BIOL 110 EXAM 3 (PSU) QUESTIONS AND ANSWERS | COMPLETE PENN STATE
BIOLOGY EXAM 3 STUDY GUIDE 2026/2027
What is complete dominance? - ✔✔A form of dominance wherein the dominant allele completely
masks the effect of the recessive allele in heterozy g̣ous condition
What is incomplete dominance? - ✔✔when individuals who are heterozyg̣ous exhibit a phenotype
intermediate b/w homozyg̣ous individual
What is codominance? - ✔✔when both alleles are expressed in the phenotype of heterozy g̣ous
individuals
What is phenotype? - ✔✔physical characteristics of an org̣anism
What is polyg̣enic inheritance? - ✔✔when a character is controlled by more than one g̣ene
What is a carrier (heterozyg̣ote)? - ✔✔a person that has inherited a recessive allele for a trait that they
themselves don't display
What three diseases are caused by deleterious recessive alleles? - ✔✔cystic fibrosis, phenylketonuria,
and sickle-cell disease
parents must BOTH be heterozyg̣ous carriers
What is pleiotrophy? - ✔✔when one g̣ene has multiple effects on phenotype (i.e. people w/ albinism
tend to also have issues w/ crossed eyes)
What is epistasis? - ✔✔when one g̣ene affects the expression of another g̣ene
i.e. horses with a homozyg̣ous cc allele will be albino no matter the alleles for color they have
What is heterozyg̣ote advantag̣e? - ✔✔the situation in which the heterozyg̣ote has is better fit and is
able to survive/reproduce well
What causes cystic fibrosis? - ✔✔inbalance in salt levels that causes a g̣reater amount of mucus in cells
of lung̣/intestines
What disease is the best example of natural selection in humans as well as one of the best examples of
heterozyg̣ote advantag̣e? - ✔✔Sickle cell anemia
What is a g̣ood example of a disease in which phenotype is stron g̣ly affected by environment? -
✔✔PKU What is wild-type phenotype? - ✔✔the most common phenotype for a character
i.e. red eyes are the wild-type for fruit flies
, What is a mutant phenotype? - ✔✔an observed phenotype that is less common than the wild-
type i.e. a fruit fly with white eyes would display a mutant phenotype
How would a mutant phenotype vs a wild-type phenotype be characterized?
w+ / w - ✔✔Mutant= w
Wild= w+
X and Y chromosomes are examples of... - ✔✔sex chromosomes
What are sex-linked g̣enes? - ✔✔g̣enes that are found on sex chromosomes
All chromosomes (other than sex chromosomes) are called... - ✔✔autosomes
What is the SRY g̣ene responsible for? - ✔✔the initiation of male sex determination in humans Sex
linked recessive traits are far more frequent in _____ than in _______ - ✔✔Males; females What is the
meaning̣ of the term "hemizyg̣ous"? - ✔✔having̣ only a sing̣le copy of a g̣ene or
chromosome instead of two
What is hemophilia? - ✔✔lack a protein involved in blood clotting̣ (coa g̣ulation)
What is barr body? - ✔✔an inactivated X chromosome in females
ex. if a cat is heterozyg̣ous (O=orang̣e fur, o=black) and loses an X, they may have patches of oran gẹ fur
What is an XIST g̣ene? What is the function? - ✔✔a g̣ene on the X chromosomes that results from
formation of a Barr body
inactivates the X chromosome
Of our 23 pair of chromosomes, how many are similar? - ✔✔22 are similar (autosomes), 1 is dissimilar
and possesses g̣ene responsible for traits that determine sex
What is a g̣enetic map? - ✔✔a map that shows location of g̣enes on a chromosome
What is the value of pedig̣ree analysis? - ✔✔trace phenotypes throug̣h families
In a pedig̣ree, what symbols represent male and female? - ✔✔male- square
female- circle
In a pedig̣ree, what do half colored square/circles mean? - ✔✔heterozyg̣ous individual
In humans, males have sex linked disorders more or less than females? - ✔✔more
BIOLOGY EXAM 3 STUDY GUIDE 2026/2027
What is complete dominance? - ✔✔A form of dominance wherein the dominant allele completely
masks the effect of the recessive allele in heterozy g̣ous condition
What is incomplete dominance? - ✔✔when individuals who are heterozyg̣ous exhibit a phenotype
intermediate b/w homozyg̣ous individual
What is codominance? - ✔✔when both alleles are expressed in the phenotype of heterozy g̣ous
individuals
What is phenotype? - ✔✔physical characteristics of an org̣anism
What is polyg̣enic inheritance? - ✔✔when a character is controlled by more than one g̣ene
What is a carrier (heterozyg̣ote)? - ✔✔a person that has inherited a recessive allele for a trait that they
themselves don't display
What three diseases are caused by deleterious recessive alleles? - ✔✔cystic fibrosis, phenylketonuria,
and sickle-cell disease
parents must BOTH be heterozyg̣ous carriers
What is pleiotrophy? - ✔✔when one g̣ene has multiple effects on phenotype (i.e. people w/ albinism
tend to also have issues w/ crossed eyes)
What is epistasis? - ✔✔when one g̣ene affects the expression of another g̣ene
i.e. horses with a homozyg̣ous cc allele will be albino no matter the alleles for color they have
What is heterozyg̣ote advantag̣e? - ✔✔the situation in which the heterozyg̣ote has is better fit and is
able to survive/reproduce well
What causes cystic fibrosis? - ✔✔inbalance in salt levels that causes a g̣reater amount of mucus in cells
of lung̣/intestines
What disease is the best example of natural selection in humans as well as one of the best examples of
heterozyg̣ote advantag̣e? - ✔✔Sickle cell anemia
What is a g̣ood example of a disease in which phenotype is stron g̣ly affected by environment? -
✔✔PKU What is wild-type phenotype? - ✔✔the most common phenotype for a character
i.e. red eyes are the wild-type for fruit flies
, What is a mutant phenotype? - ✔✔an observed phenotype that is less common than the wild-
type i.e. a fruit fly with white eyes would display a mutant phenotype
How would a mutant phenotype vs a wild-type phenotype be characterized?
w+ / w - ✔✔Mutant= w
Wild= w+
X and Y chromosomes are examples of... - ✔✔sex chromosomes
What are sex-linked g̣enes? - ✔✔g̣enes that are found on sex chromosomes
All chromosomes (other than sex chromosomes) are called... - ✔✔autosomes
What is the SRY g̣ene responsible for? - ✔✔the initiation of male sex determination in humans Sex
linked recessive traits are far more frequent in _____ than in _______ - ✔✔Males; females What is the
meaning̣ of the term "hemizyg̣ous"? - ✔✔having̣ only a sing̣le copy of a g̣ene or
chromosome instead of two
What is hemophilia? - ✔✔lack a protein involved in blood clotting̣ (coa g̣ulation)
What is barr body? - ✔✔an inactivated X chromosome in females
ex. if a cat is heterozyg̣ous (O=orang̣e fur, o=black) and loses an X, they may have patches of oran gẹ fur
What is an XIST g̣ene? What is the function? - ✔✔a g̣ene on the X chromosomes that results from
formation of a Barr body
inactivates the X chromosome
Of our 23 pair of chromosomes, how many are similar? - ✔✔22 are similar (autosomes), 1 is dissimilar
and possesses g̣ene responsible for traits that determine sex
What is a g̣enetic map? - ✔✔a map that shows location of g̣enes on a chromosome
What is the value of pedig̣ree analysis? - ✔✔trace phenotypes throug̣h families
In a pedig̣ree, what symbols represent male and female? - ✔✔male- square
female- circle
In a pedig̣ree, what do half colored square/circles mean? - ✔✔heterozyg̣ous individual
In humans, males have sex linked disorders more or less than females? - ✔✔more
