Biology Question Bank: Genetic Basis of Inheritance

Physics Chemistry  Biology  Mathematics
Physics Question Bank Chemistry Question Bank Biology Question Bank Maths Question Bank
Maharashtra State Board > Science > Biology Question Bank > Genetic Basis Of Inheritance > You are Here

1 Mark Questions

Q1 Define: Heredity

  • The transmission of characters from one generation to the next, that is from parents to offsprings (progeny) is known as heredity.

Q2 Define: Genetics

  • Genetics is a branch of a biology that deals with the study of heredity and variations.

Q3 Who coined the term ‘genetics’?

  • The term ‘genetics’ was coined by William Bateson in 1906.

Q4 Who gave the first scientific explanation regarding inheritance? When?



  • The first scientific explanation regarding inheritance was given by Gregor Johan Mendel in 1866.

Q5 What is Mendel’s law of Inheritance also known as?

  • Mendel’s law of Inheritance and his study are known as ‘Mendelism’

Q6 Why is Mendel known as “Father of Genetics”?

  • The first scientific explanation regarding inheritance was given by Gregor Johan Mendel in 1866. He performed experiments on garden pea in a very scientific manner and proposed postulates. He laid down foundations of genetics. Hence Mendel is known as “Father of Genetics”

Q7 Who is known as the father of Genetics?

  • Gregor Johan Mendel is known as the father of Genetics

Q8 What are Mendelian factors also known as?



  • Mendelian factors are known as genes.

Q9 In what capacity did Mendel join Augustinian Monastery of Brunn?

  • After graduation, Mendel joined Augustinian Monastery of Brunn as a priest.

Q10 What was the title of paper which Mendel presented in 1865?

  • The title of paper which Mendel presented in 1865 was “Experiments in plant hybridization”.

Q11 It was based on Mendel’s principles that three laws known as Mendel’s Laws of Inheritance were postulated. Who postulated these laws?

  • Correns postulated Mendel’s Laws of Inheritance.

Q12 Which journal published the paper entitled “Experiments in plant hybridization” in 1866?

  • “Annual Proceedings of Natural History Society” published the paper entitled “Experiments in plant hybridization” in 1866.

Q13 Name the scientists who rediscovered Mendel’s work in the year 1900.



  • In 1900 eminent biologists, Karl Correns of Germany, Hugo de Vries of Netherlands and Erich Von Tschermak of Austria working independently discovered Mendel’s work.

Q14 What is the botanical name of garden Pea?

  • The botanical name of garden Pea is Pisum Sativum L

Q15 What is an Allele?

  • Two or more alternative forms of a gene present at the same loci of homologous chromosomes and controlling the same character are called alleles.

Q16 What is emasculation?

  • Emasculation is a process of removal of stamens before the formation of pollen grains (anthesis).
  • This is done in the bud condition. The bud is carefully open and all stamens (9 + 1) are removed carefully. The stigma is protected against any foreign pollen with the help of a muslin bag.

Q17 Give an example of incomplete dominance.

  • a flower of four o’ clock plant (Mirabilis jalapa) is pink (Rr) as a result of cross-pollination between a red flower (RR) and a white flower (rr) when neither the white or the red alleles are dominant.
  • Another example: a flower of Snapdragon (Antirrhinum majus) is pink (Rr) as a result of cross-pollination between a red flower (RR) and a white flower (rr) when neither the white or the red alleles are dominant.

Q18 Give an example of multiple alleles.



  • The example of multiple alleles is ABO blood groups in human beings.
  • Another example: Multiple alleles in Drosophila which results in the series of wing abnormality ranging in size from normal wings to no wings.

Q19 Give an example of pleiotropy.

  • The phenomenon of controlling more than one characters at the same time is called pleiotropy or pleiotropism.  Example of pleiotropy is sickle cell anaemia.

Q20 Give an example of polygenic inheritance

  • These characters are determined by two or more gene pairs and they have an additive or cumulative effect.  The example of polygenic inheritance is human skill colour.

2 Marks Questions

Q1. Define: a) Genotype b) Phenotype

Genotype:

  • It is the genetic constitution of an individual with respect to a single character or a set of characters.
  • In garden pea plant, genotype for a tall plant is TT or Tt. For a dwarf plant, the genotype is tt.

Phenotype:



  • The external appearance of an individual for a given trait is called phenotype.
  • In garden pea plant Height of a stem is a character. Its two variants are tall (T) and dwarf (t). Thus tall and dwarf are phenotypes.

Q2. Define the term Dihybrid cross.

  • It is a cross that involves the study of inheritance of two pairs of contrasting characters at a time.
  • The inheritance of yellow round seed character and green wrinkled character is an example of a dihybrid cross.

Q3. Define the term Monohybrid cross.

  • It is a cross that involves the study of inheritance of only one pair of contrasting character at a time.
  • The inheritance of tall and dwarf characters is an example of a monohybrid cross.

Q4. Explain the terms
a) Factor:

  • It is a unit of heredity. This concept was given by Mendel.
  • The unit of inheritance and expression of a particular character is controlled by inheritable units called factor (gene) which are present in pairs in parental cells and singly in the gametes.
  • It is responsible for the inheritance and expression of character.

b) Alleles:



  • The two (or more) alternative forms of a gene (factor) are called alleles of each other. They occupy identical positions on homologous chromosomes.
  • For example in pea plant, the gene for producing seed shape may occur in two alternative forms: smooth (S) and wrinkled (s). Genes for smooth wrinkled seeds are alleles of each other and occupy the same locus on homologous chromosomes.

c) Emasculation:

  • Emasculation is a process of removal of stamens before the formation of pollen grains (anthesis).
  • This is done in the bud condition. The bud is carefully open and all stamens (9 + 1) are removed carefully.
  • The stigma is protected against any foreign pollen with the help of a muslin bag.

d) F1 generation:

  • The progeny (offspring) produced from a cross is called first filial or F1 generation.
  • It shows uniform expression.

e) Dihybrid:

  • It is heterozygous for two traits and produced in a cross between two pure parents differing in two pairs of contrasting character.
  • e.g. Hybrid tall produced in a cross between pure tall bearing white flowers and dwarf parent bearing purple flowers.

Q5. Explain the statements.

a) A test cross is a back cross, but back cross is not necessarily a test cross.



  • Case – 1: When the F1 generation is crossed with Recessive Parent:
  • The recessive parent can produce only one type of gamete ‘t’, while the hybrid of the first generation can produce two types of gametes ‘T’ and ‘t’. Thus half the progeny (F2 generation) will have genotype ‘Tt’ (tall) and remaining half ‘tt’ (dwarf).
  • Case – 2: When the F1 generation is crossed with Dominant Parent:
  • The dominant parent can produce only one type of gamete ‘T’, while the hybrid of the first generation can produce two types of gametes ‘T’ and ‘t’. Thus 100 % progeny is tall. half the progeny will have genotype ‘TT’ (Pure tall) and remaining half ‘Tt’ (Hybrid tall).
  • A test cross is a cross used to find the genotype of F1 generation. The test cross is a cross between an individual with unknown genotype for a particular trait with a recessive plant for their trait, While back cross is a cross between an individual with unknown genotype for a particular trait with a recessive or dominant plant for their trait.  Back cross cannot indicate the genotype of F1 generation. Hence a test cross is a back cross but a back cross is not a test cross.

b) Law of dominance is not universally applicable

  • The law of dominance is significant and true but is not universally applicable.
  • There are some cases where dominance is not complete or absent. Thus there are cases of incomplete dominance or co-dominance.
  • This cases can be explained by studying cases of deviations from Mendelian inheritance. Hence the law of dominance is not universally applicable.

c) Law of segregation is universally applicable.

  • Members of an allelic pair in hybrid remain together without mixing with each other and separate or segregate during gamete formation. Thus gametes receive only one of the two factors and are pure for a given trait. Hence this law is also known as the Law of Purity of Gametes.
  • All sexually reproducing higher organisms are diploid (2n) i.e. with the two sets of chromosomes and gametes are haploid (n) i.e. with one set of chromosome. Therfore the law of segregation is universally applicable.

Q6. Distinguish between incomplete dominance and co-dominance.

Incomplete dominance Co-dominance
Incomplete dominance is the one in which neither of the parental genes are able to express themselves independently in the progeny but a blend of both is expressed. Co-dominance is the one in which both parental genes are expressed equally in the progeny. None the of the parental gene is able to repress each other
The resulting progeny resembles neither of its parents. The phenotype of hybrids is intermediate between the phenotypes of parents. The resulting progeny resembles both to both of its parents at the same time. The phenotype of hybrid expresses both the traits from either parent.
Example : In snapdragon flower, if a pure (homozygous) red coloured flower is crossed with pure(homozygous)white coloured flower then the F1 generation includes pink coloured  flower (heterozygous). Example: A coat colour in cattle. If one with red coat (skin with red colour hair) is crossed with one having white coat then the F1 hybrid would have roan colour hair(.i.e. patches of both red and white colour hair on skin)


Q7. Distinguish between genotype and phenotype.



Genotype   Phenotype
It is the genetic constitution of an individual with respect to a single character or a set of characters. The external appearance of an individual for a given trait is called phenotype.
It is determined by inheritance pattern It can directly be seen
Genotype cannot be determined by phenotype. E.g. the gene constitution of a tall plant may be TT or Tt The phenotype can be determined by genotype. E.g. genotype (Tt) means a tall plant
In garden pea plant, genotype for a tall plant is TT or Tt. For a dwarf plant, the genotype is tt. In garden pea plant Height of a stem is a character. Its two variants are tall (T) and dwarf (t). Thus tall and dwarf are phenotypes

3 Marks Questions

Q1. How many traits did Mendel study? Enlist them.

  • Mendel studied the following seven traits because they seemed to inherit independently of other traits.


Q2. Define Monohybrid cross. Give its typical graphic representation.

  • It is a cross that involves the study of inheritance of only one pair of contrasting character at a time.
  • The inheritance of tall and dwarf characters is an example of a monohybrid cross.

Graphic Representation of Monohybrid Cross:


Q3. What is the law of segregation also known as? Explain why it is called so.

  • The law of segregation is also known as the law of purity of gametes.
  • Members of an allelic pair in hybrid remain together without mixing with each other and separate or segregate during gamete formation. Thus gametes receive only one of the two factors and are pure for a given trait. Hence this law is also known as the Law of Purity of Gametes.

Q4. Distinguish between homozygous and heterozygous.

Homozygous Heterozygous
When both the alleles of a gene are similar, then the individual is called homozygous for the trait. When both the alleles of a gene are dissimilar, then the individual is called heterozygous for the trait.
The genotype for a characteristic, for example stem length (tall/dwarf) is expressed as TT or tt, The genotype is expressed as Tt,
They contain either both the dominant or recessive allele. They contain one dominant and one recessive allele.
On self-pollinating, the progeny possesses the same genotype and phenotype On self-pollinating the progeny possesses 3 genotypes, and mostly 2 or 3 phenotypes.
They are true breeding and a pure line can be obtained. Not true breeding

Q5. Explain – Why was Mendel successful.



  • Mendel studied the inheritance of one character at a time whereas earlier scientists had considered the organism as a whole. Initially, Mendel considered inheritance of one trait only. (Monohybrid). Then he studied two traits together (dihybrid) and then three (Trihybrid).
  • He started with pure line i.e. true breeding. He maintained a complete statistical record by counting an actual number of offspring.
  • He carried out experiments up to the second and the third generations.
  • He conducted ample crosses and reciprocal crosses to eliminate chance.
  • He dealt with a large sample size.

Q6. Write a brief note on Mendel’s life.

  • Gregor Johann Mendel was born on July 22, 1822, in a village of Austria. In 1853, upon completing his graduation at the University of Vienna, he returned to the monastery in Brunn and was given a post of priest and a teaching position at a secondary school. He performed a number of experiments with garden pea plant at this monastery and proposed laws of inheritance.
  • He presented his work in 1865 for the first time before Brunn Society for the Study of Natural Science His work was published in the proceedings of the society in 1866. His work was ignored at that time. The ignorance was may be due to his work was ahead of his time and he published his work in an obscure journal.
  • In 1900 eminent biologists, Karl Correns of Germany, Hugo de Vries of Netherlands and Erich Von Tschermak of Austria working independently discovered Mendel’s work.
  • The concept of factors was given by Mendel. Mendel proposed that the characters are transmitted from one generation to the next through particle. He called these particles as factors. Nowadays these factors are called genes.
  • The first scientific explanation of inheritance was given by Mendel in 1866. He performed a series of experiments on garden pea in a scientific manner and proposed rules. which are called Mendel’s Laws of Inheritance. His work is known as Mendelism. He laid down a foundation of Genetics hence he is called Father of genetics.

Q7. Describe Monohybrid Artificial Cross of the Selected parents to raise F1 generation.

  • A cross between two pure (homozygous) pattern in which the inheritance pattern of only one of contrasting characters is studied is called monohybrid cross.
  • It is a cross between two pure (obtained by true breeding) parents differing in a single pair of contrasting characters.

The Procedure of Monohybrid Cross Experiment:

  • Step – 1: He selected pure line plants by ensuring that the selected male (pure dwarf) and female parent plants (pure tall) are breeding true for the selected trait or traits by selfing them for three generations. Thus pure line plants are homozygous for given trait.
  • Step – 2: Emasculation, Dusting and Raising F1 Generation (Hybridization):
  • Emasculation: Emasculation is a process of removal of stamens before the formation of pollen grains (anthesis). This is done in the bud condition. The bud is carefully open and all stamens (9 + 1) are removed carefully. The stigma is protected against any foreign pollen with the help of a muslin bag.
  • Dusting and Raising F1 Generation: The pollens from selected male flower are dusted on the stigma of an emasculated female flower. The cross-pollinated flowers were enclosed in separate bags (bagging) to avoid further deposition of pollens from another source. During the pollination, it was assured that the pollen is mature and the stigma is receptive. This is an artificial cross. Mendel crossed many flowers, collected seeds and raised F1  generation. The plants used as parents are said to represent parental generation and is designated as P1. The progeny obtained as a result of the crossing between parents is called the first filial (offspring) generation and is represented as F1. All plants of F1 generation were tall.
  • Punnett Square for F1 Generation:

T (tall) is a dominant character t (dwarf) is a recessive character.

5 Marks Questions

Q1. What are characters or traits (2 or more) controlled by a single gene called? Explain with an example. Why its phenotypic ratio is 2:1 instead of 3:1.?

  • The phenomenon of controlling more than one characters at the same time is called pleiotropy or pleiotropism. Such genes are called pleiotropic genes. These genes produce more than one phenotypic effects which are totally unrelated.
  • The pleiotropic effect is produced by a gene owing to a cascade (succession) of reactions during some metabolic pathway which is influenced by the original gene product and contributes to different phenotypic effects.
  • Sometimes, the pleiotropic gene effect may produce various abnormal phenotypic features which are collectively called syndromes.
  • If the effects of the pleiotropic gene become the cause of the death of an individual, then the pleiotropic gene is called the lethal gene. The lethal genes cause a great deviation from the normal development of an individual. Hence, that individual does not survive.
  •  As a result of the lethal effect, Mendel’s monohybrid ratio of 3:1 gets modified and changed into 2:1. This lethal gene is seen either in the homozygous dominant condition or homozygous recessive condition.

Q2. Which plant did Mendel select for his experiments? Why? Explain any three characteristics of the same.

  • Mendel selected Garden Pea (Pisum Sativum L) for his experiments.

Reasons for Selection of Garden Pea (Pisum Sativum L) for the experiment:

  • Garden pea is an annual plant and completes the life cycle within three or four months. Due to this short lifespan, he was able to take three generations in a year.
  • It is a small herbaceous plant that produces many seeds and so he could grow thousands of pea plants in a small plot behind the church.
  • It is naturally self-pollinating and was available in the form of many varieties with contrasting characters. There were no intermediate characters.
  • Flowers are large enough for easy emasculation required for artificial cross and produce fertile offspring.
  • The contrasting characters are as in the following table

Q3. A plant with red flowers is crossed with a plant with white flowers and the plant does not show incomplete dominance or co-dominance. Predict diagrammatically the above and Add a note on the type of cross.

  • If it does not show incomplete dominance or codominance, then the plant is exhibiting dominance. Now let us assume the red is dominant over white (assumption as dominant/recessive not mentioned in the question)
  • We consider following Mendelian cross.

Pure red-flowered plant (RR)  X Pure white-flowered plant (rr)

The gametes formed are R, R, and r,r

Rr —- Hybrid showing red flower.

  • This shows the dominance of a trait over the other and dominant trait gets expressed in F1 hybrid. All the flowers of F1 generation are hybrid red.
  • By selfing F1 generation F2 generation obtained.

Hybrid red (Rr)  X Hybrid red (Rr)

The gametes formed are R and r

  • The resultant phenotype ratio in F2 generation is 3 red : 1 white i.e. 3:1
  • The resultant genotype ratio in F2 generation is 1 pure red : 2 hybrid red : 1 pure white i.e. 1:2:!

Q4. Every time Mendel performed dihybrid cross he found two parental combinations and two new. Which principle did he apply? And what law was established?

  • For dihybrid cross, Mendel selected pea plant having yellow and round seeds (YYRR) as the female parent and pea plant having green and wrinkled (yyrr) seeds as the male parent. He obtained pure line by selfing these plants for three generations. He confirmed that pea plant having yellow and round seeds are producing yellow and round seeds and pea plant having green and wrinkled seeds are producing green and wrinkled seeds.
  • The pollens from selected male flower are dusted on the stigma of the emasculated female flower. This is artificial cross. Mendel crossed many flowers, collected seeds and raised F1 generation. The female plant produces gametes with genes YR while male plant produced gametes with genes yr.
  • Yellow and round are dominant alleles, hence all F1 Generation was with yellow and round seeds. All the plants produced in F1 generation with yellow and round seeds (YyRr), which are heterozygous for both the alleles and are called dihybrid.
  • Mendel allowed natural pollination in each F1 hybrid; collected seeds separately and F2 generation is obtained.

  • He found seeds of four types, yellow round, yellow wrinkled, green round and green wrinkled in the ratio 9:3:3:1.
  • Out of these four types, two were parental combinations. Viz. yellow round and green wrinkled and two were new combinations like yellow wrinkled and green round.
  • In all Mendelian dihybrid crosses the ratio in which four different phenotypes occurred was 9:3:3:1. This ratio is called the dihybrid ratio.
  • Phenotypic ratio i.e. the ratio of the yellow round, yellow wrinkled, green round and green wrinkled in the ratio 9:3:3:1.
  • From this, a new law was established called the law of independent assortments.
  • The Law of Independent Assortment:
  • When two homozygous parents differing in two pairs of contrasting traits are crossed, the inheritance of one pair is independent of other.
  • In other words, when a dihybrid (or polyhybrid) forms gametes, assortment (distribution) of alleles or different traits is independent of their original combinations in the parents. This law can be explained by the help of dihybrid cross and dihybrid ratio.
  • It is immaterial whether both dominant characters enter the hybrid from the same or two different parents but the segregation and assortment remain the same.
  • The appearances of new combination prove the law. The law is universally applicable.

Q5. What did H.Nilsson – Ehle discover with reference to wheat kernel colour ? Give the graphic representation of the same.

  • Swedish geneticist H. Nilsson-Ehle discovered polygenic inheritance in wheat kernel colour.
  • He crossed a red kernelled variety of wheat with white kernelled variety. In F1 generation all plants have grains with intermediate colour between red and white. In F2 generation five different phenotypic expressions (the darkest red, medium red, intermediate red, light red, white) appeared in the ratio 1:4:6:4:1.
  • Nilson Ehle suggested that the kernel colour in wheat is controlled by two pairs of genes, Aa and Bb. Genes A and B determine red colour. a and b which do not produce red colour pigment and their expression is a white colour of the kernel.

heredity

Maharashtra State Board > Science > Biology Question Bank > Genetic Basis Of Inheritance > You are Here
Physics Question Bank Chemistry Question Bank Biology Question Bank Maths Question Bank
Physics Chemistry  Biology  Mathematics

Leave a Comment

Your email address will not be published. Required fields are marked *