Science · World of living · chapter 8 of 13

Class 10 Science Chapter 8: Heredity case study question with answers

One case-based question of the kind the board asks in Section E: a passage and a table, then 3 parts worth 4 marks in all, with the answer and the marking scheme for each. Written from the NCERT chapter.

Case study · 4 marks

Students of Class 10B surveyed the earlobes of everyone in the class. The lowest part of the ear was either closely attached to the side of the head or hung free below the point of attachment. Every student also asked both parents about their earlobes. Priya found that her earlobes are attached, although both her parents have free earlobes.

Earlobe	Number of students
Free	28
Attached	12
Total	40

Part 1 · 1 mark

What percentage of the class has attached earlobes?

(a) 12%(b) 30%(c) 40%(d) 70%

Show answer

Answer: (b) 30%

12 of 40 students: 12/40 × 100 = 30%. (70% have free earlobes.)

Part 2 · 1 mark

Free and attached earlobes are best described as

(a) two variants of one trait found in human populations(b) a trait found only in girls(c) changes produced by the way the ear grows after birth(d) two traits that always blend in the child

Show answer

Answer: (a) two variants of one trait found in human populations

The earlobe is attached in some people and free in others; these are two variants found in human populations.

Part 3 · 2 marks

Using the idea that every child has two versions of each trait, explain how Priya can have attached earlobes when neither parent does.

Answer and marking scheme

Each parent contributes practically equal genetic material, so Priya carries one version of the trait from her father and one from her mother. Each parent can carry a version that is not expressed in them, just as the shortness factor was carried unseen in Mendel's F1 tall plants. Priya received that hidden version from both parents, so it shows in her.

one version from each parent (1)
a version hidden in each parent passed on to Priya (1)

All 40 students share the basic design of the human body, yet no two of them, other than identical twins, look exactly alike. Explain both observations.

Answer and marking scheme

Inheritance passes on a common basic body design from the parents, so every child bears all the basic human features. Each child also gets a mix of versions of traits from both parents through sexual reproduction, which generates variation, so children differ from their parents and from one another.

inheritance passes on the common basic design (1)
sexual reproduction mixes both parents' versions, giving variation (1)

← Chapter 7: How do Organisms Reproduce?Chapter 9: Light: Reflection and Refraction →