Heredity — Class 10 Science PYQs

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 :

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 $F_1$ generation.
Answer the following questions :
(a) Why only tall pea plants were observed in $F_1$ progeny ?
(b) By which method did Mendel obtain $F_2$ progeny ?
(c) (i) Write one difference between dominant and recessive trait.
OR
(c) (ii) Write two observations made by Mendel about $F_1$ progeny.

If pea plants with round and green seeds ($RRyy$) are crossed with pea plants having wrinkled and yellow seeds ($rrYY$), the seeds developed by the plants of $F_1$ generation will be :

Assertion (A) : A human child bears all the basic features of human beings.
Reason (R) : It looks exactly like its parents, showing very little variations.

(a) What are chromosomes ?
(b) Explain in brief how stability of DNA content of a species is ensured in sexually reproducing organisms ?

In one of Mendalian experiments, when $F_1$ generation pea plants with round yellow seeds were self-pollinated, pea seeds with the following combinations were obtained in $F_2$ generation :
| Seeds | Round yellow | Round green | Wrinkled yellow | Wrinkled green |
| Number | 800 | 275 | 268 | 90 |
Analyse the result and describe the mechanism of inheritance of traits which explains the above results.

(a) How many chromosomes are present in human beings ? Out of these how many are sex chromosomes ?
(b) Explain how, in sexually reproducing organisms, the number of chromosomes in the progeny is maintained.

The number of chromosomes in a cell division is halved. This kind of cell division is observed in :

Assertion (A) : A mango seed will germinate to form a mango tree.
Reason (R) : Heredity determines the process by which traits and characteristics are reliably inherited from parents to offspring.

The lowest part of the ear called earlobe, is closely attached to the side of the head in some of us (Figure 'X'), and not in others, called free earlobe (Figure 'Y'). Attached and free earlobes are two variants found in human populations. The gene for free earlobe is dominant over attached earlobes.
(a) A man with attached earlobes marries a woman having free earlobes. 50% of their children have free earlobes and 50% have attached earlobes. Explain the inheritance of this trait and write the trait combinations of the progeny.
(b) Write the gene combinations of the father and the mother in the above case.