modern synthesis concepts from laboratory genetics
DESCRIPTION
Modern Synthesis concepts from Laboratory Genetics. P = G + E Phenotype = Genotype + Environment. 1. 2. Environmental effects on phenotype are not inherited 3. Heredity is based on particles (genes). They retain identity and do not blend. They give rise to continuous and - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: Modern Synthesis concepts from Laboratory Genetics](https://reader036.vdocuments.us/reader036/viewer/2022062517/56813879550346895da0285d/html5/thumbnails/1.jpg)
Modern Synthesis concepts from Laboratory Genetics
P = G + EPhenotype = Genotype + Environment
1.
2. Environmental effects on phenotype are not inherited
3. Heredity is based on particles (genes). They retain identity and do not blend. They give rise to continuous and discrete variation.
4. Genes mutate at relatively low rates. Recombination is an important aspect of evolution.
5. Environmental factors can influence mutation rates but do not yield specific mutations that are seemingly the best for surviving in a particular environment.
![Page 2: Modern Synthesis concepts from Laboratory Genetics](https://reader036.vdocuments.us/reader036/viewer/2022062517/56813879550346895da0285d/html5/thumbnails/2.jpg)
Chromosomes, Genes, and Alleles
Traits are determinedby genes (primarily)
Different forms of a gene
are called alleles
Many different genes (loci)per chromosome
Locus A
Locus B
Locus C
![Page 3: Modern Synthesis concepts from Laboratory Genetics](https://reader036.vdocuments.us/reader036/viewer/2022062517/56813879550346895da0285d/html5/thumbnails/3.jpg)
Genetically “simple,” single locus traits: Mendel’s peas
Seed Shape
Seed Color
Flower Color
Pod Shape
Pod Color
Flower Position
Plant Stature
Trait or Charcteristic
![Page 4: Modern Synthesis concepts from Laboratory Genetics](https://reader036.vdocuments.us/reader036/viewer/2022062517/56813879550346895da0285d/html5/thumbnails/4.jpg)
Dominance / Recessivity
aa Aa AA aa Aa AA
Additivity
PhenotypePhenotype
Mode of Gene Action
Discrete Phenotypes Continuous Phenotypes
![Page 5: Modern Synthesis concepts from Laboratory Genetics](https://reader036.vdocuments.us/reader036/viewer/2022062517/56813879550346895da0285d/html5/thumbnails/5.jpg)
Quantitative traits depend on multiple underlying loci
one locusone locus + environment
two loci + environment
four loci + environment
many loci + environment
![Page 6: Modern Synthesis concepts from Laboratory Genetics](https://reader036.vdocuments.us/reader036/viewer/2022062517/56813879550346895da0285d/html5/thumbnails/6.jpg)
DiploidAdult
C E
Allele for Brown Coat
Allele for Black Eyes
![Page 7: Modern Synthesis concepts from Laboratory Genetics](https://reader036.vdocuments.us/reader036/viewer/2022062517/56813879550346895da0285d/html5/thumbnails/7.jpg)
C
C
c
c
E
E
e
e
C E
What if Mate these ?
What will the offspring’s genotype be?
Cc Ee
![Page 8: Modern Synthesis concepts from Laboratory Genetics](https://reader036.vdocuments.us/reader036/viewer/2022062517/56813879550346895da0285d/html5/thumbnails/8.jpg)
C
C
c
c
E
E
e
e
C
c
e
e
DNAReplication
Hybrid Mouse Genotype
Cc Ee
C
c
E
eSister
chromatids
Sister chromatids{Homologous
Pair
{HomologousPair
![Page 9: Modern Synthesis concepts from Laboratory Genetics](https://reader036.vdocuments.us/reader036/viewer/2022062517/56813879550346895da0285d/html5/thumbnails/9.jpg)
Genetic recombination:chromosomal segments are exchangedbetween homologues during Meiosis I
C
C
c
c
E
E
e
e
![Page 10: Modern Synthesis concepts from Laboratory Genetics](https://reader036.vdocuments.us/reader036/viewer/2022062517/56813879550346895da0285d/html5/thumbnails/10.jpg)
Genetic recombination: New combination of alleles
C
C
c
c
E
E
e
e
![Page 11: Modern Synthesis concepts from Laboratory Genetics](https://reader036.vdocuments.us/reader036/viewer/2022062517/56813879550346895da0285d/html5/thumbnails/11.jpg)
C
C
c
c
E
E
e
e
Separation of DNA
Meiosis II
Meiosis II
C
C
c
c
E
E
e
e
Meiosis I
GAMETES
![Page 12: Modern Synthesis concepts from Laboratory Genetics](https://reader036.vdocuments.us/reader036/viewer/2022062517/56813879550346895da0285d/html5/thumbnails/12.jpg)
C
C
c
c
E
E
e
e
Sperm Gametes
C
C
c
c
E
E
e
e
ALL
POSSIBLE
Egg Gametes Genotype
CC/EE
Cc/EE
CC/Ee
Cc/Ee
WHAT GENOTYPES IF MATE TWOHYBRID MICE (Cc / Ee)?
![Page 13: Modern Synthesis concepts from Laboratory Genetics](https://reader036.vdocuments.us/reader036/viewer/2022062517/56813879550346895da0285d/html5/thumbnails/13.jpg)
CCEE CCEe
CCEe
CcEeCcEE
CcEE
CcEe
CCee
CcEe
CcEe
Ccee
Ccee
ccEE
ccEe
ccEe
ccee
CE
CE Ce
Ce
ce
ce
cE
cE
AllPossibleSpermGametes
All Possible Egg Gametes
Cc / Ee x Cc / Ee
I. Law of Segregation
c
C C
c
E e
E e
II. Law ofIndependentAssortment
![Page 14: Modern Synthesis concepts from Laboratory Genetics](https://reader036.vdocuments.us/reader036/viewer/2022062517/56813879550346895da0285d/html5/thumbnails/14.jpg)
Mendel’s 1st law: Characters are controlled by pairs of genes which separate during the formation of the reproductive cells (meiosis)
Mendel’s 2nd law: When two or more pairsof genes segregate simultaneously, they doso independently.
![Page 15: Modern Synthesis concepts from Laboratory Genetics](https://reader036.vdocuments.us/reader036/viewer/2022062517/56813879550346895da0285d/html5/thumbnails/15.jpg)
“Exceptions” to Mendel’s Second Law
From Thomas Hunt Morgan (1909): 2,839 flies
Eye color A: red a: purpleWing length B: normal b: vestigial
AABB x aabb
AaBb x aabb
AaBb Aabb aaBb aabbExp 710 710 710 710Obs 1,339 151 154 1,195
![Page 16: Modern Synthesis concepts from Laboratory Genetics](https://reader036.vdocuments.us/reader036/viewer/2022062517/56813879550346895da0285d/html5/thumbnails/16.jpg)
Morgan’s explanation
A A
B B
a a
b b
F1: A a
B b
a a
b b
F2:A a
B b
a a
b b
A a
b b
a a
B b
Crossover has taken place
![Page 17: Modern Synthesis concepts from Laboratory Genetics](https://reader036.vdocuments.us/reader036/viewer/2022062517/56813879550346895da0285d/html5/thumbnails/17.jpg)
Parental types: AaBb, aabbRecombinants: Aabb, aaBb
The proportion of recombinants between the two genes (or characters) is called the recombination fraction between these two genes.
It is usually denoted by r or . For Morgan’s traits: r = (151 + 154)/2839 = 0.107
If r < 1/2: two genes are said to be linked.
If r = 1/2: independent segregation (Mendel’s second law).
![Page 18: Modern Synthesis concepts from Laboratory Genetics](https://reader036.vdocuments.us/reader036/viewer/2022062517/56813879550346895da0285d/html5/thumbnails/18.jpg)
A a
B b Meiosis
Probability of recombination = 0.3
A aB b Meiosis
Probability of recombination = 0.1
AB
Ab
aB
ab
All allele combinations in gametes NOTequally probable
= 0.15
= 0.15
= 0.35
= 0.35
AB
Ab
aB
ab
= 0.05
= 0.05
= 0.45
= 0.45
Linked Loci
All allele combinations in gametes NOTequally probable
![Page 19: Modern Synthesis concepts from Laboratory Genetics](https://reader036.vdocuments.us/reader036/viewer/2022062517/56813879550346895da0285d/html5/thumbnails/19.jpg)
Concept: The closer two loci are on a chromosome, the lower the probability of recombination.
Why important?
(1) Allows one to determine the linear order of genes on a chromosome (make a genome map).
(2) Maps allow for the localization of genes, mutant phenotypes, and QTL in the genome.