MMSC 491 EXAM 2 VERIFIED STUDY GUIDE
Genotype - Answers - combination of alleles that a patient possesses
Homozygous - Answers - somatic cells, if both alleles are the same at an individual
locus
Heterozygous - Answers - somatic cells, if alleles are different even by a single
nucleotide at the same locus
Hemizygous - Answers - applies to gametes. Men have two types of sex chromosomes
(XY) so most DNA sequences on X do not have a direct equivalent on their Y, therefore
men are hemizygous
Phenotype - Answers - the observable manifestation of the genotype
- Environmental factors and epigenetic effects change them as well
Single gene associations - Answers - mendelian genetics: dominant, recessive, co-
dominant
Dominant - Answers - when a human monogenic disorder (or trait) is determined by a
nuclear gene, the trait is said to be dominant if it is manifested in the heterozygote (who
carries a normal allele and a mutant allele)
Recessive - Answers - if the trait is not manifested in the heterozygote
Co-dominant - Answers - sometimes two different phenotypes that result from mutations
at a single gene locus can be simultaneously displayed by the heterozygous
- The ABO blood group locus (AB blood group)
Compound heterozygote - Answers - when an affected individual with two different
mutant alleles
- One variant on one homolog and another on the other homolog
- Child is born to parents with two different mutant alleles
consanguineous - Answers - couples who have one or more recent ancestors in
common
Autosomal dominant - Answers - disease locus present on an autosome so they can be
either sex
- Equally likely to transmit the disorder
- When an affected parent has a child with an unaffected person each child have a 50%
chance of developing the disease
, - Manifested in heterozygotes, normally carry one mutant allele and one normal allele at
the disease locus
Autosomal recessive - Answers - person affected can be of either sex and is typically
born from unaffected parents that are both heterozygotes
- The chance that each child is affected is 25%, risk of both parents giving their mutant
allele
Carriers - Answers - Asymptomatic but carry one wild type allele
X-linked recessive - Answers - allele located on X chromosome
- Since males only have one X chromosome, they get whatever X allele they are dealt
- Males have a 50% chance since the mother is heterozygous and they can get either
the recessive or dominant allele
- The percent chance that of all the children get the mutant allele is 25%
- affected individuals are mostly male, usually born to unaffected parents, mothers often
carriers
Because of X-inactivation, females carriers of an X-linked mutation are mosaics -
Answers - some of their cells have normal X chromosome inactivated and other cells
have the mutant X inactivated
X-linked dominant - Answers - A male with the dominant allele will be affected while the
male with a recessive allele will be unaffected since males only have one X
chromosome
- Since females have two X chromosomes they need to have the dominant allele to be
affected
- Affected males have only affected daughters as they have the dominant affected allele
and give it to every female
- Affected females can have affected or unaffected offspring depending on if the mother
is heterozygous
- Significantly more affected females than affected males, females typically have milder
expression
- Phenotype is so severe in males that they die in the prenatal period
Y-linked - Answers - gene associated with a trait on the Y chromosome, only males
- Any male that is affected must always pass their affected Y to their sons
- No affected females as they never inherit the Y chromosome from their fathers
Barr Body - Answers - a cell from an XX female that has a single inactivated X
chromosome
Germline mosaicism - Answers - mutation that is limited to the gonads and can be
transmitted to offspring
Genotype - Answers - combination of alleles that a patient possesses
Homozygous - Answers - somatic cells, if both alleles are the same at an individual
locus
Heterozygous - Answers - somatic cells, if alleles are different even by a single
nucleotide at the same locus
Hemizygous - Answers - applies to gametes. Men have two types of sex chromosomes
(XY) so most DNA sequences on X do not have a direct equivalent on their Y, therefore
men are hemizygous
Phenotype - Answers - the observable manifestation of the genotype
- Environmental factors and epigenetic effects change them as well
Single gene associations - Answers - mendelian genetics: dominant, recessive, co-
dominant
Dominant - Answers - when a human monogenic disorder (or trait) is determined by a
nuclear gene, the trait is said to be dominant if it is manifested in the heterozygote (who
carries a normal allele and a mutant allele)
Recessive - Answers - if the trait is not manifested in the heterozygote
Co-dominant - Answers - sometimes two different phenotypes that result from mutations
at a single gene locus can be simultaneously displayed by the heterozygous
- The ABO blood group locus (AB blood group)
Compound heterozygote - Answers - when an affected individual with two different
mutant alleles
- One variant on one homolog and another on the other homolog
- Child is born to parents with two different mutant alleles
consanguineous - Answers - couples who have one or more recent ancestors in
common
Autosomal dominant - Answers - disease locus present on an autosome so they can be
either sex
- Equally likely to transmit the disorder
- When an affected parent has a child with an unaffected person each child have a 50%
chance of developing the disease
, - Manifested in heterozygotes, normally carry one mutant allele and one normal allele at
the disease locus
Autosomal recessive - Answers - person affected can be of either sex and is typically
born from unaffected parents that are both heterozygotes
- The chance that each child is affected is 25%, risk of both parents giving their mutant
allele
Carriers - Answers - Asymptomatic but carry one wild type allele
X-linked recessive - Answers - allele located on X chromosome
- Since males only have one X chromosome, they get whatever X allele they are dealt
- Males have a 50% chance since the mother is heterozygous and they can get either
the recessive or dominant allele
- The percent chance that of all the children get the mutant allele is 25%
- affected individuals are mostly male, usually born to unaffected parents, mothers often
carriers
Because of X-inactivation, females carriers of an X-linked mutation are mosaics -
Answers - some of their cells have normal X chromosome inactivated and other cells
have the mutant X inactivated
X-linked dominant - Answers - A male with the dominant allele will be affected while the
male with a recessive allele will be unaffected since males only have one X
chromosome
- Since females have two X chromosomes they need to have the dominant allele to be
affected
- Affected males have only affected daughters as they have the dominant affected allele
and give it to every female
- Affected females can have affected or unaffected offspring depending on if the mother
is heterozygous
- Significantly more affected females than affected males, females typically have milder
expression
- Phenotype is so severe in males that they die in the prenatal period
Y-linked - Answers - gene associated with a trait on the Y chromosome, only males
- Any male that is affected must always pass their affected Y to their sons
- No affected females as they never inherit the Y chromosome from their fathers
Barr Body - Answers - a cell from an XX female that has a single inactivated X
chromosome
Germline mosaicism - Answers - mutation that is limited to the gonads and can be
transmitted to offspring
