km Flashcards
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Human Genetics
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Human Blood Groups
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Blood type is determined by surface proteins called antigens
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Two major types: ABO and Rh +/-
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For example: A+ or O- blood
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ABO Blood Types- controlled by multiple alleles and co dominated alleles
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IA (A allele) codes for a A type protein
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IB (B allele) codes for B type protein
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i (O allele)
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Rh Type
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Rh is another surface protein
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Having the Rh protein means your positive
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Lack of Rh protein means your negative
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A+ means they have the A antigen and Rh antigen
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Alleles controlled by complete dominance
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R=Rh positive r=Rh negative
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RR=Rh+
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Rr=Rh+
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rr=Rh negative
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Rh+ is more common than Rh-
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Hemolytic Disease
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Rh incompatibility between mom and child
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ABO not an issue for incompatibility because the type of antibodies made for those markers are different and cannot cross placenta as easily
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Can occur when a mom is Rh- and the fetus is Rh+
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If some fetal cells mix with moms
can cause an immune reaction agfaist them and cause anemia in fetus
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First brith is usually normal
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Rhogam-treatment to prevent this now by injecting mother to kill any fetal cells in her bloodstream
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Chromosomal Theory of Inheritance
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1902: Walter Sutton
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States that genes are located on chromosomes
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Each gene occupies a specific place on each chromosome
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Genes can exist in several forms called alleles
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Gene LInkage
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If genes are located on chromosomes and entire chromosomes are inherited together then groups of genes are passed on together
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This some genes are linked and do not undergo independent assortment as Mendel stated
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Thomas Hunt Morgan and Fruit Flies
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Crossed purebred gray bodies and nromal wings with purebred black bodies and small wings
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gray/normal are dominant traits
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All F1 flies were grey/normal (GgNn)
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Crossed F1 flies with homozygous recessive or (ggnn)
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What would you expect?
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25% Gray/Normal
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25% Black/Normal
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25% Gray/Small
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25% Black/Small
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Morgans Results
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41.85% Gray/Normal
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25% Black/Normal
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41.5% Gray/Small
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25% Black/Small
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Lack of independent assortment pointed to genes bein glinked
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Linkage groups are sets of inherited together (or genes on the same chromosome)
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Why werent the genes always linked?
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Answer: crossing over which produces new combinations of alleles or recombinants
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More Morgan and Drosophilia
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He worked with many mutants
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Discovered a white eyed mutant-rare
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Crossed his white eyed male with a normal red eyed female
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The F1 results: 100% red eyed flies
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F2 results: 75% red and 25% white BUT: all white eyes were male!
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Conclusion: eye color allele is on the X chromosome thus it is sex linked
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Sex Linked Traits
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Any traits that are found on sex crhomosomes
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Often called X linked because so few genes on the Y
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Recessive sex linked traits are seen more often in males because they only have one X
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Females have 2 Xs thus if they get an recessive allele on one they still have the other X as a back up
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Recessive sex linked traties can be found in males
just not as often
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Examples in humans: hemophilia and colorblindness
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X Inactivation on Barr Bodies
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Men have only one X functional in each cell because they also have a Y
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Females have 2Xs but only one is active
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Early on in embryonic development one X becomes randomly inactive in each embryonic cell
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The inactive X is called a Barr body because of how it looks under the microscope
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Inacgtive X becomes covered in a special type of RNA tpo inactive it
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Some types of cat colors
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Genetic Disorders
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Most gventeic disorders are autosomal recessive because they make a mutant form of a protein that doesnt function properly
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Can be autosomal dominant
sex linked recessive or sex inked dominant
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Pedigrees can be used to track inheritance
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Cystic fibrosis
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Autosomal recessive
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Most common genetic disorder among caucasians
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Parents can be carriers and be unaware
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Cl-ion channels do not function well
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Mucous builds up on surface of tissues and organs
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Prone to lung infections
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Phenylketonuria (PKU)
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Autosomal recessive
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Lack enzyme for breaking down phenylabnine
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Need a low phenylalaniene diet otherwise it can build up in brain and cause damage
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Sickle Cell Anemia
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Autosomal recessive
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Mutation in hemoglobin gnee
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RBCs can become stiff and sickle shaped
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Most common symptom is pain-anywhere
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Causes pain
swelling
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HEterozygote advantage
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Though the condition of sickle cell anemia is autosomal recessive the allele for sickle cells are codominant
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HH is normal
hh is sickle cell anemia
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Hh has some sickle cells but not too many
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Sickle cell allele (h) is more prevalent in Africa than US
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Provides protection against malria because sickle cells kill parasites
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Huntingtons Disease
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Autosomal dominant
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Caused by mutation in a gene on chromosome 4
where CAG repeats
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Excessive repeats cause3 an abnormal protein that blocks the function of the normal ones
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Neurological symptoms; appear later in life
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Sex linked Recessive Disorders
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More common in males than females
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Females can be carriers
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Passed mother to son directly
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Examples
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Colorblindness
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Hemophilia
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Muscular dystrophy
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Sex linked dominant exist tooo; hypertrichosis or werewolf syndrome
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Hemophilai
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Types A and B
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Differ in mutatiojns that affect molecules in teh clotting cascade (factor VIII or IX)
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Without one part of cascade clots cannot form
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Common among royals because of intermarriage
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Today: able to synthesize factors and inject
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Colorblindness
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The retina in the eye has light sensitive cells called rods and cones
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Rods- light sensitive
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Cones respond to different wavelengths (color) of light because of protein called opsin
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3 main opsins: red
green
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Mutations of colorblindness
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Most mutations are red/green
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Some people are missing entire red or green gene together
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Fewer are blue/green
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Not black/white vision typically
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Colorblindness tests mix each color together
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Duchennes Muscular Dystrophy
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Characterized by enlargement of the muscles; degenerate over time
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Gene for dystrophin is one fo the larges themes known of; 79 exons
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Dystrophin protein si part of cytoskleton of muscle cells
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Typical mutations cause premature translation termination (nonsense)
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Becker MD is a milder form of the disase
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Sex influenced Traits
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Baldness
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Alleles for baldness are influenced by the sex hormones
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Therefroe
men and women exhibit baldness differently
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Baldness allele acts dominant in men
but not in women
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If expressed in women
usually after menopause
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Pre-Natal Diagnosis
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Diagnosis for a genetic disorder for an adult can be done with a blood sample
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Prenatal diagnosis of a fetus can be done in 2 major ways”:
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Amniocentesis (14-20 weeks)
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CVS or Chormoic Vili Sampling (10-13 weeks)
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CVS does not detect neutral tube defects like an amino
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Gene Therapy
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With all this information we are trying to find ways to not just treat these disorders but perhaps cure them
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Gene theraphy is based in idea of trying to replace a bad copy of a gene with a good copy or normal copy
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The challenge is finding a safe way to give the person a new gene; not as easy as it sounds!
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We need a vector or vehicle to deliver the gene to the correct cells
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first trials doen in 199 with a basic cold virus used; we added genes to the capsid
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The patient died in 4 days from multiple organ failure; massive immune response
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Scientists are working on new alternatives
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Possible vectors
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Various types of viruses; each with different sucesses for different reasones
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Liposome: little bag of DNA surrounded by a lipid barrier
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These can help give a godo copy of a gene for those that have one that doesnt function properly
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What about Huntingtons? The good gene is already there
the bad one just interferes with it
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Technique called RNAi developed
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RNAi
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Discovered by accidnet
as are many things in science
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Cells have a system in place to protect against some vital infections
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They recognize vital mRNAs and degrade them and any that look like them
including those normal ones in the cell
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dsRNA is the type of RNA that catazlyzes this system to begin working
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Pedigrees: What is a pedigree chart?
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Specifically it is a diagram in which several generations of a family and the occurrence of certain genetic characteristics are shown
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Pedigree charts show a record of the family of an individual
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They can be used to study the transmission of hereditary contition
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Determine the risk of passing on a genetic disorder to offspring
in addition to prenatal testing
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They are particularly useful when there are large families and a good family record over several generations
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Here are just some of the patterns of inheritance we discussed:
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Autosomal dominant: Huntingtions
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In a pedigree:
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Affected are assumed to be heterozygous
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All unaffected individauls are homozygous fo the normal recessive allele
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Autosomal recessive: cystic fibrosis
sickle cell anemia
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In a pedigree:
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All affected are homozygous
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Unaffected are assuend to be homozygous normal
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Carriers may or may not be shown with a half shaded circle/square
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Sex linked recessive: hemophilia
muscular dystrophy
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In a pedigree:
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Males get their X from their mother
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Fathers pass their X to daughters only
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Females express it only if they get a copy from both parents
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Female carriers may or may not be shown with a half shaded circle
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Expressed in males if present
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Recessive in females
