EXAM 2 CERTIFICATION TEST WITH
ACCURATE ANSWERS
◉ Parent-of-origin effects. Answer: parental origin influences
phenotype.
-Mechanisms of parent-of-origin effects: genomic imprintings
-Methyl (CH3) groups covalently attached to DNA near gene
promotors, so transcription factors cannot gain access to express the
imprinted gene. This is seen as diseased inherited from a parent.
-For certain genes in mammals, parental origin does influence the
phenotype such as age of onset or symptom severity. Two
mechanisms of parent-of-origin effects are genomic imprinting and
differences between the developmental timetables of sperm and
oocytes
◉ Describe the mode of inheritance of a mitochondrial trait.
Answer: from a mother
◉ Explain how mitochondrial DNA differs from nuclear DNA.
Answer: Mutation rate: mtDNA does not have precise and refine
enzymes like the nuclear DNA has (polymerase, proof-reading). Lots
of molecules that can damage DNA in mitochondria. There aren't
radicals or free species floating around in nucleus, where there is in
mitochondria.
,◉ Explain how linked traits are inherited differently from Mendelian
traits. Answer: In Mendelian inheritance, each parent contributes
one of two possible alleles for a trait. If the genotypes of both
parents in a genetic cross are known, Mendel's laws can be used to
determine the distribution of phenotypes expected for the
population of offspring. In linked traits certain genes may only affect
progeny depending on the maternal or paternal genotype.
◉ Discuss the basis of linkage in meiosis. Answer: Two genes are
said to be under linkage, or linked, when they reside in the same
chromosome. These do not separate in meiosis (except for the
phenomenon of crossing over).
Linked alleles, for example, A-b and a-B, form the gametes A-b and a-
B that maintain the linkage of the alleles. This type of linkage is
called complete linkage. In the first division of meiosis (meiosis I)
however the crossing over phenomenon may occur. Chromosomes
from a pair of homologous may exchange extremities and some once
linked alleles, for example, A-b and a-B, recombine to form different
gametes, in the case, A-B and a-b. If genes are farther apart on
chromosome it will be easier for them to separate by crossing over.
◉ Explain how linkage is the basis of genetic maps and genome-
wide association studies. Answer: One of the major successes of
human genetics was the identification of multiple mutations in the
CFTR gene as the cause of cystic fibrosis. This was achieved by
genotyping families affected by cystic fibrosis using a collection of
, genetic markers across the genome, and examining how those
genetic markers segregate with the disease across multiple families.
This technique, called linkage analysis, was subsequently applied
successfully to identify genetic variants that contribute to rare
disorders like Huntington disease. When applied to more common
disorders, like heart disease or various forms of cancer, linkage
analysis has not fared as well. This implies the genetic mechanisms
that influence common disorders are different from those that cause
rare disorders
◉ Exceptions to Mendel's Law. Answer: Most genes don't exhibit
simple inheritance. Genotypic ratios persist but phenotypic ratios
may vary due to outside-the-gene influences
◉ Outside-the-gene influences. Answer: -multiple alleles (a series of
three or more alternative or allelic forms of a gene, only two of
which can exist in any normal, diploid individual)
-other nuclear genes (a gene located in the cell nucleus of a
eukaryote. The term is used to distinguish nuclear genes from the
genes in the mitochondrion which host their own genetic system
and can produce proteins from scratch)
-non-nuclear genes (genes located in the mitochondria or cytoplasm
which host their own genetic system)
-gene linkage
-environment (exposome)
-lethal alleles
ACCURATE ANSWERS
◉ Parent-of-origin effects. Answer: parental origin influences
phenotype.
-Mechanisms of parent-of-origin effects: genomic imprintings
-Methyl (CH3) groups covalently attached to DNA near gene
promotors, so transcription factors cannot gain access to express the
imprinted gene. This is seen as diseased inherited from a parent.
-For certain genes in mammals, parental origin does influence the
phenotype such as age of onset or symptom severity. Two
mechanisms of parent-of-origin effects are genomic imprinting and
differences between the developmental timetables of sperm and
oocytes
◉ Describe the mode of inheritance of a mitochondrial trait.
Answer: from a mother
◉ Explain how mitochondrial DNA differs from nuclear DNA.
Answer: Mutation rate: mtDNA does not have precise and refine
enzymes like the nuclear DNA has (polymerase, proof-reading). Lots
of molecules that can damage DNA in mitochondria. There aren't
radicals or free species floating around in nucleus, where there is in
mitochondria.
,◉ Explain how linked traits are inherited differently from Mendelian
traits. Answer: In Mendelian inheritance, each parent contributes
one of two possible alleles for a trait. If the genotypes of both
parents in a genetic cross are known, Mendel's laws can be used to
determine the distribution of phenotypes expected for the
population of offspring. In linked traits certain genes may only affect
progeny depending on the maternal or paternal genotype.
◉ Discuss the basis of linkage in meiosis. Answer: Two genes are
said to be under linkage, or linked, when they reside in the same
chromosome. These do not separate in meiosis (except for the
phenomenon of crossing over).
Linked alleles, for example, A-b and a-B, form the gametes A-b and a-
B that maintain the linkage of the alleles. This type of linkage is
called complete linkage. In the first division of meiosis (meiosis I)
however the crossing over phenomenon may occur. Chromosomes
from a pair of homologous may exchange extremities and some once
linked alleles, for example, A-b and a-B, recombine to form different
gametes, in the case, A-B and a-b. If genes are farther apart on
chromosome it will be easier for them to separate by crossing over.
◉ Explain how linkage is the basis of genetic maps and genome-
wide association studies. Answer: One of the major successes of
human genetics was the identification of multiple mutations in the
CFTR gene as the cause of cystic fibrosis. This was achieved by
genotyping families affected by cystic fibrosis using a collection of
, genetic markers across the genome, and examining how those
genetic markers segregate with the disease across multiple families.
This technique, called linkage analysis, was subsequently applied
successfully to identify genetic variants that contribute to rare
disorders like Huntington disease. When applied to more common
disorders, like heart disease or various forms of cancer, linkage
analysis has not fared as well. This implies the genetic mechanisms
that influence common disorders are different from those that cause
rare disorders
◉ Exceptions to Mendel's Law. Answer: Most genes don't exhibit
simple inheritance. Genotypic ratios persist but phenotypic ratios
may vary due to outside-the-gene influences
◉ Outside-the-gene influences. Answer: -multiple alleles (a series of
three or more alternative or allelic forms of a gene, only two of
which can exist in any normal, diploid individual)
-other nuclear genes (a gene located in the cell nucleus of a
eukaryote. The term is used to distinguish nuclear genes from the
genes in the mitochondrion which host their own genetic system
and can produce proteins from scratch)
-non-nuclear genes (genes located in the mitochondria or cytoplasm
which host their own genetic system)
-gene linkage
-environment (exposome)
-lethal alleles
