Primary Mechanism of Duplication : Unequal Crossing Over
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Primary Mechanism of Duplication : Unequal Crossing Over. Crossing over Between Daughter Strands. Addition (duplication). Deletion. (tandom duplications). Crossing over Between Daughter Strands. Addition. Deletion. Polyploidization : complete genome duplication. Processed

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Primary Mechanism of Duplication : Unequal Crossing Over

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Primary mechanism of duplication unequal crossing over

Primary Mechanism of Duplication : Unequal Crossing Over

Crossing over

Between Daughter

Strands

Addition (duplication)

Deletion

(tandom duplications)

Crossing over

Between Daughter

Strands

Addition

Deletion


Primary mechanism of duplication unequal crossing over

Polyploidization : complete genome duplication


Primary mechanism of duplication unequal crossing over

Processed

Pseudogene

Creation of a processed pseudogene.


Primary mechanism of duplication unequal crossing over

a

Duplication

TD

a

b

Speciation

TS

a

b

a

b

Species 2

Species 1

aandbare said to be paralogous genes

aspecies1andaspecies2are said to be orthologous genes


Primary mechanism of duplication unequal crossing over

Examples of Duplicated Genes


Primary mechanism of duplication unequal crossing over

Fate of Duplicated Loci

  • Both copies retain original function

    e.g. rRNA genes

    (2) Gain new function through mutation and selection

    e.g. globin genes

    (3) Become functionless pseudogenes

    e.g globin genes


Primary mechanism of duplication unequal crossing over

Time of duplication may be estimated by observing the

phylogenetic distribution of genes

All vertebrates but jawless fish have a and b

H1: Two independent gene losses

H2: Duplication


Primary mechanism of duplication unequal crossing over

Repeated Duplication Creates Gene Families


Primary mechanism of duplication unequal crossing over

Globins are differentially expressed during development


Primary mechanism of duplication unequal crossing over

Point mutations generally arise

during DNA synthesis or repair

Error rate of DNA polymerases

and the

Efficiency of DNA repair

are heritable traits.


Chromosomes genes and alleles

Locus A

Many different genes (loci)

per chromosome

Locus B

Locus C

Different forms of a gene

are called alleles

Chromosomes, Genes, and Alleles

Traits are determined

to a great extent by genes


Primary mechanism of duplication unequal crossing over

Basic Unit of DNA


Primary mechanism of duplication unequal crossing over

Nucleic acids are long chains of nucleotides


Primary mechanism of duplication unequal crossing over

In humans 35,000?? different proteins are specified by the

simple linear arrangement

of four bases

The Watson-Crick Model of DNA


Nucleotide bases

Nucleotide Bases

Adenine

Guanine

Cytosine

Thymine

}

Purines

Complimentary

}

Pyrimidines


Primary mechanism of duplication unequal crossing over

C T T G

| | | |

3’ OH---dR---P---dR---P---dR---P---dR---P 5’

Schematic Representation of DNA

G A A C

5’ P---dR---P---dR---P---dR---P---dR---OH 3’

| | | |

G A A C


Classes of gene

Classes of Gene

  • Protein-coding genes : transcribed and translated

  • RNA specifying genes : transcribed

  • Untranscribed genes


Primary mechanism of duplication unequal crossing over

Schematic of Eukaryotic Protein-Coding Locus

5’ UTR

3’ UTR

Intron 2

Intron 1

5’

3’

Exon 1

Exon 2

Ex 3

GT AG

GT AG

Regulatory

Sequences

Initiation

codon

Stop

codon


Primary mechanism of duplication unequal crossing over

How does mRNA specify the amino acid sequence of the protein?

Every three nucleotides forms a codon : each codon

codes for an amino acid


Primary mechanism of duplication unequal crossing over

Figure 4.3 The Genetic Code (Codons of mRNA)

Note : different codons specify the same amino acid

(i.e. Code is Degenerate)


Primary mechanism of duplication unequal crossing over

Example of RNA specifying gene :rDNA array

NTS

18S

28S

ITS-1

ITS-2

ETS

5.8S

1 array in Tetrahymena

19,300 copies in Amphiuma

200 copies in Human


Primary mechanism of duplication unequal crossing over

28S

ITS

NTS

ETS

18S

ITS

28S

NTS

c

b

a

d

c

28S

human

a

d

b

c

c

28S

chimp

a

d

b

c

c

28S

pygmy chimp

a

d

c

b

c

28S

gorilla

aBamHI

bHindI

cBgIII

dHpaI

Arnheim, 1983


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