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Lecture 12

Biology 1001A Lecture 12.pdf

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Western University
Biology 1001A
Beth Mac Dougall- Shackleton

Biology 1001A | 2012 LECTURE NOTES Lecture 12 Inheritance in Populations –––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– - Which of the following is a true characteristic of dominant alleles? a. They are the most evolutionarily fit alleles. b. They are the most common alleles in a population c. They inhibit the expression of recessive alleles d. They determine the phenotype of heterozygotes - Answer: Only d - If you mated a pure-breeding black pig with a pure-breeding brown pig, what do you think the piglets will look like? - Answer: all black piglets - the allele for black colour must be dominant to the allele for brown colour - if two F1s were crossed, what would the resulting piglets look like? - Answer: Some would be black and some would be brown in Mendel’s 3:1 ratio Why is it dominant? - why is the black allele dominant over brown? - skin and hair pigments are created in specialized cells called melanocytes - two kinds of melanin can be made, one in each colour - to melanin is shipped in melanosomes to the skin cells, resulting in the pigmentation of the skin and hair - when MC1R is “on”, cyclic AMP (cAMP) levels in the cell are high and the melanocyte produces - The as both kinds of melanosomes - the black allele is insensitive to hormone control and cAMP is always high - when both of these alleles are together, - two alleles (black and brown) in the nucleus get transcribed, spliced, exported out of the nucleus, find ribosomes, taken t o the ER and those proteins get packaged into vesicles and put into the Golgi and get sent to the cell membrane for export - pig cell has both receptors functioning at the same time - it doesn’t matter what the brow allele is doing because the black allele keeps the black melanin level high at all times - the black allele never interferes with the brown allele in any way - this is one mechanism that will be dominant because it is always on, as opposed to the other allele which is only on for part of the time - dominance arises from expression of the allele, not competition between the two alleles - what will be the phenotype of B R heterozygotes? - Answer: brown piglets - the brown allele is recessive to black but is dominant to red Biology 1001A | 2012 - dominance and reces
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