oogenesis. Therefore, the egg possesses 24 chromosomes instead of 23. When the egg fuses with a sperm, the zygote has three copies of chromosome 21 resulting in trisomy.

Q36. (i) State the principle of independent assortment. (ii) How would the following affect the phenomenon of independent assortment? (a) Crossing over (b) Linkage

Solution

(i) The law of independent assortment states that the alleles of different characters located in different pairs of homologous chromosomes are independent of one another in their segregation during gamete formation and in coming together into the offspring by fertilisation, both processes occurring randomly. (ii) (a) Crossing over: Crossing over influences linked genes. As a result, 50% recombination is obtained in the test cross progeny. (b) Linkage: It influences recombination which is less than 50%.

Q37. A non-haemophilic couple was informed by their doctor that there is a possibility of a haemophilic child to be born to them. Explain the basis on which the doctor conveyed this information. Give the genotypes and the phenotypes of all possible children who could be born to them?

Solution

The doctor must have conveyed this information on the basis of pedigree analysis. Pedigree analysis is a strong tool used to trace the inheritance of a specific trait, abnormality or a disease. Because  both  the parents are non-haemophilic, their  genotypes will be                                                

Q38. (a) You are given tall pea plants with yellow seeds whose genotypes are unknown. How would you find the genotype of these plants? Explain with the help of a cross. (b) Identify a, b and  c in the table  given  below:   Sr. No. Pattern of inheritance Monohybrid F₁ phenotypic expression 1. Co-dominance a 2. b The progeny resembled only one of the parents 3. Incomplete dominance c    

Solution

(a) Test cross will be performed to know the genotype of the given tall pea plants with yellow seeds.       If all the plants of the F₁ generation are tall with yellow seeds, then the parent is homozygous dominant (Case i). If the plants in the F₁ generation are in the ratio 1:1:1:1, then the parent plant is heterozygous dominant. (b) a: Both the forms  of a trait are equally  expressed in the F1 generation. b: Dominance c: Phenotypic expression of the F₁ generation is somewhat intermediate between the two parental forms of a trait.