Chapter 11: Introduction to Chapter 11: Introduction to GeneticsGenetics

California content standards: Genetics 2c, d, g; 3a, bCalifornia content standards: Genetics 2c, d, g; 3a, b

2c. 2c. Students know Students know how random how random chromosome segregation explains the chromosome segregation explains the probability that a particular allele will be in probability that a particular allele will be in a gamete. a gamete. 2d. 2d. Students know Students know new combinations of new combinations of alleles may be generated in a zygote alleles may be generated in a zygote through the fusion of male and female through the fusion of male and female gametes (fertilization).gametes (fertilization).2g. 2g. Students know Students know how to predict how to predict possible combinations of alleles in a possible combinations of alleles in a zygote from the genetic makeup of the zygote from the genetic makeup of the parents. parents.

3a. 3a. Students know Students know how to predict the how to predict the probable outcome of phenotypes in a probable outcome of phenotypes in a genetic cross from the genotypes of the genetic cross from the genotypes of the parents and mode of inheritance parents and mode of inheritance (autosomal or X-linked, dominant or (autosomal or X-linked, dominant or recessive). recessive). 3b. 3b. Students know Students know the genetic basis for the genetic basis for Mendel's laws of segregation and Mendel's laws of segregation and independent assortment.independent assortment.

11-1 Key Words

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

Quizon these

termsThursday!

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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First clues to understanding First clues to understanding how traits are inherited came how traits are inherited came

from Gregor Mendel, an from Gregor Mendel, an Austrian monk, in the mid Austrian monk, in the mid

1800’s.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:

• Unique because:

• 20,000 pea plants

• Used statistics

• Took detailed notes

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Mendel’s experiments:Mendel’s experiments:•Why peas? Flower structure

–Mendel knew that –the male part of each flower produces pollen, (containing sperm).

–the female part of the flower produces egg cells.

• During sexual reproduction, sperm and egg cells join in a process called fertilization.

• Fertilization produces a new cell.

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Mendel’s experiments:Mendel’s experiments:

• Why peas?

• Flower structure

• Presence of distinctive traits (wrinkled vs. smooth, color, etc.)

• Fast reproduction11-1

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, if allowed to self-pollinate, would produce offspring identical to themselves. •Mendel wanted to produce seeds by joining male and female reproductive cells from two different plants.•He cut away the pollen-bearing male parts of the plant 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

•This process is called cross-pollination.

•Mendel was able to produce seeds that had 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.

All plants were tall when grown.All plants were tall when grown.

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F1F1generationgeneration

hybridshybrids

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Mendel’s F1 Crosses on Pea Plants

HybridHybrid• The offspring of crosses between

parents with different traits

• Mendel’s F1 hybrid plants all had the character of only one of the parents.

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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 was that biological inheritance is determined by factors that are passed from one generation to the next.

Today, scientists call the factors that determine traits genes.

Is that shortness trait lost forever?

No baby, its only hidden.

• Each of the traits Mendel studied was controlled by one gene that occurred in two contrasting forms that produced different characters for each trait.

• The different forms of a gene are called alleles.

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• Mendel’s second conclusion is called the principle of dominance.

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

• An organism with a dominant An organism with a dominant allele for a trait will allele for a trait will always exhibit always exhibit that form of the traitthat form of the trait..

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

2 dominants

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dominant

dominantdominant

recessiverecessive

1 dominant + 1 recessive 1 dominant + 1 recessive

2 recessive 2 recessive

What happens during segregation?

SegregationSegregation

Mendel crossed the F1 generation with itself to produce the F2 (second filial) generation.The 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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• Mendel assumed that a dominant allele had masked the corresponding recessive allele in the F1 generation.

• The trait controlled by the recessive allele showed up in some of the F2 plants.

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The reappearance of the trait The reappearance of the trait controlled by the recessive allele controlled by the recessive allele indicated that at some point the indicated that at some point the allele for shortness had been allele for shortness had been separated, or separated, or segregatedsegregated, from the , from the allele for tallness. allele for tallness.

• Mendel suggested that the alleles for tallness and shortness in the F1 plants 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 segregate from each alleles segregate from each other so thatother so that each gamete each gamete carries only a single copy of carries only a single copy of each geneeach gene. .

Therefore, each FTherefore, each F11 plant plant produces produces two types of gametestwo types of gametes——those with the allele for those with the allele for tallness, and those with the tallness, and those with the allele for shortness.allele for 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.

Gene-Chromosome TheoryGene-Chromosome Theory

25-1 in “Bear Book”

Mendel concluded that forms of Mendel concluded that forms of a trait must remain separate in a trait must remain separate in

offspring.offspring.Offspring receives 1 trait from Offspring receives 1 trait from

each parent.each parent.Traits are coded for by Traits are coded for by genesgenes..

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GenesGenes: sections of a : sections of a chromosome that code for a chromosome that code for a

trait.trait.

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Alleles

• To agree with Mendel’s findings, each body cell should have 2 copies of each trait (allelesalleles).

–e.g. 2 copies of the gene for height

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Different forms of a trait are Different forms of a trait are called called allelesalleles..

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Alleles of 1 gene

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Alleles

Gene 1Gene 1 Gene 1Gene 1A A

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Homologous pair

HomozygousDominant

Alleles

Gene 1Gene 1 Gene 1Gene 1A a

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Homologous pair

Heterozygous

Alleles

Gene 1Gene 1 Gene 1Gene 1a a

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Homologous pair

Homozygousrecessive

Alleles

a a A A

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Exact copies(homologouschromatids)

One from mom, one from dad(homologous

pair)

} }Allele for brown eyes

allele for blue eyes

Anatomy of aAnatomy of achromosomechromosome

Gene for eye color:

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