NCERT Solution for Class 10 Science Ch 8 Heredity
NCERT Solutions for Class 10 Science Chapter 9 Heredity and Evolution provides the answers to all the textbook questions with a thorough analysis of the concept. Discover important concepts and the method of giving their solutions with the NCERT Solutions given here, which are carefully answered by our highly qualified teachers. Intext questions are also answered with adequate explanations, wherever necessary. Furthermore, we make sure that relevant content on NCERT Solutions Class 10 is regularly updated as per the CBSE Board. We also ensure that the answers that we deliver are tailored to meet various criteria that teachers look for when awarding marks.
➤ NCERT Solution for Class 10 Science Ch 16 - Sustainable Management of Natural Resources
Chapter 9 of NCERT Solutions is a very crucial and scoring chapter, as many questions would appear in the CBSE Board exams. Students will obtain an in-depth knowledge of the concepts as per the latest syllabus of the CBSE Board.
➤ NCERT Solution for Class 10 Science Ch 15 - Our Environment
Intext Questions, Page - 129
1. If a trait A exist 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 ?
Answer:
The trait B which exist in 60% of the population is likely to have an arisen earlier. This is because the traits (or variations) produced in an organism during successive generation get accumulated in the populations of the species.
2. How does the craetion of variations in a species promote survival ?
Answer:
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. For 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.
Intext Questions, Page - 133
1. How do Mendel's experiments show that traits may be dominant or recessive ?
Answer:
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 or F1 generation (see Figure 1). No dwarf pea plants (or short pea plants) were obtained in the first generation of progeny. From this Mendel concluded that the first generation (or F1 cross) showed the traits of only one of the parent plants : tallness. The trait of the other parent plant, dwarfness, did not show up in the progeny of first generation.
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| Figure 1 : A cross of tall and dwarf pea plants. |
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 3 : 1. In other words, in the F2 generation, three - fourth plants were tall and one - fourth were dwarf (see Figure 2). 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. Mendal said that the trait of dwarfness of one of the parent pea plant had not been lost, it was merely concealed or supressed in the first generation to re - emerge in the second generation. Mendel called the repressed trait of 'dwrfness' as 'recessive trait' and the expressed trait of 'tallness' as the 'dominant trait'. In this way, Mendel's experiments with tall and dwarf pea plants showed that the traits may be dominant or recessive.
2. How do Mendel's experiments show that traits are inherited independently ?
Answer:
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 geenration. Now, when Mendel further crossed the tall pea plants of the F1 generation, he found that 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.
3. A man with blood group A marries a woman with blood group O and their daughter has blood group O. Is this information enough to tell you which of the traits - blood group A or O - is dominant ? Why or why not ?
Answer:
No, this information is not enough to tell us which of the traits, blood group A or blood group O, is dominant. This is because :
- if the blood group A is dominant trait and blood group O is recessive trait, the daughter can have blood group O, and
- even if the blood group A is recessive trait but blood group O is dominant trait, the daughter can still have blood group O.
Let us discuss these two possibilities in detail.
Possibility 1 : When blood group A is dominant trait but blood group O is recessive trait
When father's blood group A is dominant trait, it can have two genotypes : IAIA and IAIO . And when mother's blood group O is recessive trait it can have only one genotype : IOIO (because it should have two recessive alleles). Now, if one recessive allele IO comes from father and one recessive allele IO comes from mother, then the daughter can also have the genotype IOIO which can give her blood group O.
Possibility 2 : when blood group A is recessive trait but blood group O is dominant trait
When father's blood group A is recessive trait, it can have only one genotype : IAIA (because it should have two recessive alleles). And when mother's blood group O is dominant trait, then it can have two genotypes : IOIO and IOIA. Now, if one dominant allele IO comes from the mother and one recessive allele IA comes from the father, the daughter will have the genotype IOIA which will again giver her blood group O.
4. How is the sex of the child determined in human beings ?
Answer:
Genetics is involved in the determination of the sex of child. This can be explained as follows : The chromosomes which determine the sex of a child are called sex choromosomes. There are two type of sex chromosomes, one is called X chromosome and the other is called Y chromosome.
- A male (man or father) has one X chromosome and one Y chromosome. This means that half the male gametes or half the sperms will have X chromosomes and the other half will have Y chromosomes.
- A female (woman or mother) has two X chromosomes (but no Y chromosomes). This means that all the females gametes called ova (or eggs) will have only X chromosomes.
The sex of a child depends on what happens at fertilisation :
- If a sperm carrying X chromosome fertilises an ovum (or egg) which carries X chromosome, then the child born will be a girl (or female). This is because the child will have XX combination of sex chromosomes.
- If a sperm carrying Y chromosome fertilises an ovum (or egg) which carries X chromosome, then the child born will be a boy (or male). This is because the child will have XY combination of sex chromosomes.
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| Determination of sex of a child |
Exercises, Page - 133
1. A Mendelian experiment consisted of breeding tall pea plants bearing violet flowers with short pea plants bearing white flowers. The progeny all bore violet flowers, but almost half of them were short. This suggests that the genetic make up of the tall parent can be depicted as
(a) TTWW
(b) TTww
(c) TtWW
(d) TtWw
Answer:
(c) TtWW
Explanation : T is the gene for tallness, t is the gene for shortness (or dwarfness), W is the gene for violet colour and w is the gene for white colour. Now, in this case, all the progeny bore violet flowers, so the parent tall plant must contain only the dominant genes for colour (which is violet colour). That is, the parent plant should have the gene pair WW. Again, since almost half of progeny plants were short, this means that the parent tall plant should contain genes for tallness as well as shortness. That is, the parent plant should have genes Tt in it. Now, combining Tt and WW, the genetic make up of the parent plant becomes TtWW.
2. A study found that children with light - coloured eyes are likely to have parents with light - coloured eyes. On this basis, can we say anything about whether the light eye colour trait is dominant or recessive ? Why or why not ?
Answer:
Just on the basis of of the statement that children with light - coloured eyes are likely to have parents with light - coloured eyes, we cannot say whether the light eye colour trait is dominant or recessive. This is because two copies of a trait (say eye colour) are inherited from both parents (one from father and the other from mother) and unless we know the nature of the two eye - colour traits, we cannot tell which is dominant and which is recessive. Recessive traits appear only when both the parents contribute recessive genes. So, from the statement given here we can only presume that both the parents are contributing recessive genes.
3. Outline a project which aims to find the dominant coat colour in dogs.
Answer:
In order to find the dominant coat colour (or dominant hair colour) in dogs, we should first select pure - bred male and female dogs having black colour and pure - bred male and female dogs having brown colour. Then :
- cross the pure - bred black male dog with pure - bred brown female dog.
- also, cross the pure - bred brown male dog with pure - bred black female dog . Observe the coat colour (or hair colour) of progeny (or puppies) produced.
- If all the progeny (or puppies) are black in colour, then black will be the dominant coat colour in dogs.
- If however, all the progeny (or puppies) are brown in colour, then brown will be the dominant coat colour in dogs.
4. How is equal genetic contribution of male and female parents ensured in the progeny ?
Answer:
The equal genetic contribution of male and female parents in a progeny is ensured through the special type of reproductive cells (called gametes) which have only half the amount DNA as compared to other body cells (called non - reproductive cells). So, when the gametes from male and female parents combine during sexual reproduction to form a fertilised egg called zygote, they contribute eual amount of DNA (half each) . For example, the normal body cells of human beings contain 46 chromosomes each (made of DNA). Now, the human sperm cell (or male gamete) has 23 chromosomes and human egg cell (or female gamete) has also 23 chromosomes. So, the combination of 23 chromosomes from male and an equal number of 23 chromosomes from female during sexual reproduction ensures equal genetic contribution of male and female parents in the progeny (to give 23 + 23 = 46 chromosomes).