Transcript one gene - Central Magnet School

Mrs. Stewart
Central Magnet School
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Genetic disorder - a disease caused by
abnormalities in an individual’s genetic
material.
Both environmental and genetic factors play
a role in the development of disease.
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What is a genotype?
◦ The actual genetic makeup of an organism (the true
“genes” for a specific trait – the actual alleles)
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What is a phenotype?
◦ The physical expression of a trait
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R = able to roll tongue; r = not able to roll
tongue
◦ Which one is dominant?
◦ Which one is recessive?
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Using R = can roll tongue, and r = can’t roll
tongue:
◦ Write a homozygous dominant genotype
◦ Write a homozygous recessive genotype
◦ Write a heterozygous genotype
Rr
RR
rr
 Why is a heterozygous referred to as a carrier
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How many pairs of chromosomes do we have?
◦ 23
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What is the 23 pair called?
◦ Sex chromosomes
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What is an autosome?
◦ Every chromosome that is NOT a sex chromosome
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Gene- a segment of DNA that contains instructions
for the production of a protein.
Diseases and disorders result when a gene is
mutated resulting in a protein product that can no
longer carry out its normal job.
In this course, we will consider four
different types of genetic disorders:
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Single-gene
Multifactorial
Chromosomal
Mitochondrial
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Single gene disorders are caused by
changes or mutations that occur in the DNA
sequence of one gene.
Single gene disorders are inherited in
recognizable patterns:
◦ Autosomal dominant
◦ Autosomal recessive
◦ Sex linked
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Genetic testing looks at genotype to
determine if someone has a genetic disorder,
will develop one, or is a carrier.
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A man and a woman are both carriers for
sickle cell disease, an autosomal recessive
trait. What is the risk of their having an
affected child?
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S = No sickle cell; s = sickle cell disease
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Draw a punnett square to find answer
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Each parent is heterozygous for the
condition and has the genotype Ss (where
“s” is the recessive sickle cell allele). Each
parent passes one allele to the child, so
there is a 25% chance that the child will
have sickle cell disease.
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Multifactorial disorders are caused by a
combination of environmental factors and
mutations in multiple genes.
◦ Development of heart disease is associated with
multiple genes, as well as lifestyle and
environmental factors.
◦ Different genes that influence breast cancer
development have been found on chromosomes
6, 11, 13, 14, 15, 17 & 22.
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Many of the most common chronic illnesses
are multifactorial.
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Humans have 46 chromosomes in their
body cells.
◦ 44 autosomes
◦ 2 sex chromosomes
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Because chromosomes carry genetic
information, problems arise when there are
missing or extra copies of genes, or breaks,
deletions or rejoinings of chromosomes.
Karyotypes - pictures of the paired
chromosomes of an individual
◦ important in diagnosing chromosomal disorders.
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Mitochondria (the organelles in your
cells that convert energy) contain DNA.
A mitochondrial disorder is caused by
mutations in nonchromosomal DNA of
mitochondria.
◦ a relatively rare type of genetic disorder
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Mitochondrial DNA is unique in that it
is passed solely from mother to child
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Carrier screening determines whether an
individual carries a copy of an altered gene
for a particular recessive disease even though
they do not show the trait phenotypically.
◦ Essentially this tells if a person is heterozygous for
a particular trait
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Carrier screening is often used if a particular
disease is common in a couple’s ethnic
background or if there is a family history of
the disease.
Example: Tay-Sachs disease or sickle cell
disease.
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PGD is used following in vitro fertilization to
diagnose a genetic disease or condition
before the embryo is implanted in the
uterus.
◦ A single cell is removed from an embryo and
examined for chromosome abnormalities or
genetic changes.
◦ Parents and doctors can then choose which
embryos to implant.
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Secrets of the Sequence – Chosen Child
video
◦ http://www.youtube.com/watch?v=a5SB9t7m0Vs
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Prenatal diagnosis allows parents to diagnose
a genetic condition in their developing fetus.
Techniques such as amniocentesis, chorionic
villi sampling (CVS), and regular scheduled
ultrasound allow parents to monitor the
health of the growing fetus.
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The most widespread type of genetic
screening, newborn screening is used to
detect genetic or metabolic conditions for
which early diagnosis and treatment are
available.
State tests for newborns typically screen
anywhere from 4 to over 30 genetic or
metabolic disorders.
◦ Testing protocol and mandates vary from state to
state.
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The goal of newborn screening is to identify
affected newborns quickly in order to
provide quick treatment and care.
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In this activity, you will assume the role of a
genetic counselor and meet with clients faced
with difficult decisions regarding genetic
disorders and genetic testing.
Your goal is to effectively explain the disease
or disorder to your clients as well as to
outline potential options for genetic testing
and screening and overall management of
disease.