Chapter 11: Introduction to Chapter 11: Introduction to GeneticsGenetics

11-1 Key Words

• GeneticsGenetics• FertilizationFertilization• True-breedingTrue-breeding• TraitTrait• HybridHybrid• GeneGene• AlleleAllele• SegregationSegregation• Gamete Gamete

11-1 The Work of Gregor Mendel

IntroIntroEvery living thing-Every living thing-plant or animal, plant or animal,

microbe or human-microbe or human-has a set of has a set of

characteristics characteristics inherited from its inherited from its

parents.parents.

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DefinitionDefinition

• GeneticsGenetics: : the scientific study the scientific study of heredity.of heredity.

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Gregor Mendel, an Austrian Gregor Mendel, an Austrian monk (mid 1800’s)monk (mid 1800’s)

His basic principles of His basic principles of heredity are still heredity are still accepted today.accepted today.

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Mendel’s experiments:Mendel’s experiments:

• 20,000 pea plants

• Used statistics

• Detailed notes

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Mendel’s experiments:Mendel’s experiments:

• Why peas?

• Flower structure

–Mendel knew –the male part of each flower produces pollen

–the female part of the flower produces egg cells.

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Mendel’s experiments:Mendel’s experiments:

• Why peas?

• Flower structure

• Presence of distinctive traits

• Fast reproduction

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Genes and DominanceA trait is a specific characteristic that varies from one individual to another.

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Mendel’s work not recognized for 30 years (after his death).

That’s just

wrong!

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Gregor Mendel’s Peas•Mendel had true-breeding pea plants: that, produce offspring identical to themselves.

•He cut away the pollen-bearing male parts and dusted the plant’s flower with pollen from another plant.

•These were the “P” generation.These were the “P” generation.

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Gregor Mendel’s Peas

Cross Pollination two different parents

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Pure linesPure lines Seed produced

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Mendel’s experiments:Mendel’s experiments:

• What What did he did he do?do?

• Seed was produced. This Seed was produced. This seed was grown and seed was grown and called the first filial or called the first filial or “F1” generation.“F1” generation.

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F1F1generationgeneration

hybridshybrids

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Mendel’s F1 Crosses on Pea Plants

Remember Remember what a what a diploid diploid organism organism is?is?

1 “allele” 1 “allele” from each from each parentparent

Hybrid

Yy

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Mendel's first conclusion: biological inheritance is determined by factors that are passed from one generation to the next.

genes

Is that shortness trait lost forever?

No baby, its only hidden.

• The principle of dominance: that some The principle of dominance: that some alleles are alleles are dominantdominant and others are and others are recessiverecessive..

• An organism with a dominant allele: An organism with a dominant allele: always exhibit that form of the traitalways exhibit that form of the trait..

• An organism with the recessive allele: An organism with the recessive allele: will exhibit that form will exhibit that form only when the only when the dominant allele for that trait is dominant allele for that trait is notnot present.present.

What happens during segregation?

SegregationSegregation

Mendel crossed the F1 generation with itselfThe traits controlled by recessive alleles reappeared in one fourth of the F2 plants.

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•Mendel's F2 Generation

P GenerationF1 Generation

Tall Tall Tall Tall Tall TallShort Short

F2 Generation

Segregation

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The reappearance of the trait The reappearance of the trait controlled by the recessive allele: controlled by the recessive allele: the allele for shortness had been the allele for shortness had been separated, or separated, or segregatedsegregated, from the , from the allele for tallness. allele for tallness.

• segregated from each other during the formation of the sex cells, or gametes.

When each FWhen each F11 plant flowers and plant flowers and produces gametes, the two produces gametes, the two alleles segregatealleles segregate

Each FEach F11 plant produces plant produces two two types of gametestypes of gametes——allele for allele for tallness, and the allele for tallness, and the allele for shortness.shortness.

Alleles separate during gamete formation.

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– Gametes are also known as

• genes.

• sex cells.

• alleles.

• hybrids.

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–The offspring of crosses between parents with different traits are called

• alleles.

• hybrids.

• gametes.

• dominant.

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In Mendel’s pea experiments, the male gametes are the

• eggs.

• seeds.

• pollen.

• sperm.

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In a cross of a true-breeding tall pea plant with a true-breeding short pea plant, the F1 generation consists of

• all short plants.

• all tall plants.

• half tall plants and half short plants.

• all plants of intermediate height.

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If a particular form of a trait is always present when the allele controlling it is present, then the allele must be

• mixed.

• recessive.

• hybrid.

• dominant.

Law of dominanceLaw of dominance

When an organism is hybrid for a pair of contrasting traits, only the dominant trait can be seen in the

hybrid.

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T + T = Tall

T + t = Tall

t + t = short

PP

F1F1

×

×

F2F2

Parental

First filial

Second filial

Mendel’sMendel’sCrossesCrosses((ReviewReview))

75% yellow, 25% green75% yellow, 25% green

PP

F1F1

××

××

F2F2

Parental

First filial

Second filial

Mendel’sMendel’sCrossesCrosses

3:1 Ratio3:1 Ratio

The Law of SegregationThe Law of Segregation

• Factors that occur in pairs Factors that occur in pairs separate from each other separate from each other during gamete formation during gamete formation and recombine at and recombine at fertilization.fertilization.

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If blending hypothesis were true, what would Mendel

have seen in F1 generation?

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