Class 10 Genetics: Basic Concepts Mock Test (ICSE)

Topics in Genetics: Basic Concepts

• Mendel's laws
• Monohybrid and dihybrid crosses
• Genotype, phenotype, dominant and recessive
• Sex determination in humans
• Sex-linked inheritance: haemophilia and colour blindness

Genetics: Basic Concepts practice questions with answers

1. Q1Multiple choice·1 mark
   Haemophilia in humans is an example of:

   1. (a)Y-linked inheritance
   2. (b)X-linked recessive inheritance
   3. (c)Autosomal dominant inheritance
   4. (d)Autosomal recessive inheritance
   Show answer and step marks

   1. Correct option: (b) X-linked recessive inheritance+1

   Answer: (b)
2. Q2Multiple choice·1 mark
   The human sex chromosomes responsible for determining a male child are:

   1. (a)YY
   2. (b)XO
   3. (c)XX
   4. (d)XY
   Show answer and step marks

   1. Correct option: (d) XY+1

   Answer: (d)
3. Q3Multiple choice·1 mark
   Mendel's Law of Segregation states that:

   1. (a)The recessive character is always expressed in the F2 generation
   2. (b)Dominant genes mask recessive genes completely in all generations
   3. (c)Genes on different chromosomes are inherited independently
   4. (d)Alleles separate during gamete formation so that each gamete carries only one allele for each gene
   Show answer and step marks

   1. Correct option: (d) Alleles separate during gamete formation so that each gamete carries only one allele for each gene+1

   Answer: (d)
4. Q4Multiple choice·1 mark
   An organism possessing two identical alleles for a particular gene pair is termed:

   1. (a)Hemizygous
   2. (b)Hybrid
   3. (c)Homozygous
   4. (d)Heterozygous
   Show answer and step marks

   1. Correct option: (c) Homozygous+1

   Answer: (c)
5. Q5Long answer·4 marks
   (a) Define genotype and phenotype. Give one suitable example for each using the height of pea plants. [2] (b) Differentiate between a dominant allele and a recessive allele. [2]
   Show answer and step marks

   1. Genotype definition: the genetic make-up of an organism, i.e. the alleles it carries for a trait.+0.5
   2. Genotype example for pea height: $TT$, $Tt$ or $tt$.+0.5
   3. Phenotype definition: the observable expression of a trait, produced by the genotype.+0.5
   4. Phenotype example for pea height: tall or dwarf.+0.5
   5. Dominant allele definition and property: An allele that expresses its phenotypic trait even when present in a heterozygous condition (e.g., $T$).+1
   6. Recessive allele definition and property: An allele whose expression is masked in the presence of a dominant allele and only expresses itself in the homozygous condition (e.g., $t$).+1

   Answer: (a) Genotype: the genetic make-up (alleles) of an organism, e.g. $TT$, $Tt$ or $tt$; phenotype: the observable expression of a trait, e.g. tall or dwarf. (b) A dominant allele (e.g. $T$) expresses itself even in the heterozygous condition, while a recessive allele (e.g. $t$) is masked by the dominant one and expresses itself only when homozygous ($tt$).

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