Mr. Cruz 11-3 Exploring Mendelian Genetics

11-3 EXPLORING MENDELIAN 11-3 EXPLORING MENDELIAN GENETICSGENETICS

Mr. Alejandro CruzMr. Alejandro Cruz

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CIDEB11-3 Exploring Mendelian Genetics

What is allele segregation?What is allele segregation? Do alleles segregate independently?Do alleles segregate independently? What is a two-factor cross?What is a two-factor cross? What is the principle of independent What is the principle of independent

assortment?assortment? What inheritance patterns exist aside from What inheritance patterns exist aside from

simple dominance?simple dominance?

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Mendel crossed True breeding plantsMendel crossed True breeding plants Round = R Round = R Wrinkled = rWrinkled = r Yellow = YYellow = Y Green = yGreen = y Round Yellow peas = RRYYRound Yellow peas = RRYY Wrinkle Green peas = rryyWrinkle Green peas = rryy

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RRYY

Round yellow peasRrYy

rryy

Heterozygous dominant

for round yellow

How is the genotype of the offspring different from that of the dominant parents?

The offspring are heterozygous

F1

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The two-factor crossThe two-factor cross F1 plants were heterozygous for both F1 plants were heterozygous for both

seed shape and seed color genesseed shape and seed color genes RrYyRrYy F2 generation?F2 generation? Gametes?Gametes?

R r Y yRy

RY

rY

ry

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Alleles for seed shape segregated independently of those for seed color

Principle of independent assortment

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Mendel´s PrinciplesMendel´s Principles The inheritance of biological characteristics is The inheritance of biological characteristics is

determined by individual units called genesdetermined by individual units called genes In cases in which two or more forms of the gene In cases in which two or more forms of the gene

(alleles) for a single trait exist, some forms of the (alleles) for a single trait exist, some forms of the gene may be dominant and others may be gene may be dominant and others may be recessiverecessive

In most sexually reproducing organisms, each In most sexually reproducing organisms, each adult has two copies of each gene (one from each adult has two copies of each gene (one from each parent). These genes are segragated from each parent). These genes are segragated from each other when gametes are formedother when gametes are formed

The alleles for different genes segregate The alleles for different genes segregate independently from one another independently from one another

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Incomplete DominanceIncomplete Dominance One allele is not completely dominant One allele is not completely dominant

over anotherover another The heterozygous phenotype is The heterozygous phenotype is

somewhere in between the two somewhere in between the two homozygous phenotypeshomozygous phenotypesFour O´clock

(Mirabilis)

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INCOMPLETE

DOMINANCE

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(1) What would be the offspring if you (1) What would be the offspring if you crossed a white Mirabilis with a pink crossed a white Mirabilis with a pink Mirabilis?Mirabilis?

(2) What would be the offspring if you (2) What would be the offspring if you crossed a red and a pink Mirabilis?crossed a red and a pink Mirabilis?

(3) What would be the offspring if you (3) What would be the offspring if you crossed two pink Mirabilis (F1)?crossed two pink Mirabilis (F1)?

ANSWER TO 1

ANSWER TO 3

ANSWER TO 2

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CodominanceCodominance

Both alleles contribute Both alleles contribute to the phenotypeto the phenotype

In humans

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Multiple AllelesMultiple Alleles Genes that have more than two allelesGenes that have more than two alleles = more than two possible alleles exist= more than two possible alleles exist Example: coat color in rabbitsExample: coat color in rabbits 1 gene: four different alleles1 gene: four different alleles

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Polygenic TraitsPolygenic Traits Traits controlled by two or more genesTraits controlled by two or more genes They show a wide range of phenotypesThey show a wide range of phenotypes Example: color of the eye in fruit flies, uses three Example: color of the eye in fruit flies, uses three

genes for making the reddish-brown pigmentgenes for making the reddish-brown pigment

SKIN COLOR

IN HUMANS

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Applying Mendel´s Applying Mendel´s principlesprinciples Thomas Hunt Morgan looked for a Thomas Hunt Morgan looked for a

model organism to study geneticsmodel organism to study genetics Fruit flyFruit fly Why is it an ideal organism for Why is it an ideal organism for

genetics?genetics? They are smallThey are small Easy to keep in the laboratoryEasy to keep in the laboratory Produce large numbers of offspring in a Produce large numbers of offspring in a

short timeshort timeMendel´s principles apply to plants and also animals including humans

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Section 11- 3

THE END

Mr. Cruz

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This presentation prepared by This presentation prepared by .. M.E.C. Alejandro CruzM.E.C. Alejandro Cruz Centro de Investigación y Desarrollo de Educación BilingüeCentro de Investigación y Desarrollo de Educación Bilingüe Universidad Autónoma de Nuevo LeónUniversidad Autónoma de Nuevo León

UANL UANL

THE END

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The principle of independent assortment The principle of independent assortment states that genes for different traits can states that genes for different traits can segregate independently during the segregate independently during the formation of gametesformation of gametes

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White-PinkWW RW

W

W

W

R

RW

RW WW

WW

CLICK THE ARROW

TO GO BACK

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Red-PinkRR RW

W

R

R

R

RR

RW RW

RR

CLICK THE ARROW

TO GO BACK

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Pink-PinkRW RW

W

W

R

R

RR

RW WW

RW

CLICK THE ARROW

TO GO BACK

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Mr. Cruz 11-3 Exploring Mendelian Genetics