mendel and the gene idea chapter 14 20tutorial.htm

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