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2023 Form Four Biology Notes (New Syllabus)

Institution: Secondary

Course: Biology

Posted By: 35824167

Document Type: DOCX

Number of Pages: 54

Price: KES 130
  
    

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Summary

download form four Biology notes updated. it covers in details the examinable areas by the knec.
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.
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.


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