Intro…GENETICSIntro…GENETICS

MENDEL & MEIOSISMENDEL & MEIOSIS

MENDEL’S LAWS OF HEREDITYMENDEL’S LAWS OF HEREDITY

I. WHY MENDEL SUCCEEDEDI. WHY MENDEL SUCCEEDED Gregor Mendel – father of geneticsGregor Mendel – father of genetics 11stst studies of studies of heredityheredity – the passing of – the passing of

characteristics to offspringcharacteristics to offspring GeneticsGenetics – study of heredity – study of heredity The characteristics passed on called The characteristics passed on called

traitstraits

1. MENDEL CHOSE HIS 1. MENDEL CHOSE HIS SUBJECT CAREFULLYSUBJECT CAREFULLY

Used garden peas for a model organismUsed garden peas for a model organism Have male & female Have male & female gametesgametes (sex cells) (sex cells) Male & female same flowerMale & female same flower Know what Know what pollinationpollination & & fertilizationfertilization

meanmean He could control the fertilization processHe could control the fertilization process Not many traits to keep track ofNot many traits to keep track of

2. MENDEL WAS A CAREFUL 2. MENDEL WAS A CAREFUL RESEARCHERRESEARCHER

USED CAREFULLY CONTROLLED USED CAREFULLY CONTROLLED EXPERIMENTSEXPERIMENTS

STUDIED ONE TRAIT AT A TIMESTUDIED ONE TRAIT AT A TIME KEPT DETAILED DATAKEPT DETAILED DATA

II. MENDEL’S MONOHYBRID II. MENDEL’S MONOHYBRID CROSSESCROSSES

MENDEL STUDIED 7 TRAITS CAREFULLYMENDEL STUDIED 7 TRAITS CAREFULLY seed shape/color, flower color/position, pod seed shape/color, flower color/position, pod

color/shape, plant heightcolor/shape, plant height Mendel crossed plants w/ diff. traits to Mendel crossed plants w/ diff. traits to

see what traits the offspring would havesee what traits the offspring would have These offspring are called These offspring are called hybridshybrids – –

offspring of parents w/ different traitsoffspring of parents w/ different traits A A monohybridmonohybrid cross is one that looks at cross is one that looks at

only only oneone trait (let’s look at plant height trait (let’s look at plant height – tall or short)– tall or short)

A. THE 1A. THE 1STST GENERATION GENERATION

Mendel crossed two plants – 1 tall & Mendel crossed two plants – 1 tall & 1 short1 short

These plants are called the parental These plants are called the parental generation (generation (P generationP generation))

The offspring were all called the 1The offspring were all called the 1stst filial generation (filial generation (FF11 generation generation))

All the offspring were tallAll the offspring were tall

B. THE 2B. THE 2NDND GENERATION GENERATION

Next, Mendel crossed two plants Next, Mendel crossed two plants from the from the FF11 generation generation

The offspring from this cross are The offspring from this cross are called the 2called the 2ndnd filial generation ( filial generation (FF22 GENERATIONGENERATION))

Mendel found that ¾ of the offspring Mendel found that ¾ of the offspring were tall & ¼ were short (the short were tall & ¼ were short (the short plants reappeared!!!!!!)plants reappeared!!!!!!)

VOCABULARY:

AlleleGenotypePhenotypeDominantRecessiveTraitHeterozygousHomozygous

Laws:

Independent Assortment

Segregation

TO GO ANY FURTHER, WE TO GO ANY FURTHER, WE MUST UNDERSTAND ALLELES, MUST UNDERSTAND ALLELES, DOMINANCE, & SEGREGATIONDOMINANCE, & SEGREGATION

GenesGenes – a section of DNA that codes for – a section of DNA that codes for one proteinone protein These genes are what control & produce These genes are what control & produce

traitstraits The genes Mendel studied came in two The genes Mendel studied came in two

forms (tall/short - round/wrinkled - forms (tall/short - round/wrinkled - yellow/green…….etc.)yellow/green…….etc.)

Alternate forms of a gene are called Alternate forms of a gene are called allelesalleles

Alleles are represented by a one or two Alleles are represented by a one or two letter symbol (e.g. T for tall, t for short)letter symbol (e.g. T for tall, t for short)

ALLELES CONT’DALLELES CONT’D

THESE 2 ALLELS ARE NOW KNOWN THESE 2 ALLELS ARE NOW KNOWN TO BE FOUND ON COPIES OF TO BE FOUND ON COPIES OF CHROMOSOMES – ONE FROM EACH CHROMOSOMES – ONE FROM EACH PARENTPARENT

THE RULE OF DOMINANCETHE RULE OF DOMINANCE A A dominantdominant trait is the trait that will trait is the trait that will

always be expressed if at least one always be expressed if at least one dominant allele is presentdominant allele is present

The dominant allele is The dominant allele is alwaysalways represented by a capital letterrepresented by a capital letter

A recessive trait will A recessive trait will onlyonly be expressed if be expressed if bothboth alleles are recessive alleles are recessive

Recessive traits are represented by a Recessive traits are represented by a lower case letterlower case letter

DOMINANCE CONT’DDOMINANCE CONT’D

LET’S USE TALL & SHORT PEA LET’S USE TALL & SHORT PEA PLANTS FOR AN EXAMPLEPLANTS FOR AN EXAMPLE

WHICH OF THESE WILL SHOW THE WHICH OF THESE WILL SHOW THE DOMINANT & RECESSIVE TRAIT?DOMINANT & RECESSIVE TRAIT?

TT Tt TT Tt tttt

DOMINANT TRAIT RECESSIVE TRAITDOMINANT TRAIT RECESSIVE TRAIT

THE LAW OF SEGREGATIONTHE LAW OF SEGREGATION

MENDEL ASKED HIMSELF……..”HOW MENDEL ASKED HIMSELF……..”HOW DID THE RECESSIVE SHORT PLANTS DID THE RECESSIVE SHORT PLANTS REAPPEAR IN THE F2 GENERATION?”REAPPEAR IN THE F2 GENERATION?”

HE CONCLUDED THAT EACH TALL HE CONCLUDED THAT EACH TALL PLANT FROM THE F1 GENERATION PLANT FROM THE F1 GENERATION CARRIED TWO ALLELES, 1 DOMINANT CARRIED TWO ALLELES, 1 DOMINANT TALL ALLELE & ONE RECESSIVE TALL ALLELE & ONE RECESSIVE SHORT ALLELESHORT ALLELE

SO ALL WERE TtSO ALL WERE Tt

SEGREGATION CONT’DSEGREGATION CONT’D HE ALSO CONCLUDED THAT ONLY HE ALSO CONCLUDED THAT ONLY

ONE ALLELE FROM EACH PARENT ONE ALLELE FROM EACH PARENT WENT TO EACH OFFSPRINGWENT TO EACH OFFSPRING

HIS CORRECT HYPOTHESIS WAS HIS CORRECT HYPOTHESIS WAS THAT SOMEHOW DURING THAT SOMEHOW DURING FERTILIZATION, THE ALLELES FERTILIZATION, THE ALLELES SEPARATED (SEGREGATED) & SEPARATED (SEGREGATED) & COMBINED WITH ANOTHER ALLELE COMBINED WITH ANOTHER ALLELE FROM THE OTHER PARENTFROM THE OTHER PARENT

The law of segregation states that The law of segregation states that during gamete formation, the alleles during gamete formation, the alleles separate to different gametesseparate to different gametes

F1 GENERATIONF1 GENERATIONFATHERFATHER MOTHERMOTHER

T tT t T tT t

TT TT TT tt tt ttF2 GENERATIONF2 GENERATION

- the law of dominance explained the - the law of dominance explained the heredity of the offspring of the f1 heredity of the offspring of the f1 generationgeneration

- the law of segregation explained the - the law of segregation explained the heredity of the f2 generationheredity of the f2 generation

PUNNETT SQUAREPUNNETT SQUARE

CROSS T T X TtCROSS T T X Tt

CONT’DCONT’D

T T X T tT T X T tTT TT

TT

tt

TT TT TT TT

TT tt TT tt

PHENOTYPES & GENOTYPESPHENOTYPES & GENOTYPES

PHENOTYPEPHENOTYPE – The Physical appearance – – The Physical appearance – how an organism looks – the Traithow an organism looks – the Trait

GENOTYPEGENOTYPE – the Allele combination…Aa – the Allele combination…Aa or AA or aa…….also Ttyy or ttyy or TTYYor AA or aa…….also Ttyy or ttyy or TTYY HOMOZYGOUSHOMOZYGOUS – 2 ALLELES SAME – 2 ALLELES SAME HETEROZYGOUSHETEROZYGOUS – 2 ALLELES DIFFERENT – 2 ALLELES DIFFERENT

Like Homo-Sexual…Like Homo-Sexual… Hetero-SexualHetero-Sexual Same gender couple Same gender couple Different gender Different gender

couplecouple

ANSWER ON YOUR SHEETANSWER ON YOUR SHEET

TRAITS = BLUE SKIN & YELLOW SKINTRAITS = BLUE SKIN & YELLOW SKIN

BBBB – IS THIS HOMOZYGOUS OR – IS THIS HOMOZYGOUS OR HETEROZYGOUS?HETEROZYGOUS?

IS BLUE SKIN OR YELLOW SKIN IS BLUE SKIN OR YELLOW SKIN DOMINANT? DOMINANT?

HOMOZYGOUSHOMOZYGOUS

BLUEBLUE

MENDEL’S DIHYBRID CROSSESMENDEL’S DIHYBRID CROSSES

MONOHYBRID – MENDEL LOOKED AT MONOHYBRID – MENDEL LOOKED AT ONE TRAITONE TRAIT

IN HIS DIHYBRID CROSSES – HE IN HIS DIHYBRID CROSSES – HE LOOKED AT 2 TRAITS LOOKED AT 2 TRAITS

WANTED TO SEE IF TRAITS ARE WANTED TO SEE IF TRAITS ARE INHERITED TOGETHER OR INHERITED TOGETHER OR INDEPENDENTLYINDEPENDENTLY

DIHYBRID CROSSDIHYBRID CROSS

TOOK TWO TRUE BREEDING PLANTS TOOK TWO TRUE BREEDING PLANTS FOR 2 DIFFERENT TRAITS FOR 2 DIFFERENT TRAITS (ROUND/WRINKLED SEEDS ------- (ROUND/WRINKLED SEEDS ------- YELLOW/GREEN SEEDS)YELLOW/GREEN SEEDS)

11STST GENERATION GENERATION WHAT WOULD HAPPEN IF HE CROSSED JUST WHAT WOULD HAPPEN IF HE CROSSED JUST

TRUE BREEDING ROUND W/ TRUE TRUE BREEDING ROUND W/ TRUE BREEDING WRINKLED (ROUND IS BREEDING WRINKLED (ROUND IS DOMINANT)DOMINANT)ALL THE OFFSPRING ARE ALL THE OFFSPRING ARE

ROUNDROUND

DIHYBRID CROSS – 1DIHYBRID CROSS – 1STST GENERATION CONT’DGENERATION CONT’D

SO WHAT DO YOU THINK HAPPENED SO WHAT DO YOU THINK HAPPENED WHEN HE CROSSED TRUE BREEDING WHEN HE CROSSED TRUE BREEDING ROUND/YELLOW SEEDS WITH TRUE ROUND/YELLOW SEEDS WITH TRUE BREEDING WRINKLED/GREEN SEEDSBREEDING WRINKLED/GREEN SEEDS

ALL THE F1 WERE ROUND ALL THE F1 WERE ROUND AND YELLOWAND YELLOW

DIHYBRID CROSS – 2DIHYBRID CROSS – 2NDND GENERATIONGENERATION

TOOK THE F1 PLANTS AND BRED TOOK THE F1 PLANTS AND BRED THEM TOGETHER (PHENOTYPE WAS THEM TOGETHER (PHENOTYPE WAS ROUND/YELLOW X ROUND/YELLOW)ROUND/YELLOW X ROUND/YELLOW)

22NDND GENERATION GENERATION FOUND ROUND/YELLOW - 9FOUND ROUND/YELLOW - 9 FOUND ROUND/GREEN - 3FOUND ROUND/GREEN - 3 FOUND WRINKLED/YELLOW - 3FOUND WRINKLED/YELLOW - 3 FOUND WRINKLED/GREEN - 1FOUND WRINKLED/GREEN - 1 ( 9 : 3 : 3 : 1 RATIO) ( 9 : 3 : 3 : 1 RATIO)

EXPLANATION OF 2EXPLANATION OF 2NDND GENERATIONGENERATION

MENDEL CAME UP W/ 2MENDEL CAME UP W/ 2NDND LAW – THE LAW – THE LAW OF INDEPENDENT ASSORTMENTLAW OF INDEPENDENT ASSORTMENT Genes for different traits (Pea color, and Genes for different traits (Pea color, and

flower color) are inherited independently flower color) are inherited independently of each otherof each other

Just because you have brown hair, Just because you have brown hair, doesn’t mean you will be short!doesn’t mean you will be short!

DIHYBRID CROSSESDIHYBRID CROSSES

A LITTLE DIFFERENTA LITTLE DIFFERENT H h G g X H h G gH h G g X H h G g What are the possible Allele What are the possible Allele

combinations?combinations? USE THE USE THE FOILFOIL METHOD METHOD

First, Outer, Inner, LastFirst, Outer, Inner, Last

H h G g X H h G gH h G g X H h G g

1. HG1. HG

2. Hg2. Hg

3. hG3. hG

4. hg4. hg

FOIL – FIRST, OUTSIDE, INSIDE, LASTFOIL – FIRST, OUTSIDE, INSIDE, LAST

BOTH PARENTS BOTH PARENTS ARE THE SAME ARE THE SAME

NOW LET’S DO A DIHYBRID NOW LET’S DO A DIHYBRID CROSSCROSS

H h G g X H h G gH h G g X H h G gHGHG HgHg hGhG hghg

HGHG

HgHg

hGhG

hghg

HHGGHHGG HHGgHHGg HhGGHhGG HhGgHhGg

HHGgHHGg HHggHHgg HhGgHhGg HhggHhgg

HhGGHhGG HhGgHhGg hhGGhhGG hhGghhGg

HhGgHhGg HhggHhgg hhGghhGg hhgghhgg

WHAT ARE THE PHENOTYPIC WHAT ARE THE PHENOTYPIC RATIO’S?RATIO’S?

H h G g X H h G gH h G g X H h G gHGHG HgHg hGhG hghg

HGHG

HgHg

hGhG

hghg

HHGGHHGG HHGgHHGg HhGGHhGG HhGgHhGg

HHGgHHGg HHggHHgg HhGgHhGg HhggHhgg

HhGGHhGG HhGgHhGg hhGGhhGG hhGghhGg

HhGgHhGg HhggHhgg hhGghhGg hhgghhgg

DD:DD:

Dr:Dr:

rD:rD:

rr:rr:

99

33

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PROBABILITYPROBABILITY Does real life follow Punnett Squares??Does real life follow Punnett Squares?? NO!!!!!! – only shows what will NO!!!!!! – only shows what will

PROBABLY occurPROBABLY occur Like flipping a coin 10 times:Like flipping a coin 10 times:

PROBABILITY says you’ll get heads 50% of PROBABILITY says you’ll get heads 50% of the time.the time.

But you may not … try it.But you may not … try it. Certainly over time, with hundreds and Certainly over time, with hundreds and

hundreds of flips, YES, you’ll end up with hundreds of flips, YES, you’ll end up with 50% heads 50% heads