CBSE Class 10 Biology Heredity Worksheet Set 13

This printable CBSE Class 10 Biology worksheet on Heredity has 24 short questions with answers that fit on two pages: 15 fill in the blanks and 9 true or false statements. It revises Mendel's pea plant experiments, dominant and recessive traits, the 3 : 1 and 9 : 3 : 3 : 1 ratios, chromosomes and sex determination, and acquired and inherited traits.

Fill in the Blanks

Question 1. Fill in the blank: Mendel performed his experiments on ...............
Answer:
garden pea (Pisum sativum)
Mendel chose the garden pea because it is easy to grow, has a short life cycle and shows clear contrasting traits.
In simple words: Mendel worked on garden pea plants.

Teacher's Note:
1. Remember the scientific name Pisum sativum.
2. Mendel is called the Father of Genetics.

Question 2. Fill in the blank: According to modern concept, Mendel's factor is called a ....................
Answer:
gene
Mendel called the units of inheritance factors; they are now called genes, which are sections of DNA on the chromosomes.
In simple words: Mendel's factors are our genes.

Teacher's Note:
1. Genes are sections of DNA.
2. Different forms of a gene are called alleles.

Question 3. Fill in the blank: Mendelian factors or genes as well as chromosomes are present in ................
Answer:
pairs
Both the genes (alleles) and the chromosomes occur in pairs in a body cell, one of each pair from each parent.
In simple words: Chromosomes and genes both come in pairs.

Teacher's Note:
1. In a gamete only one of each pair is present.
2. Fertilisation restores the pairs.

Question 4. Fill in the blank: The traits which express themselves in F1 generation are called ................
Answer:
dominant
A dominant trait is expressed in the F1 generation and masks the recessive trait.
In simple words: Traits seen in F1 are dominant.

Teacher's Note:
1. Write dominant traits with capital letters.
2. The hidden trait is called recessive.

Question 5. Fill in the blank: The phenotypic ratio between tall and dwarf is ................
Answer:
3 : 1
Selfing the F1 (Tt) plants gives TT, Tt, Tt and tt, that is 3 tall plants for every 1 dwarf plant.
In simple words: Three tall plants for each dwarf plant.

Teacher's Note:
1. This is the monohybrid ratio in F2.
2. The genotype ratio is 1 : 2 : 1.

Question 6. Fill in the blank: The phenotypic ratio in dihybrid cross is .................
Answer:
9 : 3 : 3 : 1
In the F2 generation of a dihybrid cross, the four phenotypes appear in the ratio 9 : 3 : 3 : 1.
In simple words: Four seed types appear in the ratio 9 : 3 : 3 : 1.

Teacher's Note:
1. Remember: 9 + 3 + 3 + 1 = 16 combinations.
2. Two of the four types are new combinations.

Question 7. Fill in the blank: There are ................ pairs of chromosomes in human.
Answer:
23
Humans have 46 chromosomes, which make 23 pairs: 22 pairs of autosomes and 1 pair of sex chromosomes.
In simple words: Humans have 23 pairs of chromosomes.

Teacher's Note:
1. 46 chromosomes make 23 pairs.
2. One of the 23 pairs is the sex chromosome pair.

Question 8. Fill in the blank: The offspring can be of two types with XX and ................ chromosomes.
Answer:
XY
An offspring with XX sex chromosomes is a girl and one with XY is a boy.
In simple words: XX is female and XY is male.

Teacher's Note:
1. The Y chromosome comes from the father.
2. The mother always gives an X.

Question 9. Fill in the blank: The traits which are acquired by an organism during its lifetime are called ................ .
Answer:
acquired traits
Acquired traits are developed during the lifetime of an individual and are not passed on to the offspring.
In simple words: Traits gained in life are acquired traits.

Teacher's Note:
1. They do not change the DNA of germ cells.
2. Example: learning a skill such as music.

Question 10. Fill in the blank: Transmission of traits from one generation to the next generation is called ................
Answer:
heredity
Heredity is the passing of traits from the parents to the offspring.
In simple words: Passing of traits to the next generation is heredity.

Teacher's Note:
1. Genes carry the hereditary information.
2. Genetics is the study of heredity and variation.

Question 11. Fill in the blank: ................ traits are unable to express in a hybrid.
Answer:
Recessive
In a hybrid (for example Tt) the dominant allele hides the recessive trait, which is expressed only in the homozygous condition (tt).
In simple words: The recessive trait stays hidden in a hybrid.

Teacher's Note:
1. Recessive traits are written with small letters.
2. They reappear in F2.

Question 12. Fill in the blank: Two types of nucleic acids are DNA and ................ .
Answer:
RNA
The two nucleic acids are DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).
In simple words: The two nucleic acids are DNA and RNA.

Teacher's Note:
1. Learn the full forms.
2. DNA carries the genetic information.

Question 13. Fill in the blank: Chromosome consists of a DNA molecule and .................
Answer:
protein
A chromosome is made of DNA and histone proteins.
In simple words: Chromosomes are made of DNA and protein.

Teacher's Note:
1. DNA is the carrier of genes.
2. Chromosomes are seen when the cell divides.

Question 14. Fill in the blank: If tall plant contains TT gene then dwarf plant contains ................ .
Answer:
tt
A tall pure plant is TT and a pure dwarf plant is tt; the recessive trait needs two copies of t.
In simple words: Dwarf plants are tt.

Teacher's Note:
1. Tt plants are also tall.
2. Only tt plants are dwarf.

Question 15. Fill in the blank: Mendel choose ................................ characters in Pea for his experiments.
Answer:
seven (pairs of contrasting)
Mendel studied seven pairs of contrasting characters such as tall/dwarf, round/wrinkled seeds and violet/white flowers.
In simple words: Mendel studied seven pairs of contrasting characters.

Teacher's Note:
1. Learn the seven pairs.
2. He studied one character at a time first.

True or False

Question 16. State whether true or false: Variations arising during the process of reproduction cannot be inherited.
Answer:
False
Variations that arise in the gametes or through errors in DNA copying are passed to the offspring and are inherited; they can build up over generations.
In simple words: Variations in the DNA can be inherited.

Teacher's Note:
1. Contrast with acquired traits of the body.
2. Variations arise in both asexual and sexual reproduction.

Question 17. State whether true or false: Sex is determined by different factors in various species.
Answer:
True
In humans the sex chromosomes decide the sex, in some reptiles the incubation temperature decides it, and snails can change sex.
In simple words: Different species use different methods.

Teacher's Note:
1. Give the three examples.
2. Humans: XX and XY.

Question 18. State whether true or false: Changes in the non-reproductive tissues caused by environmental factors are inheritable.
Answer:
False
Changes in the non-reproductive (body) tissues do not change the DNA of the germ cells, so they are not inherited.
In simple words: Changes in the body are not passed to children.

Teacher's Note:
1. Only germ-cell DNA is passed on.
2. These are acquired traits.

Question 19. State whether true or false: Exchange of genetic material takes place in asexual reproduction.
Answer:
False
Exchange of genetic material between two parents happens in sexual reproduction; asexual reproduction involves a single parent.
In simple words: Genes from two parents mix only in sexual reproduction.

Teacher's Note:
1. Asexual reproduction has one parent.
2. Variation there is due to DNA copying errors.

Question 20. State whether true or false: A cross between a true tall and pure dwarf pea plant resulted in production of all tall plants because tallness is the dominant trait.
Answer:
True
TT × tt gives all Tt plants, which are tall because T is dominant over t.
In simple words: All F1 plants are Tt and tall.

Teacher's Note:
1. Write the cross TT × tt.
2. The dwarf trait is hidden.

Question 21. State whether true or false: Both the parents contribute DNA equally to the offspring.
Answer:
True
Each parent gives one gamete with half the chromosomes (23), so the child gets half of its DNA from the father and half from the mother.
In simple words: A child gets half the DNA from each parent.

Teacher's Note:
1. This is the basis of inheritance rules.
2. Gametes have half the DNA of body cells.

Question 22. State whether true or false: Sex of the child is determined by the type of ovum provided by the mother.
Answer:
False
All ova carry an X chromosome. The sex is decided by the sperm: X gives a girl and Y gives a boy.
In simple words: The sperm, not the ovum, decides the sex.

Teacher's Note:
1. The mother has only XX.
2. The father gives X or Y.

Question 23. State whether true or false: A recessive trait can also be common as blood group O.
Answer:
True
Blood group O is a recessive trait but it is quite common in the population, so a recessive trait need not be rare.
In simple words: A recessive trait can be common.

Teacher's Note:
1. Common does not mean dominant.
2. Blood group O is ii.

Question 24. State whether true or false: Attached ear lobe is recessive trait.
Answer:
True
Free earlobes are dominant (F) and attached earlobes are recessive (ff), so attached earlobes appear only in homozygous ff individuals.
In simple words: Attached earlobes need two recessive alleles.

Teacher's Note:
1. Free earlobes: FF or Ff.
2. Attached earlobes: ff.