Bihar Board Class 12 Biology Solutions Chapter 5 Principles of Inheritance and Variation Textbook Questions and Answers, Additional Important Questions, Notes.
BSEB Bihar Board Class 12 Biology Solutions Chapter 5 Principles of Inheritance and Variation
Bihar Board Class 12 Biology Principles of Inheritance and Variation Text Book Questions and Answers
Question 1.
Mention the advantages of selecting pea plant for experiment by Mendel.
Answer:
The advantages of selecting pea plant for experiment by Mendel are as follows :
The pea plant were manifested by two opposing traits, e.g. tall or dwarf plant, yellow or green seeds. This allowed him to set up a basic framework of rules governing inheritance.
Mendel selected the true-breeding pea plant varieties, as pair which were similar except for one character with contrasting traits.
Question 2.
Differentiate between the following :
(a) Dominance and Recessive
(b) Homozygous and Hetrozygous .
(c) Monohybrid and Dihybrid.
Answer:
(a) Difference between dominance and recessive :
Dominance – The phenotype of the F, heterozygote Tt is a exactly like the TT parent in appearance and in a pair of dissimilar factor, one dominates the other and hence is called dominant factor or dominance.
Recessive – If T (for tallness) is dominant overt (for dwarf ness), it is called recessive.
(b) Difference between Homozygous and Heterozygous :
Homozygous refers to identical. For example in a true-breeding tall or
dwarf pea variety, the allelic pair of genes for height are identical it is referred as homozygous. A homozygous parent produces all gametes that are similar.
Heterozygous – When the hybrids have both dominance and recessive characters, there hybrids contain alleles which express constrasting traits, such plants are heterozygous. A heterozygous produces two kinds of gametes each having one allele with equal proportion.
(c) Difference between monohybrid and dihybrid :
Monohybrid – Genes control one factor, for example height, it is monohybrid.
Dihybrid – When genes control more than one factor it is referred to as dihybrid.
Question 3.
A diploid organism is heterozygous for 4 loci, how many types of gametes can be produced?
Answer:
When the tall and dwarf plant produces gametes, by the process of meiosis, the alleles of the parental pair segregate from each other and only one allele is transmitted to a gamete. The segregation of alleles is a random process and thus, there is 50 percent chance of a gamete containing either allele.
Question 4.
Explain the Law of Dominance using monohybrid cross.
Answer:
Law of Dominance :
(a) Characters are controlled by descrete units called factors.
(b) Factors occur in pairs.
(c) In a dissimilar pair of factors one member of the pair dominates (dominant) and the other (recessive).
(d) In a monohybrid cross only one of the parental characters in the F, and the expression of both in the F2. It also explains the proportion of 3:1 obtained at the F2.
Question 5.
Define and design a testcross.
Answer:
The crossing of a tall plant from F2 with a dwarf plant is called testcross.
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 and a single locus.
Answer:
From the Punnett Square, it can be seen that 1 / 4 th of the random fertilization leads to TT, 1 / 2 lead to Tt and 1 / 4 th to tt. Though the F1 have a genotype of Tt, but the phenotypic character seen is ‘tali’. At F3 1 / 3Ath of the plants are tall, where some of them are TT while others are Tt. Within the geophytic pair Tt, only one character ‘T’ tall is expressed. Hence the character T or ‘tali’ is said to dominate over the other allele ‘t’ or ‘dwarf’ characters. It is thus due to this dominance of the character over the other that all the F. are tall and the F2 – 3/ 4of the plants are tall.
Question 7.
When a cross in made between tall plant 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:
The proportion of plenotype in the offspring could be expected to be in tall and green is as follows.
The genotype of the parents can be written as TTYY and ttyy. The gametes Ty and ty unite on fertilization to produce TtYy. The yellow colour is dominant over green and tall shape is dominant over dwarf shape. For (b) TTYY and ttyy TtYy.
Question 8.
Two heterozygous parents are crossed. If the two loci are linked what would be the distribution of phenotypic features in F, generation for a dihybrid cross.
Answer:
According to Morgan, when he carried dihybrid cross in Drosophilia, he observed that the two genes did not segregate independently of each other and the F, ratio deviated very significantly from the 9:3:3: l ratio. When the genes in a dihybrid cross are situated on the same chromosome, the proportion of parental gene combinations are much higher than the non-parental type.
Question 9.
Briefly mention the contribution of T.H. Morgan in genetics.
Answer:
Contribution of T.H. Morgan in genetics :
– Experimental verification of the chromosomal theory of inheritance by T.H. Morgan led to discovering the basis for the variation that sexual production produced.
– Morgan carried out several dihybrid crosses in Drosophila to study genes that were sex-linked. The crosses were similar to the dihybrid crosses carried only by Mendel in peas. For example, when Morgan hybridised yellow-bodied, white-eyed females to brown-bodied, red-eyed males and intercrossed their F, progency, he observed independently of each other and the F, ratio derivated very significantly from the 9:3:3:l ratio.
– Morgan knew that the genes were located on the X chromosome and when the two genes in a dihybrid cross were situated on the same chromosome, the proportion of parental gene combinations were much higher than the non-parental type. He attributed this due to the physical association or linkage at two genes and coined the terms linkage to describe this physical association of genes on chromosomes and the term recombination to describe the generation of non-parental gene combinations.
– Morgan also found that even when genes are grouped on the same chromosome some genes were very lightly linked while others were loosely linked. For example he found that the genes white and yellow were very lightly linked and showed 1.3 per cent recombination while white and miniature wing shewed 37.2 per cent recombination.
Question 10.
What is pedigree analysis. Suggest such an analysis.
Answer:
Study of the family history about inheritance of a particular trait provides an alternative. Such an analysis of traits in a several of generations of a family is called the pedigree analysis. In a pedigree analysis, the inheritance of a particular trait is represented in the family tree over generations.
In human genetics, pedigree study provide a strong tool, which is used to trace the inheritance of a special trail, abnormality or disease.
Question 11.
How is sex determined in human beings?
Answer:
The genetic makeup of the sperm determines the sex of the child. There is an equal probability of fertilisation of the ovum with the sperm carrying either X or Y chromosome. In case, the ovum fertilizes with a sperm carrying X- chromosome the zygote develops to a female (XX) and the fertilization of ovum with Y- chromosome carrying sperm result into a male offspring.
Question 12.
A child has blood group C). If the father of blood group A and mother blood group B, work out the genotypes of the parents and find out the expected genotype of the other offsprings.
Answer:
According to the table showing the genetic basis of blood group in human population, when allele of parent 1 is (IA) and allele from parent II is (IB) then the genotype of offspring will be IAIB and blood type of offsprings will be AB.
Question 13.
Explain the following terms with examples :
(a) Co-dominance
(b) Incomplete dominance
Answer:
(a) Co-dominance – In co-dominance the F( generation resembles both parents. For example, ABO blood groups are controlled by the gene I. The plasma membrane of the red blood cells has sugar polymers that protrude from its surface and the structure of the kind of sugar is controlled by the gene. The gene (I) has three alleles IA, IB and i. The alleles IA and IB produced a slightly different form of the sugar while allele i doesn’t produce any sugar.
Since humans are diploid organisms, each person possesses any two of the three I gene alleles. IA and IB and completely dominant over i, in other words, when IA and i are present only IA expresses, and when IB and i are present IB expresses. But when IA and IB are present together they both express their own types of sugar; this is due to co-dominance. Thus red blood cells have both A and B types of sugar.
(b) Incomplete dominance – When the F1 has a phenotype that does not resemble either of the two parents it is called incomplete dominance. For example, in a cross between true-breeding red-flowered (RR) and true-breeding white-flowered plants (rr), the F1 (Rr) was pink. When the F1 was seif pollinated the F2 resulted in the ratio 1(RR) Red :
2(Rr) Pink: 1 (rr) white. Here the genotype ratios were same but the phenotype ratios changed from the 3 : 1 dominant: recessive ratio. This is became R was not completely dominant over r and it made it possible to distinguish Rr as pink from RR(red) and rr (white).
Question 14.
What is point mutation? Give one example.
Answer:
Sometimes mutation arise due to change in a single base pair of DNA. This is known as mutation. A typical example of such a mutation is sickle cell anaemia.
Question 15.
Who has proposed the chromosomal theory of the inheritance?
Answer:
Walter Satton.
Question 16.
Mention any two autosomal genetic disorders with their symptoms.
Answer:
(a) Sickle cell anaemia – Symptoms: The mutant haemoglobin molecule undergoes polymerisation under low oxygen tension causing the shape of the RBC from biconcave disc to elongated sickle like structive.
(b) Phenylketonuria – Symptoms: The affected individual lacks an enzyme that converts the amino and phenylalanine into tyrosine. This phenylalanine is accumulated and converted into phenyl pyruvic acid and other derivatives.
Accumulation of these in brain results in mental retardation. There are also excreted through urine become of its poor absorption by kidneys.
Bihar Board Class 12 Biology Principles of Inheritance and Variation Additional Important Questions and Answers
Very Short Answer Type Questions
Question 1.
Who started the idea of inheritance?
Answer:
Gregor Mendel.
Question 2.
On which plants did Mendel conduct hybridisation experiments?
Answer:
Garden peas.
Question 3.
What do you mean by homozygous?
Answer:
Homozygous means, identical.
Question 4.
What are alleles?
Answer:
Genes which code for a pair/collection of contrasting traits are known as alleles.
Question 5.
What is a dominant factor?
Answer:
When a pair of disimilar factor (genes), dominates the other factor it is called dominant factor.
Question 6.
What are heterozygous plants?
Answer:
When the hybrids contain alleles which express contrasting traits, the plants are heterozygous.
Question 7.
Who developed the Punnett square?
Answer:
Reginald C. Punnett.
Question 8.
What is the polarity of DNA strands?
Answer:
It is a graphical representation to calculate the probability of all possible genotypes of offspring in a genetic cross.
Question 9.
Name the two laws of Inheritance.
Answer:
(a) Law of Dominance, (b) Law of Segregation.
Question 10.
Name the three scientists who in 1900, independently rediscovered Mendel’s result on the inheritance of characters.
Answer:
de Vries, Correns and von Tschermak.
Question 11.
Why are chromosomes called columned bodies?
Answer:
Because they are visualised by staining.
Question 12.
What did Mendel establish in the first stage of his experiment?
Answer:
In his first stage, Mendel satisfied himself that each fourteen varieties i.e. seven pairs of contrasting forms were true-breeding.
Question 13.
What is Monohybrid cross?
Answer:
Monohybrid cross is a cross where two forms of a single trait are hybridised.
Question 14.
When hybrid organisms are allowed to self pollinate, what is name given to offsprings that constitute the next generation?
Answer:
Second Filial (F2) generation.
Question 15.
Define Genetics.
Answer:
It states that allele pairs separate or segregate during gamete formation, and the paired condition is restarted by random fusion of gametes during fertilization.
Question 16.
What is genotype?
Answer:
It is the genetic constitution of an organism.
Question 17.
What is phenotype?
Answer:
Phenotype is the appearance i.e. physical, biochemical and physiological, of an individual which results from the interaction of environment and his genotype.
Question 18.
What are autosomes?
Answer:
All the chromosomes other than the sex chromosomes are called autosomes.
Question 19.
Why are males in humans referred to as heterogametic?
Answer:
Because males produce two types of gametes, either x or y in jsy type sex chromosomes.
Question 20.
How many pairs of chromosomes Drosophila melanogaster has?
Answer:
Four pairs of chromosomes.
Short Answer Type Questions
Question 1.
How did Mendel interpret his result to postulate the principle af Dominance?
Answer:
Mendel observed that the altr ate forms of a trait could retain their identity in the hybrid and reemerge unchanged in the subsequent generations. Mendel concluded that the Factors were transmitted from parents to the offsprings. Each factor contained information about the form of a trait. The factor associated with the form which was expressed in the hybrid offspring was Dominant. The factor associated with the form which remained hidden in the F1 but reappeared in F2 was RECESSIVE (Mendel’s factor is now recognized as the gene).
Question 2.
Compare Genotype and Phenotype.
Answer:
| GENOTYPE | PHENOTYPE |
| (i) It is the genetic constitution of an organism. | (i) it is the observable characteristics of an organism. |
| (ii) The genotype of a sexually produced diploid individual is established at the time the zygote is produced. | (ii) The phenotype of the genotype of individual changes with development and age. |
| (iii) It is not influenced by the environment. | (iii) It is influenced by the any iron ment. |
Question 3.
If the offspring with the unknown dominant genotype is crossed with an individual homozygous recessive for the trait (e.g. green seed) and the phenotype of the F, progeny is examined, illustrate your answer with possibility. ,
Answer:
Possibility 1: If the unknown is homozygous (yy), crossing with green recessive (yy) gives all yellow offspring (Hybrid) i.e. Yy.
Possibility 11: If the unknown is heterozygous (Yy), crossing with green recessive (yy) results in 50% yellow (Yy) and 50% green (yy) progeny.
Question 4.
Epistatic interactions between genes cause departures from Mendelian phenotypic dihybrid ratio. Support your answer with an example of flower colour in sweet pea, Lathyrus odoratus.
Answer:
In Lathyrus odoratus, the dominant allele determines the formation of purple flower colour. But neither PP or pp will express colour unless another gene C is present in the dominant from i.e. CC or cc. Recessive cc will interfere with colour formation PP or PP, thereby leading to white flowers.
A cross between purple PPCC and White PCCC gives all purple PPCC F1 hybrids, selling of the hybrids pp cc gives rise to purple and white-flowered offsprings in the ratio 9: 7. Instead of normal Mendelian ration i.e. 9:3:3: 1.
Question 5.
What is pedigree analysis? What are the symbols used in such an analysis?
Answer:
Pedigree analysis is a system to analyse the distribution and movement of the traits in the family tree.
(i) The circles (O) denote females and the Squares (I) denote males.
(ii) Solid symbols 
represent the trait being studied and open symbols denote normal form.
(iii) A symbol with a CRC ss line 
indicates carrier of a recessive trait.
(iv) Parents are joined by horizontal lines.
(v) Their offsprings are connected to a horizontal line below the parents, in order of the birth.
Question 6.
Explain chromosomal determination of sex in XY organisms.
Answer:
(i) Sex is determined at the time of fertilisation.
(ii) The two sexes are produced in approximately equal numbers as there is equal probability for an ovum to be fertilised by the sperm containing X or a Y chromo¬somes as shown.
Question 7.
Distinguish between a leading strand and a lagging strand.
Answer:
| LEADING STRAND | LAGGING STRAND |
| (i) A leading strand which is formed in a continuous stretch in the 5’- 3’ direction with the help of DNA polymers on one of the parent strand of DNA. | (i) A lagging strand is formed in small pieces of DNA referred to as OKAZAKL fragments and then join together by DNA ligase. |
| (ii) The overall direction of this strand5′-3’is established at the time the zygote is produced. | (ii) Through the small pieces grow in 5’-3’ direction, but the overall direction of this strand is 3’ 5’. |
Question 8.
What is genetic code? Give its characteristics.
Answer:
Genetic code refers to the sequence of the. four bases adenine, guanine, cytosine and thymine on a strand of DNA which represent a code that controls the construction of proteins and enzymes to make up cytoplasm of the organism and directs its functioning.
Characteristics :
(i) Triplet code – A particular sequence of 3 bases would code for particular amino acids and this triplet is called CODON. Three codon i.e. UAA, UAG and UGA serve as STOP CODONS and one codon AUG serves as INITIATING CODON.
(ii) Non-overlapping – In a mRNA molecule, the sequence of three at a time starting from a specific position in a non, overlapping fashion.
(iii) Degenerate – Many amino acids may have more than one codon and codons specifying the some aminoacids are called degenerate. They differ in only the third base.
(iv) Universal – The same code dictionary is used by all organisms irrespective of their phylogenies and so it is called universal. Exception to this found in. m-DNA.
Question 9.
What are Mendelian disorders?
Answer:
Mendelian disorders are determined by alteration or mutation in the single gene. These disorders one transmitted to the offspring on the principle of inheritance. The falter of inheritance of such mendelian disorders can be traced in a family by the pedigree analysis. Some Mendelian disorders are Haemophilia. Cystic fibrosis, Colour blindness, sickle cell anaemia etc.
Question 10.
How are chromosomal disorders caused?
Answer:
Chromosomal disorders are caused due to absence or excess or abnormal arrangement of one or more chromosomes. The total number of chromosomes of a normal human being is 46 (23 pairs). Out of there, 22 pairs are autosomers and one pair of chromosomes are sex chromosomes. Sometimes other an additional copy of a chromosome may be included in an individual or an individual may lack one of any one pair of chromosomes.
Long Answer Type Questions
1. Write some comparison between chromosomes and genes.
Answer:
| CHROMOSOMES | GENES |
| (1) There occur in pairs | (1) There also occur in pairs. |
| (2) At the time of gamete formation they segregate. | (2) At the time of gamete also segregate. |
| (3) One of each pair is transmitted to a gamete. | (3) Only one of each pair is transmitted to a gamete. |
| (4) Independent pairs segregate independently of each other. | (4) One pair segregates independently of another pair. |