Biology

GENETICS

Introduction

  • Genetics is the study of inheritance.
  • The fact that the offspring of any species resemble the parents indicates that the characters in the parents are passed on to the offspring.
  • Factors that determine characters (genes) are passed on from parent to offspring through gametes or sex cells.
  • In fertilization the nucleus of the male gamete fuses with the nucleus of the female gamete.
  • The offspring show the characteristics of both the male and the female.
  • Genetics is the study of how this heritable material operates in individuals and their offspring.

Variations within Plant and Animal Species

Variation

  • The term variation means to differ from a standard.
  • Genetics also deals with the study of differences between organisms belonging to one species.
  • Organisms belonging to higher taxonomic groups e.g. phyla or classes are clearly different.
  • Although organisms belonging to the same species are similar, they show a number of differences or variations such that no two organisms are exactly the same in every respect.
  • Even identical twins, though similar in many aspects, are seen to differ if they grow in different environments.
  • Their differences are as a result of the environment which modifies the expression of their genetic make-up or genotype.
  • The two causes of variations are the genes and the environment.
  • Genes determine the character while the environment modifies the expression of that character.
See also  RECEPTION, RESPONSES AND CO┬ČORDINATION IN ANIMALS

Continuous and Discontinuous Variation

Continuous Variations

  • The differences between the individual are not clear-cut.
  • There are intermediates or gradations between any two extremes.
  • Continuous variations are due to action of many genes e.g. skin complexion in humans.
  • In continuous variation, the environment has a modifying effect in that it may enhance or suppress the expressions of the genes.
  • Continuous variation can be represented in form of a histogram.
  • Example of continuous variation in humans is weight, height and skin complexion.
  • Linear measurements:
  • In humans, height shows gradation from tall, to tallest.
  • So does the length of mature leaves of a plant.
  • In most cases, continuous variation is as a result of the environment.
See also  PRACTICAL APPLICATIONS OF GENETICS

Discontinuous Variations

  • These are distinct and clear cut differences within a species.

Examples include:

  • Ability to roll the tongue.
  • An individual can either roll the tongue or not.
  • Ability to taste phenylthiourea (PTC); some individuals can taste this chemical others cannot.
  • Blood groups – and individual has one of the four blood groups A, B AB or O.
  • There are no intermediates.
  • Albinism – one is either an albino or not.
  • Discontinuous variations are determined by the action of a single gene present in an individual.
See also  ADAPTATION FOR SURVIVAL

See also

Growth and Development in Animals

ROLE OF GROWTH & HORMONES IN PLANTS

PRIMARY AND SECONDARY GROWTH

TYPES OF GERMINATION

CONDITIONS NECESSARY FOR GERMINATION

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