Chapter 14
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Chapter 14 . Genetics. Introduction. Pre 1800s – blending hypothesis 1850s – Gregor Mendel. Pisum sativum – what makes pea good genetic model? - - - - Pea character (gene) = Pea trait (allele) = . self fertilization Vs. cross fertilization. The monohybrid cross.

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Chapter 14

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Chapter 14

Chapter 14

Genetics


Introduction

Introduction

  • Pre 1800s – blending hypothesis

  • 1850s – Gregor Mendel


Chapter 14

Pisumsativum– what makes pea good genetic model?

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-

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  • Pea character (gene) =

  • Pea trait (allele) =


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  • self fertilization

    Vs. cross fertilization


The monohybrid cross

The monohybrid cross

  • Cross true breeding parental plants (P)

  • produces F1 generation


Character gene trait allele dominant phenotype recessive phenotype

-character (gene)-trait (allele)- dominant phenotype- recessive phenotype


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F1 plants all purple


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  • Cross F1 plants

    F2 plants = ~250 white ~750 purple

A monohybrid

Is this quantitative or qualitative data?


Mendel s conclusions

Mendel’s Conclusions


Dominance

Dominance

Allele = Alternative version of gene

Dominant allele PRecessive allele p

Each individual inherits 2 alleles/gene

GenotypePhenotype?

PP homozygous dominant

pp homozygous recessive

Pp heterozygous


Dominant allele masks expression of recessive allele

Dominant allele masks expression of recessive allele

Find the dominant allele

Pick symbols

What is the phenotype of plant with genotype Rr?

What is genotype of a green plant?


Genotype

Genotype?


Segregation

Segregation

  • The 2 alleles segregate in gametes during meiosis

  • Random segregation

Pea chromosome 1

Genotype of plant?

Phenotype of plant?

Human chromosome 11 gene for beta globin

Genotype Hbb/Hbb


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  • Mendel did not know about:

    • DNA/chromosomes/genes

    • Crossing over or the cell cycle

    • Linked alleles


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In mice, black fur is dominant over white fur

Cross heterozygous mouse with homozygous recessive mouse

Possibilities?


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In mice, black fur is dominant over white furCross heterozygous mouse with homozygous recessive mouse

  • Make an allele key

  • Show the cross

    3. Write the phenotypes under the genotypes

    4. Determine the parental gametes (random segregation)

    5. Add to Punnett square

    6. Determine offspring


Punnett square

Punnett square

What is the expected ratio of phenotypes?

Genotypes?

In a litter of 3, how many are expected to be white?

Which phenotype is the recessive phenotype?


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  • In cats striping is dominant over non-stripes. Mate two heterozygous cats.


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The Scottish fold is a dominant trait

Genotypes FF Ffff

Phenotypes?

The original Scottish Fold was a white barn cat named Susie, found in Scotland


Test cross

Test cross

Scottish fold cat -> Is she Ff or FF?

If FF, then cross toff kittens?

If Ff, then cross to ff  kittens?

A test cross is always a cross to a homozygous individual.


Review

Review

  • All possible one gene crosses

    B = black fur allele

    b = white fur allele

  • BB X BB  all black

  • BB X Bb 

  • BB X bb 

  • Bb X Bb 

  • Bb X bb 

  • bb X bb  all white


The dihybrid cross 2 genes

The Dihybrid cross (2 genes)


Independent assortment

Independent Assortment

2 genes

Y = yellow pea alleleR = round pea allele

y = green pea alleler = wrinkled

Phenotypes of peas


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X

RRYY

rryy

True-breeding yellow, round X true-breeding green, wrinkled

Allele key?

P Genotype?

Gametes? (always 4 per parent in 2 gene cross)

R = round allele Y = yellow

r = wrinkled y = green

RY and ry


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Parental generation: RRYY X rryy

Gametes ?

F1 generation?

Gametes of F1 generation?

F2 generation?


F2 generation

F2 generation

Ratio of genotypes?

Ratio of phenotypes?


Extensions of mendel

Extensions of Mendel

Codominance

Both alleles expressed in phenotype

Ex. Blood type I gene

Alleles IA IB

Phenotype of IA IB ?


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multiple alleles

Ex. blood type

Alleles IA IB i

IAIA IBIB IA IB

IAiIBiii


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polygenic inheritance

multiple genes affect characteristic

Ex. skin – at least 3 genes

Height


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  • environmental effects

    A particular genotype may have a phenotypic range

  • Ex

    • Does blood color have a norm?

    • Skin color?


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?


Recessively inherited disorders

Recessively inherited disorders

A allele  normal protein

a allele  malfunctioning or no protein

AA

Aa heterozygotes are carriers

aa

disorders range from fetal lethal to mild


Ex albinism a allele does not code for functional melanin protein

Ex. albinism a allele does not code for functional melanin protein

Chromosome 11


Recessive traits

Recessive traits

bb = blond hair

bb = blue eyes

ii = type O blood


Dominantly inherited disorders

Dominantly inherited disorders

A allele  abnormal protein

a allele  normal protein

AA

Aa

aa


Achondroplasia d allele causes dwarfism

Achondroplasia D allele causes dwarfism


Multifactorial disorders

Multifactorial disorders

Genetic component + environment (aging, diet, chemicals, radiation, etc.)


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