EXAM 2 STUDY GUIDE WITH
TESTED SOLUTIONS
◉ Codominance. Answer: Heterozygous phenotype results from the
expression of both alleles.
-ABO gene encodes a cell surface protein (Ia allele produces A
antigen, Ib allele produces B antigen, and i or Io allele does not
produce antigens
-alleles Ia and Ib are codominant and both are completely dominant
to i
◉ Epistasis. Answer: Phenomenon where one gene affects the
expression of a second gene
-example: Bombay phenotype, the H gene is epistatic to the I gene. H
protein places a molecule at the cell surface to which the A or B
antigens are attached. hh genotype=no H protein. Without H protein
the A or B antigens can not be attached to the surface of the red
blood cell. All hh genotypes have the phenotype of type O, although
the ABO blood group can be anything (A, B, AB, or O)
◉ Pleiotropy. Answer: phenomenon where one gene controls several
functions or has more than one effect
,◉ Penetrance. Answer: all-or-none expression of a single gene
(either they have it or they dont)
-genotype is incompletely penetrant if some individuals do not
express the phenotype
◉ Expressivity. Answer: severity or extent
-phenotype is variably expressive if symptoms vary in intensity
among different people (example: Huntington's Disease)
◉ Genetic heterogeneity. Answer: different genes can produce
identical phenotypes
-hearing loss=132 autosomal recessive forms
-osteogenesis imperfecta=at least two different genes involved
-Alzheimer disease=at least four different genes involved
◉ Phenocopy. Answer: trait that appears inherited but is caused by
the environment. May have symptoms that resemble an inherited
trait or occur within families
-example: exposure to teratogens, thalidomide causes limb defects
similar to inherited phocomelia
◉ Mitochondrion. Answer: organelle providing cellular energy.
Contains small circular DNA called mtDNA (37 genes without
noncoding sequences). No crossing over and little DNA repair,
, mutations in mitochondrial DNA are identified as diseases-
inheritance maternal (mitochondrial genes/diseases are transmitted
from mother to all of her offspring)
-examples of diseases from mutations in mtDNA: mitochondrial
myopathies (weak and flaccid muscles) and Leber optical atrophy
(impaired vision)
-ooplasmic transfer technique can enable woman to avoid
transmitting a mitochondrial disorder
◉ Mutation rate in mitochondrion is greater than nuclear DNA-less
DNA repair? High exposure to free radicals-why?. Answer: Mode of
inheritance is from mother. Mutation rate: mtDNA does not have
precise and refine enzymes like the nuclear DNA has (polymerase,
proof-reading). Lots of molecules that can damage DNA in
mitochondria. There aren't radicals or free species floating around in
nucleus, where there is in mitochondria.
◉ Heteroplasmy. Answer: condition where the mtDNA sequence is
not the same in all copies of the genome (mitochondrion will have
different alleles for the same gene).
-random assortment during cytokinesis
-if an oocyte is heteroplasmic, differing number of copies of a mutant
mtDNA may be transmitted (phenotype reflects the proportion of
mitochondria bearing the mutation)
TESTED SOLUTIONS
◉ Codominance. Answer: Heterozygous phenotype results from the
expression of both alleles.
-ABO gene encodes a cell surface protein (Ia allele produces A
antigen, Ib allele produces B antigen, and i or Io allele does not
produce antigens
-alleles Ia and Ib are codominant and both are completely dominant
to i
◉ Epistasis. Answer: Phenomenon where one gene affects the
expression of a second gene
-example: Bombay phenotype, the H gene is epistatic to the I gene. H
protein places a molecule at the cell surface to which the A or B
antigens are attached. hh genotype=no H protein. Without H protein
the A or B antigens can not be attached to the surface of the red
blood cell. All hh genotypes have the phenotype of type O, although
the ABO blood group can be anything (A, B, AB, or O)
◉ Pleiotropy. Answer: phenomenon where one gene controls several
functions or has more than one effect
,◉ Penetrance. Answer: all-or-none expression of a single gene
(either they have it or they dont)
-genotype is incompletely penetrant if some individuals do not
express the phenotype
◉ Expressivity. Answer: severity or extent
-phenotype is variably expressive if symptoms vary in intensity
among different people (example: Huntington's Disease)
◉ Genetic heterogeneity. Answer: different genes can produce
identical phenotypes
-hearing loss=132 autosomal recessive forms
-osteogenesis imperfecta=at least two different genes involved
-Alzheimer disease=at least four different genes involved
◉ Phenocopy. Answer: trait that appears inherited but is caused by
the environment. May have symptoms that resemble an inherited
trait or occur within families
-example: exposure to teratogens, thalidomide causes limb defects
similar to inherited phocomelia
◉ Mitochondrion. Answer: organelle providing cellular energy.
Contains small circular DNA called mtDNA (37 genes without
noncoding sequences). No crossing over and little DNA repair,
, mutations in mitochondrial DNA are identified as diseases-
inheritance maternal (mitochondrial genes/diseases are transmitted
from mother to all of her offspring)
-examples of diseases from mutations in mtDNA: mitochondrial
myopathies (weak and flaccid muscles) and Leber optical atrophy
(impaired vision)
-ooplasmic transfer technique can enable woman to avoid
transmitting a mitochondrial disorder
◉ Mutation rate in mitochondrion is greater than nuclear DNA-less
DNA repair? High exposure to free radicals-why?. Answer: Mode of
inheritance is from mother. Mutation rate: mtDNA does not have
precise and refine enzymes like the nuclear DNA has (polymerase,
proof-reading). Lots of molecules that can damage DNA in
mitochondria. There aren't radicals or free species floating around in
nucleus, where there is in mitochondria.
◉ Heteroplasmy. Answer: condition where the mtDNA sequence is
not the same in all copies of the genome (mitochondrion will have
different alleles for the same gene).
-random assortment during cytokinesis
-if an oocyte is heteroplasmic, differing number of copies of a mutant
mtDNA may be transmitted (phenotype reflects the proportion of
mitochondria bearing the mutation)
