BIO 110 EXAM 3 QUESTIONS AND ANSWERS | COMPLETE BIOLOGY EXAM 3
STUDY GUIDE 2026/2027
carrier - ANS ✔✔person (or other organism) who is heterozygous for a recessive trait and does not
display the trait or show symptoms of the condition
codominance - ANS ✔✔a relationship between the alleles of a gene wherein the alleles in a
heterozygote are both fully expressed. This results in offspring with a phenotype that is neither
dominant nor recessive and is a unique phenotype
complete dominance - ANS ✔✔a relationship between alleles of a gene wherein the allele that is
dominant completely masks the effect of the allele that is recessive in the heterozygote
epistasis - ANS ✔✔the phenomenon where the effect of one gene is dependent on the presence of one
or more other genes. In other words, one gene influences the expression of another gene.
heterozygote advantage - ANS ✔✔a phenomenon wherein the heterozygous genotype has a higher
relative fitness than either the homozygous dominant or homozygous recessive genotype.
incomplete dominance - ANS ✔✔relationship between alleles in which one allele for a specific trait is
not completely expressed over its paired allele. This results in a third phenotype in which the expressed
physical trait is a combination of the phenotypes of both alleles.
multiple alleles - ANS ✔✔the condition wherein a gene has three or more possible alleles
pedigree - ANS ✔✔a diagram that shows the occurrence of phenotypes of a particular gene from one
generation to the next
pleiotropy - ANS ✔✔a phenomenon where one gene influences two or more seemingly unrelated
phenotypic traits
polygenic inheritance - ANS ✔✔occurs when one characteristic is controlled by two or more genes
quantitative character - ANS ✔✔a phenotype that depends on the combined actions of many genes and
the environment
autosome - ANS ✔✔a non-sex chromosome
barr body - ANS ✔✔the inactive X chromosome typically in a female somatic cell. Barr bodies occur in
any mammalian cell in which there are 2 or more X chromosomes
hemizygous - ANS ✔✔the condition of having only a single copy of a gene or chromosome instead of the
typical two copies. Males are hemizygous for genes on the X and Y chromosome
mutant phenotype - ANS ✔✔a phenotype that is less common in a population than the wild-type
phenotype. For example, in fruit flies white eyes are a mutant phenotype
, sex-linked genes - ANS ✔✔genes that are carried on either sex chromosome
SRY gene - ANS ✔✔the gene that is responsible for the initiation of male sex determination in humans.
The SRY gene codes for a transcription factor that turns on other genes related to male development
wild-type phenotype - ANS ✔✔the most common phenotype for a character in a population. for
example, in fruit flies red eyes are the wild-type phenotype
XIST gene - ANS ✔✔the gene on the X chromosome of mammals that results on the formation of a Barr
body. The XIST gene inactivates the X chromosome
complete linkage - ANS ✔✔the situation in which two genes are so close together that alleles of these
genes are not separated by crossing over
genetic map - ANS ✔✔a map that shows the location of genes on a chromosome
genetic recombination - ANS ✔✔the production of gametes and offspring with combinations of alleles
that differ from those found in either parent
linkage map - ANS ✔✔a chromosome map that shows the position of genes relative to each other in
terms of recombination frequency, rather than a specific physical distance along each chromosome
linked genes - ANS ✔✔genes that are closer than 50 map units apart on a chromosome
map unit - ANS ✔✔a unit for measuring genetic linkage. defined as the distance between genes for
which the expected cross-over frequency is 1%
recombinant chromosome - ANS ✔✔chromosomes that results from a cross-over event
recombination frequency - ANS ✔✔the frequency of crossing-over between two locations on a
chromosome
antiparallel - ANS ✔✔two polymers (such as DNA) are antiparallel if they run parallel to each other but
with opposite alignments
DNA polymerase - ANS ✔✔an enzyme that synthesize DNA molecules from deoxyribonucleotides, the
building blocks of DNA. DNA polymerase adds nucleotides to the 3' end of a newly synthesized strand of
DNA.
excision repair - ANS ✔✔a DNA repair mechanism that removes damaged DNA bases that could result in
mutation
Helicase - ANS ✔✔an enzyme involved in DNA replication that separates double-stranded DNA into
single strands, thus allowing each strand to be copied
STUDY GUIDE 2026/2027
carrier - ANS ✔✔person (or other organism) who is heterozygous for a recessive trait and does not
display the trait or show symptoms of the condition
codominance - ANS ✔✔a relationship between the alleles of a gene wherein the alleles in a
heterozygote are both fully expressed. This results in offspring with a phenotype that is neither
dominant nor recessive and is a unique phenotype
complete dominance - ANS ✔✔a relationship between alleles of a gene wherein the allele that is
dominant completely masks the effect of the allele that is recessive in the heterozygote
epistasis - ANS ✔✔the phenomenon where the effect of one gene is dependent on the presence of one
or more other genes. In other words, one gene influences the expression of another gene.
heterozygote advantage - ANS ✔✔a phenomenon wherein the heterozygous genotype has a higher
relative fitness than either the homozygous dominant or homozygous recessive genotype.
incomplete dominance - ANS ✔✔relationship between alleles in which one allele for a specific trait is
not completely expressed over its paired allele. This results in a third phenotype in which the expressed
physical trait is a combination of the phenotypes of both alleles.
multiple alleles - ANS ✔✔the condition wherein a gene has three or more possible alleles
pedigree - ANS ✔✔a diagram that shows the occurrence of phenotypes of a particular gene from one
generation to the next
pleiotropy - ANS ✔✔a phenomenon where one gene influences two or more seemingly unrelated
phenotypic traits
polygenic inheritance - ANS ✔✔occurs when one characteristic is controlled by two or more genes
quantitative character - ANS ✔✔a phenotype that depends on the combined actions of many genes and
the environment
autosome - ANS ✔✔a non-sex chromosome
barr body - ANS ✔✔the inactive X chromosome typically in a female somatic cell. Barr bodies occur in
any mammalian cell in which there are 2 or more X chromosomes
hemizygous - ANS ✔✔the condition of having only a single copy of a gene or chromosome instead of the
typical two copies. Males are hemizygous for genes on the X and Y chromosome
mutant phenotype - ANS ✔✔a phenotype that is less common in a population than the wild-type
phenotype. For example, in fruit flies white eyes are a mutant phenotype
, sex-linked genes - ANS ✔✔genes that are carried on either sex chromosome
SRY gene - ANS ✔✔the gene that is responsible for the initiation of male sex determination in humans.
The SRY gene codes for a transcription factor that turns on other genes related to male development
wild-type phenotype - ANS ✔✔the most common phenotype for a character in a population. for
example, in fruit flies red eyes are the wild-type phenotype
XIST gene - ANS ✔✔the gene on the X chromosome of mammals that results on the formation of a Barr
body. The XIST gene inactivates the X chromosome
complete linkage - ANS ✔✔the situation in which two genes are so close together that alleles of these
genes are not separated by crossing over
genetic map - ANS ✔✔a map that shows the location of genes on a chromosome
genetic recombination - ANS ✔✔the production of gametes and offspring with combinations of alleles
that differ from those found in either parent
linkage map - ANS ✔✔a chromosome map that shows the position of genes relative to each other in
terms of recombination frequency, rather than a specific physical distance along each chromosome
linked genes - ANS ✔✔genes that are closer than 50 map units apart on a chromosome
map unit - ANS ✔✔a unit for measuring genetic linkage. defined as the distance between genes for
which the expected cross-over frequency is 1%
recombinant chromosome - ANS ✔✔chromosomes that results from a cross-over event
recombination frequency - ANS ✔✔the frequency of crossing-over between two locations on a
chromosome
antiparallel - ANS ✔✔two polymers (such as DNA) are antiparallel if they run parallel to each other but
with opposite alignments
DNA polymerase - ANS ✔✔an enzyme that synthesize DNA molecules from deoxyribonucleotides, the
building blocks of DNA. DNA polymerase adds nucleotides to the 3' end of a newly synthesized strand of
DNA.
excision repair - ANS ✔✔a DNA repair mechanism that removes damaged DNA bases that could result in
mutation
Helicase - ANS ✔✔an enzyme involved in DNA replication that separates double-stranded DNA into
single strands, thus allowing each strand to be copied
