Heredity — Class 10 Science PYQs

Choose the correct statements with reference to chromosomes :
(i) carry hereditary information from parents to next generation.
(ii) are thread-like structures located inside the nucleus of an animal cell.
(iii) always exist in pairs in human gametes.
(iv) are involved in the process of cell division.

The number of chromosomes in parents and offspring of a particular species undergoing sexual reproduction remains constant due to :

Identify the traits that cannot be transmitted from parents to the off springs :
(i) Swimming technique
(ii) Blood group
(iii) Eye colour
(iv) Dancing skills
Options :

Question Nos. 8 & 9 consists of two statements : Assertion

In a cross carried out by Mendel, when he crossed tall pea plant (TT) with a short pea plant (tt) in $\text{F}_1$ progeny (first generation), all the plants were found to be tall. Select the correct reason from the given options.

Mendel took garden pea plants with different characteristics, such as height to study the inheritance pattern of factors (genes). He crossed tall pea plant with short pea plant and obtained all the tall plants in the $\text{F}_1$ generation.
Answer the following questions :
(a) Why only tall pea plants were observed in $\text{F}_1$ progeny ?
(b) By which method did Mendel obtain $\text{F}_2$ progeny ?

(c) (i) Write one difference between dominant and recessive trait.

(c) (ii) Write two observations made by Mendel about $\text{F}_1$ progeny.

"Variation is useful for the survival of species over time." Explain this statement with the help of an example.

Do all variations in a species have equal chances of surviving in the environment in which they find themselves ? Explain.

Mendel used a number of easily observable contrasting characters of garden pea plant. List any two pairs of such characters. Also mention the dominant and recessive character in each pair.

A blue colour flower (BB) bearing plant is crossed with a plant with white coloured flowers (bb).
(a) State the colour of the flowers you would expect in their $\text{F}_1$ progeny.
(b) What must be the percentage of white flower plants in the $\text{F}_2$ generation, if the $\text{F}_1$ plants are self-pollinated ?
(c) State the expected ratio of genotypes BB and bb in $\text{F}_2$ progeny.

"Each organism has two sets of all genes, one inherited from each parent i.e. both parents contribute equally to the DNA of the progeny during sexual reproduction”.
If such is the case, then how is the stability of DNA of the species ensured ? Discuss.

Mendel took garden pea plants with different characteristics, such as height to study the inheritance pattern of factors (genes). He crossed tall pea plant with short pea plant and obtained all the tall plants in the $\text{F}_1$ generation.
Answer the following questions :
(a) Why only tall pea plants were observed in $\text{F}_1$ progeny ?
(b) By which method did Mendel obtain $\text{F}_2$ progeny?
(c) (i) Write one difference between dominant and recessive trait.
OR
(c) (ii) Write two observations made by Mendel about $\text{F}_1$ progeny.

Read the following passage and answer the questions that follow :
Indian scientists helped crack the DNA code of ‘bread-wheat' genome, which would help improve global food security. It will allow faster breeding for climate-resilient varieties with drought, heat and frost tolerance, disease-resistant and superior quality grain. It may also help people suffering from allergy to wheat gluten. The information generated will help identify genes controlling yield, grain quality, resistance to diseases, etc. A variety of grains can thus be produced.
(a) Write the full form of DNA.
(b) What type of cell division is involved in the formation of gametes ?
(c) (i) Variations confer an advantage to an individual to survive. Justify.
OR
(c) (ii) How do genes control characteristics or traits ?

The genotype of green stemmed tomato plant is denoted by 'GG' and that of purple stemmed tomato plant as 'gg'. Hybrid of a cross between these two were self-pollinated to obtain $\text{F}_2$ progeny. What will be the ratio of GG, Gg and gg in this $\text{F}_2$ progeny ?

Two pea plants, one with round green seeds (RRyy) and another with wrinkled yellow (rrYY) seeds were crossed with each other which produced $F_1$ progeny that have only round yellow (RrYy) seeds. When $F_1$ plants are self-pollinated, the $F_2$ progeny will have which new combination of characters, as compared to the parents :
(i) Round, yellow
(ii) Round, green
(iii) Wrinkled, yellow
(iv) Wrinkled, green
Correct options are :

Round, green seeded pea plant (RRyy) was crossed with wrinkled, yellow seeded pea plant (rrYY), and $\text{F}_1$ progeny is produced.
All plants of $\text{F}_1$ progeny will have :

Mendel crossed pea plants having yellow seeds (YY) with pea plants having green seeds (yy). Yellow seeds are obtained in $\text{F}_1$ progeny which undergoes self-pollination to produce $\text{F}_2$ progeny. Select the option showing the result of $\text{F}_2$ progeny.

Two pea plants one with round green seeds (RRyy) and another with wrinkled yellow seeds (rrYY) were crossed. All the seeds of
(F₁) progeny have round, yellow seeds (RrYy). When
(F₁) plants are self-pollinated, the
(F₂) progeny will have new combination of characters.
(i) Round, yellow
(ii) Round, green
(iii) Wrinkled, yellow
(iv) Wrinkled, green
Choose the option that shows new combination of characters in
(F₂) progeny.

Use the following information for Pea plants :
Dominant allele for tall plants – T
Recessive allele for short plants – t
Dominant allele for purple flowers – P
Recessive allele for white flowers – p
(a) Perform a cross between pure plant dominant for both the traits with another plant which is recessive for both the traits and work out the progeny upto $\text{F}_2$ generation.
(b) What is the probability of obtaining tall plants with white flowers in $\text{F}_2$ progeny?

Sex is determined by different factors in various species. However, in human beings, it is determined genetically.
Which amongst the following option(s) is/are correct for human beings ?
(i) Gamete carrying X chromosome from female parent.
(ii) Gamete carrying X chromosome from male parent.
(iii) Gamete carrying Y chromosome from male parent.
Options:

When a human egg is fertilized by a sperm having ‘Y’ chromosome, the zygote has the following combination of chromosomes :

Assertion (A): In some reptiles, the temperature at which the fertilized eggs are kept determines whether the egg will develop into a male or a female.
Reason (R) : In human beings, the sex is determined genetically.

Describe how the sex of a new born individual is determined in humans.

(a) A couple are parents to 4 daughters in a sequence, and do not have any son. Does this indicate that the husband does not produced Y-chromosome bearing sperms ? Explain.
(b) What are the chances of this couple bearing yet another daughter ? Show with the help of a cross.

(a) Giving two examples, justify the statement that the sex of the offspring in all animals is not always genetically determined.
(b) Differentiate between the sex chromosomes of male and female human beings.