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Mendelelian Mendelelian GeneticsGenetics

GPS: Using Mendel’s laws, explain the role of Meiosis in reproductive variability

Gregor Gregor MendelMendel

(1822-1884)(1822-1884)Studied the Studied the inheritanceinheritance of of traits in traits in pea pea plantsplantsDeveloped the Developed the laws of laws of geneticsgeneticsaka aka “Father of “Father of Genetics”Genetics”

Mendel stated Mendel stated that physical traits that physical traits are inherited as are inherited as “particles”“particles”

Mendel did not Mendel did not know that the know that the “particles” were “particles” were actually actually GENESGENES

Particulate InheritanceParticulate Inheritance

Genetic TerminologyGenetic Terminology

TraitTrait - any characteristic - any characteristic that can be passed from that can be passed from parent to offspring parent to offspring HeredityHeredity - passing of traits - passing of traits from parent to offspring from parent to offspring GeneticsGenetics - study of - study of heredity heredity

Types of Genetic Types of Genetic CrossesCrossesPunnett Square Punnett Square - - cross cross

involving a single traitinvolving a single traite.g. flower color e.g. flower color AKA AKA Monohybrid crossMonohybrid crossDihybrid crossDihybrid cross - - cross cross involving two traits involving two traits e.g. flower color & plant heighte.g. flower color & plant height

Punnett SquarePunnett SquareA diagram used A diagram used to show the to show the probabilityprobability of a of a trait being trait being present in present in offspring.offspring.

““Genes”Genes”

AllelesAlleles - - two forms of a two forms of a gene gene (dominant & recessive)(dominant & recessive) DominantDominant - - stronger of two stronger of two genes. Expressed in a cross; genes. Expressed in a cross; represented byrepresented by aa capital letter (R)capital letter (R) RecessiveRecessive - - gene that shows up gene that shows up less often in a cross; is dominated less often in a cross; is dominated or or overpoweredoverpowered by the dominant by the dominant gene; represented by agene; represented by a lowercase lowercase letter (r)letter (r)

More TerminologyMore Terminology

GenotypeGenotype – – genetic makeup genetic makeup oror gene combination for a gene combination for a traittrait (e.g. RR, Rr, rr) (e.g. RR, Rr, rr) PhenotypePhenotype - - the physical the physical feature resulting from a feature resulting from a genotypegenotype (e.g. red, white) (e.g. red, white)

GenotypesGenotypesHomozygousHomozygous genotype - genotype -

gene combination where gene combination where both alleles are the same both alleles are the same (e.g. RR or rr);(e.g. RR or rr); also called also called pure bred pure bred  HeterozygousHeterozygous genotype - genotype - gene combination where gene combination where the alleles are different the alleles are different ((e.g. Rr);e.g. Rr); also called also called hybridhybrid

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Mendel’s LawsMendel’s Laws

Law of DominanceLaw of Dominance •Some alleles are Some alleles are dominant dominant and some are and some are recessiverecessive..

•When combined in a When combined in a hybrid, the dominant hybrid, the dominant overpowers the overpowers the recessive.Like recessive.Like RrRr

•The dominant form of The dominant form of the trait ALWAYS shows the trait ALWAYS shows in the phenotype.in the phenotype.

Law of DominanceLaw of DominanceT = tallT = tall ( (dominantdominant))

t = shortt = short ( (recessiverecessive))

TT – tallTT – tall

Tt – tallTt – tall

tt - shorttt - short

R = roundR = round ( (dominantdominant))

r = wrinkledr = wrinkled ((recessiverecessive))

RR – roundRR – round

Rr – roundRr – round

rr - wrinkledrr - wrinkledY = yellowY = yellow ((dominantdominant))

y = greeny = green ( (recessiverecessive))

YY – YY –

YYyy – –

yyyy - -

P = purpleP = purple ((dominant)dominant)

p = whitep = white ( (recessiverecessive))

PP – PP –

PPpp – –

pppp - -

Law of SegregationLaw of Segregation

During meiosis, the During meiosis, the two allelestwo alleles responsible for a trait responsible for a trait separateseparate from each other. from each other. (when the homologous (when the homologous chromosomes separate)chromosomes separate)

Alleles for a trait are Alleles for a trait are "recombined" at fertilization"recombined" at fertilization

Study diagram!!!

Law of Law of SegregationSegregation

Let’s Practice Using SpongeBob!!!Assignments For Today!!

Begin Spongebob Practice Sheet

Watch Video to Better Understand How to use Punnett Squares.

Practice Doing Punnett Squares – Spongebob Worksheet.

Complete Lecture Quiz

Paper Pet Genetics

Power Notes

MaleGametes

Male Parent M E I O S I s

Meiosis

Female Parent

Female Gametes

Law of Independent Law of Independent AssortmentAssortment

Alleles for Alleles for differentdifferent traits are traits are distributed to the gametes distributed to the gametes independently of one independently of one another.another.

This law can be illustrated This law can be illustrated using using dihybrid crossesdihybrid crosses..

GENOTYPE vs. PHENOTYPEB – brown eyes (B – brown eyes (dominantdominant))b – blue eyes (b – blue eyes (recessiverecessive))What are the possible genotypes for brown What are the possible genotypes for brown

eyes?eyes?What are the possible genotypes for blue What are the possible genotypes for blue

eyes?eyes?

W – widow’s peak ( W – widow’s peak ( ?? ) ) w – no widow’s peak ( w – no widow’s peak ( ?? ) )Possible genotypes for having a widow’s Possible genotypes for having a widow’s

peak:peak:

Possible genotypes for not having a widow’s Possible genotypes for not having a widow’s peak:peak:

HETEROZYGOUS vs. HOMOZYGOUSF – free earlobe (F – free earlobe (dominantdominant))f – attached earlobe (f – attached earlobe (recessiverecessive) ) FF – homozygousFF – homozygousFf – Ff – ff -ff -

H – hitchhiker’s thumb ( H – hitchhiker’s thumb ( ?? ) )h – no hitchhiker’s thumb ( h – no hitchhiker’s thumb ( ?? ) )HH – HH – hh – hh – Hh - Hh -

PUNNETT PUNNETT SQUARESSQUARES

Trait: Seed ShapeTrait: Seed Shape

Alleles: Alleles: RR – Round – Round rr – Wrinkled – Wrinkled

Cross: Cross:

homozygous homozygous RoundRound seedsseeds xx Wrinkled Wrinkled seedsseeds

xx

Genotype:Genotype:

PhenotypePhenotype:

GenotypicGenotypic

Ratio:Ratio:

PhenotypicPhenotypic

Ratio:Ratio:

Trait: Seed ShapeTrait: Seed Shape

Alleles: Alleles: RR – Round – Roundrr – Wrinkled – Wrinkled

Cross: Cross:

Heterozygous RoundHeterozygous Round seeds seeds xx HeterozygousHeterozygous Round Round seedsseeds

xx

Genotype:Genotype:

PhenotypePhenotype:

G.Ratio:G.Ratio:

P.Ratio:P.Ratio:

Trait: Seed ShapeTrait: Seed ShapeAlleles: Alleles: RR – Round – Roundrr – Wrinkled – WrinkledCross:Cross: Homozygous Homozygous RoundRound seeds xseeds x Heterozygous Heterozygous

Round Round seedsseeds

Genotype:Genotype:

PhenotypePhenotype: GenotypicGenotypicRatio:Ratio:

PhenotypicPhenotypicRatio:Ratio:

MaleGametes

Male Parent M E I O S I s

Meiosis

Female Parent

Female Gametes

MaleGametes

Male Parent M E I O S I s

Meiosis

Female Parent

Female Gametes

Dihybrid Cross

▪Examines the cross of 2 different Examines the cross of 2 different traitstraits

Y = Yellow (Y = Yellow (dominantdominant))

y = green (y = green (recessiverecessive))

R = Round (R = Round (dominantdominant))

r = wrinkled (r = wrinkled (recessiverecessive))

Cross 2 heterozygous yellow, Cross 2 heterozygous yellow, heterozygous round plants: what are heterozygous round plants: what are the genotypes?the genotypes?

Seed color

Seed shape

Y = Yellow Y = Yellow y = green y = green R = Round R = Round r = wrinkled r = wrinkled

YyRrYyRr

YyRrYyRr

Summary of Mendel’s Summary of Mendel’s lawslaws

LAWLAW PARENT PARENT CROSSCROSS OFFSPRINGOFFSPRING

DOMINANCEDOMINANCE TT x ttTT x tt tall x shorttall x short

Tt Tt 100% tall 100% tall

SEGREGATIONSEGREGATION Tt x TtTt x Tt tall x talltall x tall

75% tall 75% tall 25% short25% short

INDEPENDENT INDEPENDENT ASSORTMENTASSORTMENT

RrGg x RrGgRrGg x RrGg round & round & green x green x round & round & greengreen

9/16 round seeds & green 9/16 round seeds & green pods pods

3/16 round seeds & yellow 3/16 round seeds & yellow pods pods

3/16 wrinkled seeds & 3/16 wrinkled seeds & green pods green pods

1/16 wrinkled seeds & 1/16 wrinkled seeds & yellow podsyellow pods

Non-Mendelian Non-Mendelian Inheritance Inheritance

Incomplete DominanceIncomplete DominanceOne trait is not dominant over the One trait is not dominant over the

other. other.

The offspring’s trait is a mixture of The offspring’s trait is a mixture of the 2 parents.the 2 parents.

+

CodominanceCodominanceOne trait is not dominant over the One trait is not dominant over the

other.other.Both alleles are expressed in the Both alleles are expressed in the

offspring.offspring.

++ ==WW BB WB

++

==

Homozygous Homozygous RedRed

RoanRoan

Homozygous WhiteHomozygous White

Human Blood typeHuman Blood type

POLYGENETIC TRAITPOLYGENETIC TRAIT

▪Trait produced by 2 or more genes that interact

▪Human skin color

▪Human eye color

Order of dominance: brown > green > blue.

SEX LINKED TRAITSSEX LINKED TRAITS

▪Genes located on sex chromosomes are Genes located on sex chromosomes are called sex-linked genes. called sex-linked genes.

▪Y chromosome genes in mammals are Y chromosome genes in mammals are responsible for male characteristics.responsible for male characteristics.

▪X chromosome genes in mammals affect X chromosome genes in mammals affect many traits.many traits.

SEX LINKED TRAITSSEX LINKED TRAITSMost sex linked (X-linked) disorders are Most sex linked (X-linked) disorders are

recessive and show up only in males.recessive and show up only in males.

Females are carriers of sex linked Females are carriers of sex linked disordersdisorders

PEDIGREESPEDIGREES

▪A pedigree is a chart for tracing A pedigree is a chart for tracing genes in a familygenes in a family

▪Trace phenotypes to infer the Trace phenotypes to infer the genotypesgenotypes

-Male carrier

Autosomal genes: widow’s peak-Male without trait

-Male with trait

-Female without trait

-Female with trait

-Female carrier

-Male carrier

Sex Linked genes: colorblindness M – normal color visionM – normal color vision

m - colorblindm - colorblind

-Male without trait

-Male with trait

-Female without trait

-Female with trait

-Female carrier

-Male carrier