NCERT solutions for class 12 biology chapter 5 principles of inheritance and variation: Have you ever wondered why an elephant always gives birth only to a baby elephant and not any other animal? Or why a mango seed forms only a mango plant and not any other plant? Given that they do, are the offspring identical to their parents? Or do they show differences in some of their characteristics? These are several related questions which you will study in solutions for NCERT class 12 biology chapter 5 principles of inheritance and variation as in this you will get questions from interesting topics, as they are dealt with, scientifically, in a branch of biology known as Genetics. This subject deals with the inheritance, as well as the variation of characters from parents to offspring. CBSE NCERT solutions for class 12 biology chapter 5 principles of inheritance and variation will provide solutions to the questions based on two important topics that are Inheritance and variation. Inheritance is the process by which characters are passed on from parent to progeny, as it is the basis of heredity. Variation is the degree by which progeny differ from their parents. NCERT solutions for class 12 biology chapter 5 principles of inheritance and variation will provide you answers related to questions based on variation among living beings. Also, go through the NCERT solutions, if you want answers from any other class (6-12) then, it is the easiest way to get all the solutions of NCERT.
Solutions for NCERT class 12 biology chapter 5 principles of inheritance and variation is helpful if you want to understand the concepts like, work of Mendel and all the laws given by him.
Here are the important topics of NCERT Solutions for Class 12 Biology Chapter 5 Principles of Inheritance and Variation given below:
5.1 Mendel’s Laws of Inheritance
5.2 Inheritance of One Gene
5.2.1 Law of Dominance
5.2.2 Law of Segregation
220.127.116.11 Incomplete Dominance
5.3 Inheritance of Two Genes
5.3.1 Law of Independent Assortment
5.3.2 Chromosomal Theory of Inheritance
5.3.3 Linkage and Recombination
5.4 Sex Determination
5.6 Genetic Disorders
5.6.1 Sex Determination in Humans
5.6.2 Sex Determination in Honey Bee
5.8 GENETIC DISORDERS
5.8.1 Pedigree Analysis
5.8.2 Mendelian Disorders
5.8.3 Chromosomal Disorders
As Mendel proposed the principles of inheritance, which are today referred to as ‘Mendel’s Laws of Inheritance’. There are different types of law that you will study. For example:
- Law of Dominance
- Law of Segregation
- Law of Independent Assortment, etc.
After going through this chapter thoroughly, you will be able to solve these questions:
If you have any problem in solving them, then NCERT solutions for class 12 biology chapter 5 principles of inheritance and variation are there for you.
NCERT solutions for class 12 biology chapter 5 Principles of Inheritance and Variation Excercise:
Q1. Mention the advantages of selecting pea plant for experiment by Mendel.
The advantages of selecting garden pea (Pisum sativum) for experiments by Mendel were –
1. Pea has many visibly distinct contrasting characters.
2. The life span of the pea plant is short and they produce many seeds in one generation.
3. Pea flowers are bisexual and show self-pollination, reproductive whorls being enclosed by corolla.
4. It is easy to artificially cross-pollinate the pea flowers. The hybrids thus produced were fertile.
Q2. Differentiate between the following –
(a) Dominance and Recessive
The phenomenon wherein a factor (allele) expresses itself in the presence or absence of its dominant factor, is called dominance.
It can only express itself in the absence of its dominant factor.
It forms a complete functional enzyme that perfectly expresses it.
It forms an incomplete defective enzyme which fails to express itself when present with its dominant allele, i.e., in heterozygous condition.
(b) Homozygous and Heterozygous
|It contains two similar alleles for a particular trait. E.g TT, tt
||It contains two dissimilar alleles for a particular trait. E.g. Tt
|It can produce only one gametes
||It can produce two types of gametes
|It involves a cross between individuals differing in only one pair of characters
||It is a cross between individuals differing in two pairs of contrasting characters.
|The cross between tall (TT) and dwarf (tt) pea plants is monohybrid
||The cross between plants having yellow round (YYRR) seeds with those having green wrinkled (yyrr) seeds is dihybrid
Q4. Explain the Law of Dominance using a monohybrid cross.
According to Mendel’s law of dominance. traits are controlled by two different forms of the same gene. These alternative forms of a gene are called alleles. Among the two alleles, one is dominant while the other one is recessive. The dominant allele suppresses the expression of the recessive allele. Therefore whenever the two alleles are present together, the dominant one masks the expression of the recessive allele. However, it doesn't mean that the recessive allele has lost its existence. It remains hidden in F1 generation and reappears in the next generation. A monohybrid cross is given below.
In this cross, it can be seen that in F1 generation only tall plants were seen, no plant was dwarf. However in the F2 generation, the F1 progeny was self crossed, three genotypes were observed, among these, the hybrids were showing the dominant trait.
Q5. Define and design a test-cross.
A test cross is a cross between an individual showing a dominant trait with the one having its homozygous recessive trait in order to know whether the dominant trait is homozygous or heterozygous. If the ratio of a test cross is 1:1, it shows that the dominant trait is heterozygous.
(b) dwarf and green.
The cross between tall plant with yellow seeds (TtYy) and tall plant with green seed (Ttyy), will look like
Hence there will be only one plant with dwarf and green seed trait.
Linkage refers to the physical association of genes on the same chromosomes. The genes that show linkage are called linked genes. These linked genes show the same kind of inheritance pattern and are inherited together in the next generation. For example, a cross between yellow body and white eyes and wild type parent in a Drosophila will produce wild type and yellow-white progenies. It is because yellow bodied and white-eyed genes are linked. Therefore, they are inherited together in progenies. The percentage of parental types and recombinant types is 98.7% and 1.3% respectively.
Q9. Briefly mention the contribution of T.H. Morgan in genetics.
Contribution of T.H. Morgan in genetics
1. T.H Morgan discovered the chromosomal theory of inheritance.
2. He carried out many dihybrid crosses on Drosophila to study sex-linked disease.
3. Morgan discovered the phenomena called linkage to define the physical association of genes and recombination to describe the origin of non-parental gene combination.
Q10. What is pedigree analysis? Suggest how such an analysis, can be useful.
The analysis of inherited traits in several generations of a family is called the pedigree analysis. The inheritance of a particular trait is represented in a family tree over several generations. It is used to trace the inheritance of a particular trait, abnormality and disease. By pedigree analysis, genetic counsellors can help in preventing certain genetic disorders like haemophilia, sickle cell anaemia in the future generation of that family.
Q11. How is sex determined in human beings?
Sex determination in human beings
In humans, out of 23 pairs of chromosomes, 22 pairs are exactly the same in males and females called autosomes. However, a pair of the X chromosome is present in females and XY in males. During spermatogenesis, male produce two types of gametes (sperms), 50% carries Y chromosome and remaining 50% contain X chromosome. On the other hand, female produces only one kind of gamete (ovum) having X chromosomes only. When sperm having Y chromosome fertilizes the ovum the sex of the baby is male and when sperm carrying X chromosome fertilizes the egg, the sex of the baby is female.
Q13. Explain the following terms with example
It refers to the phenomenon of two alleles lacking dominance-recessive relationship and both expressing themselves in the heterozygous condition. In human beings, ABO blood grouping is controlled by gene I. The gene has three alleles IA, IB and i. One person may have any two of these three alleles. Among these alleles, IA, IB are dominant over i. Alleles and . When IA and IB are present together, both express themselves because of co-dominance.
(b) Incomplete dominance
Incomplete dominance is the phenomenon of neither of the two alleles being dominant so that expression in the hybrid is a fine mixture or intermediate between the expressions of two alleles. In snapdragon (Mirabilis jalapa), there are two types of pure breeding plants, red flowered and white flowered. On crossing the two, F1 plants possess pink flowers. On selfing them, F2 generation has 1red: 2 pink: 1white. The pink flower is due to incomplete dominance
Q16. Mention any two autosomal genetic disorders with their symptoms.
The two autosomal genetic disorders are as follows
1. Sickle cell anaemia – It is an autosome linked recessive trait in which mutant haemoglobin molecules undergo polymerization under low oxygen tension causing a change in the shape of the RBC from biconvex disc to elongated sickle like structure. The defect is caused by the substitution of Glutamic acid (Glu) by Valine (Val) at the sixth position of the beta globin chain of the haemoglobin molecule. The substitution of amino acid in the globin protein results due to the single base substitution at the sixth codon of the beta-globin gene from GAG to GUG. Symptoms include rapid heart rate, breathlessness, delayed growth and puberty, weakness, fever, decreased fertility etc.
2. Down syndrome- It is an autosomal genetic disorder caused by trisomy of chromosome 21. Symptoms of Down syndrome include short stature with a round head, protruding tongue, slanting eyes, broad short hands etc.
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