IBDP Biology Chapter 10 Notes

genetics and evolution


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In this chapter, we understand chromosomal behaviour, gene pools and speciation. We start the discussion with meiosis wherein we discuss crossing over and Law of independent assortment, i.e. how the separation of one pair of alleles is independent of another pair. Then we talk about the Law of Segregation, i.e. that during gametogenesis the pair of alleles separate in such a manner that offspring receives one allele from each parent. In his experiments, Mendel used pea plant. Linked genes, i.e. genes found on the same chromosome and usually pass onto the next generation together, are an exception to the law of segregation.

Variations are of two types: continuous (polygenic inheritance of skin colour) and discontinuous/discrete (ABO blood grouping). Chi-square tests are done to check the accuracy of possible ratios that are obtained by crossing by finding whether the difference between the observed and expected is quite significant or not. Gene pool can be defined as all the genetic information present in reproducing members of a population at a given time.

Hardy Weinberg equation p + q = 1 is used to calculate the alleles frequency. Variation in allelic frequency by natural factors leads to selection either directional or stabilising, or disruptive). Then we discuss Reproductive isolation caused by geographical, temporal or behavioural causes. The rate of speciation can be judged by gradualism or punctuated equilibrium (sudden).