B = Allele for Normal Color Vision

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. Take one pedigree chart from your assigned folder – put your names on it

2. Read the background information on the green sheet

3. Read the questions/instructions on the white sheet in your folder

4. Answer all questions on your pedigree chart paper (half-sheet)

5. 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