Genetics test bank
GENETICS- Chaviva Korb - CORRECT ANSWERS
Lecture 1: - CORRECT ANSWERS
- DNA is packaged as chromatin, chromosomes become visible during mitosis. -
CORRECT ANSWERS
Homologues- (maternal and paternal forms of same chromosome) - CORRECT
ANSWERS
Meiosis: G1, S, G2, M. Before replication phase, chromosomes have one chromatid and
after replication, chromosomes have 2 sister chromatids, held together at the
centromere. Ends with 4 daughter cells with 1 chromatid each. - CORRECT ANSWERS
Key differences from mitosis: Homologs pair (Prophase I), Sister centromeres act as a
single centromere (Metaphase I), Sister chromatids remain attached (Anaphase I),
Meiosis I is a reduction division- meaning start meiosis I with 46 units and end meiosis I
with 23 units ( 2 chromatids in each haploid daughter cells), Meiosis II is an equational
division (identical to mitosis). - CORRECT ANSWERS
Recombination occurs in Prophase I. Crossing over and recomb is Exchange of
homologous segments between non-sister chromatids. - CORRECT ANSWERS
Homologues move apart during anaphase I-disjunction. 223 possible combinations of
chromosomes. In cytokinesis I, Cells divide into two haploid daughter cells. One cell
receives most of the cytoplasm and the other becomes the first polar body which
doesn't go through Meiosis II. Meiosis I ends after ovulation. Non dysjunction in meiosis
I: can cause problems like Trisomy 21. - CORRECT ANSWERS
-Brief interphase between first and second meiotic divisions. No S phase occurs in
Meiosis II. - CORRECT ANSWERS
-In the second meiotic division a second polar body forms during oogenesis. In
oogenesis, egg is arrested in metaphase II until fertilization. - CORRECT ANSWERS
After Meiosis there is a Reduction of chromosome number 2nn. (diploid vs. haploid
cells)- Notation 'n' has to do with amount of DNA (#of nucleotides), not the necessarily
the # of chromosomes. - CORRECT ANSWERS
Lecture 2: Patterns of Inheritance - CORRECT ANSWERS
,Medelian Inheritance- determined by a single major gene. Based on independent
assortment. Dihybrid cross (2 genotypes) with ry, Ry, rY, Ry set up on both
sidesphenotypic ratio of 9:3:3:1-yellow round, green round, yellow wrinkled, green
wrinkled, If get 9:3:3:1 you know that segregation is independent. - CORRECT
ANSWERS
Multifactorial inheritance-multiple genetic and non-genetic factors involved - CORRECT
ANSWERS
Compound heterozygous: has two different mutant alleles for a character - CORRECT
ANSWERS
Linkage-2 genes physically near each other on a chromosome will not assort randomly
in meiosis. Tightly linked: will get 2 types of gametes ex. PL and pl. Unlinked: will get 4
types of gametes PL, Pl, pL, pl. - CORRECT ANSWERS
The frequency of recombination between two genes is proportional to the distance
between the genes. The closer the genes are on the chromosome the less likely
crossing over occurs. Linkage map: 1% recombination = 1 map unit = 1 centiMorgan
(cM), Map distances are additive. - CORRECT ANSWERS
The non-random association between alleles at two locations on a chromosome is
called linkage disequilibrium. If the frequency of chromosomes with AB=Ab=aB=ab then
the genes are in equilibrium. If frequency of 1 allele is seen more (A more than B for ex)
then genes are in linkage disequilibrium. - CORRECT ANSWERS
Autosomal dominant inheritance Examples: - CORRECT ANSWERS
Achondroplasia- FGFR3 mutations, Always full penetrance with achondroplasia (so
normal parents have a child with aplasia then it's a new mutation). Heterozygous b/c
homozygotes usually die in utero - CORRECT ANSWERS
Neurofibromatosis- NF1 (neurofibromin) and NF2 (merlin) mutations. - CORRECT
ANSWERS
Incomplete dominance- mixed phenotype. In cases of disease, Dominant disorders are
more severe in homozygotes then in heterozygotes (termed also "semidominant") Ie.
Familial Hypercholesterolemia. - CORRECT ANSWERS
Co-dominance- phenotypic expression of two different alleles for a locus ie. Blood type.
- CORRECT ANSWERS
Autosomal recessive inheritance: Examples: Cystic fibrosis, Tay-Sachs disease, Sickle-
cell disease - CORRECT ANSWERS
,Pseudodominance: the inheritance of an autosomal recessive trait mimics an autosomal
dominant pattern - CORRECT ANSWERS
Males are hemizygous with respect to X-linked genes. - CORRECT ANSWERS
X-linked dominant inheritance: Affected females are twice as common as affected
males but males usually more severely affected or the disorder may be lethal in males
(Rett syndrome). - CORRECT ANSWERS
X-linked recessive: incidence is much higher in males and affected males do not usually
transmit the disorder unless mother is a carrier. Heterozygote females are usually
unaffected, but some may express the condition with variable severity as determined by
the pattern of X inactivation. A significant proportion of isolated cases are due to new
mutation (Duchenne muscular dystrophy-DMD). - CORRECT ANSWERS
Pseudoautosomal inheritance- group of genes on the inactive x chromosome are NOT
inactivated. Diseases associated with these genes are inherited similar to autosomal
inheritance. - CORRECT ANSWERS
Same amount of X-linked gene products between males and females achieved through
dosage compensation. Lyon Hypothesis states that the inactive X is NOT randomly
chosen in each cell Ex. A structurally abnormal X is preferentially inactivated.
Inactivation is NOT complete- some genes can escape inactivation (ie. Those with a
functional homolog on the Y). Inactivation is NOT permanent- reversed in development
of germ cells (not passed on to gametes). - CORRECT ANSWERS
The key player is the X-linked gene XIST→ X (inactive) specific transcript. XIST is
transcribed to produce a non-coding RNA that "coats" the X-chromosome and
inactivates it. XIST is only expressed from the inactive X. The histones on the coated X
undergo methylation which causes the chromosome to condense (heterochromatin),
forming a Barr body. - CORRECT ANSWERS
-Some genes do not have Y homologue and do not undergo inactivation (e.g. steroid
sulfatase gene) - CORRECT ANSWERS
-Random/skewed inactivation may result in affected/totally healthy heterozygotes. -
CORRECT ANSWERS
Variable expression of X-inactivation: On both extremes, a heterozygous female with
recessive x-linked disease could manifest the disease. In a case with a dominant X-
linked trait, in which almost all of a females X chromosomes with mutation is inactive,
might not manifest this disease. Identical twins could even have diff phenotypes due to
skewed X inactivation. - CORRECT ANSWERS
Mosaicism- X chromosome inactivation occurs randomly and inactivation pattern is
passed to cell progeny. Result: functional mosaicism in which female is a mosaic with
, respect to expression of genes on X chrom. Ex. Calico Cat, B - dominant orange, b -
recessive gene black, Genes for white: autosomal. - CORRECT ANSWERS
Genetic Heterogeneity can be the result of Locus Heterogeneity , Allelic Heterogeneity,
and Modifier Loci. - CORRECT ANSWERS
Locus Heterogeneity- a single disorder, trait, or pattern of traits caused by mutations in
genes at different chromosomal loci. Ex. retinitis pigmentosa has autosomal dominant,
autosomal recessive, and X-linked origins. However, only one mutant locus is needed
for the phenotype to manifest - CORRECT ANSWERS
Allelic heterogeneity - Many genetic loci possess more than one mutant allele. In the
CFTR gene, nearly 1400 mutations found. Some mutations cause classical CF +
pancreatic insufficiency + congenital absence of vas deferens, others cause lung
disease with normal pancreatic fxn. Other cause only male sterility. - CORRECT
ANSWERS
Modifier gene: A gene that affects the phenotypic expression of another gene. Specific
alleles of one or more genes (modifier genes) can sometimes dramatically modify the
clinical severity of the phenotype produced by mutations in a disease-causing gene.This
source of clinical heterogeneity is often referred to as genetic background. Ex. Twins
with the same mutation in cystic fibrosis but one is severely sick and one only
moderately sick- explained by modifier genes. - CORRECT ANSWERS
Candidate loci acting as modifiers for CFTR mutations:TGFB1 (cytokine transforming
growth factor b and MLB2 (Mannose-binding lectin). Different alleles of these genes
modify the severity of CF - CORRECT ANSWERS
Clinical/phenotypic heterogeneity: multiple phenotypes of one single gene ex. USH2A
gene, codes for protein important in development of the inner ear and retina. Can be
blind and deaf (type II Usher syndrome) or just blind (Retinitis Pigmentosa). -
CORRECT ANSWERS
Other factors affection phenotype include environmental factors ie. G6PD mutation OR
soil pH and hydrangea color. Also Sex-related factors ie Hemochromatosis, AR, caused
by iron overload, is less common in females due to lower iron intake/menstrual iron loss.
- CORRECT ANSWERS
G6PD (glucose-6-phosphate dehydrogenase) Deficiency (X-linked)- Can lead to
hemolytic anemia, many ppl with this disorder never experience any symptoms.
Hemolytic anemia can be triggered by environmental factors such as bacterial/viral
infections, drug (sulfa, malaria medications), eating fava beans or inhaling fava bean
plant pollen. - CORRECT ANSWERS
GENETICS- Chaviva Korb - CORRECT ANSWERS
Lecture 1: - CORRECT ANSWERS
- DNA is packaged as chromatin, chromosomes become visible during mitosis. -
CORRECT ANSWERS
Homologues- (maternal and paternal forms of same chromosome) - CORRECT
ANSWERS
Meiosis: G1, S, G2, M. Before replication phase, chromosomes have one chromatid and
after replication, chromosomes have 2 sister chromatids, held together at the
centromere. Ends with 4 daughter cells with 1 chromatid each. - CORRECT ANSWERS
Key differences from mitosis: Homologs pair (Prophase I), Sister centromeres act as a
single centromere (Metaphase I), Sister chromatids remain attached (Anaphase I),
Meiosis I is a reduction division- meaning start meiosis I with 46 units and end meiosis I
with 23 units ( 2 chromatids in each haploid daughter cells), Meiosis II is an equational
division (identical to mitosis). - CORRECT ANSWERS
Recombination occurs in Prophase I. Crossing over and recomb is Exchange of
homologous segments between non-sister chromatids. - CORRECT ANSWERS
Homologues move apart during anaphase I-disjunction. 223 possible combinations of
chromosomes. In cytokinesis I, Cells divide into two haploid daughter cells. One cell
receives most of the cytoplasm and the other becomes the first polar body which
doesn't go through Meiosis II. Meiosis I ends after ovulation. Non dysjunction in meiosis
I: can cause problems like Trisomy 21. - CORRECT ANSWERS
-Brief interphase between first and second meiotic divisions. No S phase occurs in
Meiosis II. - CORRECT ANSWERS
-In the second meiotic division a second polar body forms during oogenesis. In
oogenesis, egg is arrested in metaphase II until fertilization. - CORRECT ANSWERS
After Meiosis there is a Reduction of chromosome number 2nn. (diploid vs. haploid
cells)- Notation 'n' has to do with amount of DNA (#of nucleotides), not the necessarily
the # of chromosomes. - CORRECT ANSWERS
Lecture 2: Patterns of Inheritance - CORRECT ANSWERS
,Medelian Inheritance- determined by a single major gene. Based on independent
assortment. Dihybrid cross (2 genotypes) with ry, Ry, rY, Ry set up on both
sidesphenotypic ratio of 9:3:3:1-yellow round, green round, yellow wrinkled, green
wrinkled, If get 9:3:3:1 you know that segregation is independent. - CORRECT
ANSWERS
Multifactorial inheritance-multiple genetic and non-genetic factors involved - CORRECT
ANSWERS
Compound heterozygous: has two different mutant alleles for a character - CORRECT
ANSWERS
Linkage-2 genes physically near each other on a chromosome will not assort randomly
in meiosis. Tightly linked: will get 2 types of gametes ex. PL and pl. Unlinked: will get 4
types of gametes PL, Pl, pL, pl. - CORRECT ANSWERS
The frequency of recombination between two genes is proportional to the distance
between the genes. The closer the genes are on the chromosome the less likely
crossing over occurs. Linkage map: 1% recombination = 1 map unit = 1 centiMorgan
(cM), Map distances are additive. - CORRECT ANSWERS
The non-random association between alleles at two locations on a chromosome is
called linkage disequilibrium. If the frequency of chromosomes with AB=Ab=aB=ab then
the genes are in equilibrium. If frequency of 1 allele is seen more (A more than B for ex)
then genes are in linkage disequilibrium. - CORRECT ANSWERS
Autosomal dominant inheritance Examples: - CORRECT ANSWERS
Achondroplasia- FGFR3 mutations, Always full penetrance with achondroplasia (so
normal parents have a child with aplasia then it's a new mutation). Heterozygous b/c
homozygotes usually die in utero - CORRECT ANSWERS
Neurofibromatosis- NF1 (neurofibromin) and NF2 (merlin) mutations. - CORRECT
ANSWERS
Incomplete dominance- mixed phenotype. In cases of disease, Dominant disorders are
more severe in homozygotes then in heterozygotes (termed also "semidominant") Ie.
Familial Hypercholesterolemia. - CORRECT ANSWERS
Co-dominance- phenotypic expression of two different alleles for a locus ie. Blood type.
- CORRECT ANSWERS
Autosomal recessive inheritance: Examples: Cystic fibrosis, Tay-Sachs disease, Sickle-
cell disease - CORRECT ANSWERS
,Pseudodominance: the inheritance of an autosomal recessive trait mimics an autosomal
dominant pattern - CORRECT ANSWERS
Males are hemizygous with respect to X-linked genes. - CORRECT ANSWERS
X-linked dominant inheritance: Affected females are twice as common as affected
males but males usually more severely affected or the disorder may be lethal in males
(Rett syndrome). - CORRECT ANSWERS
X-linked recessive: incidence is much higher in males and affected males do not usually
transmit the disorder unless mother is a carrier. Heterozygote females are usually
unaffected, but some may express the condition with variable severity as determined by
the pattern of X inactivation. A significant proportion of isolated cases are due to new
mutation (Duchenne muscular dystrophy-DMD). - CORRECT ANSWERS
Pseudoautosomal inheritance- group of genes on the inactive x chromosome are NOT
inactivated. Diseases associated with these genes are inherited similar to autosomal
inheritance. - CORRECT ANSWERS
Same amount of X-linked gene products between males and females achieved through
dosage compensation. Lyon Hypothesis states that the inactive X is NOT randomly
chosen in each cell Ex. A structurally abnormal X is preferentially inactivated.
Inactivation is NOT complete- some genes can escape inactivation (ie. Those with a
functional homolog on the Y). Inactivation is NOT permanent- reversed in development
of germ cells (not passed on to gametes). - CORRECT ANSWERS
The key player is the X-linked gene XIST→ X (inactive) specific transcript. XIST is
transcribed to produce a non-coding RNA that "coats" the X-chromosome and
inactivates it. XIST is only expressed from the inactive X. The histones on the coated X
undergo methylation which causes the chromosome to condense (heterochromatin),
forming a Barr body. - CORRECT ANSWERS
-Some genes do not have Y homologue and do not undergo inactivation (e.g. steroid
sulfatase gene) - CORRECT ANSWERS
-Random/skewed inactivation may result in affected/totally healthy heterozygotes. -
CORRECT ANSWERS
Variable expression of X-inactivation: On both extremes, a heterozygous female with
recessive x-linked disease could manifest the disease. In a case with a dominant X-
linked trait, in which almost all of a females X chromosomes with mutation is inactive,
might not manifest this disease. Identical twins could even have diff phenotypes due to
skewed X inactivation. - CORRECT ANSWERS
Mosaicism- X chromosome inactivation occurs randomly and inactivation pattern is
passed to cell progeny. Result: functional mosaicism in which female is a mosaic with
, respect to expression of genes on X chrom. Ex. Calico Cat, B - dominant orange, b -
recessive gene black, Genes for white: autosomal. - CORRECT ANSWERS
Genetic Heterogeneity can be the result of Locus Heterogeneity , Allelic Heterogeneity,
and Modifier Loci. - CORRECT ANSWERS
Locus Heterogeneity- a single disorder, trait, or pattern of traits caused by mutations in
genes at different chromosomal loci. Ex. retinitis pigmentosa has autosomal dominant,
autosomal recessive, and X-linked origins. However, only one mutant locus is needed
for the phenotype to manifest - CORRECT ANSWERS
Allelic heterogeneity - Many genetic loci possess more than one mutant allele. In the
CFTR gene, nearly 1400 mutations found. Some mutations cause classical CF +
pancreatic insufficiency + congenital absence of vas deferens, others cause lung
disease with normal pancreatic fxn. Other cause only male sterility. - CORRECT
ANSWERS
Modifier gene: A gene that affects the phenotypic expression of another gene. Specific
alleles of one or more genes (modifier genes) can sometimes dramatically modify the
clinical severity of the phenotype produced by mutations in a disease-causing gene.This
source of clinical heterogeneity is often referred to as genetic background. Ex. Twins
with the same mutation in cystic fibrosis but one is severely sick and one only
moderately sick- explained by modifier genes. - CORRECT ANSWERS
Candidate loci acting as modifiers for CFTR mutations:TGFB1 (cytokine transforming
growth factor b and MLB2 (Mannose-binding lectin). Different alleles of these genes
modify the severity of CF - CORRECT ANSWERS
Clinical/phenotypic heterogeneity: multiple phenotypes of one single gene ex. USH2A
gene, codes for protein important in development of the inner ear and retina. Can be
blind and deaf (type II Usher syndrome) or just blind (Retinitis Pigmentosa). -
CORRECT ANSWERS
Other factors affection phenotype include environmental factors ie. G6PD mutation OR
soil pH and hydrangea color. Also Sex-related factors ie Hemochromatosis, AR, caused
by iron overload, is less common in females due to lower iron intake/menstrual iron loss.
- CORRECT ANSWERS
G6PD (glucose-6-phosphate dehydrogenase) Deficiency (X-linked)- Can lead to
hemolytic anemia, many ppl with this disorder never experience any symptoms.
Hemolytic anemia can be triggered by environmental factors such as bacterial/viral
infections, drug (sulfa, malaria medications), eating fava beans or inhaling fava bean
plant pollen. - CORRECT ANSWERS
