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Lecture 11

Biology 1001A Lecture 11.pdf

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Western University
Biology 1001A
Beth Mac Dougall- Shackleton

Biology 1001A | 2012 LECTURE NOTES Lecture 11 Inheritance of Variation –––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– - genes for making parts specific to one sex do not have to be located on a sex chromosome Mendel: Think Like a Scientist in 1850’s - people used to believe that inheritance was a blending process - it was thought that the traits expressed by offspring would be an intermediate of the two parents - Mendel changed the way that people think about inheritance - ex: a blue parent and red parent would have a purple child, WRONG - the problem was that two medium height people could have a child taller than either of them, hence the blending hypothesis was clearly wrong - polygenic traits shown continuous variation in a population - dominant alleles make your skin darker, recessive alleles make your skin lighter - “mayonnaise” people have no dominant allele, whereas “coal” people have 6 dominant alleles - “cinnamon” people can have either “mayonnaise” or “coal” children - the cinnamon people are not a blend, they are a combination of alleles - when you cross intermediates together, you can get the extremes back for polygenic traits (controlled by many genes); this good evidence for the particulate nature of inheritance - Mendel thought like a scientist and used quantitative results - statistics had not been invented, therefore Mendel’s quantitative approach was revolutionary - led to Mendel’s explanatory model - variation in traits due to different alleles - alleles segregate randomly into gametes - Mendel’s first law: alleles are thrown randomly into gametes - organism inherit two alleles for each trait - with no knowledge of how reproduction worked, he hypothesized that there were two alleles for each trait expressed in an individual - appearance of heterozygotes is determined by the dominant allele - the allele that determines the phenotype of a heterozygote is the dominant allele - dominant alleles are expressed when present - gametes come from meiosis ▯ - the probability of these results is given by the product rule - pea plan
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