Notesale: Turn your study into money

Document Preview

Extracts from the notes are below, to see the PDF you'll receive please use the links above

---

(a) Dominant epistasis (12: 3: 1):
When dominant allele ‘A’ masks the expression of ‘B’ ‘A’ is epistatic gene of ‘B’
...
Therefore it is called dominant epistasis
...
Therefore, in 9: 3: 3: 1 ratio both 9 and 3 are expressing the ‘A’ gene
the ratio is now 12: 3: 1
...
wikimedia
...
jpg
Example:

Complete dominance at both gene pairs, but one gene, when dominant, epistatic to the other
...


(b) Recessive epistasis (9:3:4):
Recessive alleles at one locus (aa) mask the phenotypic expression of other gene locus (BB, Bb
or bb) such epistasis is called recessive epistasis
...
The phenotypic ratio is 9: 3: 4
...

In Mouse coat colour
...

Gene pair ‘B’ agouti colour dominant over black
...

Agouti 9/16
Black 3/16

Albino 4/16

(c) Duplicate recessive gene (9: 7):
If both gene loci have homozygous recessive alleles and both of them produce identical
phenotype the F2 ratio 9:3:3:1 would be 9:7
...
Both dominant alleles when are present together only then they can
complement each other
...

Examples:
Complete dominance at both gene pairs, but either recessive homozygote is epistatic to the effect
of the other gene
...

Gene pair ‘B’ – Colour dominant over colourless (white)
...
When dominant is
present it will show its phenotype
...

Example:
Complete dominance at both gene pairs, interaction between both dominance to give new
phenotypes
...

Gene pair ‘B’ sphere shape dominant overlong
...
39
...
e
...

Example:
Complete dominance at both gene pairs, but either gene when dominant, epistatic to the other
...
The F2 ratio will become 13: 3
...

Example:
Complete dominance at both gene pairs, but one gene when dominant epistatic to the other, and
the second gene when homozygous recessive, epistatic to the first
...

Gene pair ‘B’: colour is dominant to white
...




---