Mendelian GeneticsMendelian Genetics

Hopefully a ReviewHopefully a Review

Gregor MendelGregor Mendel German/Austrian German/Austrian

monk in the mid monk in the mid 1800s1800s

Father of genetics, Father of genetics, heredityheredity

Mendel's LawsMendel's Laws Tested the Tested the

properties of properties of inheritance using inheritance using peaspeas

Heredity VocabularyHeredity Vocabulary A A charactercharacter is a is a

heritable feature, i.e. heritable feature, i.e. eye coloreye color

A A genegene codes for a codes for a charactercharacter

A A traittrait is a specific is a specific variant, i.e. brown eyesvariant, i.e. brown eyes

An An alleleallele codes for a codes for a specific traitspecific trait

P Generation P Generation (original parent (original parent generation)generation)

F1F1 – first set of – first set of offspringoffspring

F2F2 – second set – second set of offspring of offspring (produced by F1 (produced by F1 generation)generation)

Either-Or TraitsEither-Or Traits Mendel studied Mendel studied

either-or traits, either-or traits, such as flower colorsuch as flower color

Flowers were Flowers were either purple either purple or whiteor white

Continuums (i.e. Continuums (i.e. height) are usually height) are usually caused by multiple caused by multiple genesgenes

Mendel's StudyMendel's Study Mendel Crossed Mendel Crossed

White and Purple White and Purple flowersflowers

All of the F1 All of the F1 generation were generation were purplepurple (not an (not an intermediate)intermediate)

F2 generation was F2 generation was 3/43/4thth purple, 1/4 purple, 1/4thth whitewhite

Mendel's ReasoningMendel's Reasoning The heritable factor The heritable factor

for white flowers was for white flowers was present in the F1 present in the F1 generation, but not generation, but not expressedexpressed

The heritable factor The heritable factor for purple flowers for purple flowers must must dominatedominate the the heritable factor for heritable factor for white flowerswhite flowers

The Scientific ProcessThe Scientific Process

Mendel performed Mendel performed nearly a thousand nearly a thousand trials on flower trials on flower colorcolor

Also observed the Also observed the same patterns in 6 same patterns in 6 other charactersother characters

Found similar Found similar resultsresults

Mendel's HypothesesMendel's Hypotheses

1)1) Different versions of Different versions of genes (alleles) genes (alleles) account for variations in inherited account for variations in inherited characterscharacters

2)2) For each character, an organism inherits one For each character, an organism inherits one allele from its mother, one from its fatherallele from its mother, one from its father

a) (Mendel made this assumption with no a) (Mendel made this assumption with no knowledge of chromosomes!)knowledge of chromosomes!)

3)3) If the two alleles are different one will be If the two alleles are different one will be dominant and fully expresseddominant and fully expressed, while the , while the other will have no effect on the individual's other will have no effect on the individual's appearanceappearance

AllelesAlleles

Alleles are the specific genes coding for a Alleles are the specific genes coding for a particular traitparticular trait

Mendel's Hypotheses Mendel's Hypotheses con.con.

4) The two alleles for each character 4) The two alleles for each character separateseparate when gametes are created when gametes are created (Mendel's law of segregation)(Mendel's law of segregation) Mendel made this claim before Mendel made this claim before

chromosomes were discovered and long chromosomes were discovered and long before meiosis/mitosis was understoodbefore meiosis/mitosis was understood

But he was mostly right, we do But he was mostly right, we do inherit inherit one set of alleles from each parentone set of alleles from each parent

Dominant and Dominant and Recessive FeaturesRecessive FeaturesDominantDominant

Exhibited if either of Exhibited if either of a person’s genes are a person’s genes are the the dominant alleledominant allele

Individuals can have Individuals can have 1 or 2 dominant 1 or 2 dominant alleles, in most cases alleles, in most cases it doesn’t matterit doesn’t matter

RecessiveRecessive

Exhibited if Exhibited if both both of of a person’s genes a person’s genes are the are the recessiverecessive alleleallele

A recessive trait can A recessive trait can only be expressed only be expressed with 2 recessive (0 with 2 recessive (0 dominant) allelesdominant) alleles

Punnett SquaresPunnett Squares Let B code for the allele for Purple Let B code for the allele for Purple

flowers and b code for the allele flowers and b code for the allele for white flowersfor white flowers

The original purple flowers were The original purple flowers were all BB (both alleles were the all BB (both alleles were the same)same)

The original white flowers MUST The original white flowers MUST HAVE BEEN bb (the only way they HAVE BEEN bb (the only way they could be white)could be white)

The F1 CrossThe F1 Cross

The F2 Generation The F2 Generation Punnet SquarePunnet Square

Phenotype vs. Phenotype vs. GenotypeGenotype

The The phenotypephenotype of an organism is its of an organism is its appearance for that characterappearance for that character

The The genotypegenotype is the genetic make up is the genetic make up

Bb or BBBb or BB bbbb

TestcrossTestcross We can determine the We can determine the

genotype of an organism by genotype of an organism by crossing (mating) it with an crossing (mating) it with an individual with recessive individual with recessive allelesalleles

If the offspring are a mix of If the offspring are a mix of phenotypes, then the phenotypes, then the organism was heterozygousorganism was heterozygous

If the offspring all exhibit the If the offspring all exhibit the dominant pattern, then the dominant pattern, then the organism was homozygous organism was homozygous dominantdominant

Dihybrid CrossesDihybrid Crosses What if we cross What if we cross

individuals individuals differing in 2 differing in 2 characters?characters?

Will the dominant Will the dominant alleles stick alleles stick together and the together and the recessive alleles recessive alleles stick together?stick together?

NO!!!! Alleles Sort NO!!!! Alleles Sort IndependentlyIndependently

Each allele is Each allele is inherited inherited independently independently (unless they are (unless they are on the same on the same chromosome)chromosome)

RrYy x RrYy leads RrYy x RrYy leads to 9:3:3:1 patternto 9:3:3:1 pattern

Probability/ The Probability/ The Multiplication RuleMultiplication Rule

The odds of 2 events The odds of 2 events both happening = the both happening = the odds of one times the odds of one times the odds of the otherodds of the other

I.e. the odds of pulling a I.e. the odds of pulling a red jack out of a deck = red jack out of a deck = 1/2 * 1/13 = 1/26 (or 1/2 * 1/13 = 1/26 (or 2/52)2/52)

The odds of rolling 3 6’s The odds of rolling 3 6’s in a row = 1/6 * 1/6 * 1/6 in a row = 1/6 * 1/6 * 1/6 = 1/216= 1/216

The Multiplication RuleThe Multiplication Rule

Assume Assume heterozygous heterozygous parentsparents

Probability of both Probability of both alleles ending up alleles ending up recessive = recessive = probability of probability of receiving allele receiving allele from mother * from mother * probability of probability of receiving allele receiving allele from fatherfrom father= ½ * ½ = ¼= ½ * ½ = ¼

Multiplication RuleMultiplication Rule Assume parents are Assume parents are

YyRrYyRr The odds of giving a The odds of giving a

recessive trait are ½ recessive trait are ½ for each characterfor each character

The odds of a parent The odds of a parent giving 2 recessive giving 2 recessive alleles (yr) is ¼ (1/2 * alleles (yr) is ¼ (1/2 * ½)½)

Thus the odds of Thus the odds of offspring ending up offspring ending up with 2 recessive traits with 2 recessive traits from both parents is ¼ from both parents is ¼ * ¼ = 1/16 * ¼ = 1/16

The Addition RuleThe Addition Rule

The odds of either of The odds of either of 2 events occurring is 2 events occurring is found by adding found by adding themthem

I.e. the odds of I.e. the odds of rolling a 1 or a 6 = rolling a 1 or a 6 = 1/6 + 1/6 = 1/31/6 + 1/6 = 1/3

The odds of pulling The odds of pulling an Ace or a King = an Ace or a King = 1/13 + 1/13 = 2/13 1/13 + 1/13 = 2/13

The Rule of AdditionThe Rule of Addition There are two There are two

possibilities to end possibilities to end up heterozygous up heterozygous with heterozygous with heterozygous parentsparents

To find the To find the probability of probability of ending up ending up heterozygous you heterozygous you add the individual add the individual oddsodds ¼ + ¼ = ½

The other methodThe other methodMake a dihybrid or trihybrid crossMake a dihybrid or trihybrid cross

List every possible combination of List every possible combination of alleles each parent could givealleles each parent could give

So for 2 MmNn individuals, you So for 2 MmNn individuals, you would have:would have:

MN Mn mN mn

MN MMNN MmNn MmNN MmNn

Mn MMNn MMnn MmNn Mmnn

mN MmNN MmNn mmNN mmNn

mn MmNn Mmnn mmNn mmnn

Calculating the Calculating the ProbabilityProbability

Imagine a tri-hybrid cross, with two Imagine a tri-hybrid cross, with two parents who are MmNnOo. What are parents who are MmNnOo. What are the odds of ending up recessive in all the odds of ending up recessive in all 3 characters?3 characters?

Chances of ending up recessive for Chances of ending up recessive for each character individually = ¼ each character individually = ¼

so the odds of ending up recessive in so the odds of ending up recessive in 3 is ¼ * ¼ * ¼ = 1/64 3 is ¼ * ¼ * ¼ = 1/64

As a Group Calculate…As a Group Calculate…(assume MmNnOo (assume MmNnOo

parents)parents)1.1. What are the odds of ending up What are the odds of ending up

MmNnOoMmNnOo

2.2. MMNNooMMNNoo

3.3. MmNNOoMmNNOo

4.4. Expressing the dominant trait for M Expressing the dominant trait for M and N but recessive trait for oand N but recessive trait for o

5.5. Dominant in exactly 2 of the 3 traitsDominant in exactly 2 of the 3 traits

Quick PracticeQuick Practice

A mother is AaBBDdee. What possible A mother is AaBBDdee. What possible alleles can her eggs have?alleles can her eggs have?

Two AaBb individuals mate. What are the Two AaBb individuals mate. What are the odds their offspring are homozygous odds their offspring are homozygous dominant in both? dominant in both?

An AAbbDD man mates with a woman An AAbbDD man mates with a woman heterozygous in all 3 traits. What are the heterozygous in all 3 traits. What are the odds an offspring has the same genotype odds an offspring has the same genotype as one of their parents?as one of their parents?

An AABBDDEEFFGG man mates with an An AABBDDEEFFGG man mates with an aabbddeeffgg woman. What % of their aabbddeeffgg woman. What % of their offspring will be heterozygous?offspring will be heterozygous?

ReviewReview Some alleles Some alleles

dominate othersdominate others We inherit one allele We inherit one allele

from each parentfrom each parent Alleles are inherited Alleles are inherited

separatelyseparately Probability is Probability is

observed in the long observed in the long runrun

The Relationship Between The Relationship Between Genotype and Phenotype is Genotype and Phenotype is

Rarely So Simple!Rarely So Simple! Mendel was lucky, he Mendel was lucky, he

chose characters chose characters controlled by 1 gene, controlled by 1 gene, where 1 trait is where 1 trait is completely dominantcompletely dominant

Things are not Things are not always so simplealways so simple

Doesn't mean Doesn't mean Mendel is wrong! Mendel is wrong!

Incomplete DominanceIncomplete Dominance For some characters, For some characters,

heterozygous heterozygous individuals exhibit individuals exhibit phenotypes that are a phenotypes that are a mix of the 2 allelesmix of the 2 alleles

i.e. red and white i.e. red and white flowers can produce flowers can produce pink flowerspink flowers

Pink flowers produce Pink flowers produce red, white and pink red, white and pink offspringoffspring Not blending!Not blending!

Codominance/ Multiple Codominance/ Multiple AllelesAlleles

The two alleles can The two alleles can both be expressed both be expressed at the same timeat the same time

i.e. Blood Typesi.e. Blood Types A and B are A and B are

dominant to O (3 dominant to O (3 alleles)alleles)

A and B are A and B are codominantcodominant

Blood TypesBlood Types AA or AO individuals AA or AO individuals

produce A antigensproduce A antigens BB or BO individuals BB or BO individuals

produce B antigensproduce B antigens AB produce bothAB produce both OO produce noneOO produce none Individuals cannot Individuals cannot

receive blood with A receive blood with A or B antigens unless or B antigens unless their blood produces their blood produces themthem

3 Important Points 3 Important Points About DominanceAbout Dominance

1)1) Ranges from complete dominance to Ranges from complete dominance to incomplete dominance to codominanceincomplete dominance to codominance

2)2) The dominant allele does not suppress or The dominant allele does not suppress or interact with the other allele. The recessive interact with the other allele. The recessive allele simply isn't expressed by the cellsallele simply isn't expressed by the cells

3)3) A trait being dominant does not A trait being dominant does not necessarily mean it is more common in the necessarily mean it is more common in the populationpopulation

Dominant but Rare Dominant but Rare TraitsTraits

6 fingers6 fingers

DwarfismDwarfism

Widow’s PeakWidow’s Peak

DimplesDimples

Cleft chinCleft chin

Ear wigglingEar wiggling

Hair on middle of fingersHair on middle of fingers

PedigreesPedigrees Obviously in Obviously in

humans we can't humans we can't choose who breeds choose who breeds with whomwith whom

Mendelian patterns Mendelian patterns are observed using are observed using pedigreespedigrees

Geneticists collect Geneticists collect information about a information about a specific trait from a specific trait from a familyfamily

How to Read Pedigree How to Read Pedigree ChartsCharts

Squares represent Squares represent males, circles males, circles represent femalesrepresent females

A line represents A line represents matingmating

Shading Shading represents that represents that the trait is presentthe trait is present

How Can You Spot a How Can You Spot a Recessive Trait?Recessive Trait?

If it appears If it appears in offspring in offspring but neither but neither parent had itparent had it

Both parents Both parents must have must have been carriersbeen carriers

ff

ff Ff

Ff Ff ffFf

FF or Ff

Ff

Ff

How Can you Spot a How Can you Spot a dominant trait?dominant trait?

If two parents If two parents have the trait, have the trait, but the offspring but the offspring does not!does not!

The parents must The parents must be heterozygous be heterozygous and have a and have a recessive recessive offspringoffspring

Ff Ff

Ff Ff Ff Ffffff

ff ffff ffFf Ff