Biology For Class X - Chapter No. 6 - Inheritance - Review Exercise From Text Book

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CHAPTER 6: INHERITANCE
Review Exercise From Text Book

By Mrs. Ayesha Arif
Vice Principal
(Jauhar Progressive School)

A. MULTIPLE CHOICE QUESTIONS
Choose the correct answer:
i) Branch of biology deals with the study of heredity and variation is called:
(a)Inheritance
(b) Heredity
(c) Genetics ✓
(d) Evolution

ii) The way by which gene transmits characters from parents to offspring is:
(a) Genetics
(b) Inheritance ✓
(c) Heredity
(d) Allele

iii) Two similar chromosomes in a cell which are similar in shape, size and position of centromere called:
(a) Chromatids
(b) Arms
(c) Homologous ✓
(d) Homology

iv) The chemical material of a chromosome is called:
(a) Chromatin ✓
(b) Chromeres
(c) Chromonema
(d) Chromatid

v) The outer part of DNA helix made up of sugar and phosphate is called:
(a) Nucleoprotein
(b) Rungs
(c) upright ✓
(d) Phosphoester

vi) The small segment of DNA which has information to code one protein is called:
(a) Nucleotide
(b) Polynucleotide
(c) Gene ✓
(d) Exon

vii) The exact duplication of DNA is called:
(a) Duplication
(b) Replication ✓
(c) Transcription
(d) Translation

viii) If both the parents donate same factors of a character is called:
(a) Homologous
(b) Heterologous
(c) Homozygous ✓
(d) Heterozygous

ix) The Genetic constitution of a trait is called:
(a) Genotype ✓
(b) Phenotype
(c) Genome
(d) Phenyl

B. SHORT QUESTIONS
1. What is gene and how it works?
Ans: GENES:
Gene is the smallest segment of DNA which has genetic information in the form of code to synthesize a protein. Life of every organism, every character of his structure, function and behaviour, all the level of biological organization is programmed and controlled by a set of instructions. These instructions are in the form of coded biological information called 'Genes'. Thus:
Genes are the basic unit and structure of Biological information. They are unit of inheritance which is copied and inherited from generation to generation.

LOCATION:
Each gene is located at specific position on the chromosomes .This position of gene on chromosome is called Gene Locus (loci).

FUNCTION:

• Gene is the localised part of DNA which has a coded information to synthesize a protein which works as enzyme.
• Each gene has specific function e.g. a gene determines the height of plant; another gene determines the colour of their petals etc.
• The coded information may change due to any reason which is called genetic variation caused by mutation. This genetic variation among off spring lead to tremendous variety in their traits.
• The variation in the genes of a trait give rise two or more than two alternative forms of a gene. These alternative form of gene are called alleles or allomorph.
• All the inherited characters are determined by genes which are transmitted from generation to generation.

2. Define following terms:
(a) Homologous Chromosome
(b) Heterologous Chromosome
(c) Dominant allele
(d) Allele
(e) Recessive allele
(f) Homozygous
(g) Heterozygous
(h) Parental generation
(i) Filial one Generation
(j) Second Filial Generation
(k) Phenotype
(l) Genotype
(m) Heredity
(n) Genetics
(o) Inheritance
(p) Variations
Ans: (a) Homologous Chromosome:
The two chromosomes which are similar in their shape, size and position of centromeres and are present in same cell are called homologous pair of Chromosomes. These homologous sets of chromosomes provide the physical traits basis of heredity of an organism.

(b) Heterologous Chromosome:
A heterologous chromosome is a chromosome that contains different set of genes for a given trait. 

(c) Dominant allele:
The factor (gene) which express and masks the expression of other factor in heterozygous condition is said to be Dominant factor (allele).
For example:
(i) Mendel represent it with capital letter like T for tall, which is a dominant character.
(ii) The allele for brown eyes is dominant. Therefore in pair one copy of brown eye is needed to have brown colour eye.


(d) Allele:
"The alternative form of gene developed as a result of variation is called allele or allomorph."
Alleles are described as either dominant or recessive depending on their associated traits. Some gene may have as many as 300 alleles. A diploid cell thus have any two of these alleles while a haploid have one allele.

(e) Recessive allele:
The factor which is unable to express or masked in heterozygous condition is said to be recessive allele.
For example:
(i) It represents by small letter of same alphabet like t for small (dwarf).
(ii) Allele for blue eye is recessive. Therefore in a pair both (two) copies of blue eye is needed to have blue eye colour.

(f) Homozygous:
An individual having same factors (allele) of a trait called homozygous. For example, TT (factor for tallness).

(g) Heterozygous:
An individual having different factors of a trait called heterozygous. For example, Tt (factors of tallness and dwarfness both).

(h) Parental generation:
The original true breeding organisms were called parental generation or P1 by Mendel.

(i) Filial one Generation:
The offspring of true breeding organism were called First Filial Generation or F1.

(j) Second Filial Generation:
The offspring of filial one generation produced by crossing self-fertilization were called Second Filial generation or F2.

(k) Phenotype:
It is the physical appearance of the trait on the basis of inherited genes like tall, dwarf, round seed, wrinkled seed etc.

(l) Genotype:
The genetic makeup or genetic constitution of a trait like TT, Tt, tt etc.

(m) Heredity:
The characteristics of the offspring’s to resemble their parents is called heredity.
In other words:
"Heredity is the way by which genes transmit characters from parents to offspring".

(n) Genetics:
The branch of biology which deals with the study of heredity and Variations is called genetics.

(o) Inheritance:
The process by which characters are transmitted from parents to off springs is called inheritance.

(p) Variations:
The differences in characters such as height, colour etc among individual of same species are called variations. Variation may be caused either by the effect of environment or by the changes in the genetic material.

3. Which of the phenomena of inheritance is there where both factor express in heterozygous condition.
Ans: INCOMPLETE DOMINANCE OR PARTIAL DOMINANCE:
The term ”incomplete dominance” was proposed by Carl Correns in 1899.
The phenomenon of inheritance where both alleles of a trait express in heterozygous condition and their expression get blended to produce new phenotype is called incomplete dominance or partial Dominance.

4. List out the factors which are involved in theory of natural selection.
Ans: THEORY OF NATURAL SELECTION:
Charles Darwin a naturalist Englishman proposed the Theory of Natural selection as a mechanism for evolution in the year 1859, through his “Origin Of Species”.

FACTORS WHICH ARE INVOLVED IN NATURAL SELECTION:
The main factors which are involved in this theory are as follows:

1. Over Production:
2. Struggle for Existence:
3. Heritable Variation:
4. Natural selection:

5. Relate artificial selection with natural selection.
Ans: RELATION OR DIFFERENCE BETWEEN NATURAL AND ARTIFICIAL SELECTION:

NATURAL SELECTION	ARTIFICIAL SELECTION
Natural selection is a process of adaptation by an organism to the changing environment by bringing selective changes to its genotype or genetic composition.	Artificial selection, also called selective breeding, is the process where humans identify desirable traits in animals and plants and use these traits to develop desirable phenotypic traits by breeding.
Natural selection is a natural process.	Artificial selection is an artificial or human-made process.
Natural selection takes place in natural populations within natural conditions.	Artificial selection takes place in domesticated populations put together by humans.
The chances of survival of a fit organism increase as a result of natural selection.	The chance of survival of an organism might be at risk if not performed correctly.
Natural selection is a slow process that completes after many generations.	Artificial selection is a faster process that completes within days or weeks with more apparent effects.
Natural selection is not as controlled as artificial selection as natural processes control it.	Artificial selection can be more controlled as humans control it.
Natural selection might occur on all organisms living on the earth.	Artificial selection can be selective and can be performed on selected groups of animals and plants.
Natural selection is based on the adaptive characteristics of animals.	Artificial selection is based on the desirable characters selected by humans.
Only beneficial or favorable traits are inherited over the successive generations by natural selection.	Artificial selection only allows the selected traits to be passed through successive generations.
Natural selection affects the entire population of a species.	Artificial selection only affects the selected individuals.
Natural selection results in a large amount of biological diversity.	Artificial selection only brings desirable changes and desirable traits and brings a decrease in genetic diversity.
Natural selection facilitates speciation and evolution over many generations.	Artificial selection doesn’t facilitate evolution.
Natural selection exerts on a wide-scale on the natural environment.	Artificial selection exerts only on selected individuals that are economically important.
Hybrid vigor is seen in offspring after natural selection.	Hybrid vigor is lost during artificial selection due to the preservation of desired traits.
Natural selection is a natural process, so no human effort is required.	The artificial selection might be labor-intensive and expensive.
After natural selection, the proportion of heterozygous genotype becomes high.	After artificial selection, the proportion of homozygous genotype becomes high.
Some examples of natural selection include the selection of long-necked giraffes and the changes in the size and shape of beaks of birds according to their feeding habits.	Some examples of artificial selection include dog breeding to produce new breeds of dogs and cross-breeding in cash crops like wheat and rice.

OR

Natural Selection:
Natural selection is a natural process of adaptation by an organism to the changing environment by bringing selective changes to its genotype or genetic composition. It is a slow process that completes after many generations. After natural selection, the proportion of heterozygous genotypes becomes high.

Artificial Selection:
Artificial selection, also called selective breeding, is the process where humans identify desirable traits in animals and plants and use these traits to develop desirable phenotypic traits by breeding. It is a faster process that completes within days or weeks with more apparent effects. After artificial selection, the proportion of homozygous genotype becomes high.

More Short Question & Answers

6. How coiling of long DNA is coiled in very small chromosome and nucleus of cell?
Ans: The DNA of a chromosome exists as one very long double stranded, a duplex, which extends unbroken through the entire length of the chromosome. This long DNA (more than 7 feet or 2 meter) is coiled to fit into a much smaller spaces.
If we gently disrupt a eukaryotic nucleus and examine the DNA with an electron microscope, we find that coiling of long DNA is coiled in very small chromosome and nucleus of cell. It is because the histone is positively charged while DNA is negatively charged. This beads of histone and DNA is called nucleosome. When the string of nucleosomes wraps up into high order coil called super coil. This super coiled chromomers form chromosome.

Source: Special Thanks To Sir Syed Arif Ali


C. EXTENSIVE RESPONSE QUESTIONS
i) Describe the Waston and Crick model of DNA?
Ans: Watson and Crick Model Of DNA:
The model of DNA was suggested by James Watson and Francis Crick, in 1953. This model is based on X-Rays, Photographs and chemical analysis of DNA. According to this model:

• Double Helix:
  (i) DNA is a double helical structure.
• Backbone of DNA:
  (ii) Each helix is a polynucleotide chain which are twisted around each other.
  (iii) The outer part is called Upright, which are made up of deoxyribose sugar and phosphate. The inner part called Rungs, made up of paired nitrogenous bases.
• Pairing of Bases:
  (iv) Both helix are complementary to each other which are held together by hydrogen bonds.
  (v) The complementary helix have complementary base pairs i.e Adenine pairs with Thymine and Cytosine always pairs with Guanine.

STRUCTURE OF DNA

ii) How gene expresses describe in detail? OR What do you understand by Central dogma of Protein synthesis?
Ans: CENTRAL DOGMA:
"A set of beliefs where a gene expresses by synthesizing a protein is termed as central dogma."
This protein is work as enzyme, which carry down a chemical reaction to produce a metabolic product. This metabolic product either develops a character or lead to develop a character.

RNAs:
DNA is located in the nucleus of eukaryotic cell while the protein synthesis and metabolic reactions occur in cytoplasm under the instructions of DNA (genes). Therefore DNA requires some other molecules to carry its genetic information from nucleus to cytoplasm. These molecules are different types of RNAs (Ribo Nucleic Acid).

GENE EXPRESSION:
All functions in the body of an organism are controlled by genes. A function expressed or performed by a gene is called gene expression.

Process of Gene Expression:
Genetic information flows from DNA to mRNA and then to ribosomes in cytoplasm. This is a two step process of gene expression for protein (enzyme) synthesis.

1. Transcription
2. Translation

1. Transcription:
The step of protein synthesis where information which contained in a specific segment of DNA (gene) is copied in complimentary from (genetic codes) i.e. RNA. This RNA carries information of DNA sequences to ribosome from nucleus to cytoplasm are called messenger RNA or mRNA. The process of copying DNA information to mRNA is called Transcription.

2. Translation:
In the second step two other types of RNA called tRNA(transfer RNA) and ribosomal RNA(rRNA) translate the information of mRNA into the specific sequence of amino acids which help to synthesize the proteins. This process is called Translation.

iii) State and explain the law of Segregation of Mendel's. OR State and explain the law of Purity of gametes of Mendel's.
Ans: LAW OF SEGREGATION (MENDEL’s FIRST LAW) OR LAW OF PURITY OF GAMETES:
Statement:

"In an organism, the factors (genes) exist in pairs but during gametes formation these factors segregate cleanly from each other, so each gamete has only one factor of a trait."

Experiment:

• Mendel when crossed pure tall and dwarf plants, he got all tall plants in F1 generation but unlike the P1 tall, these plants of F1 generation were heterozygous (Tt).
• Mendel did not stop his experiment here. He planted all the seeds of F1 generation and allowed them to self pollinate.
• He observed that in the generation (F2), both Parental type i.e. tall and dwarf stem varieties were produced. When he counted these, he found that in F2 generation, the two types of individuals were present in the ratio of 3:1, tall and dwarf respectively.

Results:
Mendel perceived from these results that

• When the plants of F1 generation form their gametes, the factors (allele) separate or segregate again in such a way that only one of the two alleles enters each gamete.
• On the basis of these observation, results and conclusions from experiment he presented the law called the "Law of segregation or law of purity of gametes".

iv) Explain the inheritance of dihybrid cross by law. OR State and explain the law of Independent assortment.
Ans: LAW OF INDEPENDENT ASSORTMENT:
Statement:

"The genes of assorted traits are independent in their inheritance."
OR
"Members of one pair of genes separate from each other during gametes formation."

Dihybrid - Cross And Dihybrid Ratio:
Mendel crossed between two individuals (pea plant) differing in two traits. He called it Dihybrid - Cross and the ratio obtained in F2 generation is called Dihybrid-ratio.

Inheritance of two traits:
The results achieved as a consequence of dihybrid-cross is known as Inheritance of two traits.

Experiment:

• In his experiments Mendel crossed between two individual (pea plants) differing in two or more character traits as well.
• Mendel crossed yellow cotyledon and rounded seed containing plant with green cotyledon and wrinkled seed containing plant.
• The F1 generation had all plants with yellow cotyledon and round seeds.
• This proved Mendel previous finding that allele for round seed was dominant over wrinkled while yellow cotyledon over green.
• Mendel self fertilized the F1 generation and expecting any of the two following possibilities:
  i) If the genes for round seed and yellow colour are inseparable (dependent on each other), as well as those for wrinkled shape and green colour, then in F2 generation ³/₄ of the seeds will be round and yellow and ¹/₄ will be wrinkled seed and green.
  
  ii) If the genes for seed shape and cotyledon colour are separable (independent) and distributed to the gametes independent to each other, then in F2 generation some plants will produce round seeds with green cotyledon and some will have wrinkled seeds with yellow cotyledon along with parental combination.

Result:
Mendel actually obtained four different kind of phenotypes in F2 generation. Out of a total 556 seeds, he obtained four different phenotypes i.e.
Phenotype:

• Round and Yellow seeds = 315
• Wrinkled and Yellow seeds = 101
• Round and Green seeds = 108
• Wrinkled and Green seeds = 32

Genotype:

• Genotypes for round and yellow seeds RRYY, RRYy, RrYY, RrYy.
• Genotypes for round and green seeds RRyy, Rryy.
• Genotypes for wrinkled and yellow seeds rrYY, rrYy.
• Genotypes for wrinkled and green seeds rryy.

Dihybrid-cross ratio:
These numbers are in a ratio of about 9:3:3:1 for the four phenotype.

Conclusion:
It showed that the genes for seed colour and shape are independent in their inheritance. They do not necessarily stay together in the combination in which they occurred in parents.

v) Explain the Darwin theory of natural selection.
Ans: THEORY OF NATURAL SELECTION:
Charles Darwin (1809 - 1882) was an Englishman. He studied different plants and animals, collected new specimens and categorized them. In the year, 1859, he published a book “Origin Of Species” where he proposed the "Theory of Natural Selection", in which he presented the mechanism of origin of species.

FACTORS INVOLVED IN NATURAL SELECTION OR MAIN POINTS OF DARWIN'S THEORY:
The main points of the Darwin's theory are as follows:
1. Over Production:
Living organisms reproduce rapidly so that the number of their offspring could increase rapidly.

2. Struggle for Existence:
Due to the limited available resources of food, shelter, etc. the offspring of species compete not only with each other but also with the members of different species to share these resources. In this struggle a large number of individuals of each species are eliminated. As a result the population remains stable.

3. Heritable Variation:
Individual of a species differ from each other in their ability to obtain resources, withstand environmental extremes etc. These differences in character are called minor variations.
Darwin concluded that survival in struggle for existence is not random but depends upon in part on the heredity constitution of the surviving individuals. Those individuals whose inherited characters fit them best to their environment would survive and produce more offspring than less fit individuals who will vanish.

4. Natural selection:
Nature selects the fittest individuals to survive and reproduce. Therefore only the favourable variations are preserved through their inheritance to new young ones.

Conclusion:
Over millions of year of variations, natural selection and inheritance might have led to the accumulation within the species a number of characters with survival values. As a result, a species may slowly change to a better new species. 
Number of evidence are reported in support of evolution from comparative anatomy, homologous organs, analogous organs, vestigial organs and fossils.