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Standard BiologyStandard Biology Chapter 26 Inheritance Chapter 26 Inheritance

of Traitsof Traits

Section 1 Genetics, How and Section 1 Genetics, How and WhyWhy

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GeneticsGenetics

Genetics: the Genetics: the study of how study of how traits are passed traits are passed from parent to from parent to offspringoffspring– Mystery for a Mystery for a

long timelong time– Now know traits Now know traits

are passed in sex are passed in sex cellscells

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ChromosomesChromosomes

Nucleus found in Nucleus found in center of cell which center of cell which directs the cell’s directs the cell’s activitiesactivities

Chromosomes are Chromosomes are found in nucleusfound in nucleus

Chromosomes are Chromosomes are thickened and easy thickened and easy to seeto see

Remember, Remember, chromosomes are chromosomes are duplicated before duplicated before cell reproductioncell reproduction

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ChromosomesChromosomes Two kinds of cellsTwo kinds of cells Body cells- Body cells-

chromosomes in chromosomes in pairs (pairs (diploid)diploid)

Sex cells- single Sex cells- single chromosomes (so chromosomes (so ½ the number of ½ the number of chromosomes as chromosomes as body cells) body cells) (haploid)(haploid)

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Genes on ChromosomesGenes on Chromosomes

GeneGene– Small section of Small section of

chromosome that chromosome that determines a determines a specific trait; specific trait; examplesexamples Eye colorEye color Wing shapeWing shape Chemical processChemical process

– Humans have Humans have about 23,000 about 23,000 genesgenes

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Genes on ChromosomesGenes on Chromosomes

Genes are Genes are arranged on a arranged on a chromosome like chromosome like beads on a beads on a necklacenecklace

Chromosomes Chromosomes are paired, so are paired, so genes are paired genes are paired (except sex cells)(except sex cells)

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Passing Traits to Passing Traits to OffspringOffspring

Traits are passes Traits are passes from parent to from parent to offspring in sex offspring in sex cellscells

Example: Ear Example: Ear Lobe Shape p. Lobe Shape p. 548548

Female

egg

Male

sperm A= attached ear lobes

F= free ear lobes

Child will have free ear lobes

A

A

F

FAF

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Dominant and Recessive Dominant and Recessive GenesGenes

One trait dominates another like free One trait dominates another like free dominates attacheddominates attached

Free=dominate and Attached=recessiveFree=dominate and Attached=recessive Mother is pure attached (AA) or Mother is pure attached (AA) or

homozygous recessive (homo means homozygous recessive (homo means same)same)

Father is pure dominate (FF) or Father is pure dominate (FF) or homozygous dominatehomozygous dominate

Child is one Free and one Attached (FA) Child is one Free and one Attached (FA) or heterozygous (hetero means or heterozygous (hetero means different)different)

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Traits of Plants and AnimalsTraits of Plants and Animals

Trait found Trait found inin

Dominant Dominant TraitTrait

Recessive Recessive TraitTrait

FliesFlies Long wingsLong wings Short wingsShort wings

Pea plantsPea plants Purple flowersPurple flowers White flowersWhite flowers

HumansHumans Can roll Can roll tonguetongue

Can’t roll Can’t roll tonguetongue

Corn plantsCorn plants Normal heightNormal height DwarfDwarf

DogsDogs Short hairShort hair Long hairLong hair

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When Both Parents are When Both Parents are HeterozygousHeterozygous

If mother is heterozygous (FA), If mother is heterozygous (FA), she can make F eggs and A eggsshe can make F eggs and A eggs

If father is Heterozygous (FA), he If father is Heterozygous (FA), he can make F sperm and A spermcan make F sperm and A sperm

How many combinations of traits How many combinations of traits in children as possible? Table 26-in children as possible? Table 26-2 p. 5512 p. 551

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When Both Parents are When Both Parents are HeterozygousHeterozygous

Mother’s eggs: F and AMother’s eggs: F and A Father’s sperm: F and AFather’s sperm: F and A Child:Child: FF, FA, AF or AAFF, FA, AF or AA So four combinations of genes possible So four combinations of genes possible

(although FA and AF are the same)(although FA and AF are the same) Child will have free ear lobes if FF, FA Child will have free ear lobes if FF, FA

or AFor AF Child will have attached ear lobes if AAChild will have attached ear lobes if AA

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Standard BiologyStandard Biology Chapter 26 Inheritance Chapter 26 Inheritance

of Traitsof Traits

Section 2 Expected and Section 2 Expected and Observed ResultsObserved Results

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Punnett SquarePunnett Square

Easy way to look at Easy way to look at combinations of combinations of traits is with a traits is with a Punnett SquarePunnett Square– Letters used Letters used

represent genesrepresent genes– Capital letters Capital letters

dominantdominant– Lower case letters Lower case letters

recessiverecessive– Trait’s letter based Trait’s letter based

on dominanton dominant

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Punnett SquarePunnett Square

Example:Example: Free ear lobes Free ear lobes

dominant Fdominant F Attached ear Attached ear

lobes recessive flobes recessive f Homozygous Homozygous

recessive mother recessive mother ffff

Homozygous Homozygous dominant father dominant father FFFF

Mother’s genes

F

F

f f

FfFf

FfFf

Father’s genes

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Punnett SquarePunnett Square

Example when Example when parents are parents are heterozygous:heterozygous:

Mother’s genes

F

f

F f

FfFF

ffFf

Father’s genes

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Directions for Punnett Directions for Punnett SquareSquare

1.1. Draw a Punnett Square (4 boxes). Each Draw a Punnett Square (4 boxes). Each box shows possible combination of genes box shows possible combination of genes in offspring.in offspring.

2.2. Decide what genes will be in the sex cells Decide what genes will be in the sex cells of each parent.of each parent.

3.3. Write mother’s genes on top; write Write mother’s genes on top; write father’s genes on side.father’s genes on side.

4.4. Copy the letters that appear at the top of Copy the letters that appear at the top of the square into the boxes below each the square into the boxes below each letter.letter.

5.5. Copy the letters that appear at the side Copy the letters that appear at the side into the boxes next to each letter.into the boxes next to each letter.

6.6. Look at the 4 small boxes in the Punnett Look at the 4 small boxes in the Punnett Square, these are possible combinations Square, these are possible combinations in the offspring.in the offspring.

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Expected ResultsExpected Results

Get from Punnett Get from Punnett SquareSquare

What you expect What you expect to happento happen

ProbabilityProbability

Expected Results

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Observed ResultsObserved Results The numbers you The numbers you

actually getactually get They don’t match up They don’t match up

exactly with what exactly with what you expectyou expect

The greater the The greater the number of offspring, number of offspring, the closer you the closer you should get to the should get to the expected results.expected results.

Table 26-3 p. 557Table 26-3 p. 557

Expected Results

Observed results when you count the pods of this one cross:

71 yellow pods and 24 green pods

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Mendel’s WorkMendel’s Work Gregor MendelGregor Mendel

– Father of GeneticsFather of Genetics– 1865 Austrian 1865 Austrian

monk/teacher in Czechmonk/teacher in Czech– Grew garden peas, Grew garden peas,

came up with ideas came up with ideas about how traits are about how traits are inheritedinherited

– Counted 1000’s of Counted 1000’s of traits in pea plants and traits in pea plants and conducted scientific conducted scientific investigations (applied investigations (applied math to science)math to science)

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Mendel’s WorkMendel’s Work

– Traits he studied:Traits he studied: Plant heightPlant height Pod colorPod color

Pod shapePod shape Seed colorSeed color Seed shapeSeed shape Flower colorFlower color Flower positionFlower position

Always foundAlways found 3 dominate to 1 3 dominate to 1 recessive when heterozygous recessive when heterozygous parents were crossedparents were crossed

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