Lakhmir Singh & Manjit Kaur: Heredity and Evolution, Solutions- 2 | Science Class 10 PDF Download

Page No - 192

Question 1:
Which of the processes, sexual eproduction or asexual reproduction, brings about maximum variations in the offsprings ?
Solution :
Sexual Reproduction

Question 2:
Name one variation in humans connected with ears.
Solution :
Free Earlobes.

Question 3:
What constitutes the link between one generation and the next ?
Solution :
Gametes.

Question 4:
If the trait A exists in 10% of a population of an asexually reproducing species and a trait B exists in 60% of the same population, which trait is likely to have arisen earlier ?
Solution :
B.

Question 5:
Mendel said that the characteristics or traits of organisms are carried from one generation to the next by internal factors which occur in pairs. What is the modern name for these factors ?
Solution :
Genes.

Question 6:
Some plants occur in one of the two sizes : tall or dwarf. This characteristic is controlled by one pair of genes. Tallness is dominant to dwarfness. Choose suitable letters for this gene pair.
Solution :
Tt.

Question 7:
What are the chromosomes XY and XX known as ?
Solution :
Sex Chromosomes.

Question 8:
Which of the two, sperm or ovum, decides the sex of the child ?
Solution :
Sperm.

Question 9:
State whether the following statement is true or false :
The sex of an infant is not a case of inheritance of characteristics.
Solution :
False.

Question 10:
A new born child has an XY pair of chromosmes. Will it be a baby boy or a baby girl ?
Solution :
Baby boy

Question 11:
Which of the following combinations of sex chromosomes produce a male child : XX or XY ?
Solution :
XY.

Question 12:
Name the first scientist who studied the inheritance of traits from one generation to the next.
Solution :
Gregor Mendel

Question 13:
What type of plants were used by Mendel for conducting his experiments on inheritance ?
Solution :
Pea plants.

Question 14:
The gene for red hair is recessive to the gene for black hair. What will be the hair colour of a person if he inherits a gene for red hair from his mother and a gene for black hair from his father ?
Solution :
Black hair.

Question 15:
What are the four blood groups in humans ?
Solution :
A, B, AB and O.

Question 16:
Name one reptile in each case where higher incubation temperature leads to the development of : (a) male progeny, (b) female progeny.
Solution :
(a) Lizard (Agama agama)
(b) Turtle (Chrysema Picta)

Question 17:
Fill in the following blanks with suitable words :Fill in the following blanks with suitable words :
(a) Genes always work in …………………
(b) In pea plants, the gene for dwarfness is………………… whereas that for tallness is…………………
(c) Most people have………………… earlobes but some have………………… earlobes.
(d) A human gamete contains………………… chromosomes whereas a normal body cell has………………… chromosomes in it.
(e) All races of man have………………… blood groups.
(f) The………………… chromosomes for a………………… are XX whereas that for a………………… are XY.
Solution :
(a) Pairs.
(b) Recessive; Dominant.
(c) Free; attached.
(d) 23; 46.
(e) Four.
(f) Sex; Female; male.

Lakhmir Singh Biology Class 10 Solutions Page No:192

Question 18:
Which of the following represent tall plants and which represent short plants (or dwarf plants) ?Which of the following represent tall plants and which represent short plants (or dwarf plants) ?
(a) Tt
(b) tt
(c) TT
Give reason for your choice (The symbols have their usual meaning).
Solution :
(a) Tall – Tt will have tall plants because of the presence of T which is dominant gene and t is recessive gene.
(b) Dwarf plants: It is dwarf due to the presence of both the recessive genes.
(c) Tall plants: These plants are tall due to the presence of both the dominant genes.

Question 19:
A man having blood group O marries a woman having blood group B and they have a daughter. What will be the blood group of the daughter ?
Solution :
Equal chance of having blood group O or blood group B.

Question 20:
a) Name the scientist who gave the laws of inheritance.
(b) Name an animal in which individuals can change sex. What does this indicate ?
Solution :
(a) Gregor Mendel
(b) Snails: This indicates that sex is not determined genetically in some animals.

Question 21:
Explain with an example, how genes control the characteristics (or traits).
Solution :
The characteristics or traits in animals and plants are controlled by genes. For example the transmission of color of hair from the parents to the child. If a mother has black hair and the father has blonde hair and the child has black hair then the transmission of genes for hair colour from the mother and father to the child is as follows: Mother’s cell contains two genes HH for black hair. Both the genes HH are dominant genes, so the mother has black hair. Father’s cell contains two genes (hh) for blonde hair. The two genes hh are recessive genes, so the father has blonde hair. Now, during the process of reproduction, the mother transmits one of the dominant genes H for black hair to the child and the father transmits one of his recessive genes h for blonde hair to the child. Due to this, the child has the genes Hh for her hair. Now the gene H for black hair is the dominant gene but the gene h for blonde hair is the recessive gene. The dominant gene H for black hair shows its effect due to which the child has black hair.

Question 22:
(a) State one advantage of variation to a species.
(b) What are sex chromosomes ? How many sex chromosomes are there ? Name them.
Solution :
(a) The advantage of variation to a species is that it increases the chances of its survival in a changing environment.
(b) The chromosomes which determine the sex of a person are called sex chromosomes. There are two types of sex chromosomes ? X and Y chromosomes.

Question 23:
Explain how, sex is determined in human babies.
Solution :
The sex of a child depends on what happens at fertilisation:
(a) If a sperm carrying X chromosome fertilises an ovum (or egg) which carries X chromosome, then the child born will be a girl. This is because the child will have XX combination of sex chromosomes.
(b) If a sperm carrying Y chromosome fertilises an ovum (or egg) which carries X chromosome, then the child born will be a boy. This is because the child will have XY combination of sex chromosomes.

Question 24:
What do the following symbols used in the topic on heredity represent ?
(a) TT
(b) tt
(c) XX
(d) XY
Solution :
(a) Tall plant.
(b) Dwarf plant.
(c) Female.
(d) Male.

Question 25:
(a) What will you get in the F1 and F2 generations in the following cross ?
Pure tall pea plant x Pure dwarf pea plant
(b) Is it an example of monohybrid cross or dihybrid cross ?
Solution :
(a) In the F1 generation, all plants produced will be tall and in F2 generation three tall plants and one dwarf plant will be produced.
(b) It is an example of monohybrid cross.

Question 26:
In the F2 generation of a cross, progeny having different traits are produced in the ratio 3:1. State whether it is a monohybrid cross or a dihybrid cross ? Give one example of such a cross.
Solution :
It is a monohybrid cross. Example – when two hybrids tall Pea plants cross bred with each other, they will produce three tall plants and one dwarf plant in F2 generation.

Question 27:
(a) What is the genotype of dwarf plants which always produced dwarf offspring ?
(b) What is the genotype of tall plants which always produced tall offspring ?
(c) What is the genotype of

1.  dwarf plants, and
2.  tall plants, whose parental cross always produces tall offspring ?

Solution :
(a) tt.
(b) TT.
(c) (i) tt
(ii) TT.

Question 28:
(a) If a normal human cell has 46 chromosomes, how many chromosomes will be there in a human (;) sperm cell, and (ii) zygote ?
(b) What sizes of plants are produced if both parents have genes Tt ?
Solution :
(a) (i)23.
(ii) 46.
(b) Three tall plants and one dwarf plant.

Question 29:
In a human, how many chromosmes are present in :
(a) a brain cell ?
(b) a sperm in the testes ?
(c) an egg which has just been produced by the ovary ?
(d) a skin cell ?
(e) a fertilised egg ?
Solution :
(a) 46.
(b) 23.
(c) 23.
(d) 46.
(e) 46.

Question 30:
Gregor Mendel’s first law of genetics states “Of a pair of contrasted characters, only one can be represented in a gamete by its internal ‘factor’.
(a) Give the modern name for this ‘factor’.
(b) State where these factors are found in gametes.
Solution :
(a) Genes.
(b) Chromosomes.

Question 31:
Does genetic combination of mother play a significant role in determining the sex of a new born baby ?
Solution :
No, because mother has a pair of X chromosomes. All new born babies will inherit an X chromosome from mother whether they are baby boys or baby girls.

Question 32:
Give the contrasting traits of the following characters in pea plant and mention which is dominant and which is recessive :
(a) Yellow seed (b) Round seed
Solution :
(a) Green seed: Yellow is dominant: Green is recessive.
(b) Wrinkled seed: round is dominant: wrinkled is recessive.

Question 33:
(a)What is meant by ‘heredity’ ? What are the units of heredity.
(b) State Mendel’s first law of inheritance.
Solution :
(a) The transmission of characters from parents to the offspring’s is called heredity. The units of heredity are genes.
(b) According to Mendel’s first law of inheritance: The characteristics (or traits) of an organism are determined by internal ‘factors’ which occur in pairs. Only one of a pair of such factors can be present in a single gamete.

Page No - 193

Question 34:
(a) Why did Mendel choose pea plants for conducting his experiments on inheritance ?
(b) State Mendel’s second law of inheritance.
Solution :
(a) Mendel choose pea plants for studying inheritance because pea plants had a number of clear cut differences which were easy to tell apart. Another reason for choosing pea plants are they were self pollinating and many generations can be produced in a short time span.
(b) According to Mendel’s second law of inheritance: In the inheritance of more than one pair of traits in a cross simultaneously, the factors responsible for each pair of traits are distributed independently to the gametes.
(c) How does the creation of variation in a species ensure its survival ?

Question 35:
(a) What do you understand by the term ‘variation’ ?
(b) Name two human traits which show variation.
Solution :
(a) The differences in the characters among the individual of a species is called variation.
(b) Human height and free ear lobe are the traits which show variation in humans.
(c) Due to the creation of variations, a species can adjust to the changing environment around it. And this promotes the survival of the species in the changing environment. Example: The accumulation of ‘heat resistant’ variation (or trait) in some bacteria will ensure its survival even when the temperature in its environment rises too much due to a heat wave or some other reasons. On the other hand, the bacteria which did not have this variation to withstand heat would not survive under these circumstances and die.

Question 36:
(a) What are genes ? Where are they located in our body ?(a) What are genes ? Where are they located in our body ?
(b) What is meant by dominant genes and recessive genes ? Give one example of each.
(c) Explain how, characteristics (or traits) are inherited through genes.
Solution :
(a) Genes are the units of heredity which transfer characteristic from parents to their offspring’s during reproduction. Genes are located on the chromosomes.
(b) The gene which decides the appearance of an organism even in the presence of an alternative gene is known as dominant gene. The gene which can decide the appearance of an organism only in the presence of another identical gene is called a recessive gene. The dominant gene is represented by a capital letter and the corresponding recessive gene is represented by the corresponding small letter. For example, in pea plants, the dominant gene for tallness is T and the recessive gene for dwarfness is t.
(c) There is a pair of genes for each characteristic of an organism, one is dominant gene and the other is recessive gene. Each parent passes only one of the two genes of the pair for each characteristic to its progeny through gametes. Thus, the male gamete and the female gamete carry one gene for each characteristic from the gene pairs of the parents. When a male gamete fuses with a female gamete during fertilisation they make a new cell called zygote which grows and develops to form a new organism having characteristics from both the parents which it has inherited through genes.

Question 37:
(a) How do Mendel’s experiments show that traits may be dominant or recessive ?
(b) How do Mendel’s experiments show that traits are inherited independently ?
Solution :
(a) Mendel first crossed pure bred tall pea plants with pure bred dwarf pea plants and found that only tall pea plants were produced in the first generation. No dwarf pea plants were obtained in F1 generation. Mendel concluded that the first generation showed the traits of only one of the parent plants; tallness. The trait of other parent plant, dwarfness, did not show up in the progeny of first generation. Mendel then crossed the tall pea plants of the first generation (F1 Generation) and found that tall plants and dwarf plants were obtained in the second generation (or F2 generation) in the ratio of 3:1. Mendel noted that the dwarf trait of the parent pea plant which had seemingly disappeared in the first generation progeny reappeared in the second generation. In this way, Mendel’s experiments with tall and dwarf pea plants showed that the traits may be dominant and recessive.

A cross of tall and dwarf pea plant

A cross of tall plants of F₁ Generation

(b) When Mendel crossed pure-bred tall pea plants with pure-bred dwarf pea plants, he found that only tall pea plants were produced in the F1 generation. When Mendel further crossed the tall pea plants of the F1generation, he found that the tall plants and dwarf plants were obtained in the ratio 3:1 in the F2 generation. Mendel noted that all the pea plants produced in the F2 generation were either tall or dwarf. There were no plants with intermediate height (or medium height) in-between the tall and dwarf plants. In this way, Mendel’s experiment showed that the traits (like tallness and dwarfness) are inherited independently. This is because if the traits of tallness and dwarfness had blended (or mixed up), then medium sized pea plants would have been produced.