Genetics Virtual Science University 1 Genetics Texas TEK B.6 (D) - - PowerPoint PPT Presentation

Genetics

Virtual Science University

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Genetics

Texas TEK B.6 (D) The student will compare Genetic Variations

• bserved in plants, (pea plants).

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Genetics Song

• Punnet Square with 4 Alleles
• Two from Mom and two from Pop
• Each one Gives one to the Family Crop
• Genotype with two Alleles
• Is the Genetic Code for the Phenotype
• Phenotype with two Alleles
• Gives you, Your Look, Uniquely One Type

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Gregor Mendel

• Born July 22, 1822 and

died January 6, 1884.

• He was born to well off peasants.
• He entered into the Augustinian

Abbey of St. Thomas in Brunn in 1843 and was ordained a priest in 1847.

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Gregor Mendel

• He travelled to Vienna

and studied physics and natural science from 1851-1853.

• On returning to the

cloister he taught in the Augustinian Abby of St. Tomas in Brunn where he later became Abbot.

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Glossary of Genetic Terms

• Heredity is the passing of characters

from Parents to Offspring.

• Genetics is the discipline of Biology

that incorporates the mechanics of Heredity.

• Monohybrid Cross is the cross between

parent alleles and involves a pair of contrasting traits.

• True Breeding is when Offspring

displays a true Character of the Parent.

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Glossary of Genetic Terms

• P generation is the Parental Generation
• r the first two individuals that are

crossed in a breeding experiment.

• F1 generation is the first filial

generation or the offspring of the Parent Generation.

• F2 generation is the second filial

generation or the offspring of the First Filial Generation.

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Glossary of Genetic Terms

• Alleles are letters that designate

the different versions of a gene.

• Dominant is the expressed form of

a character.

• Recessive is the trait that is not

expressed when the Dominant Form of the Character is present.

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Glossary of Genetic Terms

• Homozygous the genotype expressed

when two alleles of a particular gene are the same in an individual.

• Heterozygous the genotype expressed

when two alleles of a particular gene are different in an individual.

• Genotype is the set of alleles that an

individual has for a character.

• Phenotype is the physical appearance
• f a character.

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Monohybrid Cross

• In 1856 and the following years he

undertook his investigations into hybridization of plants in the garden of the convent.

• Gregor Mendel discovered the basic

rules of inheritance.

• From 1858 to 1866, he bred garden peas

in his monastery garden and analyzed the offspring of the mating.

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Monohybrid Cross

The garden pea

was good choice

• f experimental
• rganism

because many varieties were available that bred true for clear-cut, qualitative traits

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Monohybrid Cross

– Seed texture

• round vs wrinkled

– Seed color

• green vs yellow

– Flower color

• white vs purple

– Growth habit

• Tall vs Dwarf

– Three others that also varied in a qualitative - rather than quantitative way

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Monohybrid Cross

• Peas are normally self-

pollinated because the stamen and carpel are enclosed within the petals.

• By removing the stamen

from unripe flowers, Mendel could brush pollen from another variety on the carpel when they ripened.

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Monohybrid Cross

• The stamen is the

male reproductive part of the flower.

• The carpel is the

female reproductive part of the flower.

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The First Cross

Mendel crossed a pure-breed round-seeded variety with a pure-breed wrinkled-seeded

• ne.

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Genetics Song

• Punnet Square with 4 Alleles
• Two from Mom and two from Pop
• Each one Gives one to the Family Crop
• Genotype with two Alleles
• Is the Genetic Code for the Phenotype
• Phenotype with two Alleles
• Gives you, Your Look, Uniquely One Type

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The First Cross

The parents (designated the P generation) were pure-breed because each was homozygous for the alleles at the gene location (on chromosome 7) controlling seed texture (RR for round; rr for wrinkled).

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Results of the First Cross

• All the peas produced in the second or hybrid

generation were round.

• All the peas of this F1 generation have an Rr

genotype.

• All the haploid sperm and eggs produced by meiosis

received one chromosome 7.

• All the zygotes received one R allele (from the round

parent) and one r allele (from the wrinkled parent).

• Because the round trait is dominant, the phenotype
• f all the seeds was round.
• Monohybrid Cross results on table.

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Results of the First Cross

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Second Cross

• Mendel then allowed his hybrid peas to self-

pollinate.

• Results of second cross:

–The wrinkled trait — which had disappeared in his hybrid generation — reappeared in 25% of the new crop of peas. –Random union of equal numbers of R and r gametes produced an –F2 generation

• 25% RR and 50% Rr - both with the round

phenotype

• 25% rr with the wrinkled phenotype.

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Homozygous Round crossed with Homozygous Round F1 Generation

• F2 Generation Results
• Genotypic Results

– 1 Homozygous Round – 2 Heterozygous Round – 1 Homozygous Wrinkled

• Phenotypic Results

– 3 Round – 1 Wrinkles

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Results of the Second Cross

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Third Cross

• Mendel then allowed some
• f each phenotype in the F2

generation to self-pollinate.

• His results:

– All the wrinkled seeds in the F2 generation produced only wrinkled seeds in the F3. – One-third (193/565) of the round F1 seeds produced

• nly round seeds in the F3

generation, but – two-thirds (372/565) of them produced both types

• f seeds in the F3 and -
• nce again - in a 3:1 ratio.

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Monohybrid Cross Results

What do these results mean?

• One-third of the round seeds and all of the

wrinkled seeds in the F2 generation were homozygous and produced only seeds of the same phenotype.

• But two thirds of the round seeds in the F2

were heterozygous and their self-pollination produced both phenotypes in the ratio of a typical F1 cross.

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Punnett Square

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Monohybrid Cross

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Monohybrid Cross

Interpreting the results of a Punnett square

• We now have the information for predicting the outcome
• f the cross.
• The genotypes in the four boxes of the Punnett square

are each equally likely to occur among the offspring of this cross.

• We may now tabulate the results.
• Genotypes that resulted from this monohybrid cross

(Rr x Rr) – 25% homozygous dominant – 50% heterozygous – 25% homozygous recessive

• Phenotypes that resulted from this monohybrid

cross (Rr x Rr)

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Monohybrid Cross Round Pods Crossed with Wrinkled Pods

Results Genotypic Ratio-- 4:0 Heterozygous Round Phenotypic Ratio—4:0 Round

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Monohybrid Cross Yellow Pods Crossed with Green Pods Results

• Genotypic Ratio-- 4:0 Heterozygous Yellow
• Phenotypic Ratio—4:0 Yellow

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Monohybrid Cross Yellow Pods Crossed with Green Pods Results

• Genotypic Ratio-- 4:0 Heterozygous Yellow
• Phenotypic Ratio—4:0 Yellow

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Dihybrid Cross

• In this case, we have a cross involving two traits.
• A pea plant that produces

– Round (R), Yellow (Y) seeds is crossed is crossed with a pea plant that produces wrinkled (r), green (y) seeds.

• These 8 genotypes result in 4 different phenotypes.

– 9/16 of the seeds are Round and Yellow – 3/16 of the seeds are Round and Green – 3/16 of the seeds are Wrinkled and Yellow – 1/16 of the seeds are Wrinkled and Green

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Mendel’s Conclusions

First Conclusion Inherited characteristics are controlled by factors that occur in pairs. Second Conclusion (known as Principle of Dominance and Recessiveness) States that one factor in a pair may mask the other, preventing the

• ther from having an effect.

Third Conclusion (known as Mendel’s First Law or the Law of Segregation) States that a pair of factors is segregated during the formation of gametes. Fourth Conclusion (known as Mendel’s Second Law or the Law of Independent Assortment) It is translated as seed color for instance does not have any connection with the height of the pea plant.

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