Download Independent vs. Linked Genes

Doc.3: Interchromosomic
Recombination (p.46-47)
&
Doc.4: Intrachromosomic
Recombination (p.48-49)
Independent vs. Linked Genes
• Independent (Interchromosomic) Genes:
Genes found on different chromosomes.
• Linked Genes (Intrachromosomic): Genes
found on the same chromosome.
Independent assortment
Meiosis KM
3
All F1 plants produce
yellow-round seeds (YyRr).
F1 Generation
R
y
r
R
y
r
Y
Y
LAW OF INDEPENDENT
ASSORTMENT Alleles of
genes on nonhomologous
chromosomes assort
independently during gamete
formation.
Meiosis
LAW OF SEGREGATION
The two alleles for each
gene separate during
gamete formation.
r
R
Y
y
r
R
Metaphase I
y
Y
1
1
R
r
r
R
Y
y
Anaphase I
Y
y
r
R
2
y
Y
Y
R
R
1/
4
YR
r
1/
4
yr
y
Y
Y
Y
y
r
R
2
y
Y
Gametes
r
Metaphase
II
r
r
1/
4
Yr
y
y
R
R
1/
4
yR
Doc.3: Interchromosomic Recombination
Independent Genes Test-Cross Results
• Crossing over
Crossing Over
– Produces recombinant chromosomes that carry genes derived from two
different parents
Prophase I
of meiosis
Nonsister
chromatids
Tetrad
Chiasma,
site of
crossing
over
Metaphase I
Metaphase II
Daughter
cells
Figure 13.11
Recombinant
chromosomes
•
•
50% Parental Gametes
50% Recombinant Gametes
100% Parental Gametes
0% Recombinant Gametes
> 50% Parental Gametes
<50% Recombinant Gametes
Test Cross: Dihybrid F1x birecessive Parent
Independent Assortment
4 phenotypes of equal
proportions (25% each)
Absolute Linkage
2 phenotypes of equal
proportions (50% each)
Partial Linkage Cis
4 phenotypes of unequal
proportions (birecessive
most numerous)
4 phenotypes of unequal
proportions (birecessive
least numerous)
Trans
Recombination frequency is proportional to the
distance between two genes.
(a) genes close
together:
few recombinants
RF(AB) is smaller
(b) genes far apart:
many recombinants
RF(AB) is larger
Map Units
• Map Unit (m.u.) = the distance between genes for
which one product of meiosis
out of 100 is recombinant
• RF of 1% = 1 m.u. or 1 cM
• Represent the gene map if RF is 12% between A & B,
and 28% between B & C: