Page 1 - 2-Lesson Notes-Accumulation of Variations, Inerited Traits

SAI International School
Subject- Biology
Chapter- Heredity And Evolution
Subtopic- Accumulation of variation during Reproduction,
Heredity- Inherited traits, Mendel’s work, Monohybrid cross
Module-23
Lesson notes

Accumulation of variation during Reproduction:
VARIATION- The difference in DNA sequences between individuals within a
population is called Variation. Variation occurs in germ cells i.e. sperm and egg, and
also in somatic (all other) cells.
Variations in Asexual Reproduction
• Variations are fewer.
• Occurs due to small inaccuracies in DNA copying. (Mutation)
Variations in Sexual Reproduction
• Variations are large.
• Occurs due to crossing over, separation of chromosomes or mutation.
Importance of Variation
• Depending on the nature of variation different individuals would have different
kinds of advantage. Example: Bacteria that can withstand heat will survive
better in a changing environment (if global temperature increases).
• Main advantage of variation to species is that it increases the chances of
survival in a changing environment.
Genetic variations
• The differences in the DNA sequences among every organism leading to the
diverse gene pool are called genetic variations.
• These differences lead to different/varied physical characters or biochemical
pathways.
• Inheritance from the previous generation provides both a common basic body
design, and subtle changes in it, for the next generation. Now think about
what would happen when this new generation, in its turn, reproduces.
• The second generation will have differences that they inherit from the first
generation, as well as newly created differences (see the figure given below).
• The figure would represent the situation if a single individual reproduces, as
happens in asexual reproduction.
• If one bacterium divides, and then the resultant two bacteria divide again, the
four individual bacteria generated would be very similar.
• There would be only very minor differences between them, generated due to
small inaccuracies in DNA copying. However, if sexual reproduction is
involved, even greater diversity will be generated.
• The differences in the DNA sequences among every organism leading to the
diverse gene pool are called genetic variations.
• These differences lead to different/varied physical characters or biochemical
pathways.

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