CBSE Class 10 Science HOTs Heredity Set 04

Question. Two pink coloured flowers on crossing resulted in 1 red, 2 pink and 1 white flower progeny. The nature of the cross will be
(a) double fertilisation
(b) self-pollination
(c) cross-fertilisation
(d) no fertilisation
Answer: (c) cross-fertilisation

Question. Select the incorrect statement:
(a) Frequency of certain genes in a population change over several generations resulting in evolution
(b) Reduction in weight of the organism due to starvation is genetically controlled
(c) Low weight parents can have heavy weight progeny
(d) Traits which are not inherited over generations do not cause evolution
Answer: (b) Reduction in weight of the organism due to starvation is genetically controlled

Question. The two versions of a trait (character) which are brought in by the male and female gametes are situated on
(a) copies of the same chromosome
(b) two different chromosomes
(c) sex chromosomes
(d) any chromosome
Answer: (a) copies of the same chromosome

Question. The maleness of a child is determined by
(a) the X chromosome in the zygote
(b) the Y chromosome in the zygote
(c) the cytoplasm of germ cell which determines the sex
(d) sex is determined by chance
Answer: (b) the Y chromosome in the zygote

Question. Do genetic combination of mothers play a significant role in determining the sex of new born?
Answer: No, mothers have no role in determining the sex of the new born. Mothers have a pair of X chromosome and all children will inherit an ‘X’ chromosome from their mother regardless of whether they are boys or girls. Only presence or absence of ‘Y’ chromosome present in male gametes determine the sex of new born.

Question. Why do all the gametes formed in human females have an X-chromosome?
Answer: All the gametes formed in human females have an ‘X’ chromosome because during meiosis at the time of gamete formation, one X chromosome enters each gamete.

Question. In human beings, the statistical probability of getting either a male or female child is 50: 50. Give a suitable explanation. 
Answer: The sex of a child is determined by the type of sex chromosome contributed by male gamete. The statistical probability of getting either a male or female child is 50 : 50, because the ratio of male gametes containing X chromosome and those containing Y chromosome is 50 : 50.

Question. Give the pair of contrasting traits of the following characters in pea plant and mention which is dominant and recessive
(a) yellow seed (b) round seed
Answer: (a) Seed colour — Yellow (dominant), green (recessive)
(b) Seed shape — Round (dominant), wrinkled (recessive)

Question. A woman has only daughters. Analyse the situation genetically and provide a suitable explanation.
Answer: The women produces ova with both ‘X’ chromosome and man produces sperms with X and Y chromosome. If the husband of the woman transfer X chromosome, then child will be a girl. On the other hand, if the husband transfer Y chromosome, the child will be a boy. In the case, the husband is always transferring X chromosome and hence, all the children are girl.

Question. In the following crosses write the characteristics of the progeny: 
(a) \(RR YY \times RR YY\) Round, yellow and Round, yellow
(b) \(Rr Yy \times Rr Yy\) Round, yellow and Round, yellow
(c) \(rr yy \times rr yy\) wrinkled, green and wrinkled, green
(d) \(RR YY \times rr yy\) Round, yellow and wrinkled green
Answer: (a) Round yellow
(b) Round yellow, Round green, Wrinkled yellow, Wrinkled green
(c) Wrinkled green
(d) Round yellow

Question. Study the following cross and showing self pollination in \(F_1\), fill in the blank and answer the question that follows: 
Parents: \(RR YY\) (Round, yellow) \( \times \) \(rr yy\) (wrinkled, green)
\(F_1\) — \(Rr Yy\) (Round, yellow) \( \times \) ?
Answer: \(Rr Yy\) Round, yellow.

Question. In previous question, what are the combinations of character in the \(F_2\) progeny? What are their ratios?
Answer: Round yellow – 9 ; Round green – 3
Wrinkled yellow – 3 : Wrinkled green – 1
i.e. 9 : 3 : 3 : 1.

Question. Give reasons for the appearance of new combinations of characters in the \(F_2\) progeny.
Answer: An organism can inherit each character independently. So, in the \(F_2\) progeny new combination of character appears. Tall/Short and Round/Wrinkled seed trait are independently inherited.

Question. Give the basic features of the mechanism of inheritance.
Answer: Basic features for the mechanism of Inheritance are as follows:

(i) Characters are controlled by genes.

(ii) Each gene controls one character.

(iii) Genes are located on chromosomes.

(iv) There may be two or more forms of gene.

(v) An individual possess two forms of genes whether similar or dissimilar.

(vi) One form may be dominant over the other.

(vii) The two alleles separate at the time of gamete formation.

(viii) The two forms are brought together in the zygote.

(ix) Alleles of different genes located on separate chromosomes behave independent of one another.

Question. The genotype of offspring formed from \( Tt \times tt \) will be
(a) \( TT \) and \( tt \)
(b) \( Tt \) and \( tt \)
(c) Only \( tt \)
(d) Only \( TT \)
Answer: (b) \( Tt \) and \( tt \)

Question. A pea plant with round and green pea (\( RRyy \)) seed is crossed with another pea plant with wrinkled yellow (\( rrYY \)) seeds. What could be the nature of seed in the \( F_1 \) generation?
(a) Round and Green
(b) Wrinkled and Green
(c) Wrinkled and Yellow
(d) Round and Yellow
Answer: (d) Round and Yellow

Question. Phenotypic ratio in \( F_2 \) generation in dihybrid cross is
(a) \( 3 : 1 \)
(b) \( 9 : 3 : 3 : 1 \)
(c) \( 1 : 2 : 1 \)
(d) \( 2 : 1 \)
Answer: (b) \( 9 : 3 : 3 : 1 \)

Question. A plant with red coloured flower is crossed with a plant having white flowers. The red and white colour of the flowers is controlled by a single gene. Red is dominant over white. The \( F_1 \) progeny is then self pollinated. What will be the phenotypic ratio of plants with different flower colour in \( F_2 \) generation?
(a) All plants with red flowers
(b) Red : White in the ratio \( 3 : 1 \)
(c) Pink : White in the ratio \( 3 : 1 \)
(d) Red : Pink : White in the ratio \( 1 : 2 : 1 \)
Answer: (b) Red : White in the ratio \( 3 : 1 \)

Direction: In the following Questions, the Assertion and Reason have been put forward. Read the statements carefully and choose the correct alternative from the following:
(a) Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion.
(b) Both the Assertion and the Reason are correct but the Reason is not the correct explanation of the Assertion.
(c) Assertion is true but the Reason is false.
(d) The statement of the Assertion is false but the Reason is true.

Question. Assertion: When pure breed round seed plants are crossed with pure breed wrinkled seed plants, all the plants in the \( F_1 \) progeny have round seed. When round \( F_1 \) seeds are crossed, wrinkled seeds reappear in \( F_2 \) progeny.
Reason: Traits are independently inherited.
(a) Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion.
(b) Both the Assertion and the Reason are correct but the Reason is not the correct explanation of the Assertion.
(c) Assertion is true but the Reason is false.
(d) The statement of the Assertion is false but the Reason is true.
Answer: (b) Both the Assertion and the Reason are correct but the Reason is not the correct explanation of the Assertion.

Question. Assertion: Mouse whose tails are cut, give offspring with tail.
Reason: Cutting of tails do not make any change in the genes.
(a) Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion.
(b) Both the Assertion and the Reason are correct but the Reason is not the correct explanation of the Assertion.
(c) Assertion is true but the Reason is false.
(d) The statement of the Assertion is false but the Reason is true.
Answer: (a) Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion.

Question. Why are sexually reproducing organisms capable of showing more heredity features?
Answer: Sexually reproducing organisms show more heredity features because they involve the fusion of gametes from two different parents, leading to the shuffling of genetic material and the creation of new gene combinations and variations in the offspring.

Question. What is chromosome? Where are they located in the cells?
Answer: Chromosomes are long, thread-like structures made of DNA and proteins (histones) that carry genetic information in the form of genes. They are located inside the nucleus of eukaryotic cells.

Question. Why is variation beneficial for the species, but not necessary for the individual?
Answer: Variation is beneficial for a species as it increases the chances of survival during environmental changes by allowing some individuals to adapt to new conditions. However, it is not necessary for an individual's survival because an individual can survive and reproduce perfectly well with the existing set of traits as long as the environment remains stable.

Question. On the basis of the possibilities of combination of the sex chromosomes, what percentage probability does a couple have of having a son or a daughter? Show the same by making a cross.
Answer: There is a 50% probability of having a son and a 50% probability of having a daughter.
Cross:
Parents: Male (\( XY \)) \( \times \) Female (\( XX \))
Gametes: (\( X \)), (\( Y \)) \( \times \) (\( X \)), (\( X \))
Offspring: \( XX \) (Daughter), \( XX \) (Daughter), \( XY \) (Son), \( XY \) (Son)
Ratio: 2 Daughters : 2 Sons = \( 1 : 1 \) (50% each).

Question. Explain Mendel’s experiment with peas on inheritance of traits considering two visible contrasting characters.
Answer: Mendel performed a dihybrid cross using pea plants with two contrasting characters, such as seed shape (Round vs. Wrinkled) and seed colour (Yellow vs. Green). He crossed a pure-bred round yellow seed plant (\( RRYY \)) with a pure-bred wrinkled green seed plant (\( rryy \)). All \( F_1 \) offspring were Round Yellow (\( RrYy \)). Upon selfing the \( F_1 \) plants, the \( F_2 \) generation showed four combinations: Round Yellow, Round Green, Wrinkled Yellow, and Wrinkled Green in a phenotypic ratio of \( 9 : 3 : 3 : 1 \). This demonstrated the Law of Independent Assortment.

Cellular DNA is the information source for making proteins in the cell. A section of DNA that provides information for one protein is called the gene for that protein. Thus proteins control the characteristics. Tallness is a characteristics of plant. Plants have hormones that can trigger growth. Plant height can thus depend on amount of particular hormone. Amount of that particular hormone to be made depend on the efficiency of the process of making it. If the enzyme that make this particular hormone works efficiently, a lot of hormone will be made and the plant will be tall. If there is less quantity of hormone produced, the plant will be short.

Question. What controls the trait?
Answer: According to the passage, traits are controlled by proteins, for which the information is provided by specific sections of DNA called genes.

Question. Define heredity.
Answer: Heredity is the biological process by which genetic traits and characteristics are passed from parents to their offspring through generations.

Question. Why are tall plants not always produced from tall plants?
Answer: Tall plants are not always produced from tall plants because the parent plants might be heterozygous (\( Tt \)) for the height trait. When two heterozygous plants are crossed, they can produce offspring with the homozygous recessive genotype (\( tt \)), resulting in short plants.

Question. Or What is a dominant trait?
Answer: A dominant trait is a genetic characteristic that expresses itself in the phenotype even if only one copy of the allele is present (heterozygous state, \( Tt \)), as well as when two copies are present (homozygous state, \( TT \)).