Test Bank for Human Genetics Exam Questions
(ACTUAL EXAM)/NEWEST WITH WELL SORTED QUESTIONS
AND ANSWERS /GRADED A+
GENETICS- Chaviva Korb
- DNA is packaged as chromatin, chromosomes become visible during mitosis.
Ans: Homologues- (maternal and paternal forms of same chromosome)
Ans:
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.
Ans:
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).
Ans:
Recombination occurs in Prophase I. Crossing over and recomb is Exchange of homologous segments
between non-sister chromatids.
,Ans:
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.
Ans:
-Brief interphase between first and second meiotic divisions. No S phase occurs in Meiosis II.
Ans:
-In the second meiotic division a second polar body forms during oogenesis. In oogenesis, egg is arrested
in metaphase II until fertilization.
Ans:
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.
Ans:
Lecture 2: Patterns of Inheritance
Ans:
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.
Ans:
Multifactorial inheritance-multiple genetic and non-genetic factors involved
Ans:
Compound heterozygous: has two different mutant alleles for a character
Ans:
,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.
Ans:
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.
Ans:
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.
Ans:
Autosomal dominant inheritance Examples:
Ans:
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
Ans:
Neurofibromatosis- NF1 (neurofibromin) and NF2 (merlin) mutations.
Ans:
Incomplete dominance- mixed phenotype. In cases of disease, Dominant disorders are more severe in
homozygotes then in heterozygotes (termed also "semidominant") Ie. Familial Hypercholesterolemia.
Ans:
Co-dominance- phenotypic expression of two different alleles for a locus ie. Blood type.
Ans:
Autosomal recessive inheritance: Examples: Cystic fibrosis, Tay-Sachs disease, Sickle-cell disease
, Ans:
Pseudodominance: the inheritance of an autosomal recessive trait mimics an autosomal dominant
pattern
Ans:
Males are hemizygous with respect to X-linked genes.
Ans:
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).
Ans:
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).
Ans:
Pseudoautosomal inheritance- group of genes on the inactive x chromosome are NOT inactivated.
Diseases associated with these genes are inherited similar to autosomal inheritance.
Ans:
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).
Ans:
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.
(ACTUAL EXAM)/NEWEST WITH WELL SORTED QUESTIONS
AND ANSWERS /GRADED A+
GENETICS- Chaviva Korb
- DNA is packaged as chromatin, chromosomes become visible during mitosis.
Ans: Homologues- (maternal and paternal forms of same chromosome)
Ans:
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.
Ans:
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).
Ans:
Recombination occurs in Prophase I. Crossing over and recomb is Exchange of homologous segments
between non-sister chromatids.
,Ans:
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.
Ans:
-Brief interphase between first and second meiotic divisions. No S phase occurs in Meiosis II.
Ans:
-In the second meiotic division a second polar body forms during oogenesis. In oogenesis, egg is arrested
in metaphase II until fertilization.
Ans:
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.
Ans:
Lecture 2: Patterns of Inheritance
Ans:
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.
Ans:
Multifactorial inheritance-multiple genetic and non-genetic factors involved
Ans:
Compound heterozygous: has two different mutant alleles for a character
Ans:
,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.
Ans:
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.
Ans:
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.
Ans:
Autosomal dominant inheritance Examples:
Ans:
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
Ans:
Neurofibromatosis- NF1 (neurofibromin) and NF2 (merlin) mutations.
Ans:
Incomplete dominance- mixed phenotype. In cases of disease, Dominant disorders are more severe in
homozygotes then in heterozygotes (termed also "semidominant") Ie. Familial Hypercholesterolemia.
Ans:
Co-dominance- phenotypic expression of two different alleles for a locus ie. Blood type.
Ans:
Autosomal recessive inheritance: Examples: Cystic fibrosis, Tay-Sachs disease, Sickle-cell disease
, Ans:
Pseudodominance: the inheritance of an autosomal recessive trait mimics an autosomal dominant
pattern
Ans:
Males are hemizygous with respect to X-linked genes.
Ans:
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).
Ans:
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).
Ans:
Pseudoautosomal inheritance- group of genes on the inactive x chromosome are NOT inactivated.
Diseases associated with these genes are inherited similar to autosomal inheritance.
Ans:
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).
Ans:
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.
