Which of the processes, sexual eproduction or asexual reproduction, brings about maximum variations in the offsprings ?
Name one variation in humans connected with ears.
What constitutes the link between one generation and the next ?
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 ?
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 ?
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.
What are the chromosomes XY and XX known as ?
Which of the two, sperm or ovum, decides the sex of the child ?
State whether the following statement is true or false :
The sex of an infant is not a case of inheritance of characteristics.
A new born child has an XY pair of chromosmes. Will it be a baby boy or a baby girl ?
Which of the following combinations of sex chromosomes produce a male child : XX or XY ?
Name the first scientist who studied the inheritance of traits from one generation to the next.
What type of plants were used by Mendel for conducting his experiments on inheritance ?
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 ?
What are the four blood groups in humans ?
A, B, AB and O.
Name one reptile in each case where higher incubation temperature leads to the development of : (a) male progeny, (b) female progeny.
(a) Lizard (Agama agama)
(b) Turtle (Chrysema Picta)
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.
(b) Recessive; Dominant.
(c) Free; attached.
(d) 23; 46.
(f) Sex; Female; male.
Lakhmir Singh Biology Class 10 Solutions Page No:192
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) ?
Give reason for your choice (The symbols have their usual meaning).
(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.
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 ?
Equal chance of having blood group O or blood group B.
a) Name the scientist who gave the laws of inheritance.
(b) Name an animal in which individuals can change sex. What does this indicate ?
(a) Gregor Mendel
(b) Snails: This indicates that sex is not determined genetically in some animals.
Explain with an example, how genes control the characteristics (or traits).
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.
(a) State one advantage of variation to a species.
(b) What are sex chromosomes ? How many sex chromosomes are there ? Name them.
(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.
Explain how, sex is determined in human babies.
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.
What do the following symbols used in the topic on heredity represent ?
(a) Tall plant.
(b) Dwarf plant.
(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 ?
(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.
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.
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.
(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
(c) (i) tt
(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 ?
(b) Three tall plants and one dwarf plant.
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 ?
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.
Does genetic combination of mother play a significant role in determining the sex of a new born baby ?
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.
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
(a) Green seed: Yellow is dominant: Green is recessive.
(b) Wrinkled seed: round is dominant: wrinkled is recessive.
(a)What is meant by ‘heredity’ ? What are the units of heredity.
(b) State Mendel’s first law of inheritance.
(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.