Class 10 Science Chapter 8: Heredity worksheet with answer key
A 20-mark worksheet on Heredity for about 40 minutes of class or homework: 5 multiple-choice, 3 very short answer and 3 short answer questions, written from the NCERT chapter and checked by a second reviewer. Print the PDF for the class; the answer key carries the marking scheme. Teachers may photocopy it freely.
Show answer
Answer: (a) tall
A single copy of T is enough to make the plant tall; both copies must be t for it to be short. Tt is therefore tall, with no halfway height.
Show answer
Answer: (b) XY
Men have a mismatched pair: one normal-sized X and one short Y. Women have a perfect pair, XX.
Show answer
Answer: (b) round or wrinkled seeds
Mendel worked with contrasting visible characters of garden peas such as round or wrinkled seeds, tall or short plants and white or violet flowers. The other pairs are not among them.
Show answer
Answer: (a) all round
Round seed is the dominant trait, and the F1 of pure contrasting parents shows only one parental trait with no halfway form, so every F1 seed is round.
Show answer
Answer: (b) the temperature at which the fertilised egg is kept
In some reptiles the temperature at which the fertilised eggs are kept determines whether the young developing in them will be male or female; this is an environmental cue, not a chromosome.
Show answer
No. The mother is XX and gives one X to each child. The sister is XX, so her second X came from the father; an X from the father makes a girl, a Y makes a boy.
- says no: one X from the mother only (1)
- the other X came from the father, which made her a girl (1)
Show answer
The cells were not all identical: a few carried a variation that let them withstand heat, and variants do not have equal chances of surviving in an environment. The survivors pass the variation on, so after a few generations most cells in the culture can withstand heat.
- the survivors carried a heat-tolerant variation; variants differ in chance of survival (1)
- offspring inherit it, so the culture becomes mostly heat-tolerant (1)
Show answer
In a few reptiles the temperature at which the fertilised eggs are kept decides whether the young are male or female. In snails an individual can change sex, so sex is not genetically determined.
- reptiles: incubation temperature of the eggs (1)
- snails: individuals change sex (1)
Show answer
(a) Yellow is dominant: the F1 of pure contrasting parents shows only yellow, with no blending. (b) 452 : 148 = 3.05 : 1, about 3 : 1. (c) The green trait was inherited by the F1 plants but not expressed; both traits were present in the F1, and only yellow showed.
- yellow dominant, as the only trait in the F1 (1)
- ratio about 3 : 1 worked from 452/148 (1)
- green factor was present but hidden in the F1 (1)
Show answer
(a) Tt Rr; all tall with round seeds, as both are dominant. (b) TR, Tr, tR and tr. (c) Tall with wrinkled seeds, and short with round seeds.
- F1 Tt Rr, tall with round seeds (1)
- four germ-cells TR, Tr, tR, tr (1)
- tall-wrinkled and short-round (1)
Show answer
(a) Every father makes germ-cells carrying X and germ-cells carrying Y in equal numbers, so about half the children (100 of 200) are expected to be boys. (b) The father's: an X from him gives a girl, a Y a boy. (c) The neighbour is wrong: every mother gives only an X, so she cannot decide the sex of the child.
- X and Y sperms equal, so half boys, half girls (1)
- the father's chromosome decides (1)
- mother always gives X, so she cannot decide (1)
← Chapter 7: How do Organisms Reproduce?Chapter 9: Light: Reflection and Refraction →