RBSE Solutions For Class 12 Biology Chapter 35: Mendel's Laws of Inheritance | Textbook Important Questions & Answers

RBSE Class 12 Biology Chapter 35 – Mendel’s Laws of Inheritance. In this chapter, students can learn in detail about Mendel’s experiments, different laws of Mendel, monohybrid cross, Di-hybrid cross, first filial generation, F1 generation, F2 generations, significances of Mendel’s law and reasons behind Mendel’s success, chromosomes and sex determination in humans. It also deals with the law of dominance, law of segregation, the law of independent assortment, back cross and test cross, deviations from Mendel’s law, lethal genes, multiple alleles, polygenes and a lot more.

These important questions help students to perform exceptionally well in their exams. By practising these important questions, students can analyze their preparation, get a thorough knowledge about all the important terminologies and perform their best in the examinations.

RBSE Solutions for Class 12 are the best study material for both class assignments and other board examinations. By practising these important questions, students can gain deep knowledge about the topics explained in this chapter and also help them to be well prepared for their upcoming examinations.

RBSE Class 12 Biology Chapter 35 Important Questions

RBSE Biology Chapter 35: MCQ Type Questions

Q.1. The law of independent assortment is proved by _________.

(a) All offspring of the F1 generation is long

(b) Long and dwarf plants produce in 3:1 ratio

(c) Expression of long and dwarf planets in the F2 generation

(d) Expression of plants having smooth and wrinkled seeds in the F2 generation

Sol: (d) Expression of plants having smooth and wrinkled seeds in the F2 generation.

Q.2. Which of the following is the main reason for the success of Mendel?

(a) Selection of the pea plants

(b) Maintained the records of the pedigree

(c) Studies only one character at a time of hybrid

(d) All of the above

Sol: (d) All of the above.

Q.3. A monohybrid cross gives an F2 generation is a characteristic phenotypic ratio of _________.

(a) 3:1

(b) 1:1

(c) 2:1

(d) 9:3:3:1

Sol: (a) 3:1

Q.4. The offspring produced by the crossing of red with white gives pink progeny. In this R gene represents _________.

(a) Hybrid

(b) Mutation

(c) Recessive

(d) Incomplete dominance

Sol: (d) Incomplete dominance.

Q.5. The effect of the genotype of group AB in human beings shows_________.

(a) Complimentary

(b) Codominance

(c) Dominant- Recessive

(d) Incomplete dominance

Sol: (b) Codominance

Q.6.What is the genotype ratio in the lethal gene?

(a) 9:3:3:1

(b) 1:2:1

(c) 2:1

(d) 3:1

Sol: (c) 2:1

Q.7. The factors which express its characters in the offspring is called_________.

(a) Alles

(b) Dominant factors

(c) Recessive factors

(d) All of the above

Sol: (c) Recessive factors.

Q.8. Mendel’s Law of Inheritance follows _________.

(a) Law of Dominance

(b) Law of segregation

(c) Law of Independent Assortment

(d) All of the above

Sol: (d) All of the above.

Q.9. How many pairs of chromosomes are present in the human body?

(a) 20pairs

(b) 23pairs

(c) 25pairs

(d) 46pairs

Sol: (b) 23pairs.

Q.10. The external expression of one or more characters of any individual is known as

(a) Genotype

(b) Homozygous

(c) Phenotype

(d) Heterozygous

Sol: (c) Phenotype.

RBSE Biology Chapter 35:Short Answer and Long Type Questions.

Q.1. Who is called the father of the heredity and why?

Sol: Gregor Johann Mendel (1822 – 1884) was the first person to explain the mechanism of the transmission of characters from generations to generations. Therefore, he is called the father of heredity.

Q.2. What are the monohybrid and dihybrid phenotypic ratios of the F2 generations?

Sol: The monohybrid phenotypic ratio of the F2 generations is 3:1- Dominant: Recessive.

The Dihybrid phenotypic ratio of the F2 generations is 9:3:3:1.

Q.3. What are the multiple gene characters?

Sol: Normally, phenotype expression is controlled by a pair of alleles. But when three or more alleles are responsible for one character it is called the multiple alleles.

For example- the ABO blood system.

Q.4. Where and in which organization Mendel read the research paper of his experiments?

Sol: Mendel read the research paper of his experiments in Brunn Society of Natural History from 8th Feb to 8th March 1865.

Q.5. In which language the original research paper of Mendel was published and what was its title?

Sol: The original research paper of Mendel was published in the German language.

The title was Versuche Über Pflanzenhybriden.

Q.6. Who rediscovered Mendel’s work?

Sol: The Mendel’s work was rediscovered in the early 1900s by three botanists:

Hugo De Vries (Holland)

Erich Von Tschermak (Austria)

Carl Correns (Germany).

Q.7. Write the difference between Homozygous and Heterozygous.

Sol: Difference between Homozygous and Heterozygous:

Homozygous Heterozygous
It consists of two copies of the same allele that codes for a particular trait. It consists of two different copies of alleles that code for a particular trait.
It consists of either dominant or recessive allele pairs but not both It consists of both dominant and recessive allele pairs
Formation of only one type of gametes Formation of two types of gametes
Self-breeding of homozygous resulted in the same traits over generations Self-breeding of heterozygous resulted in the combination of traits
The two types of homozygous alleles are homozygous-dominant and homozygous-recessive The three types of heterozygous alleles complete dominance, incomplete dominance, and codominance

Q.8. What is Allele?

Sol: An allele is a variant form of a gene or an alternative forms of a gene

For example- Blue colour and Black colour of the eye are two alleles of the colour of the eye gene.

An allele is a short form of Allelomorph. Similarly, for the seed of the pea plant the shape of the seed is round (R) wrinkled (r) are the two alleles.

Q.9. What are Lethal genes?

Sol: Some of the genes function both by controlling the external characteristics and also affect the viability of organisms.

L.Cuenot in 1905 presented results of his experiment on the body colour of rates. These results were different from Mendel’s law of segregation.

According to his experiments, the yellow colour of the skin is due to the gene Y and the grey colour of the skin is due to the gene y in which Y is dominant over y (grey colour).

When the yellow colour rats were crossed with the grey colour rats then the yellow and grey colour rats were produced in the ratio of 2:1.

Genotypically, the yellow coloured rats (Yy) were heterozygous and the grey coloured rats (yy) were homozygous.

The Yy yellow colour (heterozygous) rats were unable to survive. Hence, the Y gene is responsible for the yellow colour of the rats and it also affects the survival capacity.

The yellow homozygous (YY) rats can not survive, hence homozygous rats are not found at all.

Therefore, the YY genes are called lethal genes and this incidence is known as lethality.

Some lethal genes are lethal only in the homozygous recessive condition and celled recessive lethal gene, while the dominant lethal gene may be lethal even in the heterozygous conditions.

Q.10. What is the Dominant and Recessive trait?

Sol: Amongst the two alleles of a character, the character expresses in a heterozygous condition called dominant character. This incidence is known as Dominance and the gene responsible for it is called a dominant allele.

For example, Tt containing a pea plant has T for tallness and t for dwarfness and T is the dominant character.

Recessive character

Amongst the alleles of a character in the F1 generation, which is not expressed is called recessive character. It expresses only in the homozygous condition of the character.

For example, tt condition expresses the dwarfness of a plant.

Q.11.What is Polygenes?

Sol: Polygenes, also called multiple genes.

  1. The phenotype traits which are governed by three or more genes are called polygenic traits. The polygenic traits show a wide range of phenotypes. Each gene of the polygenic trait contributes to the phenotypes but to a small degree.
  2. The presence of more than one dominant gene makes the phenotype more prominent. All the dominant genes add up their effects to produce a full phenotype. Therefore, the polygenic traits are also called the quantity traits.
  3. Inheritance of such traits is called polygenic or quantitative inheritance.
  4. The polygenes may occupy two or more different loci on the same homologous chromosome pair.
  5. It was first studied in humans by Galton in 1883.
  6. The well-known examples of a polygenic trait are human skin colour and kernel colour in wheat.
  7. The other examples of polygenic traits in human beings are eye colour and body height.
  8. Example: 1- Human skin colour.
  9. The human skin colour is a polygenic effect and controlled by three pairs of genes Aa, Bb, Cc.
  10. These genes are located on different chromosomes and are inherited independently.
  11. Each gene contributes to a unit of darkness due to incomplete dominance.
  12. The colour of the skin varies from a very light and has many shades of intermediate colours. Hence, a total of 64 phenotypic combinations is possible for skin colours.

Q.12. What are the reasons and the achievements of Mendel’s success?

Sol:

Reasons for Mendel’s law:

  • Mendel with his experiments discarded all the theories given by earlier scientists, as these theories were hypothetical and were not based on the scientific experiments.
  • Initially, Mendel’s work was also not recognized by other scientists. But it was accepted after 34 years of his death.
  • Mendel, when three scientists Hugo de Vries, Karl corners and Eric Von Tschermak obtained the same results as Mendel.
  • Mendel is known as the “Father of Genetics” for his valuable contribution in the area of heredity.

Achievements of Mendle’s work are mentioned below:

  • Scientists discovered dominant and recessive characters in living beings on the basis of Mendel’s work.
  • Beneficial characters of different genera are brought together in a genus.
  • By using Mendel’s law, the discovery of immunity against diseases, continuity in adverse conditions, flowers and fruits of good quality and in quantity are developed.
  • Similarly, breeds of cows, buffalo and hen are improved.

Q.13. Write the differences between Genotype and Phenotype.

Sol: Differences between Genotype and Phenotype:

Genotype Phenotype
The hereditary information of the organism in the form of the gene in the DNA and remains the same throughout life. The characters of an organism which are visible are known as phenotypes.
The same genotype produces the same phenotype. The same phenotype may or may not belong to the same genotype.
Present inside the body as genetic material. Expression of genes as the external appearance.
The genotype is inherited from the parent to the offspring The phenotype is not inherited from the parent.
It can be determined by scientific methods such as the polymerase chain reaction. It can be determined by observing the organism.
It is affected by genes. It is affected by genotype and environmental conditions.
For eg., Blood group, eye colour, height, genetic diseases. For eg., Weight, physique, the beak of birds, etc.

Q.14.What is Codominance?

Sol: Dominance is a relationship between two alleles of one gene that affect the phenotype of one allele and masks the contribution of another allele. The dominant and recessive factor of an allele equally expresses their characters in the F1 generation. It is called codominance. The skin colour in castles is red (RR) and white (RR) is found. The cross of these gives a roan colour of the skin in the F1 generation.

Then the cross between the F1 generations gives red, roan and white skin castles in the F2 generation. The ratio of the red, roan and white coloured skin are found 1:2:1 (RR:Rr: RR). The results do not follow the Mendelian ratio with regards to the colours.

Codominance

Q.15. Write the difference between Monohybrid Cross and Dihybrid Cross.

Sol: There are two different types of breeding methods, which are used to know the working of genes and to analyze how certain traits are inherited from grandparents and parents.

A monohybrid cross is defined as the cross happening in the F1 generation offspring of parents differing in one trait only.

A dihybrid cross is a cross that happens to F1 generation offspring of differing two traits.

Differences between the Monohybrid Cross and Dihybrid Cross:

Monohybrid Cross Dihybrid Cross.
Refers to the single mixed breed. Refers to the double mixed breed.
Used to study the inheritance of a single pair of alleles. Used to study the inheritance of two different pairs of alleles.
The genotype ratio is 1:2:1. The genotype ratio is 1:2:1:2:4:2:1:2:1.
The phenotype ratio is 3:1. The phenotype ratio is 9:3:3:1.
Ratio cross-test is -1:1. Ratio cross-test is -1:1:1:1.

Q.16. Describe the incomplete dominance with an example.

Sol: Incomplete Dominance:

Incomplete dominance is a form of Gene interaction in which both alleles of a gene at a locus are partially expressed, often resulting in an intermediate or different phenotype. It is also known as partial dominance. For eg., in roses, the allele for red colour is dominant over the allele for white colour. But, the heterozygous flowers with both the alleles are pink in colour.

Examples of incomplete dominance

In Humans

The child of parents each with curly hair and straight hair will always have wavy hair. Carriers of Tay-Sachs disease exhibit incomplete dominance.

In Other Animals

The Andalusian chicken shows incomplete dominance in its feather colour.

When the rabbits with long and short furs are bred, the offsprings produced will have medium fur length.

Mechanism of Incomplete Dominance

Incomplete dominance occurs because neither of the two alleles is completely dominant over the other. This results in a phenotype that is a combination of both.

When neither of the two alleles is dominant and the phenotype of the heterozygote does not resemble any of the parents, the heterozygote expresses intermediate or a mixture of two parents’ traits

Example: The flower colour inheritance of snapdragon (dog flower). On crossing true breeding red (RR) and white flowers (rr), we get all pink colour flowers in the F1 generation, which on self-pollination give red: pink: white flowers in the ratio 1:2:1 in the F2 generation.

Incomplete Dominance

Q.17. Explain why Mendel selected Pea plants for his experiment?

Sol: The selection of garden pea by Mendel for his experiments:

Mendel carried out his work on the garden pea Pisum sativum. He selected this plant because of the following reasons:

  1. It was easily grown in large numbers in open ground and in the pots.
  2. The plant has a short life span and it completes in one season, so the study of many generations is possible in a few years.
  3. The pea plants are small, easy to crossbreed artificially.
  4. The pea plant flower being bisexual and exhibits self-fertilization in nature so that th purity of the characters can be maintained until many generations but can be easily cross-pollinated experimentally.
  5. A large number of true-breeding varieties of peas are available or we can say many contrasting characters are found in the pea plants.

Q.18. What are the three laws of inheritance proposed by Mendel?

Sol: The two experiments lead to the formulation of Mendel’s laws known as laws of inheritance which are:

  1. Law of Dominance.
  2. Law of Segregation.
  3. Law of Independent Assortment.

Q.19.What was the main aim of Mendel’s experiments?

Sol: The main aim of Mendel’s experiments was:

  1. To determine whether the traits would always be recessive.
  2. Whether traits affect each other as they are inherited.
  3. Whether traits could be transformed by DNA.

Q.20. What is a monohybrid cross? Give examples of a monohybrid cross.

Sol: A monohybrid cross is a genetic mix between two individuals with homozygous genotypes which result in an opposite phenotype.

Example of a monohybrid cross.

For monohybrid cross, Mendel began with a pair of pea plants with two contrasting traits i.e., one tall and another dwarf. The cross-pollination of both the contrasting traits resulted in tall plants. All the hybrid plants were tall. He called this as the first hybrid generation (F1) and offspring were called Filial1 or F1 progeny.

He conducted an experiment with all seven contrasting pairs. He observed that the entire F1 progeny showed one pattern in their behaviour i.e., they resembled one of the parents. Another parent character was completely absent.

Monohybrid cross

Mendel continued his experiment with self-pollination of F1 progeny plants. Surprisingly, he observed that one out of four plants were dwarf while the other three were tall. The tall and the short plants were in the ratio of 3:1.

He also noted that no progeny was in intermediate height i.e., no blending was observed. This result was the same for other traits of plants too. Therefore, Mendel named them the second hybrid generation and their offspring were called F2 progeny or Filial2.

Monohybrid cross - F1 and F2 generation

Mendel observed that traits which were absent in F1 generation had reappeared in the F2 generation. He called such suppressed traits as recessive traits and expressed traits as dominant traits. He also concluded that some ‘factors’ are inherited by offspring from their parents over successive generations.

Q.21. What are Phenotype and Genotype?

Sol: The phenotype can be defined as the set of physical characteristics of an organism, including hair colour, body weight, eye colour, the shape of the body, and height, are determined by an individual’s outcome of the interaction of the genotype with the environment.

Genotype refers to the genetic constitution of living organisms, which determines the various genetic traits of the organism. The three possible genotypes include:

  1. Homozygous dominant (PP).
  2. Heterozygous (Pp).
  3. Homozygous (pp).

Both the genotype and phenotype sound similar. Compared to genotype, phenotypic changes constantly throughout life and varies with environmental conditions.

Q.22. What are the selection characters of a pea plant?

Sol: Among the 34 contrasting characters found in a pea plant, Mendel selected totally seven pairs of contrasting characters for his study. These characters are listed in the below tabular column

Character Recessive Dominant
Height of a plant Dwarf Tall
Position of a flower Terminal Axillary
The shape of the pod Constricted Inflated
Colour of the pod Yellow Green
The shape of the seed Wrinkled Round
Colour of the seed coat White Grey
Colour of the cotyledon Green Yellow

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