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BIO 325 September 13th Lecture Notes

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BIO 325
Sanghamitra Mohanty

9/13 Lecture Wednesday, September 11, 2013 2:30 PM The characteristics of traits are carried by genes, and they exist in pairs --- in heterozygous gene pairs, one would be dominant over the other --- split independently in cell division, and independently assort One gene can have more than 2 alleles in a population ---- the characteristics are carried by a pair of alleles or one gene ---- one gene can influence multiple phenotypes, or one phenotype can be represented by multiple genes Modes of inheritance  Types of alleles  Loss-of and gain-of-function mutation  Incomplete/partial dominance  Codominance  Gene interaction  Pleiotropy  Sex-limited and sex-influenced inheritance  Conditional inheritance Alleles - alternative forms of a gene  2 types o Wild-type - most frequently observed in nature; mostly dominant in nature o Mutant type - modified genetic information Mutation - genetic information is modified  Often produces altered gene product  New phenotypes result from changes in functional activity of gene product o Eliminating enzyme function  Enzyme constitutes the major parts of proteins o Changing relative enzyme efficiency  May reduce or increase the enzyme functionality o Changing overall enzyme function  Changing the function to a completely different one Loss of function mutation - mutation causes the reduction or loss of the specific wild-type function  If loss is complete, the mutation has resulted in a null allele Gain-of-function - mutation enhances the function of the wild-type product  Example: cancer cells o Proto oncogenes  Growth factors are giving growth signals to continue the cell cycle  Can be suppressed, but cancer cells have a gain of function mutation which continues the divisions ---> oncogenes  Attract all the blood supply to the oncogenes, and making all kinds of complications  Seen in tumor cells  Mostly seen in bacteria How to write the alleles? Dominant - use uppercase letter Recessive - use lowercase letter Incomplete dominance - neither trait is dominant; offspring between parents with contrasting traits may have an intermediate phenotype  Seen in monohybrid cross o Example: flower colors --- red x white = pink  INTERMEDIATE phenotype is seen in the F1 generation o 50% of enzyme controlled of red + 50% of enzyme controlled of white  F2 generation ratio is 1:2:1 o Example: red --- pink --- whitE  Explained in a quantitative way In humans, Tay-Sachs disease --- homozygous recessive alleles  Fatal lipid-storage disorder, when hexosaminidase activity is absent  Heterozygotes appear normal, but 50% of the enzyme activity is enough to maintain a normal life o HAPLOSUFFICIENT [threshold effect] Codominance - when joint or equal
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