Chapter 5BChapter 5B

Gregor MendelGregor Mendel

• Famous pea plant studyFamous pea plant study• Mendelian geneticsMendelian genetics• ““Father of Genetics”Father of Genetics”

• Famous pea plant studyFamous pea plant study• Mendelian geneticsMendelian genetics• ““Father of Genetics”Father of Genetics”

Father of GeneticsFather of Genetics Monk and teacher.Monk and teacher. Experimented with purebred tall and Experimented with purebred tall and

short peas. short peas.

Discovered some of the basic laws of Discovered some of the basic laws of heredity.heredity.

Studied seven purebred traits in peas.Studied seven purebred traits in peas. Called the stronger hereditary factor Called the stronger hereditary factor

dominant.dominant. Called the weaker hereditary factor Called the weaker hereditary factor

recessive.recessive. Presentation to the Science Society Presentation to the Science Society

in1866 went unnoticed. in1866 went unnoticed. He died in 1884 with his work still He died in 1884 with his work still

unnoticed.unnoticed. His work rediscovered in 1900.His work rediscovered in 1900. Known as the “Father of Known as the “Father of

Genetics”. Genetics”.

Monk and teacher.Monk and teacher. Experimented with purebred tall and Experimented with purebred tall and

short peas. short peas.

Discovered some of the basic laws of Discovered some of the basic laws of heredity.heredity.

Studied seven purebred traits in peas.Studied seven purebred traits in peas. Called the stronger hereditary factor Called the stronger hereditary factor

dominant.dominant. Called the weaker hereditary factor Called the weaker hereditary factor

recessive.recessive. Presentation to the Science Society Presentation to the Science Society

in1866 went unnoticed. in1866 went unnoticed. He died in 1884 with his work still He died in 1884 with his work still

unnoticed.unnoticed. His work rediscovered in 1900.His work rediscovered in 1900. Known as the “Father of Known as the “Father of

Genetics”. Genetics”.

Mendelian GeneticsMendelian Genetics

• Began with 34 varieties of Began with 34 varieties of pea seedspea seeds

• Chose 7 sets of opposing Chose 7 sets of opposing characteristicscharacteristics

• Chart, page 113Chart, page 113

• Began with 34 varieties of Began with 34 varieties of pea seedspea seeds

• Chose 7 sets of opposing Chose 7 sets of opposing characteristicscharacteristics

• Chart, page 113Chart, page 113

Mendel’s PeasMendel’s Peas

Self-pollinationvs.

Cross-pollination

Self-pollinationvs.

Cross-pollination

Mendel’s ObservationsMendel’s Observations

He noticed that peas are easy to breed for pure He noticed that peas are easy to breed for pure traits and he called the pure strains purebreds.traits and he called the pure strains purebreds.

He developed pure strains of peas for seven He developed pure strains of peas for seven different traits (i.e. tall or short, round or different traits (i.e. tall or short, round or wrinkled, yellow or green, etc.)wrinkled, yellow or green, etc.)

He crossed these pure strains to produce He crossed these pure strains to produce hybrids.hybrids.

He crossed thousands of plants and kept He crossed thousands of plants and kept careful records for eight years.careful records for eight years.

He noticed that peas are easy to breed for pure He noticed that peas are easy to breed for pure traits and he called the pure strains purebreds.traits and he called the pure strains purebreds.

He developed pure strains of peas for seven He developed pure strains of peas for seven different traits (i.e. tall or short, round or different traits (i.e. tall or short, round or wrinkled, yellow or green, etc.)wrinkled, yellow or green, etc.)

He crossed these pure strains to produce He crossed these pure strains to produce hybrids.hybrids.

He crossed thousands of plants and kept He crossed thousands of plants and kept careful records for eight years.careful records for eight years.

Mendel’s PeasMendel’s Peas In peas many traits appear in two forms (i.e. tall In peas many traits appear in two forms (i.e. tall

or short, round or wrinkled, yellow or green.)or short, round or wrinkled, yellow or green.) The flower is the reproductive organ and the The flower is the reproductive organ and the

male and female are both in the same flower.male and female are both in the same flower. He crossed pure strains by putting the pollen He crossed pure strains by putting the pollen

(male gamete) from one purebred pea plant on (male gamete) from one purebred pea plant on the pistil (female sex organ) of another purebred the pistil (female sex organ) of another purebred pea plant to form a hybrid or crossbred. pea plant to form a hybrid or crossbred.

In peas many traits appear in two forms (i.e. tall In peas many traits appear in two forms (i.e. tall or short, round or wrinkled, yellow or green.)or short, round or wrinkled, yellow or green.)

The flower is the reproductive organ and the The flower is the reproductive organ and the male and female are both in the same flower.male and female are both in the same flower.

He crossed pure strains by putting the pollen He crossed pure strains by putting the pollen (male gamete) from one purebred pea plant on (male gamete) from one purebred pea plant on the pistil (female sex organ) of another purebred the pistil (female sex organ) of another purebred pea plant to form a hybrid or crossbred. pea plant to form a hybrid or crossbred.

Mendel’s ResultsMendel’s ResultsMendel crossed purebred tall plants with purebred short plants and the first generation plants were all tall.

When these tall offspring were crossed the result was a ratio of 3 tall to 1 short.

Mendel’s ExperimentsMendel’s Experiments

He experimentally He experimentally crosses different crosses different strains to develop strains to develop hybrids.hybrids.

He then crossed He then crossed the hybrids and the hybrids and analyzed the analyzed the results.results.

He experimentally He experimentally crosses different crosses different strains to develop strains to develop hybrids.hybrids.

He then crossed He then crossed the hybrids and the hybrids and analyzed the analyzed the results.results.

Dominant Traits RULEDominant Traits RULE• Strong Hereditary Strong Hereditary

traits cover weak traits cover weak traits.traits.

• Mendal called Mendal called stronger traitsstronger traits• DOMINANTDOMINANT

• Mendal called Mendal called weaker traitsweaker traits• recessiverecessive

• Strong Hereditary Strong Hereditary traits cover weak traits cover weak traits.traits.

• Mendal called Mendal called stronger traitsstronger traits• DOMINANTDOMINANT

• Mendal called Mendal called weaker traitsweaker traits• recessiverecessive

• Dominant traits are Dominant traits are represented by capital represented by capital letters (T) while letters (T) while recessive traits are recessive traits are represented by lower represented by lower case letters (t). try and case letters (t). try and follow the diagram on follow the diagram on the next slide while the next slide while keeping the keeping the DOMINANT and DOMINANT and recessive letters in recessive letters in mind. ( TT) (tt )mind. ( TT) (tt )

• Dominant traits are Dominant traits are represented by capital represented by capital letters (T) while letters (T) while recessive traits are recessive traits are represented by lower represented by lower case letters (t). try and case letters (t). try and follow the diagram on follow the diagram on the next slide while the next slide while keeping the keeping the DOMINANT and DOMINANT and recessive letters in recessive letters in mind. ( TT) (tt )mind. ( TT) (tt )

In the diagram above, the dominant allele is represented by ___and the recessive allele is represented by __ .

In the diagram above, the dominant allele is represented by ___and the recessive allele is represented by __ .

Mendelian GeneticsMendelian Genetics• PP11: the original parent : the original parent

generationgeneration• FF11: first filial generation; : first filial generation;

offspring of the Poffspring of the P1 1 generationgeneration• FF22: second filial generation; : second filial generation;

offspring of the Foffspring of the F1 1 generationgeneration

• PP11: the original parent : the original parent generationgeneration

• FF11: first filial generation; : first filial generation; offspring of the Poffspring of the P1 1 generationgeneration

• FF22: second filial generation; : second filial generation; offspring of the Foffspring of the F1 1 generationgeneration

If we consider your parents to be the P1 generation, which

generation are you?

If we consider your parents to be the P1 generation, which

generation are you? 1. P1. P11

2. P2. P22

3. F3. F11

4. F4. F22

1. P1. P11

2. P2. P22

3. F3. F11

4. F4. F22

The concept of unit characteristics

The concept of unit characteristics

Factors occur in pairs.Factors occur in pairs.

Genes occur in pairs because diploid organisms have

Genes occur in pairs because diploid organisms have

1. daughter chromosomes.1. daughter chromosomes. 2. homologous pairs of 2. homologous pairs of

chromosomes. chromosomes. 3. gametes.3. gametes.

1. daughter chromosomes.1. daughter chromosomes. 2. homologous pairs of 2. homologous pairs of

chromosomes. chromosomes. 3. gametes.3. gametes.

The concept of dominant & recessive

The concept of dominant & recessive

Dominant Traits RULEDominant Traits RULE• Strong Hereditary Strong Hereditary

traits cover weak traits cover weak traits.traits.

• Mendal called Mendal called stronger traitsstronger traits• DOMINANTDOMINANT

• Mendal called Mendal called weaker traitsweaker traits• recessiverecessive

• Strong Hereditary Strong Hereditary traits cover weak traits cover weak traits.traits.

• Mendal called Mendal called stronger traitsstronger traits• DOMINANTDOMINANT

• Mendal called Mendal called weaker traitsweaker traits• recessiverecessive

• Dominant traits are Dominant traits are represented by capital represented by capital letters (T) while letters (T) while recessive traits are recessive traits are represented by lower represented by lower case letters (t). try and case letters (t). try and follow the diagram on follow the diagram on the next slide while the next slide while keeping the keeping the DOMINANT and DOMINANT and recessive letters in recessive letters in mind. ( TT) (tt )mind. ( TT) (tt )

• Dominant traits are Dominant traits are represented by capital represented by capital letters (T) while letters (T) while recessive traits are recessive traits are represented by lower represented by lower case letters (t). try and case letters (t). try and follow the diagram on follow the diagram on the next slide while the next slide while keeping the keeping the DOMINANT and DOMINANT and recessive letters in recessive letters in mind. ( TT) (tt )mind. ( TT) (tt )

Dominant traitDominant trait

• A trait that is expressed A trait that is expressed and masks the expression and masks the expression of the other traitof the other trait

• Examples on page 113Examples on page 113

• A trait that is expressed A trait that is expressed and masks the expression and masks the expression of the other traitof the other trait

• Examples on page 113Examples on page 113

Recessive traitRecessive trait

• A trait which, when in the A trait which, when in the presence of a dominant presence of a dominant trait, is not expressedtrait, is not expressed

• A trait which, when in the A trait which, when in the presence of a dominant presence of a dominant trait, is not expressedtrait, is not expressed

• Capital letters (T) = Capital letters (T) = dominantdominant

• Lowercase letters (t) = Lowercase letters (t) = recessiverecessive

• A, a; B, b; R, r; etc.A, a; B, b; R, r; etc.

• Capital letters (T) = Capital letters (T) = dominantdominant

• Lowercase letters (t) = Lowercase letters (t) = recessiverecessive

• A, a; B, b; R, r; etc.A, a; B, b; R, r; etc.

Language of Genetics Problems

Language of Genetics Problems

The concept of segregation

The concept of segregation

A cell forms gametes during which process?A cell forms gametes during which process?

1. Mitosis1. Mitosis 2. Meiosis2. Meiosis 3. Cytokinesis3. Cytokinesis 4. Fertilization4. Fertilization

1. Mitosis1. Mitosis 2. Meiosis2. Meiosis 3. Cytokinesis3. Cytokinesis 4. Fertilization4. Fertilization

Monohybrid crossMonohybrid cross• A genetic cross dealing with only A genetic cross dealing with only

one set of characteristicsone set of characteristics• A genetic cross dealing with only A genetic cross dealing with only

one set of characteristicsone set of characteristics

Punnett squarePunnett square• A diagram used to show the A diagram used to show the

possible gamete possible gamete combinations from a genetic combinations from a genetic crosscross

• A diagram used to show the A diagram used to show the possible gamete possible gamete combinations from a genetic combinations from a genetic crosscross

PUNNETT SQUAREPUNNETT SQUARE

CROSS T T X TtCROSS T T X TtCROSS T T X TtCROSS T T X Tt

CONT’DCONT’D

T T X T tT T X T tT T X T tT T X T tTT TT

TT

tt

TT TT TT TT

TT tt TT tt

Allele TypesAllele Types

• Homo - SameHomo - Same• Hetero - OppositeHetero - Opposite• Pheno – PhysicalPheno – Physical• Geno - GeneticGeno - Genetic

• Homo - SameHomo - Same• Hetero - OppositeHetero - Opposite• Pheno – PhysicalPheno – Physical• Geno - GeneticGeno - Genetic

PhenotypePhenotype• The physical expression of an The physical expression of an

organism’s genes organism’s genes • Examples: tall, short, blackExamples: tall, short, black

• The physical expression of an The physical expression of an organism’s genes organism’s genes

• Examples: tall, short, blackExamples: tall, short, black

GenotypeGenotype• The genetic make-up of an The genetic make-up of an

individual; the genes it hasindividual; the genes it has• Examples: Tt, AA, bbExamples: Tt, AA, bb

• The genetic make-up of an The genetic make-up of an individual; the genes it hasindividual; the genes it has

• Examples: Tt, AA, bbExamples: Tt, AA, bb

HomozygousHomozygous• When both alleles in a cell When both alleles in a cell

are the sameare the same• Examples: tt, TT, BB, bbExamples: tt, TT, BB, bb

• When both alleles in a cell When both alleles in a cell are the sameare the same

• Examples: tt, TT, BB, bbExamples: tt, TT, BB, bb

HeterozygousHeterozygous• When both alleles in a When both alleles in a

cell are cell are NOTNOT the same the same• Examples: Bb, TtExamples: Bb, Tt

• When both alleles in a When both alleles in a cell are cell are NOTNOT the same the same

• Examples: Bb, TtExamples: Bb, Tt

LocusLocus• The site on a chromosome The site on a chromosome

where a particular gene is where a particular gene is locatedlocated

• The site on a chromosome The site on a chromosome where a particular gene is where a particular gene is locatedlocated

AlleleAllele• One of a pair of genes that has One of a pair of genes that has

the same position on the same position on homologous chromosomeshomologous chromosomes

• Examples: T or tExamples: T or t

• One of a pair of genes that has One of a pair of genes that has the same position on the same position on homologous chromosomeshomologous chromosomes

• Examples: T or tExamples: T or t

Gene ExpressionGene Expression

Are the following sentences true or Are the following sentences true or false? false?

- Homozygous organisms are true - Homozygous organisms are true breeding for a particular trait.breeding for a particular trait.

• FalseFalse

- Plants with the same phenotype - Plants with the same phenotype always have the same genotype.always have the same genotype.

• FalseFalse

Are the following sentences true or Are the following sentences true or false? false?

- Homozygous organisms are true - Homozygous organisms are true breeding for a particular trait.breeding for a particular trait.

• FalseFalse

- Plants with the same phenotype - Plants with the same phenotype always have the same genotype.always have the same genotype.

• FalseFalse

ProbabilityProbability• In Mendel’s model of segregation, In Mendel’s model of segregation,

what was the ratio of tall plants to what was the ratio of tall plants to short plants in the F2 generation? short plants in the F2 generation?

• The ratio was 3 : 1.The ratio was 3 : 1.

• In Mendel’s model of segregation, In Mendel’s model of segregation, what was the ratio of tall plants to what was the ratio of tall plants to short plants in the F2 generation? short plants in the F2 generation?

• The ratio was 3 : 1.The ratio was 3 : 1.

Incomplete DominanceIncomplete Dominance

Incomplete DominanceIncomplete Dominance• Both alleles are expressed, but Both alleles are expressed, but

neither one is dominant.neither one is dominant.• KEY: a blending of the traitsKEY: a blending of the traits• Example: Example:

• When When red snapdragonsred snapdragons are are crossed with crossed with white snapdragonswhite snapdragons, , the resulting offspring are the resulting offspring are pinkpink..

• Both alleles are expressed, but Both alleles are expressed, but neither one is dominant.neither one is dominant.

• KEY: a blending of the traitsKEY: a blending of the traits• Example: Example:

• When When red snapdragonsred snapdragons are are crossed with crossed with white snapdragonswhite snapdragons, , the resulting offspring are the resulting offspring are pinkpink..

1st generation1st generationCwCw CwCw

CrCr

CrCr

CrCwCrCw CrCwCrCw

CrCwCrCw CrCwCrCw

2nd generation2nd generation

Phenotypic:

_________

Phenotypic:

_________

CrCr CwCw

CrCr

CwCw

CrCrCrCr CrCwCrCw

CrCwCrCw CwCwCwCw

Genotypic:

_________

Genotypic:

_________1 :1 : 2 :2 : 11

1 : 2 : 11 : 2 : 1

Human exampleHuman example

• BrachydactylyBrachydactyly• BrachydactylyBrachydactyly

CodominanceCodominance• Two alleles for a gene are Two alleles for a gene are

both expressed.both expressed.• KEY: both alleles are KEY: both alleles are

expressed with no blending.expressed with no blending.• Example:Example:

• In horses, red hair + white hair In horses, red hair + white hair = roan (red and white hairs).= roan (red and white hairs).

• Two alleles for a gene are Two alleles for a gene are both expressed.both expressed.

• KEY: both alleles are KEY: both alleles are expressed with no blending.expressed with no blending.

• Example:Example:• In horses, red hair + white hair In horses, red hair + white hair

= roan (red and white hairs).= roan (red and white hairs).

Multiple AllelesMultiple Alleles

• One of several alleles can One of several alleles can be at a given locusbe at a given locus

• Example: human blood Example: human blood types (A, B, AB, O)types (A, B, AB, O)

• One of several alleles can One of several alleles can be at a given locusbe at a given locus

• Example: human blood Example: human blood types (A, B, AB, O)types (A, B, AB, O)

Human Blood TypesHuman Blood Types

Dominant Alleles

IA and IB

Recessive Allele

i

Dominant Alleles

IA and IB

Recessive Allele

i

IA IA type A blood

IA i type A

IB IB type B

IB i type B

IA IB type AB

ii type O

IA IA type A blood

IA i type A

IB IB type B

IB i type B

IA IB type AB

ii type O

Suppose a woman who has type AB blood marries a man who is heterozygous for blood type A.

What blood types might their children have?

Suppose a woman who has type AB blood marries a man who is heterozygous for blood type A.

What blood types might their children have?

type AB x heterozygous type Atype AB x heterozygous type A IAIA IBIB

IAIA

ii

IA IAIA IA IA IBIA IB

IA iIA i IB iIB i

Dihybrid CrossesDihybrid Crosses

• Genetic crosses dealing Genetic crosses dealing with TWO characteristics at with TWO characteristics at the same timethe same time

• Example: Example: green/yellow peas green/yellow peas AND tall/short pea plantsAND tall/short pea plants

• Genetic crosses dealing Genetic crosses dealing with TWO characteristics at with TWO characteristics at the same timethe same time

• Example: Example: green/yellow peas green/yellow peas AND tall/short pea plantsAND tall/short pea plants

Mendel’s Concept of Independent Assortment

Mendel’s Concept of Independent Assortment• The segregation of one set The segregation of one set

of alleles during gamete of alleles during gamete formation is not affected by formation is not affected by another set.another set.

• The segregation of one set The segregation of one set of alleles during gamete of alleles during gamete formation is not affected by formation is not affected by another set.another set.

Multiple Gene InteractionMultiple Gene Interaction• Sometimes two or more Sometimes two or more

genes working together genes working together result in a single trait.result in a single trait.

• Examples: many human Examples: many human traits such as hair color traits such as hair color and skin colorand skin color

• Sometimes two or more Sometimes two or more genes working together genes working together result in a single trait.result in a single trait.

• Examples: many human Examples: many human traits such as hair color traits such as hair color and skin colorand skin color

Sex-Linked TraitsSex-Linked Traits

Two Types of ChromosomesTwo Types of Chromosomes• AutosomesAutosomes

• non-sex-determining non-sex-determining chromosomes chromosomes

• humans = 22 pairshumans = 22 pairs• Sex chromosomesSex chromosomes

• XX = femaleXX = female• XY = maleXY = male

• AutosomesAutosomes• non-sex-determining non-sex-determining

chromosomes chromosomes • humans = 22 pairshumans = 22 pairs

• Sex chromosomesSex chromosomes• XX = femaleXX = female• XY = maleXY = male

Female = XXFemale = XXMale = XYMale = XY

XX XX

XX

YY

XX XX XXXX

XYXY XYXY

Sex-Linked TraitsSex-Linked Traits• Some genes are carried Some genes are carried

on the sex chromosomes.on the sex chromosomes.• The X and Y The X and Y

chromosomes are not chromosomes are not homologous.homologous.

• Some genes are carried Some genes are carried on the sex chromosomes.on the sex chromosomes.

• The X and Y The X and Y chromosomes are not chromosomes are not homologous.homologous.

Sex-Linked TraitsSex-Linked Traits• Males inherit more sex-linked Males inherit more sex-linked

disorders because they only disorders because they only have one gene for the trait.have one gene for the trait.

• If there is a defective gene on If there is a defective gene on X, there wouldn’t be a normal X, there wouldn’t be a normal gene on Y to counteract it. gene on Y to counteract it.

• Males inherit more sex-linked Males inherit more sex-linked disorders because they only disorders because they only have one gene for the trait.have one gene for the trait.

• If there is a defective gene on If there is a defective gene on X, there wouldn’t be a normal X, there wouldn’t be a normal gene on Y to counteract it. gene on Y to counteract it.

Sex-Linked TraitsSex-Linked Traits• Indicated with a superscript Indicated with a superscript

above the X and Y above the X and Y chromosomeschromosomes

• Example:Example:• X X HH X X hh

• X X HH Y Y

• Indicated with a superscript Indicated with a superscript above the X and Y above the X and Y chromosomeschromosomes

• Example:Example:• X X HH X X hh

• X X HH Y Y

Human ExamplesHuman Examples• Red-green colorblindnessRed-green colorblindness• HemophiliaHemophilia

• Lack a blood chemical that Lack a blood chemical that allows for blood clottingallows for blood clotting

• Red-green colorblindnessRed-green colorblindness• HemophiliaHemophilia

• Lack a blood chemical that Lack a blood chemical that allows for blood clottingallows for blood clotting

XH XH normal femaleXH Xh carrier female

A heterozygous female that A heterozygous female that does not have the disease, but does not have the disease, but she does carry the gene for the she does carry the gene for the

traittraitXh Xh hemophiliac femaleXH Y normal maleXh Y hemophiliac male

XH XH normal femaleXH Xh carrier female

A heterozygous female that A heterozygous female that does not have the disease, but does not have the disease, but she does carry the gene for the she does carry the gene for the

traittraitXh Xh hemophiliac femaleXH Y normal maleXh Y hemophiliac male

carrier female x normal male

carrier female x normal male

XHXH XhXh

XHXH

YY

XH XHXH XH XH XhXH Xh

XHYXHY XhYXhY