Vidaara.orgClass 12 · Mathematics
CodeVID-M12-WS
Principles of Inheritance and Variation — Practice Worksheet
Name: ____________________
Roll No.: __________
Date: ____________
General Instructions
- All questions are compulsory.
- Choose the correct option (A, B, C or D) for each question.
- The answer key is at the end — try the paper first!
Section A — Multiple Choice (1 mark each)
17 × 1 = 17 marks
1.
The Father of Genetics is:
- A.Charles Darwin
- B.Gregor Mendel
- C.Louis Pasteur
- D.Robert Hooke
2.
Alternative forms of a gene are called:
- A.Alleles
- B.Chromosomes
- C.Nucleotides
- D.Codons
3.
An organism with identical alleles (TT or tt) is:
- A.Heterozygous
- B.Homozygous
- C.Hybrid
- D.Recessive only
4.
The visible character of an organism is its:
- A.Genotype
- B.Phenotype
- C.Allele
- D.Gene
5.
The F1 of a tall (TT) × dwarf (tt) pea cross is:
- A.All dwarf
- B.All tall
- C.Half tall half dwarf
- D.All medium
6.
The F2 phenotypic ratio of a monohybrid cross is:
- A.1:1
- B.3:1
- C.9:3:3:1
- D.1:1:1:1
7.
The genotypic ratio of a monohybrid F2 is:
- A.3:1
- B.1:2:1
- C.9:3:3:1
- D.1:1
8.
The reappearance of the recessive trait in F2 illustrates the Law of:
- A.Segregation
- B.Independent Assortment
- C.Use and disuse
- D.Limiting factors
9.
The F2 ratio of a dihybrid cross is:
- A.3:1
- B.1:2:1
- C.9:3:3:1
- D.1:1
10.
Each trait pair being inherited independently is the Law of:
- A.Dominance
- B.Segregation
- C.Independent Assortment
- D.Linkage
11.
A blended phenotype like a pink snapdragon shows:
- A.Complete dominance
- B.Incomplete dominance
- C.Co-dominance
- D.Epistasis
12.
Human blood group AB, where both antigens appear, is an example of:
- A.Incomplete dominance
- B.Co-dominance
- C.Recessiveness
- D.Linkage
13.
The sex chromosomes of a human female are:
- A.XY
- B.XX
- C.YY
- D.XO
14.
The sex of a human child is determined by the:
- A.Mother's egg
- B.Father's sperm (X or Y)
- C.Grandparents
- D.Diet
15.
Down's syndrome is caused by an extra copy of chromosome:
- A.21
- B.X
- C.Y
- D.1
16.
A single gene affecting many different traits at once shows:
- A.Pleiotropy
- B.Linkage
- C.Co-dominance
- D.Incomplete dominance
17.
In birds, the sex chromosomes of a female are:
- A.XX
- B.XY
- C.ZW
- D.ZZ
Section B — Challenge / Olympiad (2 marks each)
7 × 2 = 14 marks
18.
A tall pea plant could be either TT or Tt. A test cross with a dwarf (tt) plant identifies it because if any dwarf offspring appear, the tall parent must be:
- A.Tt (heterozygous)
- B.TT (homozygous)
- C.tt
- D.Sterile
19.
New combinations such as round-green and wrinkled-yellow appearing in the F2 of a dihybrid cross are explained by:
- A.Independent assortment of the two trait pairs
- B.Incomplete dominance
- C.Linkage
- D.Mutation only
20.
Crossing two pink snapdragons (Rr × Rr) gives a phenotypic ratio of:
- A.1 red : 2 pink : 1 white
- B.3 red : 1 white
- C.All pink
- D.9:3:3:1
21.
A colour-blind father and a normal (non-carrier) mother have children. Their daughters will most likely be:
- A.Carriers but not colour-blind
- B.All colour-blind
- C.All affected boys
- D.Unaffected with no carrier allele
22.
Blaming the mother for the sex of a child is biologically wrong because the egg always carries an X, so the sex is decided by whether the sperm carries:
- A.X or Y
- B.Only X
- C.Only Y
- D.No chromosome
23.
In regions where malaria is common, the sickle-cell allele can persist because carriers (heterozygotes) have:
- A.Some resistance to malaria
- B.No red blood cells
- C.Extra chromosomes
- D.Immunity to all disease
24.
Crossing over reduces linkage between two genes more often when the genes are:
- A.Farther apart on the chromosome
- B.Very close together
- C.On different organisms
- D.Identical
Answer Key
Section A — Multiple Choice (1 mark each)
- (B) Gregor Mendel
- (A) Alleles
- (B) Homozygous
- (B) Phenotype
- (B) All tall
- (B) 3:1
- (B) 1:2:1
- (A) Segregation
- (C) 9:3:3:1
- (C) Independent Assortment
- (B) Incomplete dominance
- (B) Co-dominance
- (B) XX
- (B) Father's sperm (X or Y)
- (A) 21
- (A) Pleiotropy
- (C) ZW
Section B — Challenge / Olympiad (2 marks each)
- (A) Tt (heterozygous)
- (A) Independent assortment of the two trait pairs
- (A) 1 red : 2 pink : 1 white
- (A) Carriers but not colour-blind
- (A) X or Y
- (A) Some resistance to malaria
- (A) Farther apart on the chromosome
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