Genetic Influence in Disease

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64 Terms

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Define Gene

a segment of a DNA molecule that is composed of an ordered sequence of nucleotide bases (adenine, guanine, cytosine, thymine)

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What are the main functions of genes

coding for synthesis of proteins that influence all aspects of body traits and function

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Provide examples of genes

  • They include “permanent” proteins such as eye pigment, hair color, and blood type in a developing fetus, as well as more subtle inherited traits like outgoing personality or susceptibility to certain diseases

  • There are also “day-to-day” functional proteins such as hormones, antigens, antibodies, enzymes, etc

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What occurs when there is a mutation of a gene?

the protein it is responsible for often malfunctions

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If the gene that codes for lactase becomes mutated, what might happen?

lactose won’t get broken down and lactose intolerance will occur

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How does a chromosome form?

a sequence of nucleotide bases forms a gene; genes make up a DNA molecule, and that DNA molecule forms into a specialized shape

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How many chromosomes does a person receive from each parent?

23 chromosomes

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How many chromosomes does a person end up with?

23 pairs or 46 total

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How many pairs of chromosomes are autosomal?

22 pairs

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Autosomal chromosome are NOT sex chromosomes & each pair are closely alike. T/F

True

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How many pairs of chromosomes are sex chromosomes?

1

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Can a pair of alleles be alike?

They are almost exactly alike except that one can be dominant & one can be recessive (or they can both be dominant or both be recessive).

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How do we notate recessive genes in autosomal chromosome pairs?

With a lower-case letter

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How do we notate dominant genes in autosomal chromosome pairs?

With an upper-case letter

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Define genotypes

The combination of genes. Refers to a specific set of alleles

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How do we notate homozygous dominant in autosomal chromosome pairs?

GG (both uppercase)

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How do we notate homozygous recessive in autosomal chromosome pairs?

gg (both lowercase)

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How do we notate heterozygous in autosomal chromosome pairs?

Gg (one uppercase & one lowercase)

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Define phenotype

a person’s observable characteristics (anatomic, physiologic, biochemical, behavioral) as determined by genes and environment (not just a physical characteristic).

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Define genetic disorders

a disease caused by abnormalities in an individual’s genetic material

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Provide two examples for inherited disorders

sickle cell disease & PKD is caused by an inherited, altered (AKA, “mutated”) gene

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Provide an example for spontaneous disorders

free radicals form as a result of aging causes damage to the DNA protein synthesis is altered leading to gene mutations an “oncogene” develops which causes rapid, wild proliferation of cell growth cancer may develop

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State the ways to categorize genetic disorders

inherited, spontaneous, mitochondrial DNA, multifactorial, chromosomal, & single-gene disorders

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Where is DNA found on mitochondrial DNA disorders

majority of DNA is found in nucleus of cells but small bits of DNA are also found in mitochondria

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How common are mitochondrial DNA disorders

Not very common

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How do multifactorial genetic disorders occur?

combination of environmental triggers and variations / mutations of genes, plus sometimes inherited tendencies

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How does cancer occur?

various cancers such as lung cancer: begins by smoke & toxins irritating bronchial tissue one or more genes in cells of that tissue begin to be deranged—oncogenes created code for wild, uncontrolled growth of cells

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What are other multifactorial genetic disorders?

many common diseases such as hypertension (HTN), coronary artery disease (CAD) & diabetes mellitus (DM) are now known to be caused or highly influenced by a mix of environmental and inherited components.

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What does teratogen cause & what is is?

It is any influence — eg, drugs, radiation, viruses-- that can cause congenital defects

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Define congenital defects

They are abnormalities that are either detectable at birth and/or can be attributed to fetal development “glitches

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Provide examples for Teratogenic disorders

fetal alcohol syndrome

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How does fetal alcohol syndrome occur

It occurs because toxicity of alcohol causes gene mutations during gestational development

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What are thalidomide babies

born with abnormal arms and legs due to mothers taking the drug thalidomide during early pregnancy

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Define chromosomal disorders

a type of genetic disorder that results from alterations to the development or structure of a chromosome, which in turn alters the “local” genes (genes in the immediate area)--the genes’ functionality is disrupted and they don’t code proteins correctly, giving rise to the phenotype (S&S) of the disorder

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What part of the chromosomes do chromosomal disorders affect?

Either the structure or numbers of chromosomes

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Define Down’s syndrome

It is a disorder of abnormal numbers of chromosomes that is sometimes associated with pregnancies of women >35 years old

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When does Down’s syndrome occur

It occurs in very early cellular division and chromosomal distribution of a fertilized egg: instead of ending up with the normal number--46 chromosomes-- the fetus ends up with 47

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Where does the extra chromosome occur at in Down’s syndrome?

the extra chromosome occurs at site #21 -- the 21st chromosome set has three chromosomes instead of two

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What is another name for the type of down with an extra chromosome?

Trisomy 21

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What is the phenotype for trisomy 21?

It includes mental retardation and typical physical characteristics such as low-set ears, epicanthic fold to the eyes, short limbs, and a larger-than-normal tongue

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What is Philadelphia chromosome?

alterations to STRUCTURE of chromosomes

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How are chromosomal aberrations caused?

by alterations in chromosomal structure, such as deletion, duplication, or rearrangement of gene sites (translocation) on the chromosome

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Why do single-gene disorders occur?

usually due to an inherited mutated gene

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What type of recognizable patterns are single-gene disorders inherited in?

autosomal recessive, autosomal dominant, and sex-linked

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Why do autosomal recessive disorders occur?

occurs when a mutated (“diseased”), recessive (“weak”) gene partners up with an allele that is also recessive & diseased; those alleles are notated with two lower-case letters

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What will happen to the protein that is coded for in autosomal recessive disorders?

It will malfunction & an abnormality/ disease/ disorder will occur that relates to that “bad” protein

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Provide an example for autosomal recessive disorder

sickle cell anemia

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How does sickle cell anemia occur?

if during fertilization a person inherits a sickle-cell disease gene from mom – ie, a recessive, mutated Hgb-coding gene – and ALSO inherits a sickle-cell disease gene from dad, this person would have a homozygous genotype of the recessive sickle cell genes: dd MUST HAVE INHERETED FROM MOM AND DAD

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How do the abnormal recessive alleles in sickle cell anemia affect the RBCs?

those abnormal recessive alleles will code for abnormally-shaped Hgb (sickle-shaped), which will make the RBCs sickle-shaped. B/C these RBCs do not have the usual round & smooth shape, they’re more easily damaged as they go through the blood stream; ultimately this results in less-than-normal numbers of RBCs—this is the definition of anemia.

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What are the S&S of sickle cell anemia

SOB , weakness & fatigue, but also ischemic pain (especially in the joints)

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Why does SOB, weakness & fatigue occur in sickle cell anemia?

due to decreased O2 being carried to tissues of the body; this decreased carrying capacity is because of anemia: less numbers of RBCs to carry the Hgb which in turn carries the O2 & deformed Hgb simply cannot carry the usual numbers of O2 molecules

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Why does ischemic pain (especially in the joints) occur in sickle cell anemia?

the deformed RBCs “clog” up the capillaries that usually carry O2-rich blood to the tissues & this results in distal tissues that are starved of O2 & “cry out” in pain

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How does heterozygous genotype for sickle cell anemia occur?

if during fertilization a person inherits a sickle-cell disease gene from one parent but a normal Hgb-coding gene from the other parent, the person’s genotype for Hgb would be: Dd. We know that because the NORMAL gene is dominant over the sickle-cell recessive gene, the person will NOT have the disease but they may pass on the gene to offspring.

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Explain how homozygous normal works in inherited disorders

someone with the genotype DD doesn’t have to worry about either having the disease or passing it on

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Why does autosomal dominant disorders occur?

occurs when a person inherits a mutated, diseased gene that is dominant

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Provide an example for autosomal dominant disorders

polycystic kidney disease (PKD)

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How does polycystic kidney disease (PKD) occur?

if during fertilization a person inherits a kidney tissue gene that has a mutation, that gene will “want” to code for abnormal kidneys. in a dominant disease such as PKD, the mutated gene is the strong one, so even if it is paired with a normal allele, it will override the normal allele’s coding

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How does polycystic kidney disease (PKD) affect a person?

this results in the kidney tissue developing cysts, which can reduce various kidney functions and lead to kidney failure as a person goes through life

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How does the genotype notation work with PKD?

if we use the letter “P” to designate PKD, the genotype for someone that HAS the disease would look like this: PP or Pp.

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What is the genotype notation for homozygous recessive in PKD?

a genotype of pp (homozygous recessive) would NOT have the disease

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What are the S&S in polycystic kidney disease (PKD)?

  • hematuria (blood in urine), proteinuria & frequent kidney infections

  • pain at costovertebral anglmany ales and abdomen

    • kidney stones

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What is Recombinant DNA?

a form of genetic engineering

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How did recombinant DNA occur?

many alterations in DNA came about as a natural part of evolution, but now we can deliberately alter DNA in the interests of medicine and science

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What is the current application for recombinant DNA?

  • human growth hormone for children lacking it.

  • exogenous (“from outside the body”) insulin for diabetics.

  • factor VIII for hemophiliacs.

  • drugs like tPA & tenecteplase—given as “clot-buster” in patients having a myocardial infarction (MI, aka heart attack).