CBSE Class 10 Biology Heredity Worksheet Set 14

This is a second printable CBSE Class 10 Biology worksheet on Heredity with 25 quick questions and answers: definitions, one-line answers, genotype questions and cross problems. It checks terms such as gene, DNA, genotype, phenotype, sex chromosomes and the two laws of Mendel, along with small problems on ratios from monohybrid and dihybrid crosses.

Short Answer Questions and Terms

Question 1. What is DNA?
Answer:
DNA stands for deoxyribonucleic acid. It is a nucleic acid present in the chromosomes of the cell, and it carries the genetic information that is passed from parents to offspring.
In simple words: DNA is the chemical that carries genetic information.

Teacher's Note:
1. Write the full form.
2. Add that it is present in chromosomes.

Question 2. What is a gene?
Answer:
A gene is the unit of heredity. It is a section of DNA on a chromosome that provides the information for making one protein and so controls a trait.
In simple words: A gene is a piece of DNA that codes for a protein.

Teacher's Note:
1. Use the words unit of inheritance.
2. Mention protein.

Question 3. What is heredity?
Answer:
Heredity is the process by which traits (characters) are passed on from the parents to the offspring.
In simple words: Heredity is passing of traits from parents to children.

Teacher's Note:
1. Keep the answer to one line.
2. Genes carry the traits.

Question 4. Name the human traits which show variations.
Answer:
Human traits that show variation are colour of eyes, height and colour of skin. Free and attached earlobes are another example.
In simple words: Eye colour, height and skin colour differ from person to person.

Teacher's Note:
1. Name at least two traits.
2. Free and attached earlobes is a neat example.

Question 5. What is genotype?
Answer:
Genotype is the genetic constitution of an organism for a trait, that is, the description of the genes (alleles) present in it. For example, TT, Tt or tt for the height of pea plants.
In simple words: Genotype is the gene make-up, such as Tt.

Teacher's Note:
1. Give TT, Tt and tt as examples.
2. Contrast with phenotype.

Question 6. Name the term used for traits that are exhibited externally.
Answer:
Phenotype. It is the visible (observable) expression of a trait, for example tall or dwarf.
In simple words: Visible traits form the phenotype.

Teacher's Note:
1. Phenotype can be seen.
2. Genotype cannot be seen.

Question 7. State Mendel's first law of inheritance.
Answer:
Law of segregation: during gamete formation, the two alleles of a character separate (segregate) so that each gamete carries only one allele for each character.
In simple words: Each gamete gets only one allele of a pair.

Teacher's Note:
1. Also called the law of purity of gametes.
2. Mention gamete formation.

Question 8. State Mendel's second law of inheritance.
Answer:
Law of independent assortment: the genes (alleles) for different traits separate independently of each other during the formation of gametes, so the traits are inherited independently.
In simple words: Different traits are inherited independently.

Teacher's Note:
1. It is based on the dihybrid cross.
2. Quote the 9 : 3 : 3 : 1 ratio.

Question 9. What is variation?
Answer:
Variation is the difference in characteristics or traits among the individuals of a species (and between the offspring and their parents).
In simple words: Variation means differences among individuals.

Teacher's Note:
1. Give an example such as earlobes.
2. Variations arise during reproduction.

Question 10. What is monohybrid cross?
Answer:
A monohybrid cross is a cross between two individuals that differ in one pair of contrasting traits, for example a tall plant × a dwarf plant (TT × tt). The F2 phenotypic ratio is 3 : 1.
In simple words: A cross that studies one pair of contrasting traits.

Teacher's Note:
1. Compare with dihybrid cross.
2. Give the 3 : 1 ratio.

Question 11. What is the scientific name of man and garden pea?
Answer:
Man: Homo sapiens.
Garden pea: Pisum sativum.
In simple words: Homo sapiens and Pisum sativum.

Teacher's Note:
1. Write scientific names in italics.
2. Genus starts with a capital letter.

Question 12. What are sex chromosomes?
Answer:
Sex chromosomes are the pair of chromosomes that decide the sex of an individual. In human beings they are X and Y: XX in a female and XY in a male.
In simple words: X and Y chromosomes decide whether a baby is a girl or a boy.

Teacher's Note:
1. Name X and Y.
2. The other 22 pairs are autosomes.

Question 13. Give an example where sex determination is regulated by environmental factors.
Answer:
In some reptiles such as turtles and lizards, the temperature at which the fertilised eggs are incubated decides the sex of the young ones. (Snails can change sex, which also shows that sex is not always genetically determined.)
In simple words: In turtles the incubation temperature decides the sex.

Teacher's Note:
1. Name the reptile and the factor.
2. In humans the chromosomes decide the sex.

Question 14. Name the plant on which Mendel performed his experiments.
Answer:
The garden pea (Pisum sativum).
In simple words: Mendel used garden peas.

Teacher's Note:
1. Give the scientific name as well.
2. Mendel is the Father of Genetics.

Question 15. In order to ensure than Mendel gets pure breeding plants in his experiments, what did he do?
Answer:
Mendel allowed each variety to self-fertilise for several generations and chose only the plants that always gave the same trait, so that he started with pure (true breeding) plants.
In simple words: He self-pollinated each variety for many generations first.

Teacher's Note:
1. Mention several generations.
2. Pure plants are homozygous.

Question 16. What is sex of the baby that inherits Y-chromosome from the father?
Answer:
The baby is a male (boy), because the zygote has XY: the X comes from the mother and the Y from the father.
In simple words: A Y from the father makes a boy.

Teacher's Note:
1. Write XY for a male.
2. The mother always gives X.

Question 17. Which sex chromosome is found only in male human beings?
Answer:
The Y chromosome is found only in males; females have two X chromosomes.
In simple words: Only men have a Y chromosome.

Teacher's Note:
1. Males are XY.
2. Females are XX.

Question 18. How many pairs of chromosomes are present in human beings?
Answer:
23 pairs (46 chromosomes): 22 pairs of autosomes and 1 pair of sex chromosomes.
In simple words: Humans have 23 pairs of chromosomes.

Teacher's Note:
1. Give 22 + 1.
2. 46 is the number of chromosomes, not pairs.

Question 19. Which of the following traits are recessive in pea plant? Dwarfness, violet flower, wrinkled seed.
Answer:
Dwarfness and wrinkled seed are recessive traits.
Violet flower is a dominant trait (white is recessive).
In simple words: Dwarf and wrinkled are recessive; violet is dominant.

Teacher's Note:
1. Learn the seven pairs of traits.
2. Tall, violet and round are dominant.

Cross Problems and Matching

Question 20. In a mono-hybrid cross a round seeded plant was crossed with a wrinkle seeded plant. In F2 generation genotype ratio obtained was 1:2:1. How many plants were homozygous round.
Answer:
The genotypic ratio 1 : 2 : 1 means RR : Rr : rr.
Homozygous round plants are RR, which is 1 out of 4, so a quarter (25%) of the F2 plants are homozygous round.
In simple words: One out of every four F2 plants is RR.

Teacher's Note:
1. Identify RR as homozygous round.
2. Rr is round but heterozygous.

Teacher's Note:
1. Draw a Punnett square.
2. The phenotype is all yellow.

Question 22. If YYRR is round yellow, what do the following represent?
yyrr    yyRR
Answer:
Here Y stands for yellow, y for green, R for round and r for wrinkled.
yyrr = wrinkled, green seeds.
yyRR = round, green seeds.
In simple words: yy means green and rr means wrinkled; R makes the seed round.

Teacher's Note:
1. Decode each letter.
2. Small letters mean recessive traits.

Question 23. Write the genotypes for
(a) Purple flowers (heterozygous)
(b) Round seeds (homozygous)
(c) Green pods (heterozygous)
(d) Dwarf pea plants (homozygous)
Answer:
Purple, round and green are dominant traits (use P, R and G; the recessive alleles are p, r and g).
(a) Pp
(b) RR (a homozygous round seed has two dominant alleles)
(c) Gg
(d) tt (dwarfness is recessive, so a dwarf plant is always homozygous)
In simple words: Heterozygous means one capital and one small letter, like Pp.

Teacher's Note:
1. Use the capital letter for the dominant trait.
2. Dwarf plants are always tt.

Teacher's Note:
1. Work out the gametes of each parent.
2. Bb × Bb gives the 1 : 2 : 1 genotype ratio.

Teacher's Note:
1. Write the gametes for each parent.
2. Only the hybrid cross gives four phenotypes.