Mendel and Heredity

Mendel and HeredityMendel and Heredity

Section 1- The Origin of GeneticsSection 1- The Origin of Genetics

Heredity- The passing of Heredity- The passing of traitstraits from from parents to parents to offspringoffspring..

Example of traits: Example of traits: eye color, eye shape, eye color, eye shape, hair texture, heighthair texture, height

Gregor Mendel- Gregor Mendel- “Father of Genetics”“Father of Genetics”

Where was he from? Where was he from?

What was his profession? What was his profession?

What organism did he breed different varieties What organism did he breed different varieties of? of?

He was first to do what? He was first to do what?

AustriaAustriaMonkMonk

Garden PeaGarden Pea Develop rules Develop rules that accurately predict patterns of hereditythat accurately predict patterns of heredity

What branch of biology What branch of biology focuses on heredity?focuses on heredity?

GeneticsGenetics

Why were pea plants so good for Why were pea plants so good for studying heredity?studying heredity?

1. Traits of the plant were in 1. Traits of the plant were in 2 distinct forms2 distinct forms. . e.g. flower color was either e.g. flower color was either purplepurple or or whitewhite

2. The male and female parts are enclosed in 2. The male and female parts are enclosed in the same the same flowerflower. .

Why were pea plants so good for Why were pea plants so good for studying heredity?studying heredity?

3. Garden peas are 3. Garden peas are smallsmall and have a fast and have a fast growthgrowth rate and rate and reproductivereproductive cycle. cycle.

What are the 7 traits that Mendel What are the 7 traits that Mendel studied in pea plants?studied in pea plants?

..

1. Flower color1. Flower color

2. Seed color2. Seed color

3. Seed shape3. Seed shape

4. Pod color4. Pod color

5.5. Pod shapePod shape

6. Flower position6. Flower position

7. Plant height7. Plant height

Traits expressed as Simple RatiosTraits expressed as Simple Ratios

Monohybrid cross (mono= Monohybrid cross (mono= oneone)- )- a cross a cross that involves one pair of contrasting that involves one pair of contrasting traitstraits

e.g. e.g. Crossing purple flower plant with a Crossing purple flower plant with a white flower plantwhite flower plant

3 steps of Mendel’s experiments3 steps of Mendel’s experiments1. He made sure that the plants he was going to 1. He made sure that the plants he was going to

use were use were true-breedingtrue-breeding. . These original parent plants were known as These original parent plants were known as

the the P generation.P generation. 2. He 2. He cross-pollinatedcross-pollinated plants that had plants that had

contrastingcontrasting traits. He called the offspring of traits. He called the offspring of the cross the the cross the FF11 generation generation. He then . He then examined each examined each FF11 plant and recorded the plant and recorded the number of Fnumber of F1 1 plants expressing each plants expressing each traittrait..

3 steps of Mendel’s experiments3 steps of Mendel’s experiments

3. 3. He allowed the FHe allowed the F1 1 generation to generation to self-self-

pollinatepollinate and called the offspring of the F and called the offspring of the F1 1

the the FF2 2 generationgeneration. He then again . He then again countedcounted

and and characterizedcharacterized each plant. each plant.

A ratio is a A ratio is a comparison of 2 numbers comparison of 2 numbers and can be written as a fraction or and can be written as a fraction or with a colon.with a colon.

In FIn F2 2 generation, 705 purple to 224 generation, 705 purple to 224 white forms a ratio of 3:1.white forms a ratio of 3:1.

((33 purple: purple: 11 white) white)

3 steps of Mendel’s experiments3 steps of Mendel’s experiments

*****EOC Prep Question**********EOC Prep Question*****

When 2 true-breeding pea plants that show When 2 true-breeding pea plants that show contrasting forms of a trait are crossed, all of contrasting forms of a trait are crossed, all of the offspring showthe offspring show

A. Both forms of the traitA. Both forms of the trait

B. One form of the traitB. One form of the trait

C. One-fourth of each traitC. One-fourth of each trait

D. A different traitD. A different trait

Section II Mendel’s Theory Section II Mendel’s Theory

Before Mendel, many people believed in Before Mendel, many people believed in the the blendingblending hypothesis in which hypothesis in which offspring were a offspring were a blend of their parentsblend of their parents. . Mendel’s results Mendel’s results did notdid not support the support the blending hypothesis.blending hypothesis.

Mendel’s HypothesisMendel’s Hypothesis

1. For each inherited 1. For each inherited traittrait, an individual has , an individual has 2 copies of the gene- 2 copies of the gene- one from each one from each parentparent..

2. There are 2. There are alternativealternative versions of genes. versions of genes. AllelesAlleles are different versions of a gene. are different versions of a gene.

3. When 2 different alleles occur 3. When 2 different alleles occur togethertogether, one of them may be , one of them may be completely completely expressedexpressed, while the , while the other may have no other may have no observableobservable effect on the organism’s effect on the organism’s appearance.appearance.


Dominant- Dominant- expressed form of a traitexpressed form of a trait Dominant alleles are written as Dominant alleles are written as capitalcapital letters letters Recessive- Recessive- trait that was not expressedtrait that was not expressed Recessive alleles are written as Recessive alleles are written as lower-caselower-case

letters.letters.


4. When 4. When gametesgametes are formed, the are formed, the alleles in each gene in an individual alleles in each gene in an individual separateseparate independently of one independently of one another. Thus, gametes only carry another. Thus, gametes only carry 11 allele for each inherited trait. When allele for each inherited trait. When gametes gametes joinjoin during fertilization, during fertilization, each gamete contributes each gamete contributes 1 allele.1 allele.


Mendel in Modern TimesMendel in Modern Times

Homozygous- 2 alleles for a Homozygous- 2 alleles for a trait are the trait are the same.same.

Example: Example: PP or pp; YY or yyPP or pp; YY or yy

Heterozygous- 2 alleles for a Heterozygous- 2 alleles for a trait are trait are different.different.

Example: Example: Pp; YyPp; Yy


The allele for yellow pea seeds is The allele for yellow pea seeds is dominantdominant..So, Y = So, Y = yellowyellow and y = and y = greengreen

What color seeds would YY have? What color seeds would YY have? Homozygous or Heterozygous?Homozygous or Heterozygous?What color seeds would Yy have? What color seeds would Yy have? Homozygous or Heterozygous?Homozygous or Heterozygous?What color seeds would yy have? What color seeds would yy have? Homozygous or Heterozygous?Homozygous or Heterozygous?

yellow

green

yellow

The allele for freckles is dominant.The allele for freckles is dominant.So, F = So, F = frecklesfreckles and f = and f = no frecklesno freckles..

Would a child with FF have freckles?Would a child with FF have freckles?Homozygous or Heterozygous?Homozygous or Heterozygous?Would a child with Ff have freckles?Would a child with Ff have freckles?Homozygous or Heterozygous?Homozygous or Heterozygous?Would a child with ff have freckles?Would a child with ff have freckles?Homozygous or Heterozygous?Homozygous or Heterozygous?


yes

yes

no

If a pea plant is heterozygous for a particular If a pea plant is heterozygous for a particular trait, how can the alleles that control the trait trait, how can the alleles that control the trait be characterized?be characterized?

A. Two recessiveA. Two recessive

B. Two dominantB. Two dominant

C. One dominant, one recessiveC. One dominant, one recessive

D. Three dominant, one recessiveD. Three dominant, one recessive



Genotype- Genotype- the set of alleles that an individual the set of alleles that an individual hashas

Phenotype- Phenotype- the physical appearance of a traitthe physical appearance of a trait

GenotypeGenotype PhenotypePhenotype

F= frecklesF= freckles FF FF freckles freckles

f= no frecklesf= no freckles Ff freckles Ff freckles

ffff no frecklesno freckles



P = purple flowerP = purple flower pppp

p = white flowerp = white flower PpPp

PPPP

whitewhite

purplepurple

purplepurple



Y= yellow seedY= yellow seed

y = green seed y = green seed yellowyellow

yellowyellow

greengreenyyyy

YyYy

YYYY

The Laws of HeredityThe Laws of Heredity

The Law of Segregation-The Law of Segregation- 2 alleles for a 2 alleles for a trait segregate when gametes are formed.trait segregate when gametes are formed.

The Law of Independent Assortment-The Law of Independent Assortment- the the alleles of different genes separate alleles of different genes separate independently of one another during independently of one another during gamete formation.gamete formation.

Example: Gene for height separate Example: Gene for height separate differently from flower color or seed differently from flower color or seed shapeshape


Mendel found the inheritance of one Mendel found the inheritance of one trait did not trait did not influenceinfluence the inheritance the inheritance of another trait. of another trait.

For example: For example: plant height did not plant height did not influence the inheritance of another influence the inheritance of another trait such as flower colortrait such as flower color


To study how different pairs of genes To study how different pairs of genes are inherited Mendel conducted are inherited Mendel conducted dihybriddihybrid crosses. A dihybrid cross is crosses. A dihybrid cross is a cross that considers 2 a cross that considers 2 pairs of pairs of contrastingcontrasting traits. For example: traits. For example: a a cross that considers both plant height cross that considers both plant height and flower color.and flower color.



Example:Example:PPYY x ppyyPPYY x ppyypurple whitepurple whiteflowersflowers flowers flowers & && &yellow greenyellow greenseeds seedsseeds seeds

Section III Studying HereditySection III Studying Heredity

Punnett squares-Punnett squares- a diagram that predicts the a diagram that predicts the outcome of a genetic cross by considering all outcome of a genetic cross by considering all combinations of gametes in a crosscombinations of gametes in a cross

Punnett squares allow direct and simple Punnett squares allow direct and simple predictionspredictions. Punnett squares show . Punnett squares show probabilityprobability, , NOT actual NOT actual resultsresults..

Section III Studying HereditySection III Studying Heredity

Probability- Probability- the likelihood that specific the likelihood that specific events will occur.events will occur.

It can be represented as a It can be represented as a ratioratio or a or a fractionfraction or a or a percentagepercentage..

***Practice using the ***Practice using the

examples in your notesexamples in your notes

Dihybrid CrossDihybrid Cross Predictions for 2 triats: Predictions for 2 triats: You can predict 2 traits by making a You can predict 2 traits by making a dihybriddihybrid cross. cross.

Use the Use the FOILFOIL method for setting up the dihybrid method for setting up the dihybrid cross. cross.

F – First F – First O – outside O – outside I – inside I – inside L – last L – last

Practice on the two examples. Practice on the two examples.

Inheritance of TraitsInheritance of Traits

Geneticists often prepare a Geneticists often prepare a pedigreepedigree which is a which is a family history that shows how a trait is family history that shows how a trait is inherited. Pedigrees are particularly helpful if inherited. Pedigrees are particularly helpful if the trait is a the trait is a geneticgenetic disorderdisorder and the family and the family members want to know if they are members want to know if they are carrierscarriers..

Carriers- Carriers- individuals who are heterozygous for individuals who are heterozygous for an inherited disorder but do not show an inherited disorder but do not show symptoms symptoms

Inheritance of TraitsInheritance of TraitsAlbinism PedigreeAlbinism Pedigree

What do the squares represent?What do the squares represent?

What do the circles represent?What do the circles represent?

What does it mean if the shape is shaded in?What does it mean if the shape is shaded in?

males

Affected individual

females

Albinism- Albinism- the body is the body is unable to produce an unable to produce an enzyme necessary enzyme necessary for the production of for the production of melaninmelanin

Albinism is a genetic Albinism is a genetic disorder transmitted disorder transmitted by a by a recessiverecessive allele. allele.

Examine Pedigree I, which traces the dimples trait Examine Pedigree I, which traces the dimples trait through three generations of a family. Blackened symbols through three generations of a family. Blackened symbols

represent people with dimples. represent people with dimples.

Circles represent females, and squares represent males.Circles represent females, and squares represent males.

Although Jane and Joe Smith have dimples, their daughter, Clarissa, does not. Joe’s father has dimples, but his mother, and his sister, grace, do not. Jane’s father, Mr. Renaldo, her brother, Jorge, and her sister, Emily, do not have dimples, but her mother does.

Inheritance of TraitsInheritance of Traits

Sex-linked trait- Sex-linked trait- a trait whose allele is a trait whose allele is located on the X chromosomelocated on the X chromosome

Most sex-linked traits are Most sex-linked traits are recessiverecessive and are and are usually only seen in usually only seen in malesmales. .

A cross between two pea plants that produce A cross between two pea plants that produce yellow seeds results in 124 offspring: yellow seeds results in 124 offspring:

93 produce yellow seeds and 93 produce yellow seeds and

31 produce green seeds. 31 produce green seeds.

What are the likely genotypes of the plants What are the likely genotypes of the plants that were crossed?that were crossed?

B. Both YYB. Both YY

A. Both YyA. Both Yy C. Both yyC. Both yy

D. One YY, one YyD. One YY, one Yy


Traits Influenced by Several GenesTraits Influenced by Several Genes

Polygenic trait- Polygenic trait- when several genes influence one when several genes influence one traittrait

The genes for a polygenic trait may be scattered The genes for a polygenic trait may be scattered along the along the same chromosomesame chromosome or located on or located on different chromosomesdifferent chromosomes. Because of independent . Because of independent assortment and crossing-over, many different assortment and crossing-over, many different combinationscombinations appear in the offspring. appear in the offspring.

Example: eye color, skin color, height, weight, Example: eye color, skin color, height, weight, hair colorhair color

Intermediate TraitsIntermediate Traits

Incomplete dominance- Incomplete dominance- when an when an individual displays an intermediate traitindividual displays an intermediate trait

Example: Example:

1. cross red snapdragons with white 1. cross red snapdragons with white snapdragons and make pink onessnapdragons and make pink ones

2. cross straight haired parent with curly 2. cross straight haired parent with curly haired parent = child with wavy hairhaired parent = child with wavy hair

Sample ProblemSample Problem

RR = red snapdragon flowerRR = red snapdragon flowerRW = pink snapdragon flowerRW = pink snapdragon flowerWW = white snapdragon flowerWW = white snapdragon flower

Parent # 1 is Pink x Parent #2 is whiteParent # 1 is Pink x Parent #2 is whiteRW x WWRW x WWMake a Punnet Square!!!!!!!Make a Punnet Square!!!!!!!_____% red ____% white ____% pink_____% red ____% white ____% pink50500

Sample ProblemSample ProblemBB = black hair; BW = grey hair; WW = white hairBB = black hair; BW = grey hair; WW = white hair

Parent # 1 black hair BB x WWParent # 1 black hair BB x WW

Parent # 2 white hairParent # 2 white hair

Offspring:Offspring:

___% black___% black ___ % grey ___ % white___ % grey ___ % white

Make a Punnet Square!!!!Make a Punnet Square!!!!

0 0100

Traits Controlled by Genes with Traits Controlled by Genes with Three or More AllelesThree or More Alleles

Multiple Alleles- Multiple Alleles- genes with 3 or more allelesgenes with 3 or more alleles

Example: Example: ABO blood types are determined by 3 ABO blood types are determined by 3 allelesalleles

4 different blood types are: 4 different blood types are: A, B, AB,A, B, AB, and and OO

IIAA = A; I = A; IBB = B; i = O = B; i = O

Fill in the following blood types with the Fill in the following blood types with the given genotypes:given genotypes:

IIA A IIA A = ______= ______ I IAAi = ______i = ______

IIB B IIB B = ______= ______ I IBBi = ______i = ______

IIA A IIB B = ______= ______

ii = ______ii = ______

Traits Controlled by Genes with Traits Controlled by Genes with Three or More AllelesThree or More Alleles

A

ABB

O

AB

Traits with 2 Forms Displayed at the Traits with 2 Forms Displayed at the Same TimeSame Time

Codominance- Codominance- both forms of the trait are both forms of the trait are displayed (2 different dominant alleles are displayed (2 different dominant alleles are shown)shown)

*** This is different from incomplete dominance *** This is different from incomplete dominance because both traits are because both traits are displayeddisplayed..

Example: ABO blood types- Type AB blood Example: ABO blood types- Type AB blood cells carry both A and B typescells carry both A and B types

Traits influenced by the Traits influenced by the EnvironmentEnvironment

Hydrangea flowersHydrangea flowers

What color are hydrangeas What color are hydrangeas that grow in acidic soil? that grow in acidic soil? ______________________

What color are hydrangeas What color are hydrangeas that grow in neutral to that grow in neutral to basic soils? basic soils? ______________________

blue

pink

Traits influenced by Traits influenced by the Environmentthe Environment

The color of the Arctic Fox is determined by The color of the Arctic Fox is determined by temperaturetemperature..

What color is the fox in summer? ____________What color is the fox in summer? ____________

What causes the fox’s coat to darken? _________What causes the fox’s coat to darken? _________

What color does the fox turn in the winter?____What color does the fox turn in the winter?____

What advantage is this to the fox?____________What advantage is this to the fox?____________

reddish brown

Enzymes that make pigments

white

camouflage

Genetic DisordersGenetic Disorders

In order for a person to develop and In order for a person to develop and function normally, the function normally, the proteinsproteins encoded encoded by his or her genes must function by his or her genes must function precisely. Sometimes genes get precisely. Sometimes genes get damageddamaged or are or are copied incorrectlycopied incorrectly, resulting in , resulting in faultyfaulty proteins. Changes in genetic proteins. Changes in genetic material are called material are called mutationsmutations..


Sickle-Cell Sickle-Cell Anemia- Anemia- disorder that disorder that produces a produces a defective form defective form of the protein of the protein hemoglobin.hemoglobin.


The recessive allele that The recessive allele that causes sickle-cell helps causes sickle-cell helps protectprotect the cells of the cells of heterozygous individuals heterozygous individuals from the effects of from the effects of malaria. malaria. MalariaMalaria is a is a disease caused by a disease caused by a parasitic parasitic protozoanprotozoan that that invades red blood cells.invades red blood cells.


Cystic Fibrosis (CF) – Cystic Fibrosis (CF) – a fatal recessive trait; it is a fatal recessive trait; it is the most common fatal hereditary disorder the most common fatal hereditary disorder among Caucasians; thick accumulation of among Caucasians; thick accumulation of mucusmucus

About About 11 in in 2,5002,500 Caucasian infants in the U.S. is Caucasian infants in the U.S. is homozygous for the homozygous for the CFCF allele. There is no allele. There is no curecure..


Hemophilia- Hemophilia- a condition that impairs the blood’s a condition that impairs the blood’s ability to clot.ability to clot.

It is a It is a sex-linkedsex-linked trait. If the mutation appears trait. If the mutation appears on the on the XX chromosome, which a male receives chromosome, which a male receives from his from his mothermother, he does not have a normal , he does not have a normal gene on the Y chromosome to gene on the Y chromosome to compensatecompensate. . Therefore, he will develop Therefore, he will develop hemophiliahemophilia..


Huntington’s Disease (HD) – Huntington’s Disease (HD) – caused by a dominant caused by a dominant allele located on an autosome; symptoms- allele located on an autosome; symptoms- forgetfulness, irritability, loss of muscle control, forgetfulness, irritability, loss of muscle control, spasms, severe mental illness and death.spasms, severe mental illness and death.

Unfortunately, most people who have the HD allele Unfortunately, most people who have the HD allele do not know they have the disease until after they do not know they have the disease until after they have have children. children. The disease is passed The disease is passed unknowinglyunknowingly from one generation to the next. from one generation to the next.

Treating Genetic DisordersTreating Genetic Disorders

Gene therapy- replacing defective genes with Gene therapy- replacing defective genes with copies of healthy ones; allows scientists to copies of healthy ones; allows scientists to correct certain recessive disorders.correct certain recessive disorders.

What has been done successfully with the CF What has been done successfully with the CF gene?gene?

Working cf genes were attached to a cold virus which easily infects lung cells. Then, those cells produce more working cells.

Genetic DisorderGenetic Disorder

Has this been successful in humans?Has this been successful in humans?

Why?Why?

No

Most people have built up immunity to the cold virus and the lungs reject the virus and it’s cf passenger.

The mutated allele that causes Huntington’s The mutated allele that causes Huntington’s disease is:disease is:

A. Sex-linked and recessiveA. Sex-linked and recessive

B. Sex-linked and dominantB. Sex-linked and dominant

C. Autosomal and recessiveC. Autosomal and recessive

D. Autosomal and dominantD. Autosomal and dominant


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Mendel and Heredity