NCERT Solutions for Class 12 Science Biology Chapter 5 – Principles Of Inheritance And Variation
Explore the comprehensive NCERT Solutions for Class 12 Science Biology Chapter 5 on Principles of Inheritance and Variation, featuring clear, step-by-step explanations. Widely favored by class 12 Science students, these Biology solutions serve as valuable aids for efficiently completing homework assignments and preparing for exams. Free access to all questions and answers from the NCERT Book of class 12 Science Biology Chapter 5 is provided here, facilitating easy and cost-free assistance. Page No 93: Question 1: Mention the advantages of selecting pea plant for experiment by Mendel. ANSWER: Mendel selected pea plants to carry out his study on the inheritance of characters from parents to offspring. He selected a pea plant because of the following features. (a) Peas have many visible contrasting characters such as tall/dwarf plants, round/wrinkled seeds, green/yellow pod, purple/white flowers, etc. (b) Peas have bisexual flowers and therefore undergo self pollination easily. Thus, pea plants produce offsprings with same traits generation after generation. (c) In pea plants, cross pollination can be easily achieved by emasculation in which the stamen of the flower is removed without affecting the pistil. (d) Pea plants have a short life span and produce many seeds in one generation. Page No 93: Question 2: Differentiate between the following − (a) Dominance and Recessive (b) Homozygous and Heterozygous (c) Monohybrid and Dihybrid. ANSWER: (a) Dominance and Recessive Dominance Recessive 1. A dominant factor or allele expresses itself in the presence or absence of a recessive trait. A recessive trait is able to express itself only in the absence of a dominant trait. 2. For example, tall plant, round seed, violet flower, etc. are dominant characters in a pea plant. For example, dwarf plant, wrinkled seed, white flower, etc. are recessive traits in a pea plant. (b) Homozygous and Heterozygous Homozygous Heterozygous 1. It contains two similar alleles for a particular trait. It contains two different alleles for a particular trait. 2. Genotype for homozygous possess either dominant or recessive, but never both the alleles. For example, RR or rr Genotype for heterozygous possess both dominant and recessive alleles. For example, Rr 3. It produces only one type of gamete. It produces two different kinds of gametes. (c) Monohybrid and Dihybrid Monohybrid Dihybrid 1. Monohybrid involves cross between parents, which differs in only one pair of contrasting characters. Dihybrid involves cross between parents, which differs in two pairs of contrasting characters. 2. For example, the cross between tall and dwarf pea plant is a monohybrid cross. For example, the cross between pea plants having yellow wrinkled seed with those having green round seeds is a dihybrid cross. Page No 93: Question 3: A diploid organism is heterozygous for 4 loci, how many types of gametes can be produced? ANSWER: Locus is a fixed position on a chromosome, which is occupied by a single or more genes. Heterozygous organisms contain different alleles for an allelic pair. Hence, a diploid organism, which is heterozygous at four loci, will have four different contrasting characters at four different loci. For example, if an organism is heterozygous at four loci with four characters, say Aa, Bb, Cc, Dd, then during meiosis, it will segregate to form 8 separate gametes. If the genes are not linked, then the diploid organism will produce 16 different gametes. However, if the genes are linked, the gametes will reduce their number as the genes might be linked and the linked genes will be inherited together during the process of meiosis. Page No 93: Question 4: Explain the Law of Dominance using a monohybrid cross. ANSWER: Mendel’s law of dominance states that a dominant allele expresses itself in a monohybrid cross and suppresses the expression of recessive allele. However, this recessive allele for a character is not lost and remains hidden or masked in the progenies of F1 generation and reappears in the next generation. For example, when pea plants with round seeds (RR) are crossed with plants with wrinkled seeds (rr), all seeds in F1 generation were found to be round (Rr). When these round seeds were self fertilized, both the round and wrinkled seeds appeared in F2 generation in 3: 1 ratio. Hence, in F1 generation, the dominant character (round seeds) appeared and the recessive character (wrinkled seeds) got suppressed, which reappeared in F2 generation. Page No 93: Question 5: Define and design a test − cross? ANSWER: Test cross is a cross between an organism with unknown genotype and a recessive parent. It is used to determine whether the individual is homozygous or heterozygous for a trait. If the progenies produced by a test cross show 50% dominant trait and 50% recessive trait, then the unknown individual is heterozygous for a trait. On the other hand, if the progeny produced shows dominant trait, then the unknown individual is homozygous for a trait. Page No 93: Question 6: Using a Punnett square, work out the distribution of phenotypic features in the first filial generation after a cross between a homozygous female and a heterozygous male for a single locus. ANSWER: In guinea pigs, heterozygous male with black coat colour (Bb) is crossed with the female having white coat colour (bb). The male will produce two types of gametes, B and b, while the female will produce only one kind of gamete, r. The genotypic and phenotypic ratio in the progenies of F1 generation will be same i.e., 1:1. Page No 93: Question 7: When a cross in made between tall plants with yellow seeds (TtYy) and tall plant with green seed (TtYy), what proportions of phenotype in the offspring could be expected to be (a) Tall and green. (b) Dwarf and green. ANSWER: A cross between tall plant with yellow seeds and tall plant with green seeds will produce (a) three tall and green plants (b) one dwarf and green plant Page No 94: Question 8: Two heterozygous parents are crossed. If the two loci are linked what would be the distribution of phenotypic features in F1 generation for a dihybrid cross? ANSWER: Linkage is defined as the coexistence of two or more genes in the same chromosome. If the genes are situated on …