February 22nd, 2013
Bellringer:
1. In humans, red-green color blindness is a recessive, sex-linked trait. The
chromosomes and alleles associated with color blindness are represented
in this chart.
X = X chromosome
Y = Y chromosome
B = allele for normal color vision
b = allele for color blindness
Which child could NOT be born to these parents: a female (XBXb) and a
male (XBY)?
a. Color-blind daughter
b. Color-blind son
c. Daughter with normal color vision
d. Son with normal color vision
DLTs:
1. I can infer the parental genotypes and phenotypes from offspring data
presented in pedigree charts.
2. I can construct and interpret punnett squares and pedigree charts to
predict phenotypic and genotypic ratios and probabilities for different
crosses.
3. I can describe the mode of inheritance in commonly inherited disorders, by
evaluating pedigree charts.
Today:
1. Put quiz answers into clickers (if not done yet)
2. Create a class rubric for presentations
3. Finish working on presentations for the “You be the Genetic Counselor”
Activity
4. Presenting findings on Monday
“You be the Genetic Counselor” Group Activity
1.
2.
3.
4.
5.
Take one pedigree chart from your assigned folder – put your names on it
Read the background information on the green sheet
Read the questions/instructions on the white sheet in your folder
Answer all questions on your pedigree chart paper (half-sheet)
Prepare a short (3-5 minute) presentation of your disease/disorder and
your findings
a. This should include background information, mode of inheritance,
facts, pictures, etc.
6. Present your findings to the class using the class created rubric as a guide
Huntington’s Disease
albinism
achondroplasia
Albinism
Albinism (from Latin albus, "white"; see extended etymology, also called
achromia, achromasia, or achromatosis) is a congenital disorder characterized by
the complete or partial absence of pigment in the skin, hair and eyes due to
absence or defect of an enzyme involved in the production of melanin. Albinism
results from inheritance of recessive gene alleles and is known to affect all
vertebrates, including humans. While an organism with complete absence of
melanin is called an albino ( /ælˈbaɪnoʊ/,[1] or /ælˈbiːnoʊ/),[2] an organism
with only a diminished amount of melanin is described as albinoid.[3]
Albinism is associated with a number of vision defects, such as photophobia,
nystagmus and astigmatism. Lack of skin pigmentation makes for more
susceptibility to sunburn and skin cancers.
Huntington's disease
Huntington chorea
Last reviewed: April 30, 2011.
Huntington's disease is a disorder passed down through families in which nerve
cells in certain parts of the brain waste away, or degenerate.
Causes, incidence, and risk factors
Huntington's disease is caused by a genetic defect on chromosome 4. The defect
causes a part of DNA, called a CAG repeat, to occur many more times than it is
supposed to. Normally, this section of DNA is repeated 10 to 28 times. But in
persons with Huntington's disease, it is repeated 36 to 120 times.
As the gene is passed down through families, the number of repeats tend to get
larger. The larger the number of repeats, the greater your chance of developing
symptoms at an earlier age. Therefore, as the disease is passed along in families,
symptoms develop at younger and younger ages.
There are two forms of Huntington's disease.
•
The most common is adult-onset Huntington's disease. Persons with this
form usually develop symptoms in their mid 30s and 40s.
•
An early-onset form of Huntington's disease accounts for a small number of
cases and begins in childhood or adolescence.
If one of your parents has Huntington's disease, you have a 50% chance of
getting the gene for the disease. If you get the gene from your parents, you will
develop the disease at some point in your life, and can pass it onto your children.
If you do not get the gene from your parents, you cannot pass the gene onto
your children.
Hypercholesterolemia
Hypercholesterolemia is the presence of high levels of cholesterol in the
blood.[1] It is closely related to the terms "hyperlipidemia" (elevated levels of
lipids in the blood) and "hyperlipoproteinemia" (elevated levels of lipoproteins
in the blood).[1]
Cholesterol is a specific fat molecule, see the diagrammatic structure at the right.
It is one of the several fat molecules which all animal cells utilize to construct
their membranes and is manufactured within all animal cells. It is also the basis
of all the steroid hormones.
Elevated cholesterol in the blood involves abnormalities in the protein particles
which transport all fat molecules, including cholesterol, within the water of the
bloodstream. This may be related to diet, increased body fat, genetic factors
(such as LDL receptor mutations in familial hypercholesterolemia) and the
presence of other diseases such as diabetes and an underactive thyroid. The type
of hypercholesterolemia depends on which type of particle (such as low-density
lipoprotein) is present in excess.[1]
Some have proposed that hypercholesterolemia can be treated by reducing
dietary cholesterol intake. Administration of certain medications which reduce
cholesterol production or absorption is usually more effective. Rarely other
treatments including surgery (for particular severe subtypes) are performed.
•
Causes
Hypercholesterolemia is typically due to a combination of environmental and
genetic factors.[2] Environmental factors include: obesity and dietary choices.[2]
Genetic contributions are usually due to the additive effects of multiple genes
however occasionally may be due to a single gene defect such as in the case of
familial hypercholesterolaemia.[2] A number of secondary causes exist including:
diabetes mellitus type 2, obesity, alcohol, monoclonal gammopathy, dialysis,
nephrotic syndrome, obstructive jaundice, hypothyroidism, Cushing’s syndrome,
anorexia nervosa, medications (thiazide diuretics, ciclosporin, glucocorticoids,
beta blockers, retinoic acid).[2]
Achondroplasia
Achondroplasia is a disorder of bone growth that causes the most common type
of dwarfism.
Causes, incidence, and risk factors
Achondroplasia is one of a group of disorders called chondrodystrophies or
osteochondrodysplasias.
Achondroplasia may be inherited as an autosomal dominant trait, which means
that if a child gets the defective gene from one parent, the child will have the
disorder. If one parent has achondroplasia, the infant has a 50% chance of
inheriting the disorder. If both parents have the condition, the infant's chances
of being affected increase to 75%.
However, most cases appear as spontaneous mutations. This means that two
parents without achondroplasia may give birth to a baby with the condition.
Symptoms
The typical appearance of achondroplastic dwarfism can be seen at birth.
Symptoms may include:
•
Abnormal hand appearance with persistent space between the long and
ring fingers
•
Bowed legs
•
Decreased muscle tone
•
Disproportionately large head-to-body size difference
•
Prominent forehead (frontal bossing)
•
Shortened arms and legs (especially the upper arm and thigh)
•
Short stature (significantly below the average height for a person of the
same age and sex)
•
Spinal stenosis
•
Spine curvatures called kyphosis and lordosis
Red Green Color Blindness
Red green color blindness is by far the most common form of color blindness. An
individual with this form of color blindness is not actually blind to both red and
green at the same time, but rather either red color blind, or green color blind.
The outcome is however the same, an inability to tell the difference between
various hues of red and green.
Red Color Blindness – Protanopia & Protanomaly
Red color blind people can be categorised as follows:
•
Protanopia: the L-cones are missing, or non-functional, resulting in
blindness to the red portion of the spectrum.
•
Protanomaly: The L-Cones are defective, operating below normal capacity
to interfere with a person’s ability to see some shades of red.
People with defective L-cones (protanomaly) do not all suffer the same intensity
of color blindness; some may have quite mild color blindness, whereas some
may have a heavy disability. Interestingly a red color blind person will not only
have trouble distinguishing between red and green hues, but also blue and green
– one could argue that the term red green color blind is somewhat misleading!
Both forms of red color blindness are sex linked, due to the genes responsible for
providing the correct coding to create L-Cones being found in the X chromosome.
As discussed elsewhere on this website, females have two X chromosomes,
where men only have one. A female who receives a defective X chromosome is
likely only to be a carrier – and normally receives it from a color blind father. The
second X chromosome is most likely going to be healthy, and will provide
enough genetic information to ensure all 3 cone types are present in the eye.
Red color blindness is also considered a serious risk factor to drivers. Studies
have found that red color blind individuals had a strong representation among
the group of drivers who have crashed involving traffic lights and brake lights.
Someone who has defective L-cones may still be able to differentiate the colors,
but someone who has no L-cones will only see the red light as a ‘level of
darkness’ and must be extra alert.
Tay-Sachs disease
Last reviewed: November 17, 2010.
Tay-Sachs disease is a deadly disease of the nervous system passed down
through families.
Causes, incidence, and risk factors
Tay-Sachs disease occurs when the body lacks hexosaminidase A, a protein that
helps break down a chemical found in nerve tissue called gangliosides. Without
this protein, gangliosides, particularly ganglioside GM2, build up in cells,
especially nerve cells in the brain.
Tay-Sachs disease is caused by a defective gene on chromosome 15. When both
parents carry the defective Tay-Sachs gene, a child has a 25% chance of
developing the disease. The child must receive two copies of the defective gene - one from each parent -- in order to become sick. If only one parent passes the
defective gene to the child, the child is called a carrier. He or she won't be sick,
but will have the potential to pass the disease to his or her own children.
Anyone can be a carrier of Tay-Sachs, but the disease is most common among
the Ashkenazi Jewish population. About 1 in every 27 members of the Ashkenazi
Jewish population carries the Tay-Sachs gene.
Tay-Sachs has been classified into infantile, juvenile, and adult forms, depending
on the symptoms and when they first appear. Most people with Tay-Sachs have
the infantile form. In this form, the nerve damage usually begins while the baby
is still in the womb. Symptoms usually appear when the child is 3 to 6 months
old. The disease tends to get worse very quickly, and the child usually dies by age
4 or 5.
Late-onset Tay-Sachs disease, which affects adults, is very rare.
Huntington’s Disease
Please complete the following on the half sheet of paper, either on the pedigree
or on the back of the paper:
1.
Under (or right next to) each circle or square in the pedigree, write the
letters representing the genotype of each individual. You and your partner(s)
will have to determine the letters that you will use to represent the alleles.
2. What is the probability that the children of individual number 12 would
have Huntington’s Disease if the father is heterozygous for the disease? (Show a
Punnett square to support your answer)
3. What is the probability that the next child of individuals number 9 & 10
would have Huntington’s Disease?
Albinism:
Please complete the following on the half sheet of paper, either on the pedigree
or on the back of the paper:
1.
Under (or right next to) each circle or square in the pedigree, write the
letters representing the genotype of each individual. You and your partner(s)
will have to determine the letters that you will use to represent the alleles.
2.
What is the probability that the children of individual number 40 would be
albino if the mother is not albino? (show a Punnett square to support your
answer)
3. Why did albinism become more prominent in the individuals representing
the last generation?
Hypercholesterolemia:
Please complete the following on the half sheet of paper, either on the pedigree
or on the back of the paper:
1.
Under (or right next to) each circle or square in the pedigree, write the
letters representing the genotype of each individual. You and your partner(s)
will have to determine the letters that you will use to represent the alleles.
2.
What would be the phenotype of individual 16?
3.
What would be the phenotype of individual 9?
Tay Sachs Disease:
Please complete the following on the half sheet of paper, either on the pedigree
or on the back of the paper:
1.
Under (or right next to) each circle or square in the pedigree, write the
letters representing the genotype of each individual. You and your partner(s)
will have to determine the letters that you will use to represent the alleles.
2.
Explain why individuals 3, 6, and 11 probably never had children?
3. What is the probability that the children of individual number 14 would
have Tay Sachs if the father does not have any members of his family with the
disease? (show a Punnett square to support your answer)
Red-Green Colorblindness:
Please complete the following on the half sheet of paper, either on the pedigree
or on the back of the paper:
1.
Under (or right next to) each circle or square in the pedigree, write the
letters representing the genotype of each individual. You and your partner(s)
will have to determine the letters that you will use to represent the alleles.
2.
What is the phenotype of individual number 20? of individual number 17?
3. If individual number 23 has children with a man having normal color vision,
what is the probability that they could have a colorblind son? a colorblind
daughter?
Achondroplasia:
Please complete the following on the half sheet of paper, either on the pedigree
or on the back of the paper:
1.
Under (or right next to) each circle or square in the pedigree, write the
letters representing the genotype of each individual. You and your partner(s)
will have to determine the letters that you will use to represent the alleles.
2.
What is the phenotype of individual number 9?
3. If individual number 11 has children with a woman who does not have
Achondroplasia, predict the genotypes and phenotypes of their offspring. (show
a Punnett square to support your answer).