Lect4 - Lecture 4 1 Lethal allelesMost of the mutations...

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1 Lecture 4
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2 Lethal alleles- Most of the mutations that we have discussed do not affect the viability of the individual. For example the mutations that produce white eyes in Drosophila or wrinkled yellow cotyledons in the plant do not disrupt viability. This means that the mutated gene is specifically involved in determining eye color and is not involved in processes central to viability of the fly. What would be the genetic consequences if we isolated a mutation that disrupted an enzyme that was critical for the viability of the fly? For example in Drosophila, Cy is a dominant mutation that produces Cy wings in the heterozygous condition but also behaves as a recessive lethal.
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3 Curly When a heterozygous Cy male is crossed to a heterozygous Cy female, Cy to non-Cy  progeny are produced in a 2:1___ rather than the  Mendelian 3:1___ ratio + = normal or wild type gene cy= dominant Cy mutation One explanation for the ___ rather than the expected ___ ratio is that Cy behaves as a recessive lethal mutation and cy/cy individuals die prior to reaching adulthood
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4 How would you test this hypothesis? Take the progeny and perform a test cross with the homozygous recessive parent (+/+ wild- type fly)
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5 Unlike cy, most recessive lethal alleles do not have an additional dominant visible phenotype. For example let say a gene codes for an essential enzyme. GeneA (normal enzyme) Genea (mutant enzyme) The expected genotypes and phenotypes are as follows: genotype: A/A A/a a/A a/a phenotype: alive alive alive die Phenotype of survival is 3:1 Lethal mutations arise in many different genes. These mutations remain “silent” except in rare cases of
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Lect4 - Lecture 4 1 Lethal allelesMost of the mutations...

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