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Mendel and the Gene Idea Chapter 14
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Transmission of characteristics from parents to offspring = ___________________
The science that studies how those characteristics are passed on = _________
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Two ideas about how genes are passed:
____________- genetic material from parents mix (like mixing paint: blue + yellow → green) Problems: Predicts over time a freely mating population will result in a uniform population of individuals Doesn’t explain traits skipping a generation _____________- parents pass on discrete heritable units that keep their separate identities
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______________________________ Father of Genetics
Looked at one trait at a time Made experimental crosses Large sample size Kept careful records
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MENDEL’S PEA EXPERIMENTS
Peas are “self pollinating” ie., egg and sperm come from same plant Mendel’s experiments Allowed him to experiment and observe offspring produced from a variety of known genetic crosses
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MENDEL’S EXPERIMENTS ____ generation (_________) ____ generation
(______= offspring) ___ generation
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PATTERNS ARE THE KEY Image modified from:
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Genetic makeup of organism = _________
Image modified from: Image from Biology; Campbell and Reece; Pearson Prentice Hall publishing as Benjamin Cummings © 2005 Genetic makeup of organism = _________ Appearance of organism = ____________
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For each trait, an organism inherits TWO alleles.
MENDEL’S MODEL Alternative versions of genes account for variations in inherited traits. For each trait, an organism inherits TWO alleles. If the two alleles at a locus differ, one determines the organism’s appearance; the other has no effect. The two alleles for a character separate during gamete formation and end up in different gametes.
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Image modified from: http://www.newtonswindow.com/problem-solving.htm
Alternative versions of genes account for variations in inherited traits. ____________ = Observable characteristic Ex: flower color, height, pod shape ___________ = choices for a trait Ex: blue eyes, green eyes, brown eyes) From Biology; Miller and Levine; Pearson Prentice Hall publishing as Benjamin Cummings © 2005 Pearson Education Inc
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2. For each trait, an organism inherits TWO alleles.
Image from Biology; Campbell and Reece; Pearson Prentice Hall publishing as Benjamin Cummings © 2005 2. For each trait, an organism inherits TWO alleles. Organisms with two identical alleles for a gene = ____________OR ______________ Organism with two different alleles for a gene = _______________OR ___________
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3. If the two alleles at a locus differ, one determines the organism’s
appearance; the other has no effect. _________________ = allele that masks the presence of another allele __________________ = An allele that is hidden Image from Biology; Campbell and Reece; Pearson Prentice Hall publishing as Benjamin Cummings © 2005
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4. The two alleles for a trait separate during gamete formation
and end up in different gametes. = MENDEL’S LAW OF SEGREGATION Image modified from:
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Mendel’s Law of Independent Assortment
Two or more pairs of alleles segregate independently of one another during gamete formation.
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_______________ is the likelihood that a particular event will occur
EX: If you close your eyes and pick a disk, what is the probability you will pick the white one? It can be written as a: Fraction ____ Percent ____ Ratio ____
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COIN FLIP capital There are 2 possible outcomes: HEADS TAILS
COIN FLIP There are 2 possible outcomes: HEADS TAILS capital The chance the coin will land on either one is: ____ ____ ____ Alleles segregate randomly just like a coin flip. . . So can use probability to predict outcomes of genetic crosses.
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PROBABILITIES Past outcomes DON’T affect future ones!
Probability works best in predicting a large number of events. If last coin flip was heads… there is still a 50/50 chance the next flip will be heads too. The more flips. . . The closer results will be to the expected 50:50 average.
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MULTIPLICATION & ADDITION RULES
To determine the probability of two or more independent events: MULTIPLICATION RULE: Multiply the probability of one event by the probability of the other What is the probability two coins tossed simultaneously will both end up on heads? ½ X ½ = ¼
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MULTIPLICATION RULE WORKS FOR PREDICTING GENETIC CROSSES, TOO
Tt X Tt What is the probability offspring will be tt ? Each egg has a ½ chance of passing on t. Each sperm has ½ chance of passing on t. ½ X ½ = ¼ Punnett by Riedell
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½ X ½ = ¼ ¼ + ¼ = ½ ADDITION RULE
To figure out the probability of an offspring being heterozygous (Tt) T can come from mom and t from dad OR t can come from the mom and T from the dad but not both (events are mutually exclusive) 1st probability T from mom t from dad ½ X ½ = ¼ 2nd probability t from mom T from dad ½ X ½ = ¼ ¼ + ¼ = ½ Punnett by Riedell
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T t t t Tt tt Tt Tt HOW CAN YOU TELL THE GENOTYPE?
Tall plant has two possible genotypes ___ OR ___ Make a ___________ with a _____________________ T t t T T t Tt tt Tt Tt Images from: BIOLOGY by Miller & Levine; Prentice Hall Publishing ©2006
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GENES are more complicated than Mendel thought
Environment influences gene expression Spectrum of dominance Multiple allele traits Polygenic traits Gene Linkage Pleiotropy Epistasis
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Environment influences Phenotype “Nature vs Nurture”
Siamese cats and Himalayan rabbits have dark colored fur on their extremities Allele that controls pigment production is only able to function at the lower temperatures of those extremities. Images from slide show by Tracy Nelson
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Environment influences Phenotype “Nature vs Nurture”
Color of hydrangea flowers varies depending on pH of soil Images from:
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GENES are more complicated than MENDEL thought
Spectrum of DOMINANCE ____________________
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COMPLETE DOMINANCE If two alleles are present DOMINANT allele masks
the RECESSIVE allele Recessive trait shows again in F2 generation in 3:1 ratio
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INCOMPLETE DOMINANCE Heterozygous snapdragons show a blended
intermediate trait Image modified from:
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CO-DOMINANCE BOTH traits are expressed at the same time side by side in heterozygote A ROAN HORSE has both RED and WHITE hair side by side
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CO-DOMINANCE Both traits are expressed together (NO BLENDING) in heterozygote Persons with an A allele AND a B allele have AB blood type
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REMEMBER Membrane proteins with sugars attached that help cells “recognize self” = ______________ Type of sugars attached gives cell its “Blood type” I is used for blood type alleles
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BLOOD TYPES Person with IA IA OR IA i genotype
has cells with a certain glycoprotein “A” on its surface TYPE “A” BLOOD
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BLOOD TYPES Person with IB IB OR IB i genotype
has cells with a different glycoprotein “B” on its surface TYPE “B” BLOOD
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BLOOD TYPES Person with i i genotype have neither “A” nor “B”
glycoproteins on their surface TYPE “O” blood Note: Cells have other glycoproteins… just not A or B
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A and B are CO-DOMINANT Person with IA IB genotype has BOTH
glycoproteins on its surface TYPE “AB” Blood
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BLOOD TYPE FREQUENCY IN USA
40% B 10% AB 4% O 46%
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BLOOD TYPES YOU DON’T HAVE ANYTHING I DON’T HAVE!
DONOR BLOOD YOU DON’T HAVE ANYTHING I DON’T HAVE! See A blood cells as DIFFERENT! IMMUNE SYSTEM ATTACKS! Body images modified from:
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BLOOD TYPES YOU DON’T HAVE ANYTHING I DON’T HAVE! DONOR BLOOD
A and O see B cells as DIFFERENT! IMMUNE SYSTEM ATTACKS! YOU DON’T HAVE ANYTHING I DON’T HAVE! Body images modified from:
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BLOOD TYPES YOU’RE LIKE ME! DONOR BLOOD
A, B, and O see AB cells as DIFFERENT! IMMUNE SYSTEM ATTACKS! Body images modified from:
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BLOOD TYPES YOU DON’T HAVE ANYTHING I DON’T HAVE!
____ can donate to EVERY BLOOD TYPE = _____________________ NO A’s or B’s on surface to recognize as “NOT SELF” YOU DON’T HAVE ANYTHING I DON’T HAVE! Body images modified from:
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BLOOD TYPES ______ can RECEIVE FROM EVERY BLOOD TYPE
= ________________________ Body image modified from:
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ABO SYSTEM is NOT THE ONLY ONE
Rh Rh-
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OTHER BLOOD TYPES NO PROBLEMS IF: MOM is _____ & BABY is ____ Rh+ Rh+
Image modified from:
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Can be a ___________ IF: Mom is _____ Baby is _____
PROBLEM Can be a ___________ IF: Mom is _____ Baby is _____ Rh- Rh+ Image modified from: 1st baby OK but few baby cells entering mom’s bloodstream put mom’s immune system on alert for + cells. Next + baby, mom’s immune system can attack baby as it is growing = ERYTHROBLASTOSIS FETALIS Mom given shot (RhoGAM) after birth to prevent this
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CLOSER LOOK AT RELATIONSHIP
BETWEEN DOMINANCE AND PHENOTYPE REVEALS AN INTRIGUIGING FACT: DOMINANCE ? CODOMINANCE? INCOMPLETE DOMINANCE ? Depends on how you look at it!
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TAY-SACHS DISEASE Human genetic disorder in which brain cells are
Image from: TAY-SACHS DISEASE Human genetic disorder in which brain cells are unable to metabolize certain lipids because a crucial enzyme does not work properly. As these lipids build up in brain infant suffers seizures, blindness, loss of motor & mental function > > > leads to early death. At ORGANISMAL LEVEL acts as a recessive trait. Child with two copies of Tay-Sachs allele (tt-homozygous) has the disorder. Child with Tt or TT does not (COMPLETE DOMINANCE) At BIOCHEMICAL LEVEL- Tt individual has enzyme activity level in between the TT and tt person (INCOMPLETE DOMINANCE ?) At the MOLECULAR LEVEL – Tt individual makes equal number of normal and dysfunctional enzyme molecules (CODOMINANT ?)
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GENES are more complicated than Mendel thought
MULTIPLE ALLELE TRAITS have MORE THAN 2 allele choices EX: blood type Allele choices ___ ___ ___
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GENES are more complicated than MENDEL thought
POLYGENIC TRAITS are governed by the cumulative effect of MORE THAN ONE GENE Polygenic traits show a whole range of in-between phenotypes EX: human height. intelligence, skin & eye color
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The results form a bell shaped curve.
POLYGENIC traits are recognizable by their expression as a gradation of small differences (a continuous variation). The results form a bell shaped curve. Image from Biology; Campbell and Reece; Pearson Prentice Hall publishing as Benjamin Cummings © 2005
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Linked Genes Genes close together on same chromosome are called linked genes Linked genes do not exhibit independent assortment and they move together during crossing over if they are very close together on the chromosome.
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Sex Linked Genes Genes carried on the X chromosome are called X-linked traits. Red-green colorblindness, hemophilia, an Duchenne muscular dystropy are examples of X-linked traits.
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Hairy pinnae Y-LINKED GENES: Genes carried on the Y chromosome
Y-linked genes only show up in MALES SRY gene initiates male sex determination Hairy pinnae
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X and y chromosomes NON-HOMOLOGOUS partners
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PLEIOTROPY Most genes have multiple phenotypic effects
Image from Biology; Campbell and Reece; Pearson Prentice Hall publishing as Benjamin Cummings © 2005
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EPISTASIS Gene at one locus alters the phenotypic expression of a gene at another locus EX: Coat color in mice B = Black b = brown C = color deposited in coat c = color NOT deposited cc-mouse looks white even though it has color genes Image from Biology; Campbell and Reece; Pearson Prentice Hall publishing as Benjamin Cummings © 2005
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Pedigrees are diagrams that show how genes are passed on in families over several generations
Image from Biology; Campbell and Reece; Pearson Prentice Hall publishing as Benjamin Cummings © 2005 Pedigrees can be used to predict future offspring in families with genetic disorders
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Drawing a pedigree chart
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http://www. ikm. jmu. edu/Buttsjl/ISAT493/Hemophilia/hemophiliaeurope
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Human Genetic Disorders
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have to do with human genetics?
THINK ABOUT IT What does a can of Diet Coke and this song have to do with human genetics? (Answers to come in this slide show!)
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Many genetic ___________ result from
MANY HUMAN GENES HAVE BECOME KNOWN THROUGH THE STUDY OF GENETIC DISORDERS Many genetic ___________ result from changes in the DNA code so _________________ proteins are produced. DISORDERS NON-FUNCTIONING
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A mutation in an allele that causes a protein to be NON-FUNCTIONAL would appear
_______________ to the normal working allele. Examples of __________________________ GENETIC DISORDERS: ____________________ AUTOSOMAL RECESSIVE
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Phenylketonuria (PKU)
CAUSE: Mutation in gene for an enzyme the breaks down an amino acid called phenylalanine Build up causes ________________________ MENTAL RETARDATION
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Phenylketonuria (PKU)
ALL babies are tested for PKU before they leave the hospital. Treatment: Need a diet low in phenylalanine to extend life and prevent mental retardation If phenylalanine is an _____________, what type of foods should PKU patients avoid? __________________ Amino acid
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THINK ABOUT IT What does a can of Diet Coke have to do
with human genetics? LOOK AT THE WARNING LABEL ! NUTRASWEET ______________ is made with phenylalanine
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CYSTIC FIBROSIS thick mucous CAUSE:
Loss of 3 DNA bases in a gene for the ion channel protein that transports Cl- ions Salt balance is upset Causes a build up of thick mucous in lungs and digestive organs thick mucous Image from: BIOLOGY by Miller and Levine; Prentice Hall Publishing ©2006
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CYSTIC FIBROSIS Leads to: Respiratory and digestive complications, increased susceptibility to infections; “Salty skin” is a symptom More common in Caucasians but can affect all races. 30,000 people in U.S. have cystic fibrosis 1 in 31 people are carriers
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Heteroygous individual That carries one recessive allele for a
CARRIER Heteroygous individual That carries one recessive allele for a genetic disorder Doesn’t show the disorder themselves, but can pass it on to offspring
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TAY-SACHS DISEASE Human genetic disorder in which brain cells are
Image from: TAY-SACHS DISEASE Human genetic disorder in which brain cells are unable to metabolize certain lipids because a crucial enzyme does not work properly. As these lipids build up in brain infant suffers seizures, blindness, loss of motor & mental function > > > leads to early death. At ORGANISMAL LEVEL acts as a recessive trait. Child with two copies of Tay-Sachs allele (tt-homozygous) has the disorder. Child with Tt or TT does not (COMPLETE DOMINANCE) At BIOCHEMICAL LEVEL- Tt individual has enzyme activity level in between the TT and tt person (INCOMPLETE DOMINANCE ?) At the MOLECULAR LEVEL – Tt individual makes equal number of normal and dysfunctional enzyme molecules (CODOMINANT ?)
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TAY-SACHS DISEASE ___________________
AUTOSOMAL RECESSIVE CAUSE: Mutation in gene for an enzyme the breaks down a kind of lipid in the developing brain As these lipids build up in brain infant suffers seizures, blindness, loss of motor & mental function > > > leads to early death. Found more frequently in people with Jewish, Mediterranean, or Middle Eastern ancestry Image from:
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BY ____________________
DISORDERS CAUSED BY ____________________ ____________________ AUTOSOMAL CODOMINANT ALLELES CAUSE: A changed to T in gene for __________________ (protein in red blood cells that carries oxygen in blood)
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SICKLE CELL DISEASE SYMPTOMS:
Red blood cells become sickle shaped under low oxygen condition in persons with two sickle cell alleles (ss) Ss=Sickle cell trait Normally healthy, but can suffer some sickle cell episodes
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SICKLE CELL DISEASE Circulatory problems Cells stick in capillaries
Loss of blood cells (anemia) Organ damage (brain, heart, spleen) Can lead to DEATH
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SICKLE CELL DISEASE More common in _________________ 1 in 400 = have sickle cell disease 1 in 10 = carriers for allele Also affects persons of _______________ and _________________ descent Why do so many African Americans carry the sickle cell allele? MEDITERRANEAN MIDDLE EASTERN
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SICKLE CELL DISEASE Many can trace their ancestry to west
central Africa where ___________, a serious parasitic disease that infects red blood cells is common. Watch a video about sickle cell and malaria Images from:
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AT MOLECULAR LEVEL Sickle cell allele is CODOMINANT
ss- has abnormal hemoglobin; unhealthy SS-has normal hemoglobin and can be infected with malaria Ss-makes both normal and abnormal hemoglobin; resistant to malaria infection Sickle cell disease is a trade off for malaria resistance
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GENETIC LINK TO DISEASE
Many human genetic disorders may be the small “price we pay” for mutations that provide protection from otherwise lethal diseases Persons heterozygous for cystic fibrosis are resistant to typhoid Changes in Vitamin D receptors confer resistance to tuberculosis, but result in greater susceptibility to osteoporosis
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A mutation that codes for a new protein
whose action masks the normal allele appears as a ______________ mutation. Examples of _________________________ GENETIC DISORDERS: ____________________
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HUNTINGTON’S DISEASE ______________________
AUTOSOMAL DOMINANT CAUSE: Extra ______________ at end of gene on chromosome 4 The _____________ the more __________ the symptoms. more repeats severe
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HUNTINGTON’S DISEASE Begins in middle age
Huntington’s brain Begins in middle age Causes progressive loss of muscle control and mental function 1 in 10,000 people in U.S. have Huntington’s disease Normal brain
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A person with Huntington’s disease has a _____ chance of passing the disorder on to their offspring. 50% Problem: Symptoms of disorder usually don’t show until ____________ . . . so you don’t know you have it until ________ you have had children. MIDDLE AGE AFTER
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THINK ABOUT IT What does the song have to do with human genetics?
“This Land is My Land” was written by a musician named Woody Guthrie before he began to show the symptoms of Huntington’s disease. Click to hear Woody’s song
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Before 1993 there was no test for Huntington’s.
Woody Guthrie had a son named Arlo that was a popular musician during the 70’s Click to hear one of Arlo’s songs Before 1993 there was no test for Huntington’s. If one of your parents showed symptoms, you had to wait to see if it had been passed on to you.
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Arlo Guthrie is still performing today.
Arlo Guthrie is still performing today. He never developed symptoms for Huntington’s disease. If there is no cure, would you want to be tested and find out if you have the gene?
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ACHONDROPLASIA (One kind of Dwarfism)
AUTOSOMAL DOMINANT CAUSE: ___________________________ gene 1 in 25,000 births DD = lethal Dd = dwarf phenotype dd= = normal height 200,000 “little people” worldwide One of oldest known disorders – seen in Egyptian art
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ACHONDROPLASIA (One kind of Dwarfism)
Normal size head and torso; short arms and legs Problem with way cartilage changes to bone as bones grow
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Image from Biology; Campbell and Reece; Pearson Prentice Hall publishing as Benjamin Cummings © 2006
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A __________ is a picture of an organism’s chromosomes
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SEX DETERMINATION XX = female Xy = male
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Karyotype can show: Sex of baby Missing or extra chromosomes
Major deletions or translocations Can’t see individual gene changes
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