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CBSE - X - Biology

i)Differentiate between homozygous and heterozygous organisms.
ii) Briefly explain the process of fossil formation.Explain its types also.
Please answer all these questions in this post....because tomorrow is my science' board paper.

Asked by vijayjethi17 21st March 2017, 5:58 PM
Answered by Expert


Hi Vijay,

(1) Differences between homozygous and heterozygous individuals:

Homozygous individual

Heterozygous individual

  • Pure for a trait and breeds true.
  • Seldom pure and produce offspring with different genotypes on selfing.
  • Both the alleles for a character are similar.
  • Carries dissimilar alleles.
  • Can carry either dominant or recessive alleles but not both.
  • Has both dominant and recessive alleles.
  • Produces one type of gametes.
  • Produces two types of gametes.
  • Does not exhibit extra vigour
  • Can exhibit extra vigour called hybrid vigour or heterosis.

(2) Process of fossil formation:

  • Some of the invertebrates on the sea-bed died and got buried in the sand.
  • More and more sand got accumulated and formed sandstone under pressure.
  • After millions of years, dinosaurs living in the area died and their bodies were buried in the mud.
  • The mud got compressed into the rock, just above the rock containing earlier invertebrate fossils.
  • Again millions of years later, the bodies of horse-like creatures dying in the area were fossilized in the rocks above the earlier rocks.
  • Much later, due to erosion and water flow some of the rocks wore out and exposed the horse-like fossils.

(3) Types of fossils:

  • Trace fossils
  • Casts
  • Molds
  • Petrified fossils
  • Frozen fossils
Answered by Expert 21st March 2017, 6:14 PM

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