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BIO 335- Extensions of Mendel Test- Questions with 100% Correct Answers
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BIO 335- Extensions of Mendel Test- Questions with 100% Correct Answers
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BIO 335- Extensions of Mendel Test-Questions with 100% Correct Answers
What is a wild-type allele & mutant allele? - Answer For any given gene, alleles in a
natural population could include the wild-type allele/s and mutant allele/s.
Wild-type Alleles - Answer The most prevalent version of a gene in wild populations
(i.e., the "normal" version of a gene).
Wild-type proteins are made in the proper amount & function normally.
• They promote the reproductive success of the organism in their native environment
Genetic polymorphism - Answer In large populations, there may be more than
one common allele that can be considered wild-type.
Mutant alleles - Answer A less common version of a gene, that are often defective
in their ability to express a functional protein.
Due to random mutations that occur in populations & alter preexisting alleles.
Recessive Mutant Alleles - Answer Most mutations are recessive and cause loss-
of-function.
Most random mutations produce alleles that are inherited in a recessive fashion.
• Recessive mutant alleles typically produce less functional protein.
- Either because the protein is defective.
- Or they produce lower levels of the functional protein.
,mutant allele/loss of function allele - Answer Allele that has been altered by mutation.
Rare in natural populations. allele defective in its ability to express a functional protein.
recessive mutant allele ex. - Answer For Mendel's seven characters in pea plants,
the recessive alleles are due to rare mutations.
■ Ex: flower color in Pea's - The gene encodes an enzyme (protein) that is needed
to convert a colorless molecule into a purple pigment.
o Homozygous Dominant (PP) - 100% functional protein - purple flower
o Heterozygous (Pp) - 50% functional protein - purple flower
o Homozygous Recessive (pp) - 0% functional protein - white flower
Why are many defective mutant alleles inherited recessively? - Answer Recall,
diploid organisms have two copies of each gene (except sex-linked)
• A mutant allele is called recessive if the heterozygote has a normal phenotype
• In other words, one wild-type copy is sufficient to provide full function... How?
Two possible explanations (related to quantitative protein function):
1. 50% of normal levels of protein are good enough.
2. The one wild-type copy is upregulated in expression due to gene regulation,
to produce adequate amount of functional protein.
Dominant mutant alleles - Answer Less common than recessive alleles, but they do
occur in natural populations.
How can a mutant allele be dominant over a wild-type allele? One of three mechanisms
explain most dominant alleles (Gain-of-function is also used as an umbrella term):
• Gain-of-function/hypermorph.
• Dominant-negative/antimorph.
• Haploinsufficiency/neomorph.
, Gain of function mutations - Answer The gene or the protein encoded by a gene gains
a new or abnormal function.
• For example, a mutant gene may be overexpressed, thereby producing too much
of the encoded protein.
Gain-of-function mutations- what is over-expression of a gene? - Answer Producing
too much of the encoded protein
mutant - Answer The term mutant refers to phenotype. - Usually connotes an abnormal or
unusual. - or even uncommon variant that is nevertheless normal - e.x. red hair.
Mutation vs. Polymorphism - Answer A mutation is change in a DNA sequence is rare
in a population and typically affects the phenotype.
■ A polymorphism simply means many forms. It is a change in a gene that is less
rare than a mutation and more prevalent in a population.
■ Because of the confusion between the terms mutation and polymorphism, the term
"gene variant" is being used for both terms.
"Mutant" alleles can vary to a great extent, and in some cases, can become the
wild type within the population.
Which of the following phenotype is NOT due to a wild-type allele. a. Yellow-
flowered elderflower orchid b. Red-flowered elderflower orchid c. A grey elephant d.
An albino (white) elephant. - Answer d
Molecular Mechanisms of Overdominance
At the molecular level, overdominance is due to two alleles that produce
slightly different proteins
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