Question:

Assertion (A) : In dihybrid crosses involving sex-linked genes in \(\textit{Drosophila}\), \(F_2\) generation of non-parental gene combinations are observed.
Reason (R) : Two genes present on different chromosomes show linkage and recombination in \(\textit{Drosophila.}\)

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Remember that linkage applies to genes on the same chromosome, while independent assortment applies to genes on different chromosomes. Recombination can occur between linked genes due to crossing over.

Updated On: May 9, 2025

Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
Assertion (A) is true, but Reason (R) is false.
Assertion (A) is false, but Reason (R) is true.

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The Correct Option is C

Solution and Explanation

Assertion (A) states that in dihybrid crosses involving sex-linked genes in\( \textit{Drosophila}\), the \(F_2\) generation shows non-parental gene combinations. This is true. Sex-linked genes are located on the X chromosome. During meiosis in the \(F_1\) generation (which are heterozygous for these genes), recombination (crossing over) can occur between the sex chromosomes, leading to the formation of gametes with non-parental combinations of the linked genes. These non-parental combinations will be observed in the \(F_2\) generation.
Reason (R) states that two genes present on different chromosomes show linkage and recombination in\( \textit{Drosophila}\). This is false. Genes located on different chromosomes assort independently according to Mendel's law of independent assortment. Linkage occurs when genes are located on the same chromosome and tend to be inherited together. Recombination occurs due to crossing over between homologous chromosomes during meiosis, which can separate linked genes, but it doesn't apply to genes on different chromosomes in the context of linkage. Genes on different chromosomes exhibit independent assortment, resulting in non-parental combinations due to the random segregation of chromosomes. Therefore, Assertion (A) is true, but Reason (R) is false.

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Questions Asked in CBSE CLASS XII exam

Simar, Tanvi, and Umara were partners in a firm sharing profits and losses in the ratio of 5 : 6 : 9. On 31^st March, 2024, their Balance Sheet was as follows:

Balance Sheet of Simar, Tanvi, and Umara as at 31^st March, 2024

Liabilities	Amount (₹)	Assets	Amount (₹)
Capitals:		Fixed Assets	25,00,000
Simar	13,00,000	Stock	10,00,000
Tanvi	12,00,000	Debtors	8,00,000
Umara	14,00,000	Cash	7,00,000
General Reserve	7,00,000	Profit and Loss A/c	2,00,000
Trade Payables	6,00,000
Total	52,00,000	Total	52,00,000

Umara died on 30^th June, 2024. The partnership deed provided for the following on the death of a partner:

Goodwill of the firm be valued at 3 years purchase of average profits for the last 5 years. The profits/losses for the previous four years were:
- 2022-23: ₹ 3,10,000 (loss)
- 2021-22: ₹ 3,00,000 (profit)
- 2020-21: ₹ 4,00,000 (profit)
- 2019-20: ₹ 2,50,000 (profit)
Umara’s share of profit or loss till the date of her death was to be calculated on the basis of profit or loss for the year ended 31^st March 2024.
Calculate Goodwill of the firm.
Pass the necessary journal entry for the treatment of goodwill on Umara’s death.
Calculate Umara’s share in the profit or loss of the firm till the date of her death.
Pass the necessary journal entry to record Umara’s share of profit or loss till the date of her death.

CBSE CLASS XII - 2025
Profit and Loss Account

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Assertion (A) : In dihybrid crosses involving sex-linked genes in \(\textit{Drosophila}\), \(F_2\) generation of non-parental gene combinations are observed. Reason (R) : Two genes present on different chromosomes show linkage and recombination in \(\textit{Drosophila.}\)