Exam 2: Genetics Flashcards
What is a genome?
the total DNA in an organism
Why is a genome important to an organism?
a genome is required to make the organism and required for the organism to function properly
When was the human genome project begun?
in 1990
What do our genes determine?
our disease susceptibility and how we may react to certain diseases
What was the first drug produced due to the genome?
insulin
What is gene mutation?
biochemical event leading to the change of DNA sequence
What is polymorphism?
more than one normal allele (alternate forms) at the same locus
What is an example of polymorphism?
blood type
What is meant by congenital?
its a deformity acquired in-utero (not later on)
What is a genotype?
genetic composition/information stored in the triplet codes in DNA (not evident by observation)
What is a phenotype?
an expressed character trait (physical/outward expression) of the genotype
What is meant by polygenic inheritance?
multiple genes at different loci, affecting 1 trait (hair color)
What is meant by multifactorial inheritance?
same as polygenic inheritance but includes environmental factors
What is a karyotype?
numeric classification system of autosomes and sex-chromosomes
What is meant by homozygous?
the same allele
What is meant by heterozygous?
its a mixture of dominant and recessive alleles
What is gene penetrance?
the ability of a gene to express its function
What is gene expression?
the degree to which the phenotype of the gene is expressed
What is the role of chromosomes?
to store basic genetic information
How many pairs of chromosomes do humans have?
23 pairs (22 autosomes and 1 pair of sex chromosomes) - females: 46, XX
- males: 46, XY
Who is impacted by X-lined genetic disorders?
males
Where are DNA molecules stored?
in the nucleus of each human cell
What is the structure of a DNA molecule?
double stranded helix
What is the DNA carried by?
4 nitrogenous bases
What are the 4 nitrogenous bases?
guanine, adenine, cytosine, thymine
Cytosine is matched with:
guanine
Adenine is matched with:
thymine
The pyrimidine bases are:
thymine and cytosine
The purine bases are:
adenine and guanine
What is used to build proteins?
triplet codes (codons)
What is a gene?
a sequence of triple codes (hundreds to millions) that code for a specific function
Approximately how many genes do humans have?
30,000
What does DNA determine?
the type of biochemical product that the cell will form
What is the role of M-RNA?
it is used as a template to make proteins and it recognizes the start and end of gene sequence, which creates MRNA from DNA (transcription)
What is the role of T-RNA?
it delivers amino acid to the ribosomes to make proteins (protein synthesis)
What is the role of R-RNA?
it is responsible for protein synthesis
What is induction?
process by which gene expression is increased
What is an example of influences that promote induction?
external influences such as diet or radiation therapy
What is gene repression?
process by which a regulatory gene reduces or prevents expression of a gene
Gene expression is possibly influenced by:
transcription factors
There are factors allowing genes and characteristics to be expressed ________ to each person
individualistic
What are gene mutations?
accidental, rare errors in DNA
What are gene mutations corrected by?
DNA repair mechanisms in the cell
How does mutations occur?
from substituting bases, adding/deleting bases or rearranging
This point mutation switches one nucleotide for another (CAC becomes CGC):
substitution
This point mutation adds an extra nucleotide (CAC becomes CATC):
insertion
This point mutation omits a nucleotide (CAC becomes CC):
deletion
What is translocation of gene mutation?
when two breaks occur in two chromosomes from different pairs and broken fragments swap places
When can transcription errors occur?
when RNA is synthesized from DNA template
What are the cause of most early spontaneous pregnancy losses or significant fetal malformations?
gene mutations
What mutations can be inherited?
ones that occur in the germ cells (ovum/sperm)
What mutations cannot be inherited?
ones that occur in somatic cells
What are some examples of conditions caused by gene mutations during early embryonic?
- cleft pallet
- club foot
Mutations occurring later in life can cause cancer and be caused due to what factors?
exposure to environmental or chemical agents
Radiation treatments for cancer has the potential to cause:
another form of cancer
What are some examples of mutagenic agents that can cause cancer?
- radiation
- viruses
- chemicals
- uv light
- sun exposure (sun exposure -> damages cellular DNA -> skin cancer)
Genotype can never be predicted because it can be:
homozygous dominant or heterozygous
(ex: two people with the same phenotype - brown eyes - can have two different genotypes, if one is a carrier of blue eyes - Bb and BB)
What does transcription factors do?
bind to DNA that regulate time of transcription and either activate or repress gene expression
What is expressivity?
the many different ways a phenotype can be expressed; can range from mild to severe
What does expressivity depend on?
the transcription factors, they tell the DNA to express or repress a gene
(ex: polydactyly - can have a extra digit on one appendage or all and it can be full sized or smaller)
What is penetrance?
a specific genes ability to express itself in a population where everyone has the same genotype
(ex: polydactyly - if penetrance is 75% in a certain population, 75% will have an extra digit)
During penetrance, either the gene will be:
expressed or it won’t
In this type of inheritance, there are multiple genes at different loci with each gene on the loci exerting an additive effect in determining the trait:
polygenic
Polygenic inheritance has no:
environmental influence
What are some examples of polygenic inheritance?
- eye color
- skin color
In this type of inheritance, there are multiple genes at different loci, affecting the trait to be displayed and includes environmental influence
multifactorial
Multifactorial inheritance includes:
environmental influence
What are some examples of multifactorial inheritance?
- CAD (at least 15 genes)
- height (100)
- alcoholism (multiple) - diabetes (multiple)
Why is height multifactorial?
because it includes genetics and environmental
What is meant by multiple alleles?
there is more than one allele affecting the same trait (ex: ABO blood type)
_____ is the position of the gene on a chromosome:
locus
_____ is the alternate forms of the same genes at the same locus:
alleles (can be dominant or recessive)
What law refers to the predictability of genetic transmission when a single gene expression is at work?
mendel’s laws
What is an example of a homozygous individual trait according to mendel’s law?
BB or bb
What is an example of a heterozygous individual trait according to mendel’s law?
Bb
A _______ is heterozygous without expressing the trait
carrier
These disorders are caused by a defective gene at a single locus and characterized by pattern of inheritance (dominant/recessive or autosome/sex chromosome):
single gene disorders
What can single gene disorders lead to?
abnormalities in protein synthesis and enzyme production as well as some severe illnesses
These conditions types are rare due to variable penetrance but they are more common due to dominance:
single gene autosomal dominant conditions
The homozygous dominant version of this single gene autosomal dominant condition is fatal:
achondroplastic dwarfism
This single gene autosomal dominant condition leads to brittle bones due to defects in collagen synthesis:
osteogenesis imperfecta
A patient comes to the ED presenting s/sx of a MV prolapse, weak aorta, arachnodactyly, hyper-extendible joints and vertebral issues. What condition do you think this patient has?
marfans syndrome/abraham lincoln
What type of disorder is marfans syndrome?
single gene disorder (autosomal dominant)
What is meant by autosomal dominant?
a person needs one gene from one parent and is caused by a lack of certain proteins that regulate DNA to grow /develop properly
What systems are affected by marfans syndrome?
- ocular system
- cardiovascular system
- skeletal system
What are some s/sx of marfans syndrome?
- mv prolapse
- weak aorta
- arachnodactyly (long extremities)
- pectus excavatum/carinatum - outward/inward sternum
- hyper-extendible joints
- vertebral issues (scoliosis, kyphosis)
- retinal detachment
What is someone with marfans syndrome at risk for?
aneurysm in the aorta
What is the treatment for marfans syndrome?
no true treatment but you can repair the aorta and surgically repair the sternum
A patient with an intellectual disability is brought into the ED with seizures and paralysis and also suffers from vision loss. What condition does this patient have?
tay sachs
What type of disorder is tay sachs?
single gene disorder (autosomal recessive)
What effect does tay sachs have on the neurological system?
it progressively destructs neurons in the brain and spinal cord
When does the most common form of tay sachs appear?
in infancy around 3-6 months when development starts to slow and muscles weaken
What symptoms does tay sachs progress into?
- seizures
- vision/hearing loss
- intellectual disability
- paralysis
What is a diagnostic sign of tay sachs?
the cherry red spot in the eye (which is the accumulation of lipids)
How long does a patient with tay sachs live?
into early childhood
In sex linked disorders, the x-link allows females to be the carriers but not express the disease. Therefore, males will automatically express the gene if:
they get that particular x chromosome from the mom
This is a single sex linked gene that involve a group of disorders in which the blood does not clot properly
hemophilia
What do those with hemophilia lack?
normal factor VIII which prevents them from clotting normally
This is the most common form of hemophilia that lacks normal factor VIII:
hemophilia A
How can hemophilia be treated?
- by supplementing factor VIII (drug)
- can be transfused (expensive with multiple risks)
- biotech factor VIII from bacteria (less health risks)
This is a sex-linked recessive disorder affecting 8% of males and 0.04% of females
color blindness
What does color perception depend on for those who suffer from color blindness?
3 different genes, each producing chemicals sensitive to different parts of the visible light spectrum
Where are red and green detecting genes on?
x chromosome (most common)
Where is the blue detecting gene on?
autosomal trait
Multifactorial disorders are when multiple genes are involved in inheritance (threshold phenomenon) and can be:
- congenital (cleft lip/palate, club foot, congenital heart disease, urinary tract malformation)
- environmental (CAD, HIV, diabetes, cancer, bipolar, schizophrenia)
When considering environmental factors, remember that:
you have the genetic predisposition, but your environment can heighten your risk for certain diseases
What is the period of vulnerability for environmental factors on fetal development?
by 2 weeks, the CNS is extremely vulnerable and this vulnerability lasts until 20-22 wks up to 2 years
What are some examples of teratogenic agents?
- alcohol
- drugs
- radiation
- chemicals
- infectious agents
- exposure to any of these can alter genetic expression of the fetus*
This condition is a combination of physical, cognitive and behavioral abnormalities caused by alcohol during pregnancy:
fetal alcohol syndrome
Fetal alcohol syndrome is usually due to the mom having the inability to:
know she was pregnant within 2 weeks of pregnancy
Fetal alcohol syndrome can result in:
- prenatal/postnatal growth retardation
- permanent effects on CNS
- characteristic facial features (flat nose bridge, microcephaly, epicanthal foldsm short nose, thin upper lip, small chin, microcephaly, smooth philtrum, etc.)
Fetal alcohol syndrome is not hereditary but what does it influence?
the genetic cellular expression in the brain and is an alcohol induced phenotype
This is a autosomal dominant condition that progressively destroys the brain cells and is not normally manifested until after the age 30 (esp. in 40’s)
huntingtons disease
When is huntingtons disease manifested?
If a parent has the disease, 50% of the children will have it (unless the parent was homozygous dominant)
What is a sign of huntingtons disease?
dyskinesia (extremities/body parts don’t move/work together - they cannot talk or move properly)
In the blood type, multiple alleles are involved, making A and B _____ whereas O is ________
dominant; recessive
The body creates ______ to the blood type you don’t have:
antibodies
In the Rh factor, positive is ______ and negative is ______. Rh factor is inherited separately from blood type
dominant; recessive
- A+A =
- A+O =
- A+B =
- B+B =
- B+O =
- O+O =
- A
- A
- AB
- B
- B
- O
This condition is autosomal recessive (both parents) and results in harmful amounts of fat accumulation in the spleen, liver, brain, lungs and bone marrow. It is very common in people with a polish, jewish and russian background:
nieman-pick disease
Lipid storage disorders are a subgroup of diseases known as:
sphinogolipidases
What causes a complete deficiency of sphinogomyelinase?
missense mutation
What does a deficiency of sphinogomyelinase result in?
fat build up within the lysosomes causing lipids to not be destroyed and cells to become enlarged
