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human bio exam #5

Terms in this set (123)

Whose genes determine the color of your eyes?
a. Your mother's genes
b. Your father's genes
c. Both your mother's and father's genes
c. Both your mother's and father's genes
At least three different genes influence eye color. Different combinations of the alleles of the genes account for a range of eye colors from nearly black to light blue. (blue eyes, brown eyes, green eyes, hazel eyes etc)
True/False A son can inherit the gene for color blindness from his father.
false. Sons inherit the gene for color-blindness from their mother!!! This is because the gene for color-blindness is found on the X chromosome, and males inherit their X chromosome from their mother.
Allele
different versions of a gene.
Different alleles usually arose from spontaneous mutations during DNA replication that occurred in the gametes and were passed on to the offspring.
Different alleles are due to
spontaneous mutations that occurred during formation of sperm or egg cells that were passed on to the next generation.
Gregor Mendel
"Father of Genetics"
· 1850's-1860's he studied inherited traits in garden peas and discovered the laws of inheritance called "Mendelian Inheritance".
Mendel's laws of inheritance:
- Traits are inherited in a dominant and recessive pattern:
- Dominant traits always appear if at least one dominant allele is present.
- Recessive traits appear only in the absence of the dominant allele.
-Traits are passed to offspring by "factors" (genes) from each parent.
-Each sex cell formed during meiosis receives only one allele of each gene
Mendel's experiment with pea color trait in garden pea plants:
· 2 Alleles (versions) for pea color: yellow pea allele (Y) or green pea allele (y)
· Yellow allele (Y) is dominant and green allele (y) is recessive.
· Genotype for yellow peas: YY or Yy
· Genotype for green peas: yy
Three Exceptions to Mendel's Rules of Inheritance
incomplete dominance, codominance, x-linked disorders
Incomplete dominance
heterozygote has an intermediate phenotype
Examples of incomplete dominance are:
· Pink flower color (Rr) in snapdragon plants.
R is the allele for red flowers
r is the allele for white flowers
· wavy hair ( Hh) p455
H is the allele for straight hair
h is the allele for curly hair
· mild familial hypercholesterolemia (Nd) p454
N is the allele for Normal blood cholesterol level
d is the defective allele for high blood cholesterol level
· heterozygote (Nd) has mild hypercholesterolemia. They have twice the normal blood cholesterol level and are at risk for heart attacks in their 30's and 40's.
· dd person has severe hypercholesterolemia. They have up to six times the normal blood cholesterol level and are at risk for heart attacks in childhood.
· NN person has normal blood cholesterol levels and does not have hypercholesterolemia.
incomplete dominance: · Pink flower color (Rr) in snapdragon plants.
R is the allele for red flowers
r is the allele for white flowers
incomplete dominance: wavy hair ( Hh)
H is the allele for straight hair
h is the allele for curly hair
incomplete dominance: mild familial hypercholesterolemia (Nd)
N is the allele for Normal blood cholesterol level
d is the defective allele for high blood cholesterol level
incomplete dominance: heterozygote (Nd) has mild hypercholesterolemia
· They have twice the normal blood cholesterol level and are at risk for heart attacks in their 30's and 40's.
incomplete dominance: dd person has severe hypercholesterolemia
· They have up to six times the normal blood cholesterol level and are at risk for heart attacks in childhood.
incomplete dominance: NN person has normal blood cholesterol levels
and does not have hypercholesterolemia
Codominance
both alleles are equally expressed in the heterozygote.
· Example of codominance is the AB blood type. If you have type AB blood then both the A and B molecules are present in equal amounts on the surface of your red blood cells
· Other blood types are:
Type A blood (AA or AO): presence of A chemical tags on the surface of their red blood cells.
Type B blood (BB or BO): presence of B chemical tags on the surface of their red blood cells.
Type O blood (OO):missing both A and B chemical tags on the surface of their red blood cells
X-linked disorders
Disorders that arise from defective genes that are found on the X chromosome. (Xd)
X-linked disorders are more common in males
Since the defective allele is found on the X-chromosome all males whose genotype is Xd Y are affected since males have only one X chromosome.
Males receive the X-linked disorder allele (Xd) from
their mother.
Examples of X-linked disorders
: disorders that are encoded by a defective gene on the X chromosome. (Xd)
1. Red-Green colorblindness is X-linked: due to absence of light sensing proteins so that affected people have difficulty distinguishing between red and green. p297
2. Duchennes Muscular Dystrophy is X-linked: due to absence of a muscle protein whose job is to protect muscle cells from injury. Affected people have weak muscles and eventually are unable to walk, have difficulty breathing and have heart problems. p137
3. Hemophilia is X-linked (Xd): due to missing clotting factors so that their blood cannot clot and patients suffer internal bleeding. p457
x-linked: Red-Green colorblindness is X-linked
due to absence of light sensing proteins so that affected people have difficulty distinguishing between red and green.
x-linked: Duchennes Muscular Dystrophy is X-linked
due to absence of a muscle protein whose job is to protect muscle cells from injury. Affected people have weak muscles and eventually are unable to walk, have difficulty breathing and have heart problems
x-linked: . Hemophilia is X-linked (Xd)
due to missing clotting factors so that their blood cannot clot and patients suffer internal bleeding.

· Queen Victoria of England was a carrier of the hemophilia allele (XNXd).
(Queen Victoria did not have hemophilia because the normal allele XN on her second X chromosome produced enough clotting factors to enable her blood to clot normally.)
· One of her sons had hemophilia (XdY).) Her other sons were normal. (XNY)
· Her daughters were either carriers of hemophilia (XNXd ) or normal. (XNXN)
· Queen Victoria's hemophilia allele (Xd) probably arose as a spontaneous mutation because she was the first member of the British royal family to have the hemophilia allele.
Dominant Disorders
· characterized by overproduction of a defective version of a protein
· only one defective allele is needed to cause the disorder. (Dn)
· children that inherit two Dominant alleles die before birth. (DD)
D: Defective Dominant allele
n: normal recessive allele
Examples of Dominant Disorders:
Huntington's, dwarfism
Dwarfism (Dn genotype)
1. ) is caused by overproduction of a defective version of a protein that interferes with normal bone growth .

· 1/100,000 chance (very rare) that two normal stature parents will have a dwarf child as a result of a spontaneous mutation .
Huntington's disease (Dn genotype)
is a brain disorder caused by overproduction of a defective version of a protein called huntingtin. Accumulation of defective huntingtin proteins leads to destruction of brain tissue and causes uncontrolled muscle movements in all parts of the body, mental disability and death. Symptoms begin in 30's so that the individual has already had children before they know they have the disease.
Nancy Wexler spent 20 years collecting blood samples from family members with a high incidence of Huntington's disease in Venezuela. She compiled a pedigree showing the presence or absence of Huntington's disease among thousands of family members. Her work led to the discovery of the location of the Huntington's gene in 1983 and a genetic test for Huntington's disease in 1993.
Inheritance of Dominant disorders:
· If one parent is normal (nn) and the other is a heterozygote (Dn) there is a 50% chance the offspring will have the disorder and a 50% chance that they will be unaffected.
· If both parents have the disorder (Dn) there is a 25% chance that the child will be normal (nn) and a 50% chance that the child will be affected (Dn) with the disorder and a 25% chance that the child will die before birth. (DD).
Recessive Disorders
· characterized by a loss of function of a protein or a missing protein
· two defective alleles are required to cause the disorder (dd)
· most inherited human disorders are recessive.
example of recessive disorders
albinism, cystic fibrosis, sickle cell anemia, tay Sachs,
Albinism
missing enzyme causes inability to produce brown pigment (melanin).
Cystic Fibrosis
missing salt channel (p450) causes accumulation of salt inside cells and production of a thick, sticky mucus in the respiratory tract and digestive tract.
Sickle Cell Anemia
defective hemoglobin protein (p453-454) does not bind oxygen well and results in deformed, sickle-shaped red blood cells that rupture easily and clog the small blood vessels and block blood flow.
Tay Sachs Disease
missing and enzyme p. 461 whose job is to digest lipids causing accumulation of lipids in brain cells and destruction of brain tissue. Always fatal.
Inheritance of Recessive disorders:
N: Normal dominant allele
d: defective recessive allele
· (dd) two defective recessive alleles, "double dose of the defective allele" are required to cause the disorder.
· (Nd) carriers are protected by the presence of a normal allele which is sufficient for normal function.
· Patterns of Recessive Disorders:If both parents are carriers (Nd) there is a 25% chance that the child will have the disorder (dd) , 25% chance that the child will be normal (NN) and a 50% chance that the child will be a carrier (Nd).
· If one parent is a carrier (Nd) and the other is normal(NN) then there is a 50% chance that the child will be a carrier (Nd) and 50% chance the child will be normal (NN)
Heterozygote Advantage in Carriers of Recessive Disorders
If the heterozygote (carrier) is protected against an infectious disease then the number of carriers will increase in a population.
1. Carriers of sickle cell trait (Nd) are protected against malaria infection.
N is the allele for Normal hemoglobin
d is the allele for defective, sickle hemoglobin
· The malaria parasite spends part of its life cycle in human red blood cells. When the malaria parasite enters the red blood cell of a person who is a carrier of the sickle cell trait (Nd), the cell sickles and ruptures, killing the parasite before it can reproduce. Therefore, carriers of sickle cell trait (Nd) recover more quickly from a malaria infection than persons who do not have the sickle cell allele. (NN)
· Malaria is common in Africa so there is a higher incidence of carriers of sickle cell trait, and an increased incidence of sickle cell anemia. Were it not for malaria, sickle cell anemia and sickle cell trait would become rare.
1. Carriers of Cystic Fibrosis (Nd) are protected against the bacteria that cause cholera .
· The bacteria that cause cholera require CFTR channels to cause disease.
· Cholera bacteria produce a toxin that opens CFTR channels in intestinal cells causing severe diarrhea and dehydration.
· Carriers of CF have fewer CFTR channels so they are more likely to survive cholera and typhoid fever infection.
Dominant allele (uppercase letter)
must inherit one dominant allele for the trait to appear. (Aa or AA)
Recessive allele (lowercase letter)
must inherit two recessive alleles for the trait to appear. (aa)
Autosomal allele
allele is present on one of the 22 autosomes. (non-sex chromosomes)
X-linked allele
allele is present on the X chromosome
Genotype
the pair of alleles (Genes) that you inherit (AA, aa, Aa)
Phenotype
observed Physical traits
Homozygous genotype
: presence of two identical alleles (AA , aa)
Heterozygous genotype
presence of two different alleles (Aa)
Punnett square
diagram that shows the possible genotype of each offspring.
Pedigree
"family tree", chart that displays the presence or absence of an inherited disorder in families.
Disorder Alleles
D: dominant Disorder allele d: recessive disorder allele
Normal alleles
N or n
Dominant disorder inheritance
: must inherit only one dominant Disorder allele (Dn or DD) for the Disorder to appear Examples: Dwarfism, Huntington's Disease
Recessive disorder inheritance
must inherit two recessive disorder alleles (dd) for the disease to appear. (Heterozygotes are called "carriers" because they "carry" the disorder allele but are not sick. (Nd) Examples: Cystic Fibrosis, Tay-Sachs, Sickle Cell Anemia, Albinism
Exceptions to Dominant/Recessive Patterns of Inheritance
incomplete dominance, codominance, x linked

1. Incomplete dominance: heterozygotes (Aa) have an intermediate phenotype. (appears as if the physical traits of the two alleles are "blended ".) p452
· Wavy hair : Hh: wavy hair (intermediate phenotype) (HH: straight hair, hh: curly hair )p.452
· Hypercholesterolemia: Nd : moderately elevated blood cholesterol (intermediate phenotype) p452 (NN: normal blood cholesterol level, dd: very high blood cholesterol level
2. Codominant Inheritance: both alleles are equally expressed in the heterozygote.
Example: AB blood type. Both A and B molecules are present in equal amounts on the red blood cell surface
3. X-linked Recessive Disorder: disorder allele (Xd) is located on the X-chromosome. p457-458
Examples: Hemophilia, Duchennes Muscular Dystrophy, Red-Green Colorblindness
all males are affected since they have a single X chromosome. (Xd Y)
Alleles most accurately refers to:
a. homologous chromosomes
b. dominant genes
c. recessive genes
d. different versions of a gene
d. different versions of a gene
You inherit ____alleles for type of hairline.
a. one
b. two
c. three
d. four
b. two
The physical appearance of an individual is referred to as its:
a. genotype
b. phenotype
b. phenotype
Your pair of alleles is called your:
a. genotype
b. phenotype
a. genotype
Identify the following as homozygous dominant, homozygous recessive or heterozygous individuals:
a. AA
b. Aa
c. aa
a. AA homozygous dominant
b. Aa heterozygous
c. aa homozygous recessive
Different alleles result from mutations that were present in the :
a. somatic cells
b. sex cells
b. sex cells
If you have a yellow-pea plant, you can determine its genotype (Yy or YY) by performing a test cross. After test crossing the yellow-pea plant with a green-pea plant the offspring were all yellow- pea plants. What is the genotype of the parent yellow-pea plant?
a. YY
b. Yy
c. yy
a. YY
If you self-fertilize a heterozygous yellow-pea plant (Yy) with is the chance the offspring will be

heterozygous yellow-pea plants (Yy)
50%
If you self-fertilize a heterozygous yellow-pea plant (Yy) with is the chance the offspring will be:
homozygous dominant yellow-pea plants (YY)
25%
If you self-fertilize a heterozygous yellow-pea plant (Yy) with is the chance the offspring will be
homozygous recessive green-pea plants (yy)
25%
If you cross a heterozygous yellow-pea plant (Yy) with a homozygous dominant yellow-pea plant (YY),what is the chance that the offspring will be: heterozygous yellow-pea plant (Yy)
50%
If you cross a heterozygous yellow-pea plant (Yy) with a homozygous dominant yellow-pea plant (YY),what is the chance that the offspring will be: homozygous dominant yellow-pea plant (YY)
50%
If you cross a heterozygous yellow-pea plant (Yy) with a homozygous dominant yellow-pea plant (YY),what is the chance that the offspring will be: homozygous recessive green-pea plant (yy)
0%
phenotype widow's peak
Ww. WW
phenotype straight hairline
ww
A mother and father both have a widow's peak hairline and we know that their genothpe is Ww What is the chance that their child will have a widow's peak?
75% (Ww or WW)
A mother and father both have a widow's peak hairline and we know that their genothpe is Ww What is the chance that their child will have a straight hairline?
25% (ww)
Red hair is recessive to dark hair. What are the chances of dark-haired parents (Rr) having a red-haired child (rr) ?
25%
Match the type of inheritance with the trait. Wavy Hair
incomplete dominance (the heterozygous genotype Hh, results in a an intermediate phenotype of both alleles).
Match the type of inheritance with the trait. ABO blood groups
codominance (the heterozygous genotype AB, results in equal expression of both alleles).
Match the type of inheritance with the trait. Hypercholesterolemia
incomplete dominance (the heterozygous genotype, Nd, results in moderately elevated blood cholesterol levels.)
Two parents have wavy-hair (Hh) , and are expecting their first child. What is the chance that their child will have: (Hair texture is Incomplete dominant inheritance so the heterozygote is an intermediate phenotype) wavy hair Hh
50%
Two parents have wavy-hair (Hh) , and are expecting their first child. What is the chance that their child will have: (Hair texture is Incomplete dominant inheritance so the heterozygote is an intermediate phenotype) straight hair HH
25%
Two parents have wavy-hair (Hh) , and are expecting their first child. What is the chance that their child will have: (Hair texture is Incomplete dominant inheritance so the heterozygote is an intermediate phenotype) curly hair hh
25%
Two parents are heterozygous for hypercholesterolemia (Nd) having blood cholesterol levels two times the normal level. What is the probability that their child will be unaffected (NN) by this disorder?
25%
In a paternity suit the alleged father has blood type AB, the mother blood type O and the baby has blood type O. Could this alleged father be the biological father?
No. The alleged father could have either a baby with type A (AO) or type B (BO) but NOT type O (OO).
What is an "X-linked gene"?
An X-linked gene is a gene located on the X chromosome.
A normal man (XNY) and a carrier mother (XNXd) would like to know the chance that their SON will have hemophilia?
50%
Two normal parents with the following genotypes: (XN Xd , XN Y) :
XN= Normal allele
Xd= defective allele/ muscular dystrophy allele (X-linked )
Which parent is responsible for passing the muscular dystrophy allele to their son?
The mother passes the Xd allele to her son.
Two normal parents with the following genotypes: (XN Xd , XN Y) :
XN= Normal allele
Xd= defective allele/ muscular dystrophy allele (X-linked ) What is the chance that their SON will have muscular dystrophy?
50% (XdY)
Two normal parents with the following genotypes: (XN Xd , XN Y) :
XN= Normal allele
Xd= defective allele/ muscular dystrophy allele (X-linked ) What is the chance that their daughter will be a carrier of the muscular dystrophy allele (XNXd)?
50% (XNXd)
A colorblind man (XdY) marries a woman who has normal vision and is NOT a carrier.(XN XN):
XN= normal vision allele
Xd= colorblind allele (X-linked) What is the chance that their daughter will be colorblind?
0% (Xd Xd)
A colorblind man (XdY) marries a woman who has normal vision and is NOT a carrier.(XN XN):
XN= normal vision allele
Xd= colorblind allele (X-linked) What is the chance that their daughter will have normal vision and will be a carrier?
100% (XNXd)
A colorblind man (XdY) marries a woman who has normal vision and is NOT a carrier.(XN XN):
XN= normal vision allele
Xd= colorblind allele (X-linked) What is the chance that their SON will be colorblind?
0% (XdY)
A colorblind man (XdY) marries a woman who has normal vision and is NOT a carrier.(XN XN):
XN= normal vision allele
Xd= colorblind allele (X-linked) What is the chance that their SON will have normal vision?
100% (XNY)
In order for a woman to be color-blind (XdXd) which one could NOT be her parent's genotype?
(A colorblind daughter must inherit one Xd allele from each of her parents.)
a. Xd Y
b. XNY
c. Xd Xd
d. XNXd
b. XNY
Which of the following disorders is NOT X-linked?
a. Hemophilia
b. Colorblindness
c. Duchennes muscular dystrophy
d. Hypercholesterolemia (incomplete dominant disorder)
d. Hypercholesterolemia (incomplete dominant disorder)
A mother has Dwarfism which is a dominant disorder (Dn). The father is normal stature .(nn) What is the chance that their child will be a dwarf ( Dn)?
50%
A mother has Dwarfism which is a dominant disorder (Dn). The father is normal stature .(nn) What is the chance that their child will be normal stature (nn)?
50%
Both the mother and father have Dwarfism. (Dn) What is the chance that their child will be born a dwarf with the following genotype, Dn ?
50%
(The DD genotype results in a lethal phenotype so that the baby dies before birth.)
Both the mother and father have Dwarfism. (Dn) What is the chance that their child will be normal stature (nn)?
25%
Neither parent has Dwarfism but one of their children is a dwarf. (1/100,000 chance that two normal stature parents have a Dwarf child) How could this happen?
Spontaneous mutation in either the father's sperm or the mother's egg or a spontaneous mutation in the fertilized egg soon after fertilization.
Nancy Wexler interviewed thousands of people in a small town in Venezuela whose family members had a high indicence of Huntington's disease. She drew a chart to display the presence or absence of the disease trait in the affected families. This chart , "family tree" is known as a
pedigree
If Huntington's disease is always fatal why does it persist in the population?
A person only developes symptoms of the disease after age 30yr, so they could have already had children by then and unknowingly passed the mutation to their children.
All of the following are dominant disorders EXCEPT:
a. Huntington's disease
b. Hemophilia (X-linked disorder!)
c. Dwarfism
b. Hemophilia (X-linked disorder!)
Two normal parents are told by a genetic counselor that they are both carriers of cystic fibrosis and have the genotype, Nd. (neither parent has the disease cystic fibrosis)
What is the probability that their child will have the disease cystic fibrosis? (dd)
(dd) 25%
Two normal parents are told by a genetic counselor that they are both carriers of cystic fibrosis and have the genotype, Nd. (neither parent has the disease cystic fibrosis)
What is the chance that their child will be a carrier of the cystic fibrosis allele? (Nd)
(Nd) 50%
Two normal parents are told by a genetic counselor that they are both carriers of cystic fibrosis and have the genotype, Nd. (neither parent has the disease cystic fibrosis) What is the chance that their child will be unaffected and not a carrier of the CF allele? (NN)
(NN) 25%
The parents in question #1 would like to have a child that does not have cystic fibrosis. What medical technique could they use to have a child that is free of the cystic fibrosis allele?
In vitro fertilization and preimplantation genetic diagnosis. The sperm and egg are fertilized in a petri dish in the lab and then the embryos are allowed to divide to the 8 cell stage at which time a single cell is removed form each embryo and is tested for the presence of the CF allele. Those embryos that do not carry the CF allele are reimplanted into the mother's body and will develope into a baby that does not have cystic fibrosis.
An albino woman (dd) marreis a normal pigment man who does not have the albino allele. (NN) What is the probability that their child will have normal pigment and will not be a carrier?(NN)
(NN) 0%
An albino woman (dd) marreis a normal pigment man who does not have the albino allele. (NN) What is the probability that their child wil be an albino?(dd)
(dd) 0%
An albino woman (dd) marreis a normal pigment man who does not have the albino allele. (NN) What is the probability that their child will be a carrier of the albino trait? (Nd)
(Nd) 100%
An albino woman (dd) marreis a normal pigment man who does not have the albino allele. (NN) What is the phenotype of a child that is a carrier of the albino trait? (Nd)
(Nd) Normal pigment in skin, hair and eyes.
An albino (dd) man marries a normal pigment woman (Nd) What is the probability that they will have an albino child?(dd)
(dd) 50%
An albino (dd) man marries a normal pigment woman (Nd) What is the probability that their child will be free of the albino allele? (NN)
(NN) 0%
An albino (dd) man marries a normal pigment woman (Nd) What is the probability that they will have a normal pigment child who is a carrier of the albino allele? (Nd)
50% (Nd)
All of the following disorders are inherited in a recessive pattern EXCEPT:
a. Cystic fibrosis
b. Sickle Cell Anemia
c. Dwarfism
d. Albinism
c. Dwarfism (dominant disorder)
Huntington's disease
dominant disorder
Cystic fibrosis
recessive disorder
Duchenne muscular dystrophy
X-linked disorder
Achondroplasia (dwarfism)
dominant disorder
Red-Green color blindness
X-linked disorder
Hemophilia
X-linked disorder
Sickle Cell Anemia
recessive disorder
Albinism
recessive disorder
Tay Sachs disease
recessive disorder
true or false Carriers of Sickle cell trait (Nd) are protected against the parasite that causes malaria.
true The malaria parasite spends part of its life cycle inside human red blood cells. When the malaria parasite enters the red blood cell of a person with sickle cell trait, the cell sickles and ruptures, killing the parasite before it can reproduce.
If certain diseases such as sickle cell anemia and cystic fibrosis are lethal, why do the alleles for the disorder persist in a population?
If being a carrier for a disorder protects the person from an infectious disease so that those individuals that are carriers survive the infection and eventually pass the disorder allele to their children.
This is called heterozygote advantage since carriers (Nd) are heterozygous for the disorder allele and have a selective advantage in being more likely to survive an infectious disease that is common to that area.
Examples of heterozygote advantage are :
a. Carriers of sickle cell trait Nd are protected against the parasite that causes malaria.
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