BIO 2060 Exam 2 UPDATED ACTUAL
QUESTIONS And CORRECT Answers
simple mendelian inheritance - CORRECT ANSWERS Mendel's experiments assumed that traits =
affected by a single gene with 2 different alleles and that one allele = dominant to the other -->
inheritance patterns obey Mendel's laws
types of mendelian inheritance patterns involving single genes - CORRECT ANSWERS simple
mendelian, x-linked, incomplete penetrance, incomplete dominance
genetic polymorphism - CORRECT ANSWERS when more than one common allele = considered
wild-type in large populations
mutant alleles - CORRECT ANSWERS less common version of a gene - due to random mutations
that occur in DNA --> most random mutations produce alleles that = inherited in a recessive way (that
later cause a decrease in the expression/synthesis of a fully functional protein)
ex. PKU, albinism, tay-sachs diease, cystic fibrosis
why are most mutants recessive? - CORRECT ANSWERS diploid organisms have 2 copies of each
gene, one wild-type copy is enough to provide full function because 50% of normal levels of protein are
good enough or the one wild-type copy = upregulated in expression to produce an adequate amount of
functional protein
3 mechanisms enabling a mutant allele to be dominant - CORRECT ANSWERS gain-of-function
mutation: the gene gains a new or abnormal function (can be over-expressed, producing higher levels of
the protein)
dominant-negative mutations: the mutant protein acts to antagonize the normal protein
haploinsufficiency: the mutant is a loss-of-function allele, and one wild-type copy is not enough to
provide function (ex. polydactyly)
, penetrance - CORRECT ANSWERS the percentage of individuals having a particular genotype that
express the expected phenotype --> described at the population level & can be calculated
incomplete penetrance - CORRECT ANSWERS when the genotype does not always produce the
expected phenotype ex. polydactyly, a dominant disorder with cases where individuals have the allele and
have a normal number of fingers/toes (thus the gene = not fully penetrant), has variable expressivity
expressivity - CORRECT ANSWERS the degree to which a trait = expressed ex. polydactyly can
cause some to have extra functioning fingers/toes and others to just have a small flap of extra skin (low
expressivity = one extra toe, high = many extra toes/fingers)
both incomplete penetrance and variable expressivity are due to... - CORRECT ANSWERS the
environment or the effect of a modifier gene that affects the expression of the gene associated with
polydactyly and influences phenotype (can differ in different individuals)
norm of reaction - CORRECT ANSWERS the range of phenotypes seen due to environmental
effects --> to measure, start with a true-breeding strain of animals with the same genotype and subject
them to different environmental conditions (ex. eye facet number in drosophila is impacted by
temperature during development)
complete dominance - CORRECT ANSWERS when the heterozygote phenotype looks exactly like
one of the homozygotes (one of the alleles = completely dominant)
incomplete dominance - CORRECT ANSWERS the heterozygote phenotype is intermediate
between the phenotypes of the homozygotes (neither allele = completely dominant or recessive) ex.
flower color in four o'clock flowers (red, white, and pink flowers are produced - pink flowers are
hterozygotes)
overdominance - CORRECT ANSWERS aka heterozygote advantage --> when a heterozygote has
a greater reproductive success than either homozygote (ex. sickle-cell anemia --> heterozygotes HbAHbS
do not suffer from sickle cell anemia and are more resistant to malaria)
QUESTIONS And CORRECT Answers
simple mendelian inheritance - CORRECT ANSWERS Mendel's experiments assumed that traits =
affected by a single gene with 2 different alleles and that one allele = dominant to the other -->
inheritance patterns obey Mendel's laws
types of mendelian inheritance patterns involving single genes - CORRECT ANSWERS simple
mendelian, x-linked, incomplete penetrance, incomplete dominance
genetic polymorphism - CORRECT ANSWERS when more than one common allele = considered
wild-type in large populations
mutant alleles - CORRECT ANSWERS less common version of a gene - due to random mutations
that occur in DNA --> most random mutations produce alleles that = inherited in a recessive way (that
later cause a decrease in the expression/synthesis of a fully functional protein)
ex. PKU, albinism, tay-sachs diease, cystic fibrosis
why are most mutants recessive? - CORRECT ANSWERS diploid organisms have 2 copies of each
gene, one wild-type copy is enough to provide full function because 50% of normal levels of protein are
good enough or the one wild-type copy = upregulated in expression to produce an adequate amount of
functional protein
3 mechanisms enabling a mutant allele to be dominant - CORRECT ANSWERS gain-of-function
mutation: the gene gains a new or abnormal function (can be over-expressed, producing higher levels of
the protein)
dominant-negative mutations: the mutant protein acts to antagonize the normal protein
haploinsufficiency: the mutant is a loss-of-function allele, and one wild-type copy is not enough to
provide function (ex. polydactyly)
, penetrance - CORRECT ANSWERS the percentage of individuals having a particular genotype that
express the expected phenotype --> described at the population level & can be calculated
incomplete penetrance - CORRECT ANSWERS when the genotype does not always produce the
expected phenotype ex. polydactyly, a dominant disorder with cases where individuals have the allele and
have a normal number of fingers/toes (thus the gene = not fully penetrant), has variable expressivity
expressivity - CORRECT ANSWERS the degree to which a trait = expressed ex. polydactyly can
cause some to have extra functioning fingers/toes and others to just have a small flap of extra skin (low
expressivity = one extra toe, high = many extra toes/fingers)
both incomplete penetrance and variable expressivity are due to... - CORRECT ANSWERS the
environment or the effect of a modifier gene that affects the expression of the gene associated with
polydactyly and influences phenotype (can differ in different individuals)
norm of reaction - CORRECT ANSWERS the range of phenotypes seen due to environmental
effects --> to measure, start with a true-breeding strain of animals with the same genotype and subject
them to different environmental conditions (ex. eye facet number in drosophila is impacted by
temperature during development)
complete dominance - CORRECT ANSWERS when the heterozygote phenotype looks exactly like
one of the homozygotes (one of the alleles = completely dominant)
incomplete dominance - CORRECT ANSWERS the heterozygote phenotype is intermediate
between the phenotypes of the homozygotes (neither allele = completely dominant or recessive) ex.
flower color in four o'clock flowers (red, white, and pink flowers are produced - pink flowers are
hterozygotes)
overdominance - CORRECT ANSWERS aka heterozygote advantage --> when a heterozygote has
a greater reproductive success than either homozygote (ex. sickle-cell anemia --> heterozygotes HbAHbS
do not suffer from sickle cell anemia and are more resistant to malaria)
