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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

Chapter 14

Genetics

introduction
Introduction
  • Pre 1800s – blending hypothesis
  • 1850s – Gregor Mendel
slide3

Pisumsativum– what makes pea good genetic model?

-

-

-

-

  • Pea character (gene) =
  • Pea trait (allele) =
slide4

self fertilization

Vs. cross fertilization

the monohybrid cross
The monohybrid cross
  • Cross true breeding parental plants (P)
  • produces F1 generation
slide8

Cross F1 plants

F2 plants = ~250 white ~750 purple

A monohybrid

Is this quantitative or qualitative data?

dominance
Dominance

Allele = Alternative version of gene

Dominant allele P Recessive allele p

Each individual inherits 2 alleles/gene

Genotype Phenotype?

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?

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

slide14

Mendel did not know about:

    • DNA/chromosomes/genes
    • Crossing over or the cell cycle
    • Linked alleles
slide15
In mice, black fur is dominant over white fur

Cross heterozygous mouse with homozygous recessive mouse

Possibilities?

slide16
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?

slide19

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
independent assortment
Independent Assortment

2 genes

Y = yellow pea allele R = round pea allele

y = green pea allele r = wrinkled

Phenotypes of peas

slide24

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

slide25

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 ?

slide28

multiple alleles

Ex. blood type

Alleles IA IB i

IAIA IBIB IA IB

IAiIBi ii

slide30

polygenic inheritance

multiple genes affect characteristic

Ex. skin – at least 3 genes

Height

slide31

environmental effects

A particular genotype may have a phenotypic range

  • Ex
    • Does blood color have a norm?
    • Skin color?
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

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

multifactorial disorders
Multifactorial disorders

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

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