Lecture Observable Patterns OfIinheritance 2010

Observable Patterns of Observable Patterns of InheritanceInheritance

Earlobe Variation Earlobe Variation

Whether a person has attached or Whether a person has attached or detached earlobes depends on a single detached earlobes depends on a single genegene

Attached earlobes: two copies of the Attached earlobes: two copies of the recessive allele for this generecessive allele for this gene

Detached earlobes: either one or two Detached earlobes: either one or two copies of the dominant allelecopies of the dominant allele

Early Ideas about Heredity Early Ideas about Heredity

People knew that sperm and eggs People knew that sperm and eggs transmitted information about traitstransmitted information about traits

Blending theoryBlending theory Problem:Problem:

Would expect variation to disappearWould expect variation to disappear Variation in traits persistsVariation in traits persists

Gregor MendelGregor Mendel

Strong background Strong background in plant breeding and in plant breeding and mathematicsmathematics

Using pea plants, Using pea plants, found indirect but found indirect but observable evidence observable evidence of how parents of how parents transmit genes to transmit genes to offspringoffspring

Comments: GeneComments: Gene

MendelMendel never used the term, never used the term, genegene, , although he clearly made a distinction although he clearly made a distinction between, genotypes and phenotypes.between, genotypes and phenotypes.

The term, gene, was coined by The term, gene, was coined by Wilhelm Wilhelm Johannsen Johannsen (1909) based on the term, (1909) based on the term, PangenisisPangenisis which which Hugo de Vries Hugo de Vries (1889) (1889) used to describe Mendel’s concept of used to describe Mendel’s concept of inherited units that determine phenotypes.inherited units that determine phenotypes.

GenesGenes

Units of information about specific traitsUnits of information about specific traits

Passed from parents to offspringPassed from parents to offspring

Each has a specific location (locus) on a Each has a specific location (locus) on a chromosomechromosome

AllelesAlleles

Different molecular forms of a gene Different molecular forms of a gene

Arise by mutationArise by mutation

Dominant allele masks a recessive Dominant allele masks a recessive

allele that is paired with itallele that is paired with it

Allele CombinationsAllele Combinations

Homozygous Homozygous having two identical alleles at a locushaving two identical alleles at a locus AAAA or or aaaa

Heterozygous Heterozygous having two different alleles at a locushaving two different alleles at a locus AaAa

Genetic TermsGenetic Terms

A pair of homologous chromosomes

A gene locus

A pair of alleles

Three pairs of genes

Figure 11.4Page 179

Figure 11.4Page 179

Genotype & PhenotypeGenotype & Phenotype

Genotype refers to particular genes an Genotype refers to particular genes an individual carriesindividual carries

Phenotype refers to an individual’s Phenotype refers to an individual’s observable traitsobservable traits

Cannot always determine genotype by Cannot always determine genotype by observing phenotypeobserving phenotype

Parental generation P

mates to produce

First-generation offspring F1

mate to produce

Second-generation offspring F2

Monohybrid CrossesMonohybrid Crosses

Experimental intercross between Experimental intercross between

two two FF11 heterozygotes heterozygotes

AA X aa Aa (F1 monohybrids)

Aa X Aa ?

Mendel’s Mendel’s Monohybrid Monohybrid

Cross ResultsCross Results

787 tall 277 dwarf

651 long stem

207 at tip

705 purple 224 white

152 yellow428 green

299 wrinkled882 inflated

6,022 yellow 2,001 green

5,474 round 1,850 wrinkled

F2 plants showed dominant-to-recessive ratio that averaged 3:1

Figure 11.5Page 180

ProbabilityProbability

The chance that each outcome of a given The chance that each outcome of a given event will occur is proportional to the event will occur is proportional to the number of ways that event can be reachednumber of ways that event can be reached

Monohybrid Monohybrid CrossCross

IllustratedIllustrated

True-breedinghomozygous recessiveparent plant

True-breedinghomozygous dominantparent plant

An F1 plantself-fertilizesand producesgametes:

F1 PHENOTYPES

F2 PHENOTYPES

aa

Aa

AA

aaAa

Aa

Aa Aa

Aa Aa

Aa Aa

Aa Aa

Aa

Aa

AA

aa

A

A

A

A

a a

a

a

AA

Figure 11.7Page 181

Monohybrid Cross #1Monohybrid Cross #1

Long hair is dominant to short hair in Long hair is dominant to short hair in guinea pigs. Show the results of a cross guinea pigs. Show the results of a cross between a homozygous short haired male between a homozygous short haired male and a pure long haired female.and a pure long haired female.

Monohybrid Cross #1Monohybrid Cross #1

What do we know?What do we know? Both parents are homologous. Both parents are homologous. Short haired male hhShort haired male hh Long haired female HH (“H” gene is Long haired female HH (“H” gene is

dominant)dominant) hh x HHhh x HH Draw the Punnett SquareDraw the Punnett Square

#1 Punnett Square#1 Punnett Square

hh x HHhh x HH

HhHh HhHh

HhHh HhHh

All of the F1’s are hybrids, or heterogenous and they are long haired.

H

h

h

H Ova

sperm

zygotes

Meiosis2n -> n

Monohybrid #2Monohybrid #2

What is the probability that a cross What is the probability that a cross between two guinea pigs both between two guinea pigs both heterogeneous for long would produce a heterogeneous for long would produce a short haired guinea pig?short haired guinea pig?


Hh x HhHh x Hh Draw the Punnett squareDraw the Punnett square

Complete the problem (p = ¼ or 25%)Complete the problem (p = ¼ or 25%)

H h

H

h


In Holstein cattle the spotting of the coat is In Holstein cattle the spotting of the coat is due to a recessive allele while the solid due to a recessive allele while the solid colored coat is controlled by a dominant colored coat is controlled by a dominant allele. What types of offspring might be allele. What types of offspring might be produced by a cross between two spotted produced by a cross between two spotted animals?animals?


Cross: spotted cow x spotted cowCross: spotted cow x spotted cow Cross: ss x ss Cross: ss x ss (where S = solid and s = spotted)(where S = solid and s = spotted)

Is it possible to have a solid calf?Is it possible to have a solid calf?


In lemurs brown eyes are dominant over In lemurs brown eyes are dominant over blue eyes. If a heterozygous brown eyed blue eyes. If a heterozygous brown eyed female mates with a blue eyed male, what female mates with a blue eyed male, what would be the expected genotypic and would be the expected genotypic and phenotypic ratios of their offspring?phenotypic ratios of their offspring?


Cross: Brown eyed heterozygous female and a Cross: Brown eyed heterozygous female and a blue eyed male (homozygous)blue eyed male (homozygous)

B = brown and b = blueB = brown and b = blue

Bb x bb = 2 Bb and 2 bbBb x bb = 2 Bb and 2 bb Genotypic ratioGenotypic ratio Bb:bb 1:1Bb:bb 1:1 Phenotypic ratioPhenotypic ratio Brown: blue 1:1Brown: blue 1:1

Monohybrid Problem SetMonohybrid Problem Set

Form cooperative groups of 2 to 4 andForm cooperative groups of 2 to 4 and Solve the problems in the Solve the problems in the Monohybrid Monohybrid

Problem Set.Problem Set. We’ll check the answers in class.We’ll check the answers in class.

Mendel’s Theory Mendel’s Theory of Segregationof Segregation

An individual inherits a unit of information An individual inherits a unit of information (allele) about a trait from each parent(allele) about a trait from each parent

During gamete formation, the alleles During gamete formation, the alleles segregate from each other segregate from each other

Test CrossTest Cross

Individual that shows dominant phenotype Individual that shows dominant phenotype is crossed with individual with recessive is crossed with individual with recessive phenotypephenotype

Examining offspring allows you to Examining offspring allows you to determine the genotype of the dominant determine the genotype of the dominant individualindividual

BB or Bb ?Both brownphenotypes

Punnett Squares of Punnett Squares of Test CrossesTest Crosses

Homozygous recessive

a a

A

a aa

Aa Aa

aa

Homozygous recessive

a a

A

A Aa

Aa Aa

Aa

Two phenotypes 1:1 All dominant phenotype

Dihybrid Cross Dihybrid Cross

Experimental cross between individuals Experimental cross between individuals that are homozygous for different that are homozygous for different

versions of versions of twotwo traits traits

Dihybrid Cross: Dihybrid Cross: FF11 Results Results

AABB aabbx

AaBb

AB AB ab ab

TRUE-BREEDING PARENTS:

GAMETES:

F1 HYBRID OFFSPRING:

purple flowers, tall

white flowers,dwarf

All purple-flowered, tall

Figure 11.9 (1)Page 183

1/16aaBB

1/16aaBb

1/16aaBb

1/16Aabb

1/16Aabb

1/16AAbb

1/16AABB

1/16AABb

1/16AaBB

1/16AaBb

1/16AABb

1/16AaBb

1/16AaBB

1/16AaBb

1/16AaBb

1/4 AB 1/4 Ab 1/4 aB 1/4 ab

1/16aabb

1/4 AB

1/4 Ab

1/4 aB

1/4 ab

AaBb AaBbX

1/16 white-flowered, dwarf

3/16 white-flowered, tall

3/16 purple-flowered, dwarf

9/16 purple-flowered, tall

Dihybrid Cross: Dihybrid Cross: FF22 Results Results

Figure 11.9(2)Page 183

Dihybrid Problem #1Dihybrid Problem #1

A person is heterozygous for tongue-rolling and A person is heterozygous for tongue-rolling and homozygous recessive for freckles. This person homozygous recessive for freckles. This person marries an individual who is heterozygous for marries an individual who is heterozygous for both tongue-rolling and freckles. Show all the both tongue-rolling and freckles. Show all the possible genotypes for their children. possible genotypes for their children.

Tongue roller – Dominant Tongue roller – Dominant and and Non-tongue Non-tongue roller Recessiveroller Recessive

Freckles- Dominant Freckles- Dominant andand No Freckles RecessiveNo Freckles Recessive


(Tongue roller – no-freckles) x (Tongue (Tongue roller – no-freckles) x (Tongue rollerfreckles)rollerfreckles)

T = tongue rolling dominantT = tongue rolling dominant tt = non-tongue rollingtt = non-tongue rolling F = freckles dominant ff = no frecklesF = freckles dominant ff = no freckles Ttff x TtFf (the cross)Ttff x TtFf (the cross) TtffTtff produces produces TfTf and and tftf gametes gametes TtFfTtFf produces produces TFTF, , TfTf,, tFtF, and , and tf tf gametesgametes


Ttff x TtFf (symbolizes the cross)Ttff x TtFf (symbolizes the cross)

TTFf TTff TtfF Ttff

TtFf Ttff ttFf ttff

TF Tf tF tfOva

Tf

tf

sperm

zygotes


Ttff x TtFf (symbolizes the cross)Ttff x TtFf (symbolizes the cross)

TTFf TTff TtfF Ttff

TtFf Ttff ttFf ttff

TF Tf tF tfOva

Tf

tf

sperm

zygotes

Roller-frecked

Roller-no freckles

Non-rollerfreckles

Non-rollerNo freckles

Phenotypic ratios: 3:3:1:1

Independent AssortmentIndependent Assortment

Mendel concluded that the two “units” for Mendel concluded that the two “units” for the first trait were to be assorted into the first trait were to be assorted into gametes independently of the two “units” gametes independently of the two “units” for the other traitfor the other trait

Members of each pair of homologous Members of each pair of homologous chromosomes are sorted into gametes at chromosomes are sorted into gametes at random during meiosis random during meiosis

Independent AssortmentIndependent Assortment

Metaphase I:

Metaphase II:

Gametes:

1/4 AB 1/4 ab 1/4 Ab 1/4 aB

A A A A

A A A A

AAAA

B B

B B

BB

B B

BBBB

a a a a

aa aa

aaaa

bb b b

bb b b

b b b b

OR

Dihybrid Problem SetDihybrid Problem Set

Form cooperative groups of 2 to 4 andForm cooperative groups of 2 to 4 and Solve the problems in the Solve the problems in the Dihybrid Dihybrid

Problem Set.Problem Set. We’ll check the answers in class.We’ll check the answers in class.

Tremendous VariationTremendous Variation

Number of genotypes possible in Number of genotypes possible in

offspring as a result of independent offspring as a result of independent

assortment and hybrid crossing is assortment and hybrid crossing is

22nn

((nn is the number of gene loci is the number of gene loci

at which the parents differ)at which the parents differ)

Impact of Mendel’s WorkImpact of Mendel’s Work

Mendel presented his results in 1865Mendel presented his results in 1865

Paper received little noticePaper received little notice

Mendel discontinued his experiments in Mendel discontinued his experiments in 18711871

Paper rediscovered in 1900 Paper rediscovered in 1900

Dominance Relations Dominance Relations

Complete dominance Complete dominance

Incomplete dominanceIncomplete dominance

CodominanceCodominance

Incomplete Incomplete DominanceDominance

XHomozygous parent

Homozygous parent

All F1 are heterozygous

X

F2 shows three phenotypes in 1:2:1 ratio

Incomplete Dominance

Figure 11.10Page 184

Codominance: ABO Blood Codominance: ABO Blood Types Types

Gene that controls ABO type codes for Gene that controls ABO type codes for enzyme that dictates structure of a enzyme that dictates structure of a glycolipid on blood cellsglycolipid on blood cells

Two alleles (Two alleles (IIAA and and IIBB) are codominant ) are codominant when pairedwhen paired

Third allele (Third allele (ii) is recessive to others) is recessive to others

ABO Blood Type:ABO Blood Type:Allele CombinationsAllele Combinations

Range of genotypes:

Blood types:

IA IA

IA i IA IB IB i

IB IB

ii

A AB B O

or or


ABO and TransfusionsABO and Transfusions

Recipient’s immune system will attack Recipient’s immune system will attack

blood cells that have an unfamiliar blood cells that have an unfamiliar

glycolipid on surfaceglycolipid on surface

Type O is universal donor because it has Type O is universal donor because it has

neither type A nor type B glycolipidneither type A nor type B glycolipid

Pleiotropy Pleiotropy

Alleles at a single locus may have effects Alleles at a single locus may have effects on two or more traitson two or more traits

Marfan syndrome - Mutation in gene for Marfan syndrome - Mutation in gene for fibrillin affects skeleton, cardiovascular fibrillin affects skeleton, cardiovascular system, lungs, eyes, and skin system, lungs, eyes, and skin

Marfan SyndromeMarfan Syndrome

Campodactyly: Campodactyly: Unexpected Phenotypes Unexpected Phenotypes

Effect of allele varies:Effect of allele varies:

Bent fingers on both handsBent fingers on both hands

Bent fingers on one handBent fingers on one hand

No effectNo effect

Many factors affect gene expressionMany factors affect gene expression

Continuous VariationContinuous Variation

A more or less continuous range of small A more or less continuous range of small differences in a given trait among differences in a given trait among individualsindividuals

The greater the number of genes and The greater the number of genes and

environmental factors that affect a trait, the environmental factors that affect a trait, the

more continuous the variation in versions more continuous the variation in versions

of that traitof that trait

Human VariationHuman Variation

Some human traits occur as a few discrete Some human traits occur as a few discrete typestypes Attached or detached earlobes Attached or detached earlobes Many genetic disordersMany genetic disorders

Other traits show continuous variationOther traits show continuous variation HeightHeight WeightWeight Eye colorEye color IQIQ

Polygenic InheritancePolygenic Inheritance

Suppose height in humans is controlled by Suppose height in humans is controlled by three sets of genes each on a different three sets of genes each on a different chromosome (independently assorted). chromosome (independently assorted). Assume that each dominant allele Assume that each dominant allele contributes “1 unit of height” and a recessive contributes “1 unit of height” and a recessive allele produces only “½ unit of height”.allele produces only “½ unit of height”.

Two average heigth parents have the Two average heigth parents have the genotypes:genotypes:

AaBbCc x AaBbCcAaBbCc x AaBbCc

Polygenic InheritancePolygenic Inheritance

Each parent can produce 8 gametic gene Each parent can produce 8 gametic gene combinations:combinations:

ABC, ABc, AbC, aBC, Abc, aBc, abC, abcABC, ABc, AbC, aBC, Abc, aBc, abC, abc What size Punnett Square would we What size Punnett Square would we

need?need?

AABBCC

AABBCc

AABbCC

AaBBCC

AaBbCC

AaBBCc

AABbCc

AaBbCc

AABBCc

AABBcc

AABbCc

AaBBCc

AaBbCc

AaBBcc

AABbcc

AaBbcc

AABbCC

AABbCc

AAbbCC

AaBbCC

AabbCC

AaBbCc

AAbbCc

AabbCc

AaBBCC

AaBBCc

AaBbCC

aaBBCC

aaBbCC

aaBBCc

AaBbCc

aaBbCc

AaBbCC

AaBbCc

AabbCC

aaBbCC

aabbCC

aaBbCc

AaBbcc

aabbCc

AaBBCc

AaBBcc

AaBbCc

aaBBCc

aaBbCc

aaBBcc

AaBbcc

aaBbcc

AABbCc

AABbcc

AAbbCc

AaBbCc

AabbCc

AaBbcc

AAbbcc

Aabbcc

AaBbCc

AaBbcc

AabbCc

aaBbCc

aabbCc

aaBbcc

Aabbcc

aabbcc

ABC ABc Ab

CaBC

abC

aBc

Abc

abc

ABC

ABc

AbC

aBC

abC

`abc

Abc

aBc

5.5 units

5 units

4.5 units

4 units

3.5 units

6 units

3 units

ParentsAaBbCc4.5 units each

Roughly bell shaped

Polygenic inheritanceproduces a more or lesscontinuous distribution ofphenotypes. The more genesinvolved, the smoother thedistribution.

Describing Continuous Variation Describing Continuous Variation

Range of values for the trait

Nu

mb

er o

f in

div

idu

als

wit

hso

me

valu

e o

f th

e t

rait

(line of bell-shaped curve indicates continuous variation in population)

Range of values for the trait

Nu

mb

er o

f in

div

idu

als

wit

hso

me

valu

e o

f th

e t

rait

Temperature Effects Temperature Effects on Phenotype on Phenotype

Rabbit is homozygous for Rabbit is homozygous for an allele that specifies a an allele that specifies a heat-sensitive version of an heat-sensitive version of an enzyme in melanin-enzyme in melanin-producing pathwayproducing pathway

Melanin is produced in Melanin is produced in cooler areas of bodycooler areas of body


Environmental Effects on Plant Environmental Effects on Plant PhenotypePhenotype

Hydrangea macrophyllaHydrangea macrophylla Action of gene responsible for floral Action of gene responsible for floral

color is influenced by soil aciditycolor is influenced by soil acidity Flower color ranges from pink to blueFlower color ranges from pink to blue

Documents

Lecture Observable Patterns OfIinheritance 2010