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Sometimes,
things don’t always
follow Mendel’s Laws
Write the following in your
notes: I can predict an
outcome of a cross using
incomplete dominance and
codominance.
1.
Science Starter
2
2.
3.
3
1.
4
2.
3.
5
Codominance
In some instances, certain traits are codominant. That means that one
trait cannot win out over the other form of the trait. In the offspring,
both traits show up equally.
Genotype RW
Genotype WW
Genotype RR
With Codominance….
BB
BW
WW
Yo, girl.
‘Sup?
WW
RR
RW
In cows, this
red & white
pattern is
known as
roan.
T
BT
TT
BT
BT
A cross between a tan
cat (TT) and a black
cat (BB) results in a
third phenotype we
refer to as a “Tabby.”
Blood also provides us with a great
example of co-dominance. There are
four types of blood: A, B, AB, and O.
A & B are co-dominant while O is
always recessive (though seldom
written as a lower case letter.) If a
person with homozygous B blood
crosses with a person with
homozygous A blood, the genotypes
for the offspring will be AB.
o
o
B
o
A
A
A
A
B
B
o
A
B
o
o
o
Type O blood is like any other recessive trait. The only way a child
can be born with type O blood is if both parents have at least one
recessive O allele in their genotype.
The different types of blood are not necessarily interchangeable. If
you give someone the wrong blood during a transfusion, it can
result in serious medical problems and potentially even death.
When incompatible blood is mixed it clumps together and forms
clots.
A person with
blood Type A can
receive Type A
blood and Type O
blood. Why is
Type O not a
threat to the
body?
It does not have
antigens, so it is
not read as a
threat.
A person with
blood Type B can
receive Type B
blood and Type O
blood. Why is
Type O not a
threat to the
body?
It does not have
antigens, so it is
not read as a
threat.
A person with
blood Type AB
can receive Type
AB blood, Type A
blood, Type B
blood, and Type
O blood. A
person with Type
AB is known as a
universal
recipient.
A person with
blood Type O can
only receive
blood from
others with blood
type O. However,
since any
recipient can
receive O blood,
a person with O
blood is called a
universal donor.
CLOSING
1. If a child has type O blood, what must be true about the
parents?
a. both parents must have genotype oo
b. at least one of the parents must have genotype oo
c. both parents must have at least one recessive o allele
d. at least one parent must have one recessive o allele
2. If Kristina has blood AO and her husband has blood type BB,
what are the possible blood genotypes for their children?
a. BO, AB
b. B, BB
c. AB, AA
d. all of the above
3. Ava’s parents both have type O blood. What must
Ava’s blood type be?__________
a. it depends on the genotypes of her parents
b. Ava’s parents must be oo, so she must also have oo.
c. Ava could have any blood type because O is the universal
blood type
d. Ava can have any blood type except O
4. Which of the following is a genetic characteristic that Kaila could have
inherited from her parent?
A. scars from a bicycle accident
B. the color of his hair
C. the ability to bowl well
D. his handwriting ability
5. Shawn and Charlie are exploring a remote part of the Taklimakan Desert
when they discover a new species of beetle. Of the beetles they observed,
about 723 had long jaws and 250 had short jaws. What can we infer about
the genes for jaw shape?
a. The form of the gene for long jaws is recessive
b. The form of the gene for short jaws is co-dominant
c. The forms of the gene for long jaws is dominant
d. There is no way of telling from these observations
Day 2
I can predict an outcome of a cross using
incomplete dominance and codominance.
1.
2.
Science Starter
16
3.
4.
17
5. In humans, the form of the gene for brown
hair (B) is dominant over the form of the gene
for red hair (b). If two people with brown hair
have children, what can we predict about
their offspring?
1.
2.
19
3.
4.
20
5. In humans, the form of the gene for brown
hair (B) is dominant over the form of the gene
for red hair (b). If two people with brown hair
have children, what can we predict about
their offspring?
Since we don’t know the exact
phenotype of the parents, we
cannot say for sure that the
offspring will have brown hair. If
both parents have genotype Bb,
for example, then there is a 25%
chance that an offspring will
have a different hair color. The
best we can say is that the
offspring will most likely be born
with brown hair.
Incomplete Dominance
In other instances, two forms of a gene have incomplete dominance. That
means that when the two genes compete, neither wins outright. Instead, the
phenotype of the offspring present a mixture of the two traits.
For example, if in a particular flower species Red and White were co-dominant, a
mix of the two would result in pink flowers, white flowers with red stripes, or red
flowers with white stripes. Since the colors Red and White are co-dominant or
have incomplete dominance over each other, the genotype for a pink flower is
NOT written as P, but as RW.
A Punnett square showing what would
happen if you crossed a red flower
with a white flower would look like this.
R
R
W
RW
RW
W
RW
RW
RW does not mean that each of the
offspring has both red and white in the
flowers. That would be codominance.
Incomplete dominance means that
a blend of the two colors shows up
as the phenotype. In this case, red
and white blend to make pink. The
phenotype for genotype RW is pink.
Cross of two purple flowers
RB X ____
RB
____
 What are gamete possibilities?
 genotype ratio
R
25% RR 50% RB 25% BB
RR
 phenotype ratio
R
25% red 50% purple 25% blue

Can you have a
heterozygous red or no
hybrid blue flower? ___
B
red
RB
purple
B
RB
purple
BB
blue
1. Suppose the allele for black fur (B) and white fur (W) have incomplete
dominance in a small rodent. What percentage of the offspring will be gray
if a black rat mates with a white rat?
100%
2. Suppose the allele for black fur (B) and white fur (W) are codominant in
a small rodent. What percentage of the offspring will be white if a black rat
mates with a white rat? This is a trick question….;)
3. A Punnett square showing what would happen if
you crossed two pink flowers would look like this.
R
W
R
RR
RW
W
RW
WW
How many of these offspring would be pink? 50%
How many would be white? 25%
How many would be red? 25%
4. A tabby cat is a cross between a black
cat and a tan cat. The tabby cat’s
coloring demonstrates__________________.
a. That black is dominant over tan
b. That tan is dominant over black
c. That black and tan are co-dominant
d. That black and tan have incomplete dominance
5. A cross between white snapdragons (W) and red snap dragons (R)
produces snapdragons that are pink. What would be the genotype
for the pink snapdragons?
a. PP
b. WP
c. RW
d. PR
6. This is an example of:
a. Incomplete dominance
b. Complete dominance
c. Co-dominance
d. Co-recessive traits
7. Josh has a square head like Frankenstein that is caused by a
recessive form of the head-shape gene (o). Oval shaped heads
(O) are dominant. Josh doesn’t like his Frankenstein head, so
he wants to make sure that none of his children are born with
this trait. What must he do to ensure none of his children have
Frankenstein head?
a. Only marry and have children with a woman who is heterozygous for
oval head.
b. Only marry and have children with a woman who is homozygous for oval
head.
c. Marry and have children with any woman who has the oval head
phenotype.
d. Not worry because recessive traits can only be passed down if the
woman carries them
8. Haye’s parents have blood genotypes AO and
AB. Hayes could have any blood type except:
a. A
B. B
c. AB
d. O
9. Mendel’s experiments demonstrated that any time two hybrids are
cross- bred the recessive trait will appear in the phenotype of
___________% of the offspring.
a. 100%
b. 75%
c. 50%
d. 25%
10. The four blood types are _________________________
a. A, C, B, O
b. A, B, O, OO c. A, B, AB, O
d. A, B, C, and D
11. Which blood type(s) are dominant?
a. A, O
b. B, O
c. A, B
d. just O
12. If the genes for black (B) and white (W) feathers on a particular species of
bird show incomplete dominance, what would be the genotype for gray
feathers?
a. GG
b. BG
c. BW
d. WG
13. If a male pigeon has gray feathers and his mate has black feathers, what
phenotypes are possible in their children? (B- Black, W-White)
a. black, gray, or white feathers
b. black or white feathers
c. black or gray feathers
d. white or gray feathers
14. Werewolves who are purebred for the werewolf gene (WW) can turn into
werewolves any time they want to. Werewolves who are hybrid for the
werewolf gene (Ww) can only change into werewolves on the night before,
during, and after a full moon. If a female purebred werewolf breeds with a
hybrid male and they have 12 pups, how many of the pups will be
purebred werewolves?
a. 0
b. 2
c. 3
d. 6
15. Mr. Chip enjoys breeding orchids because of the enormous
challenge involved. Part of the fun is trying to cross orchids with
different colored flowers to create new hybrids. In one experiment,
he bred a maroon orchid with a gold
orchid and produced orchids with this
color and pattern which he called Royal
Benjamin. This pattern demonstrates:
a.
Incomplete dominance
b.
Co-dominance
c.
Complete dominance
16. If Mr. Chip wanted to breed and sell only Royal Benjamin hybrid
orchids, what should he do to ensure he produces the most Royal
Benjamin hybrids possible?
a.
Breed Royal Benjamins with only gold orchids.
b.
Breed Royal Benjamins with only maroon orchids.
c.
Breed Royal Benjamins only with Royal Benjamins.
d.
Breed only gold orchids with maroon orchids.
17. When a farmer cross breeds a purebred white cow with a purebred red
cow, this color pattern (known as roan) results:
What can we infer about the genes
controlling fur color in this breed of
cattle?
a. Red and white are co-dominant.
b. Red and white have incomplete
dominance.
c. White is dominant over red since
more of the cow is white than red.
d. Red is dominant to white since the
head of the cow is mostly red.
Special Note:
Many cattle and horse breeders consider the roan pattern an example of
incomplete dominance. I am not going to go into how or why, but if you
see it listed as such, go with it.
18. Bubba has type A blood. His wife, Betty-Lou, has type B blood. Their
daughter, Violula has type O blood. How is this possible?
a.
Bubba has type AA and Betty Lou has type Bo.
b.
Bubba has type Ao and Betty Lou has type BB
c.
Bubba has type Ao and Betty-Lou has type Bo
d.
There is no way for the daughter to have type O blood.
19.Two horses that are gray-blue in color are bred. Over time, these two
horses produced foals that were black, white, and gray-blue.
20. What can we infer about genes that regulate fur color in this breed of
horse?
a. Black and white have incomplete dominance
b. Black is dominant over white
c. Black and white are co-dominant
d. Black is recessive to white
Day 3
Write in your notes:
I can recognize that selective breeding can
produce plants or animals with desired traits.
1.
Science Starter
2.
35
3. In the alien species known as dwarks,
pig-noses (P) are dominant while pointy
noses (p) are recessive. If a certain dwark
(Dylan) has genotype Pp, what type nose
does he have?
a. Pointy
b. Pig-nose
c. A mix between pointy and pig-nose
d. A completely different nose shape
36
4. In Gregor Mendel’s pea experiments, the purple flower
color (P) was dominant over the white flower color. What
genotype will result in the purple flower color?
a. PP
b. Pp
c. pp
d. both PP and Pp
5. The original vampires from Transylvania were purebred
vampires (VV) meaning they were born vampires. A human
bitten by a purebred vampire turns into a vampire-human
hybrid (Vv). If two of these vampire hybrids (Cayleigh &
Jake) breed, what percentage of their offspring will be born
purebred vampires?
a. 0%
b. 25%
c. 75%
d. 100%
37
1.
2.
38
3. In the alien species known as dwarks,
pig-noses (P) are dominant while pointy
noses (p) are recessive. If a certain dwark
(Reginald) has genotype Pp, what type
nose does he have?
a. Pointy
b. Pig-nose
c. A mix between pointy and pig-nose
d. A completely different nose shape
39
4. In Gregor Mendel’s pea experiments, the purple flower
color (P) was dominant over the white flower color. What
genotype will result in the purple flower color?
a. PP
b. Pp
c. pp
d. both PP and Pp
5. The original vampires from Transylvania were purebred
vampires (VV) meaning they were born vampires. A human
bitten by a purebred vampire turns into a vampire-human
hybrid (Vv). If two of these vampire hybrids (Cayleigh &
Jake) breed, what percentage of their offspring will be born
purebred vampires?
a. 0%
b. 25%
c. 75%
d. 100%
40
Selective Breeding
Suppose a farmer has two types of corn. One type has small ears but big kernels. The
other type has big ears but tiny kernels. The farmer may plant the two types of corn next
to each other so that the pollen from each type of corn can fertilize the other type. What
the farmer hopes is that some of the corn plants will develop ears of corn that are both
big and that have big kernels too.
This type of genetic cross pollination is known as selective breeding. Selective
breeding is the process where humans try to isolate certain favorable traits in
plants and animals by crossbreeding animals and plants of the same species but
ones that have different forms of certain genes.
Selective breeding has been done for thousands of years with both plants and animals.
All domesticated cattle, horses, dogs, and cats are products of selective breeding. That
is why there are so many “breeds” of these animals. Humans cross bred these animals
in an attempt to isolate desired traits. Dogs such as Dachshunds and Bassett Hounds
are a result of hunters trying to breed the “short leg” version of the gene for leg length
into another breed of dog so that they could have a hunting dog that was short enough
to chase rabbits through the maze of rabbit trails in a thicket of woods.
SELECTIVELY-BRED DESIGNER FRUITS
USDA created
Carrots
PINEBERRY
PLUOT
GOLDEN
WATERMELON
Double Muscling- Good Science or Animal Cruelty (STOP video at 3:30.)
http://www.youtube.com/watch?v=rW54_vM9SF0
1. Mr. Moore grew two types of tomatoes in his back yard. One produced
lots of small, sweet tomatoes. The other didn’t grow as many tomatoes
but the ones that did grow were much larger. What might Mr. Moore hope
to accomplish by cross-breeding these two types of tomatoes?
By crossing these two tomato plants, he may eventually create a new hybrid
tomato plant that produces lots of large, sweet tomatoes.
2. What process did Mr. Moore use to create his hybrid in question #1?
Selective breeding.
3. Donovan is a rose grower. He grows mostly red roses, but occasionally
some of his roses turn out pure white due to a recessive form of the flower
color gene. Lots of people in his area produce red roses (and the few white
roses that grow from time to time), but none of them grow only white
roses. Donovan decides he can do better if he only produces white roses
since there is less competition. What would he need to do in order to
ensure his plants produced only white roses?
Only breed white roses with other white roses.
4. Which of the following genetic traits might cattle farmers be interested in
selectively breeding into their cattle?
a. larger size (more meat per animal)
b. less resistance to certain parasitic diseases
c. larger ears to keep them cooler in summer
d. muscle structure that allow them to run faster
5. In the sport of horse racing, race horse owners may pay $1,000,000 for the right
to allow one of their horses to breed with a champion race horse. Their hope is
that some of the genes that helped the champion become so successful will be
selective breeding.
passed on to the offspring. This is an example of _________________________
6. The tiny Chihuahua and the Great Dane are both dogs. What is the best
explanation for why these two breeds of dog differ so greatly?
First of all, Chihuahuas aren’t dogs-they
are rats that bark.
Now that we have that out of the way, the
answer is both dogs have been selectively
bred by humans for specific physical traits.
7. In Nepal, male Yaks are bred with female domestic cows to create a hybrid
animal that has good tasting meat and that can survive the high altitudes and
selective breeding
cold temperatures of Nepal. This is an example of ____________________.
Day 4
Write in your notes:
I can explain how genetic modification differs
from selective breeding.
1.
Science Starter
48
2. Unattached or “free” earlobes (E) are dominant. Attached
earlobes (e) are recessive. Justin Bieber is heterozygous
for unattached earlobes. Medeline has attached earlobes.
What is the probability that a child of theirs will have
attached earlobes?
a. 0 %
b. 50%
c. 75%
d. 100%
3. Kinsey and Caleb both have free earlobes. What
prediction can we make about children they may have?
a. The children will most likely have free earlobes
b. The children will definitely have free earlobes
c. The children will most likely have attached earlobes
d. The children will definitely have attached earlobes
49
1.
50
2. Unattached or “free” earlobes (E) are dominant. Attached
earlobes (e) are recessive. Justin Bieber is heterozygous
for unattached earlobes. Medeline has attached earlobes.
What is the probability that a child of theirs will have
attached earlobes?
a. 0 %
b. 50%
c. 75%
d. 100%
3. Kinsey and Caleb both have free earlobes. What
prediction can we make about children they may have?
a. The children will most likely have free earlobes
b. The children will definitely have free earlobes
c. The children will most likely have attached earlobes
d. The children will definitely have attached earlobes
51
Genetic ModificationGenetic modification refers to the science of gene manipulation. Genetic
manipulation is far more precise that selective breeding. Scientists have
discovered ways of removing particular genes or sections of DNA from one
organism and seeding or planting those genes in another organism. This
practice is most often done in agriculture. For example, scientists have taken
the genes from some plants and seeded these genes into agricultural crops.
Scientists have been able to develop hybrid crops. They have been able to
develop corn that is more drought and pest resistant, tomatoes that have more
vitamins, and rice and soybeans that have more nutritional value. The two
organisms do not have to be the same species. In fact, sometimes the species
are nothing alike at all.
Genetic modification has resulted in a huge increase in the amount of food that
can be grown. Many scientists see genetic modification as one means for
solving hunger in many parts of the world. Genetic modification is not without
its critics, however. Many people are concerned that manipulating genes can
cause health problems in humans. Others believe that changing the genetics of
corn can lead to problems with the corn genome.
Genetically
modified
crops can
produce
better
yielding and
larger fruits
like this
eggplant…
Future Rice Shortage
Rice is the most important food source for billions of the world’s population.
Unfortunately, as the population in these parts of the world continues to explode,
the amount of area where rice is grown has not increased. If fact, it has
decreased. For every one billion people added to the world’s population, 100
million tons of rice (paddy) need to be produced more annually. The increase in
demand for rice coupled with the lack of increase in the supply also causes the
price of rice to rise---something a poor population cannot adjust to. Where will
this rice come from?
Enter the genetically engineered “Super Rice.” Green Super Rice is
actually a mix of more than 250 different potential rice varieties and
hybrids variously adapted to difficult growing conditions such as
drought and low inputs, including no pesticide and less fertilizer, and
with rapid establishment rates to out-compete weeds, thus reducing
the need for herbicides.
Result:
Green Super Rice
• yields more tons of rice per acre
•Can grow in places where rice could not previously grow
•Requires fewer chemicals to control weeds and damage from insects
•Contains more important vitamins like Vitamin A, zinc, and other nutrients
which can dramatically decrease health issues related to malnutrition.
1. Genetic scientists at the University of Georgia crossed two breeds of cotton
to create a cotton hybrid that has the insect resistance of one of the cotton
parents and the drought resistance of the other parent. This is an example of
_______________.
a. selective breeding
b. genetic modification
c. automated breeding
2. A plant that grows wild in the Sonoran desert is resistant to most kinds of
insects. Agricultural scientists were able to isolate the gene in the plant that
gives it insect resistance and insert that gene into a variety of wheat to
produce an insect-resistant wheat. This is an example of what genetic
process?
a. selective breeding
b. genetic modification
c. automated breeding
3. McIntosh apples are known for their crisp, sweet/tart flavor. McIntosh apple
trees need about 800 chill hours in order to produce fruit the next year so they
cannot grow in the Deep South. Certain varieties of crabapples need only 200
chill hours, but the fruit is small and does not have a very good taste. What
might an apple grower hope to achieve by selectively breeding the McIntosh
with the crabapple?
The development of a hybrid apple that tastes great and requires only about
200-500 chill hours.
56
4. Buffalo (American Bison) are able to tolerate both hot and cold temperatures but
their meat is not considered by many people to be as tender or as tasty as beef.
Cattle generally have more tender, tasty meat, but the quality of their meat can be
severely compromised if the cattle are exposed to wide fluctuations in temperature.
Ranchers have cross bred cattle with buffalo/bison. What would be the ideal
characteristics ranchers would want to isolate in the “Beefalo” hybrid?
The ideal hybrid animal would have the
tnederness of beef and the ability to tolerate
a wide range of temperatures without
damaging meat quality.
5. Seth raises Mountain Sheep for their wool. About 75% of the sheep
are Golden (G) while 25% are brown (b). Carter comes to Seth’s town one
day and tells him he has a huge market for brown wool clothing in Paris
and will take all the brown wool Seth can produce. Not only that, but
Carter says he will pay double for brown wool. What can Seth do to
produce more brown sheep?
Only cross-breed the brown sheep with other brown sheep.
6. Tomatoes selectively bred to grow in the relatively arid climates of Arizona
will most likely not grow well in areas of high humidity like Georgia or
Florida because fruit attacking fungi and bacteria survive so well here. How
might scientists or tomato growers try to enhance the Arizona tomato so
that it can grow successfully in Georgia?
Scientists can try to cross-breed a tomato that has resistance to fungi with
other tomatoes to produce a hybrid tomato with the fungi resistant trait.
Scientists might also genetically modify a tomato by inserting a fungiresistance gene from some other breed of tomato or even another species of
plant into the type of tomato growers wish to grow in Georgia.
7. Which of the following adaptations would be desirable for a farmer to
selectively breed into a crop of corn?
a. insect resistance
b. drought tolerance
c. higher vitamin content
d. all of the above
8. In Maine, brook trout and salmon are cross-bred to produce a hybrid called
a splake. In the south, small ponds are often stocked with bluegill hybrids
that are a cross between a species of sunfish and a bluegill. In the larger
lakes, striped bass are crossed with largemouth bass to produce the hybrid
striped bass. Using your knowledge of hybrids that are crosses between
different species, why might these hybrids be preferred to the purebred fish
when it comes to stocking private ponds?
a. the hybrid species reproduce faster than the purebred species so the pond
fills up with fish quicker
b. the hybrid species are healthier than the purebred species so they survive
better
c. the hybrids taste bad to predators like birds, other fish, and turtles so they
don’t get eaten
d. the hybrids cannot reproduce, so their population can be controlled much
more easily and there is no chance they can take over a pond
Other Rare
Tran-species
Hybrids
Animal Hybrids
A mule is the offspring of
a male donkey and a
female horse
A tigon is a cross
between a male
tiger and a female
lion.
A liger is a cross between a
male lion and a female tiger.
Bactrian (two-hump) camels are native to
the cool steppes of Asia.
Dromedary (one hump)
camels are hot desert
dwellers.
The F1 Bactrian-Dromedary hybrid
camel is bigger, stronger, and
hardier than either of the parents.
Wolf hybrids
Coydogs are crosses
between dogs and
coyotes.
The Cama is the result of breeding a
Llama to a Camel.
Parents in background of picture.
The Zebroid is the
result of breeding
a female Horse and a
male Zebra.
The Zedonk / Zonkey is
the result of breeding
a female Donkey and
male Zebra.
Day 5
Write in your agenda:
I can recognize that changes in DNA (mutations)
can result changes in organisms.
1. These control individual genetic traits:
a. genes
b. zygotes
c. autotrophs
d. chromosomes
2. Nearly all cells in complex organisms contain two forms of the same gene
known as ______________.
a. chromosomes b. alleles
c. zygotes
d. homophones
3. If the two alleles in a gene pair are the same form of the gene, that pair is:
a. haploid
b. heterozygous
c. haploid
d. homozygous
4. If the two alleles in a gene pair are different forms of the gene, that pair is:
a. haploid
b. heterozygous
c. haploid
d. homozygous
5. If an organism is heterozygous for a trait, it is also said to be
______________ for that trait.
a. purebred
b. haploid
c. diploid
d. hybrid
6. If an organism is homozygous for a trait, it is also said to be
_______________ for that trait.
a. purebred
b. haploid
c. diploid
d. hybrid
Science Starter
67
Genetic Disorders
When DNA makes a copy of itself, a “checker” makes sure that the new
copy is identical to the original. If a problem is identified in the new
molecule of DNA, the checker either fixes it on the spot or destroys the new
molecule and starts over. This is a very efficient system that almost never
fails. Almost.
A genetic disorder is a disease that is caused by an abnormality in an
individual's DNA. Abnormalities can range from a small mutation in a
single gene to the addition or subtraction of an entire chromosome or
set of chromosomes.
Some genetic disorders are inherited from a parent. Some of the genes that
cause certain diseases are dominant, which means any child born to this
parent stands a very high risk of inheriting the gene and thus contracting
the disease.
In the next few slides, we will review some of the more common types of
genetic disorders and their causes.
http://www.youtube.com/watch?v=xBynH-oCfJM
Chromosomal Disorders
Down Syndrome is a developmental disorder caused by an extra copy
of chromosome 21. If a pair of number 21 chromosomes fails to
separate during the formation of an egg (or sperm), then when the egg is
fertilized by the sperm, the newly formed zygote ends up with three #21
chromosomes instead of two.
Genetic Disorders Caused by Defects on Specific Genes
Recessive Genetic Disorders
Cystic fibrosis is a genetic disorder that affects the respiratory and digestive systems.
People with cystic fibrosis inherit a defective gene on chromosome 7. This causes a
thick mucous to continuously build up in the respiratory and digestive tract.
Sickle cell disease– red blood cells are sickle shaped instead
of round and cannot carry enough oxygen to the body tissues.
Patients with sickle cell disease have a mutation in a gene on
chromosome 11. The heterozygous form protects people from
malaria
Genetic Disorders Caused by a Dominant Form of a
Gene
Huntington's Disease
(HD) is a brain disorder that affects a person's ability
to think, talk, and move. Huntington’s disease is
caused by a dominant gene that is passed on. The
child of an adult with HD stands a 50% chance of
inheriting the HD gene. Symptoms of Huntington’s
Disease may not become noticeable until adulthood.
Huntington’s attacks the nervous system causing
gradual muscle paralysis and loss of cognitive ability
(the ability to use your brain to think, understand
things, process the world, communicate, etc.)
Genetic Disorders Carried on Sex Chromosomes (X or Y)
Red/Green Color Blindness is typically a recessive genetic condition, and it is much
more common in men than in women. It is caused by a defect on the X
chromosome. A male’s sex genotype is XY. A female’s is XX. If a male’s X
chromosome has the red/green color blindness defect he will have the disorder since
there is no normal form of the gene to balance it out. It is extremely rare that a
woman would have the r/g CB defect on BOTH of her X chromosomes. If she has the
red/green color blindness on one of her two X chromosome but the other X
chromosome is normal, she will not experience color blindness. Remember, the
defective trait is recessive, so the normal gene for that trait would win out. In this
case, the woman considered a carrier of the r/g CB even though she does not have
the disorder.
Many people think anyone labeled as "colorblind" only sees black and white -- like
watching a black and white movie or television. This is a big misconception and not
true. It is extremely rare to be totally color blind. There are many different types and
degrees of colorblindness - more correctly called color deficiencies.
Color Blindness test:
WITHOUT SPEAKING, please write
down the numbers contained in the
circles above and below.
Hemophilia is another disorder that is carried on the X
chromosome.
Hemophilia is a bleeding disorder that slows the blood
clotting process. People with this condition experience
prolonged bleeding or oozing following an injury,
surgery, or having a tooth pulled. In severe cases of
hemophilia, heavy bleeding occurs after minor trauma or
even in the absence of injury (spontaneous bleeding).
Serious complications can result from
bleeding into the joints, muscles, brain,
or other internal organs.
A women who is a carrier for hemophilia has the genetic mutation
on one of her X chromosomes as illustrated below. She will have
another non mutated X chromosome that will usually somewhat
compensate for the defect in the other. It is not uncommon for
women who carry the hemophilia gene to have low levels of
clotting factor and have bleeding problems. A man who has
hemophilia has the genetic mutation on his only X chromosome.
He does not have another X chromosome to compensate for the
defect so he will have hemophilia.
X
HX
Y
HXX
daughter
XY
son
X
HXX
daughter
XY
son
1.Eli travels to Africa and falls in love with a beautiful woman from the Congo
Basin. In their discussion about marriage and having a family, she tells him
that she is a carrier of the sickle cell gene (Ss). Eli doesn’t have the sickle cell
trait at all (SS). What percentage of their children stand a risk of inheriting the
“s” allele?
a. 0%
b. 50%
c. 75%
d. 100%
2. Sickle cell is a recessive trait (s). What is the probability that Eli and
his wife will have children who are born WITH sickle cell?
a. 0%
b. 50%
c. 75%
d. 100%
3. What is the probability that one of their children will be a carrier of sickle
cell?
0%
b. 50%
c. 75%
d. 100%
4. Which of the following genetic disorders is a result of inheriting an extra
#21 chromosome?
a. Parkinson’s Disease b. Down Syndrome
c. Sickle Cell Disease
5.Which of the following disorders is a result of a gene that is carried on the X
chromosome?
a. red/green color blindness
b. Down Syndrome
d. Sickle Cell
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