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Mendel and the Gene Idea
Chapter 14
http://www.jic.bbsrc.ac.uk/germplas/pisum/zgs4f.htm
http://sps.k12.ar.us/massengale/genetics%20tutorial.htm
Transmission of characteristics from parents to offspring = ___________________
The science that studies how those characteristics are passed on = _________
heredity
Genetics
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
Blending
Particulate
http://www.digitalartform.com/archives/images/gradColorMix.jpg
http://www.magicbob2000.com/resources/Svengali%20cards.jpg
______________________________
• Father of Genetics• Looked at one trait at a
time• Made experimental
crosses• Large sample size• Kept careful records
http://www.jic.bbsrc.ac.uk/germplas/pisum/zgs4f.htm
Gregor Mendelhttp://strongbrains.com/science/biology/default.htm
MENDEL’S PEA EXPERIMENTS Peas are “self pollinating”
ie., egg and sperm come from same plant
http://hus.yksd.com/distanceedcourses/YKSDbiology/lessons/FourthQuarter/Chapter11/11-1/images/MendelExperiment.gif
Mendel’s experiments Allowed him to experiment and observe
offspring produced from a variety of known genetic crosses
MENDEL’S EXPERIMENTS
____ generation (_________)
____ generation(______= offspring)
___ generation
P1
F1
F2
parental
filial
PATTERNS ARE THE KEY
Image modified from:http://www.laskerfoundation.org/rprimers/gnn/timeline/1866.html http://www.accessexcellence.org/AB/GG/mendel.html
Genetic makeup of organism = _________
Appearance of organism = ____________
genotype
phenotype
Image modified from: http://www.newtonswindow.com/problem-solving.htm
Image from Biology; Campbell and Reece; Pearson Prentice Hall publishing as Benjamin Cummings © 2005
MENDEL’S MODEL
1.Alternative versions of genes account for variations in inherited traits.
2.For each trait, an organism inherits TWO alleles.
3.If the two alleles at a locus differ, one determines the organism’s appearance; the other has no effect.
4.The two alleles for a character separate during gamete formation and end up in different gametes.
____________ = Observable characteristicEx: flower color, height, pod shape
___________ = choices for a traitEx: blue eyes, green eyes, brown eyes)
Trait
Allelehttp://sps.k12.ar.us/massengale/genetics%20tutorial.htm
Image modified from: http://www.newtonswindow.com/problem-solving.htm
1.Alternative versions of genes account for variations in inherited traits.
From Biology; Miller and Levine; Pearson Prentice Hall publishing as Benjamin Cummings © 2005 Pearson Education Inc
2. For each trait, an organism inherits TWO alleles.
Image from Biology; Campbell and Reece; Pearson Prentice Hall publishing as Benjamin Cummings © 2005
Organisms with two identical alleles for a gene = ____________OR ______________
Organism with two different alleles for a gene = _______________OR ___________
HOMOZYGOUS PURE BREEDING
HETEROZYGOUS HYBRID
3. If the two alleles at a locus differ,one determines the organism’sappearance; the other has no effect.
_________________ = allele that masks the presence of another allele
__________________ = An allelethat is hidden
DOMINANT
RECESSIVE
Image from Biology; Campbell and Reece; Pearson Prentice Hall publishing as Benjamin Cummings © 2005
Image modified from: http://www.emc.maricopa.edu/faculty/farabee/BIOBK/Crossover.gif
4. The two alleles for a traitseparate during gamete formation and end up in different gametes.
= MENDEL’S LAW OFSEGREGATION
http://www.tokyo-med.ac.jp/genet/anm/mimov.gi
Mendel’s Law of Independent Assortment
Two or more pairs of alleles segregate independently of one another during gamete formation.
http://fig.cox.miami.edu/~cmallery/150/mitosis/c13x9independent-assortment.jpg
_______________ 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 ____
PROBABILITY
1/425%
1:3
COIN FLIPThere are 2 possible
outcomes:HEADS TAILS
capital
http://www.arborsci.com/CoolStuff/CoinFlip.jpg
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.
1/2 50% 1:1
PROBABILITIESPast 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.
MULTIPLICATION & ADDITION RULESTo 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
http://www.arborsci.com/CoolStuff/CoinFlip.jpg
MULTIPLICATION RULE WORKS FOR PREDICTING GENETIC CROSSES, TOO
Tt X TtWhat is the probability offspring will be
tt ?
½ X ½ = ¼
Punnett by Riedell
Each egg has a ½ chance of passing on t.
Each sperm has ½ chance of passing on t.
ADDITION RULE
To figure out the probability of an offspring being heterozygous (Tt)
1st probabilityT from momt from dad
½ X ½ = ¼
Punnett by Riedell
T can come from mom and t from dad ORt can come from the mom and T from the dad but not both (events are mutually exclusive)
2nd probabilityt from momT from dad½ X ½ = ¼
¼ + ¼ = ½
HOW CAN YOU TELL THE GENOTYPE?
Tall plant has two possible genotypes ___ OR ___
Make a ___________with a _____________________
TT
Images from: BIOLOGY by Miller & Levine; Prentice Hall Publishing ©2006
Tt
TEST CROSSHOMOzygous recessive
T T
t
t
T t t
t
Tt Tt
Tt Tt
Tt tt
Tt tt
GENES are more complicated than Mendel
thought1. Environment influences gene
expression2. Spectrum of dominance3. Multiple allele traits 4. Polygenic traits5. Gene Linkage 6. Pleiotropy7. Epistasis
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
Environment influences Phenotype
“Nature vs Nurture”
• Color of hydrangea flowers variesdepending on pH of soil
Images from: http://www.gardensablaze.com/Shrubs/ShrubsHydrangea.htm
GENES are more complicated than MENDEL
thoughtSpectrum of DOMINANCE____________________________________________________________
COMPLETE DOMINANCE
INCOMPLETE DOMINANCECO-DOMINANCE
COMPLETE DOMINANCE
If two alleles are present
DOMINANT allele masks
the RECESSIVE allele
Recessive trait shows again in F2 generation in3:1 ratio
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookTOC.html
INCOMPLETE DOMINANCE
Heterozygous snapdragonsshow a blended intermediatetrait
Image modified from: http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookTOC.html
CO-DOMINANCEBOTH traits are expressed at the same
time side by side in heterozygote
A ROAN HORSE has both RED and WHITE hair side by side
CO-DOMINANCEBoth traits are expressed together
(NO BLENDING) in heterozygote
Persons with an A alleleAND a B allele have AB blood type
• Membrane proteins with sugars attached that help cells “recognize self”
= ______________
• Type of sugars attachedgives cell its “Blood type”
• I is used for blood type alleles
GLYCOPROTEINS
http://www.mannanw.com/super-sugars.htm
REMEMBER
BLOOD TYPESPerson withIA IA OR IA igenotypehas cells with a certainglycoprotein “A” on its surface
TYPE “A” BLOOD
BLOOD TYPES Person with IB IB OR IB i genotypehas cells with a differentglycoprotein “B” on its surface
TYPE “B” BLOOD
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
A and B are CO-DOMINANT
Person with IA IB
genotype has BOTH“A” and “B” glycoproteins on its
surface
TYPE “AB” Blood
BLOOD TYPE FREQUENCY IN USA
http://www.reachoutmichigan.org/funexperiments/agesubject/lessons/newton/BldTyping.html
A 40%B 10%
AB 4%O 46%
BLOOD TYPES
See A blood cells as DIFFERENT!
IMMUNE SYSTEM ATTACKS!Body images modified from:
http://www.new-fitness.com/images/body_shapes.jpg
YOU DON’T HAVEANYTHING I DON’T HAVE!
DONORBLOOD
BLOOD TYPES
A and O see B cells as DIFFERENT! IMMUNE SYSTEM ATTACKS!
Body images modified from: http://www.new-fitness.com/images/body_shapes.jpg
YOU DON’T HAVEANYTHING I DON’T HAVE!
DONORBLOOD
BLOOD TYPES
A, B, and O see AB cells as DIFFERENT! IMMUNE SYSTEM ATTACKS!
Body images modified from: http://www.new-fitness.com/images/body_shapes.jpg
YOU’RE LIKE ME!
DONORBLOOD
BLOOD TYPES
Body images modified from: http://www.new-fitness.com/images/body_shapes.jpg
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”
UNIVERSAL DONOR
O
BLOOD TYPES
Body image modified from: http://www.new-fitness.com/images/body_shapes.jpg
______ can RECEIVE FROM EVERY BLOOD TYPE = ________________________UNIVERSAL RECIPIENT
AB
ABO SYSTEM is NOT THE ONLY ONE
Rh+ Rh-
MOM is _____& BABY is ____
OTHER BLOOD TYPESNO PROBLEMS IF:
Image modified from: http://www.wsd1.org/lessonplans/images/Body.gif
MOM is _____& BABY is _____
Rh+
Rh+
Rh+
Rh-
Can be a ___________ IF: Mom is _____ Baby is _____
Image modified from: http://www.wsd1.org/lessonplans/images/Body.gif
1st baby OK but few baby cells entering mom’s bloodstreamput mom’s immune system on alert for + cells.
Next + baby, mom’s immune system can attack baby as it isgrowing = ERYTHROBLASTOSIS FETALIS
Mom given shot (RhoGAM) after birth to prevent this
Rh+
PROBLEM
Rh-
GENES are more complicated than Mendel
thoughtMULTIPLE ALLELE TRAITS have MORE THAN 2 allele choices
EX: blood typeAllele choices ___ ___ ___A B O
GENES are more complicated than MENDEL
thoughtPOLYGENIC 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 colorhttp://www.bcps.org/offices/lis/models/life/images/grow.JPG
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
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.
http://anthro.palomar.edu/biobasis/bio_3.htm
Sex Linked GenesGenes carried on the X chromosome are
called X-linked traits.
• Red-green colorblindness, hemophilia, an Duchenne muscular dystropy are examples of X-linked traits.
http://gizmodo.com/gadgets/peripherals/samsung-develops-lcd-for-colorblind-036306.php
Y-LINKED GENES: Genes carried on the Y chromosome
Y-linked genes only show up in MALES
Hairy pinnaeSRY geneinitiates male sexdetermination
http://www.ndpteachers.org/perit/hairears.gifhttp://content.answers.com/main/content/wp/en/thumb/f/fb/200px-YChromShowingSRY2.png
X and y chromosomesNON-HOMOLOGOUS partners
PLEIOTROPY
Most genes have multiple
phenotypic effects
Image from Biology; Campbell and Reece; Pearson Prentice Hall publishing as Benjamin Cummings © 2005
EPISTASIS• Gene at one locus alters the phenotypic
expression of a gene at another locus
EX: Coat color in miceB = Black b = brown
C = color deposited in coatc = color NOT deposited
cc-mouse looks white eventhough it has color genes
Image from Biology; Campbell and Reece; Pearson Prentice Hall publishing as Benjamin Cummings © 2005
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
Drawing a pedigree chart
http://www.ikm.jmu.edu/Buttsjl/ISAT493/Hemophilia/hemophiliaeurope.html
Human Genetic Disorders
THINK ABOUT IT
What does a can of Diet Coke and this songhave to do with human
genetics?(Answers to come in this slide show!)
MANY HUMAN GENES HAVE BECOME
KNOWN THROUGH THE STUDY OF GENETIC DISORDERS
Many genetic ___________ result fromchanges in the DNA code so
_________________ proteins are produced.
DISORDERS
NON-FUNCTIONING
http://patentdocs.typepad.com/photos/uncategorized/2007/05/28/dna1.gif
A mutation in an allele that causes a protein to be NON-FUNCTIONAL would appear
_______________ to the normal working allele.
Examples of __________________________ GENETIC DISORDERS:
____________________
____________________
____________________
RECESSIVE
PHENYLKETONURIA (PKU)
TAY-SACHS DISEASE
CYSTIC FIBROSIS
AUTOSOMAL RECESSIVE
Phenylketonuria (PKU)
CAUSE: Mutation in gene for an enzyme the breaks down an amino acid called phenylalanine
Build up causes ________________________MENTAL RETARDATION
http://biology.clc.uc.edu/courses/bio104/protein.htm
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
PROTEINS !
THINK ABOUT IT
What does a can of Diet Coke have to dowith human genetics?
LOOK AT THE WARNING LABEL !
______________ is made with phenylalanineNUTRASWEET
CYSTIC FIBROSISCAUSE: • 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
CYSTIC FIBROSISLeads 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
http://www.biochem.arizona.edu/classes/bioc460/spring/rlm/RLM36.1.html
Heteroygous individualThat carries one recessive allele for a genetic disorder
Doesn’t show the disorder themselves,but can pass it on tooffspring
CARRIER
TAY-SACHS DISEASE___________________
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: http://www.djsfoundation.org/images/Steeler%20pics%20Dylan.jpg
AUTOSOMAL RECESSIVE
DISORDERS CAUSED BY ____________________
____________________SICKLE CELL DISEASE
CAUSE: A changed to T in gene for
__________________ (protein in red blood cells that carries oxygen in blood)
HEMOGLOBIN
AUTOSOMAL CODOMINANT ALLELES
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
SICKLE CELL DISEASE
Circulatory problemsCells stick in capillariesLoss of blood cells (anemia)Organ damage (brain, heart, spleen)Can lead to DEATH
SICKLE CELL DISEASEMore 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?
AFRICAN AMERICANS
MEDITERRANEANMIDDLE EASTERN
SICKLE CELL DISEASEMany can trace their ancestry to
westcentral Africa where ___________,a serious parasitic disease thatinfects red blood cells is common.
Images from: http://en.wikipedia.org/wiki/Malaria
MALARIA
Watch a video about sickle cell and malaria
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
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
DOMINANCE ?
CODOMINANCE?
INCOMPLETE DOMINANCE ?
Depends on how you look at it!
CLOSER LOOK AT RELATIONSHIP BETWEEN DOMINANCE AND PHENOTYPEREVEALS AN INTRIGUING FACT:
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 levelin between the TT and tt person (INCOMPLETE DOMINANCE ?)
At the MOLECULAR LEVEL – Tt individual makes equal number of normal and dysfunctional enzyme molecules (CODOMINANT ?)
Image from: http://www.djsfoundation.org/images/Steeler%20pics%20Dylan.jpg
HUNTINGTON’S DISEASE______________________
CAUSE: Extra 40-100 ______________ at end of gene on chromosome 4
The _____________ . . . the more __________ the symptoms.
severe
CAG repeats
http://www.healthsystem.virginia.edu/internet/huntdisease/images/cag.gif
more repeats
AUTOSOMAL DOMINANT
HUNTINGTON’S DISEASE
Begins in middle ageCauses progressive
loss of muscle control and mental function
1 in 10,000 people in U.S. have Huntington’s disease
http://www.scielo.br/img/revistas/bjmbr/v39n8/html/6233i01.htm
Huntington’s brain
Normal brain
A person with Huntington’s disease has a _____ chance of passing the disorder on totheir offspring.
Problem:Symptoms of disorder usually don’t show until ____________ . . .
so you don’t know you have it until ________ you have had children.
50%
MIDDLE AGE
AFTER
THINK ABOUT IT
What does the songhave 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 hearWoody’s song
Woody Guthrie had a son named Arlo that was a popular musician during the 70’s
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.
Click to hear one of Arlo’s songs
Arlo Guthrie is still performing today.
He never developed symptoms for Huntington’s disease.
http://www.jimdirden.com/woodyfest2004/artists/index_3.htm
If there is no cure, would you want to be tested and find out if you have the gene?
http://webs.wichita.edu/depttools/depttoolsmemberfiles/accomp/question_mark%20(WinCE).jpg
ACHONDROPLASIA(One kind of Dwarfism)
CAUSE: ___________________________ gene
200,000 “little people” worldwide
One of oldest known disorders – seen in Egyptian art
AUTOSOMAL DOMINANT
1 in 25,000 births
DD = lethalDd = dwarf phenotypedd= = normal height
ACHONDROPLASIA(One kind of Dwarfism)
Normal size head and torso; short arms and legs
Problem with way cartilage changes to bone as bones grow
Image from Biology; Campbell and Reece; Pearson Prentice Hall publishing as Benjamin Cummings © 2006
A __________ is a picture of an organism’s chromosomes
KARYOTYPE
SEX DETERMINATIONXX =
Xy =
female
male
Karyotype can show:• Sex of baby• Missing or extra chromosomes• Major deletions or translocations• Can’t see individual gene changes
http://content.answers.com/main/content/wp/en/1/11/Down_Syndrome_Karyotype.pnghttp://content.answers.com/main/content/wp/en/thumb/f/f3/220px-Down_syndrome_translocation.png