Download Genetic Disorders and Gene Therapy

Biology 30 – Ch. 27 Applied Genetics Notes
Albinism
 Albinism results from inheritance of rare recessive alleles. The condition is known to
affect mammals (including humans), fish, birds, reptiles and amphibians.
 Characterized by a partial or total lack of _______________________ in the eyes,
skin and hair (or more rarely the eyes alone).
 About 1 in 17,000 human beings has some type of albinism, although up to 1 in 70 is
a carrier of albinism genes
 Most forms of albinism are the result of the inheritance of recessive alleles (genes)
passed from both parents of an individual, though some rare forms are inherited from
only one parent.
 The eyes of an animal with albinism occasionally appear red due to the underlying
retinal blood vessels showing through where there is not enough pigment to cover
them. In humans this is rarely the case, as a human eye is quite large and thus
produces enough pigment to lend opacity to the eye, often colouring the iris pale blue.
 Animals that are albino often are hypersensitive to light due to lack of pigment in the
eyes and are extremely susceptible to sunburn and over exposure due to the lack of
melanin in their skin
Misconceptions
 A common misconception is that albinos are ____________; they are in fact fully
capable of _______________________.
 It is also thought by many that people with albinism live short life spans. This is not
true in general, but may be a distorted view of a more reasonable fact that people with
albinism have a higher risk of skin cancer if they do not use proper skin protection
when in the sun.
 It has also been misunderstood that a person or other animal with albinism will
become blind halfway through life; this is incorrect.
Genetic Disorders and Gene Therapy
Chromosomal Diseases
 Gametes have __________________________________________________
 Offspring inherit _____________________________________ a chromosome
 Caused by problems with _______________________________
Nondisjunction
 'Nondisjunction' is the failure of chromosome pairs to _________________________
___________________________________________
 This could arise from a failure of homologous chromosomes to _________________,
or the failure ___________________ to separate during _____________________.
 The result of this error is a cell with an __________________________. When a
single chromosome is lost (2n-1), it is called a _____________, in which the daughter
cell(s) with the defect will have one chromosome missing from one of its pairs.
 When a chromosome is gained, it is called ______________, in which the daughter
cell(s) with the defect will have one chromosome in addition to its pairs.
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Biology 30 – Ch. 27 Applied Genetics Notes
Amniocentesis
Used on pregnant women over __________ years of age
Performed during weeks 15-17 of pregnancy
A needle is inserted into the ____________________
Amniotic fluid with _____________ is removed
A _______________ (genetic profile) of the fetal chromosomes is prepared .
Huntington Disease
• Person gradually loses psychomotor control in adulthood
• Caused by ____________________ allele
Genetics Problem
 A woman (hh) with normal nerve physiology has a child with a man (Hh) who will
develop Huntington Disease.
 What is the chance that the child will have Huntington Disease?
Cystic Fibrosis
 As of 2002, the median age of survival of Canadians with cystic fibrosis is 37 years of
age.
 Since 1989 when Canadian researchers discovered the gene responsible for CF, global
research to find a cure for the disease has brought us closer and closer to a solution.
 The pace of CF science suggests that there is good reason to feel optimistic about the
future.
Genetics Problem
 A woman (Nn) with normal lung physiology has a child with a man (Nn) who has
normal lung physiology (both are carriers of allele)n
 What is the chance that the child will have Cystic Fibrosis?
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Biology 30 – Ch. 27 Applied Genetics Notes
Sickle Cell Disease (Sickle Cell Anemia)
• Red blood cells are sickle shaped, interfering with circulatory system and causing
anemia and pain.
• Caused by a recessive allele
Tay Sach’s Disease
 Tay-Sachs disease is an _____________________ inherited disorder, meaning a child
inherits one copy of the abnormal gene from each parent. The parents do not actually
have the disease, but carry the Tay-Sachs gene and passes it on to the baby.
 Infants usually begin to show signs of the disease between 3 months and 6 months of
age.
 Children with Tay-Sachs disease can become deaf, blind and paralyzed, and usually
die by the age of 5.
 Early signs and symptoms can include: Loss of muscle tone, exaggerated response to
sudden noises, lack of energy, loss of motor skills, such as the ability to roll over,
crawl, reach for things or sit up.
Trisomy-21: Down’s Syndrome
 1 in 600 births, short, broad nose, epicanthal fold, small oral cavity, large, furrowed
tongue, large, irregular teeth, IQs from 20 to 50
Trisomy 13: Patau’s Syndrome
 1 in 20,000 births, sloping forehead, small head & eyes, cleft lip and/or palate, heart
defects, 75% die in first year, 100% by age 6.
Trisomy 18: Edwards’ Syndrome
 1 in 11,000 births, small mouth and/or jaw, low-set/malformed ears, clenched fist,
index finger overlapping 3rd and 4th fingers, rocker-bottom feet, heart defects, hearing
loss, 90% die by age 1.
Kleinfelter’s Syndrome
 1 in 500 males (XXY), taller than average, partial breast development, small testicles,
high-pitched voice, female hair distribution, altered body proportions, hips slightly
larger than normal, IQ about 90
Turner’s Syndrome (X)
 1 in 2500 females, grow slowly, shield chest when young, low hair line, widely
spaced nipples, fail to menstruate, no ova, normal IQ; weakness in math, spatial
perception
Jacob’s Syndrome (XYY)
 “Super Male”, 1 in 1000 males, 1 in 50 in prison populations, excessively tall (2/3’s >
6 feet), IQs around 80, low threshold for control of aggression
X-Polysomy (XXX, XXXX)
 XXX, 1 in 1400 females
 Cannot be distinguished from XX females
 Problems with spontaneous abortions
 XXX have normal IQs, increasing numbers cause mental deficiency
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Biology 30 – Ch. 27 Applied Genetics Notes
Genetics & Human Diseases
 About 4,000 human diseases are thought to be inherited.
 Scientists are making good progress figuring out where genes are located on
chromosomes and in understanding how the mutations in genes cause disease
Genetic Testing
 Now have DNA tests for 30 - 40 diseases
• Cystic fibrosis, some forms of breast cancer, fragile X syndrome, Huntington
disease, Duchenne muscular dystrophy
 Tests are up to 99% accurate
 Tests can be run on embryos created by in-vitro fertilization prior to implantation
Future of Genetic Testing
Genetic tests for 1000s of genetic diseases will be available after the Proteome Project
is completed…or after scientists figure out which proteins go with which
genes…probably in 10-20 years.
Issues about Genetic Testing
 What if the news is bad? Should the fetus be aborted or allowed to live with a “cruel”
disease?
 Should insurance coverage provide care for a child having a genetic disease that was
diagnosed before birth?
 Should blood relatives be warned?
 Should our genetics be part of our records?
 Should employers be allowed to consider genetically based diseases in hiring
employees?
 Will eugenics (manipulation of the hereditary qualities of a race) be practiced?
Gene Therapy
 Gene therapy is lagging behind genetic testing
• For example, gene for cystic fibrosis was identified in 1989
• Scientists have been testing ways to insert copies of the normal gene into cells of
the respiratory tract
 It is difficult to get the gene inserted into the tissue so that it can take over control of
protein synthesis
Breeding Methods
 Selection: The process of _______________________________________.
 Inbreeding: The mating of ________________________individuals to obtain
desirable traits. Very common in self fertilizing plants.
 Hybridization: Crossing individuals that are not closely related to introduce new,
beneficial alleles to the population. New individuals are generally hardier than either
parent. This is called ________________________.
Mutations
 In biology, mutations are changes to the nucleotide sequence of the genetic material
of an organism.
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Biology 30 – Ch. 27 Applied Genetics Notes
Mutations can be caused by copying errors in the genetic material during cell division,
by exposure to ultraviolet or ionizing radiation, chemical mutagens or viruses
 Mutations create ________________________________________________.
 Less favorable (or deleterious) mutations can be reduced in frequency in the gene pool
by natural selection, while more favorable (beneficial or advantageous) mutations
may accumulate and result in adaptive evolutionary changes.
Peppered Moth
 The evolution of the peppered moth over the last two hundred years has been studied
in detail.
 Originally, the vast majority of peppered moths had light coloration, which effectively
camouflaged them against the light-colored trees and lichens which they rested upon.
 However, due to widespread pollution during the Industrial Revolution in England,
many of the lichens died out, and the trees which peppered moths rested on became
blackened by soot, causing most of the light-colored moths to die off due to predation.
At the same time, the dark-colored moths, flourished because of their ability to hide
on the darkened trees.
 This changing of color of a species due to pollution is called ____________________.

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