4. Production of one phenotype requires the presence of
dominant alleles of both the genes controlling the
character
C W
ccW
C ww
ccww
Contrasting phenotype
Anyone of the two dominant gene is unable to produce the
phenotype when alone
They complement each other to produce concerned
phenotype when they are together
4
8. Characters governed by duplicate gene action are
determined by two completely dominant genes
Duplicate gene action: The presence of a single dominant
allele of any one of the two genes governing the trait
produce the dominant
phenotype
W
wwcc Contrasting phenotype
8
13. The gene don’t directly cause the expression of the
characters but suppress the expression of other genes
Example
Leaf colour of rice: Green Purple
Gg
I suppress G i
Ineffective
13
16. Two completely dominant genes controlling a character
R W
R W
But both genes are present together, their phenotypic
effect is enhanced as the effect of the two genes
were cumulative additive
R W
16
It produces identical phenotypes when they are alone
19. Red colour in wheat is produced by the genotype R_B_, white
by the double recessive genotype, rrbb. The genotypes R_bb
and rrB_ produce brown kernels. If homozygous red variety
is crossed to a white variety what phenotypic results are
expected in the F1 and F2?
19
20. RB Rb rB rb
RB RRBB
Red
RRBb
Red
RrBB
Red
RrBb
Red
Rb RRBb
Red
RRbb
Brown
RrBb
Red
Rrbb
Brown
rB RrBB
Red
RrBb
Red
rrBB
Brown
rrBb
Brown
rb RrBb
Red
Rrbb
Brown
rrBb
Brown
rrbb
White
Punnett Square
20
21. RB Rb rB rb
RB RRBB
Red
RRBb
Red
RrBB
Red
RrBb
Red
Rb RRBb
Red
RRbb
Brown
RrBb
Red
Rrbb
Brown
rB RrBB
Red
RrBb
Red
rrBB
Brown
rrBb
Brown
rb RrBb
Red
Rrbb
Brown
rrBb
Brown
rrbb
White
Punnett Square
21
22. RB Rb rB rb
RB RRBB
Red
RRBb
Red
RrBB
Red
RrBb
Red
Rb RRBb
Red
RRbb
Brown
RrBb
Red
Rrbb
Brown
rB RrBB
Red
RrBb
Red
rrBB
Brown
rrBb
Brown
rb RrBb
Red
Rrbb
Brown
rrBb
Brown
rrbb
White
Punnett Square
22
23. RB Rb rB rb
RB RRBB
Red
RRBb
Red
RrBB
Red
RrBb
Red
Rb RRBb
Red
RRbb
Brown
RrBb
Red
Rrbb
Brown
rB RrBB
Red
RrBb
Red
rrBB
Brown
rrBb
Brown
rb RrBb
Red
Rrbb
Brown
rrBb
Brown
rrbb
White
Punnett Square for F2
Phenotypic ratio of F2 generation is Red: Brown: White = 9:6:1
23
25. The two genes affecting the character W Y
When both genes are present in recessive state a
different phenotype is produced
They produce distinct phenotype when they are alone
W Y
But when the genes are present together, the expression
of one gene masks the expression of other
YW
w y
25
26. Fruits of Cucurbita pepa will be in green, yellow and white
colour. White is dominant over both yellow and green but
yellow is dominant over green only. White colour is
determined by the dominant gene W and no other gene for
fruit colour can be expressed in its presence. Thus
dominant W is epistatic to two other fruit colour. In the
presence of homozygous recessive, ww another gene Y
determine the yellow colour. Homozygous recessive plants
for both genes, wwyy bears green fruit that the classical
ratio the first two classes of a dihybrid ratio are
phenotypic ally similar
26
29. When homozygous white fruit seeds are crossed with
homozygous green fruit seeds, the F1 is all white. Crossing
with F1 among themselves F2 produced 121 white, 28 yellow
and 9 green. Explain the results
29
30. WY Wy wY wy
WY WWYY
White
WWYy
White
WwYY
White
WwYy
White
Wy WWYy
White
WWyy
White
WwYy
White
Wwyy
White
wY WwYY
White
WwYy
White
wwYY
Yellow
wwYy
Yellow
wy WwYy
White
Wwyy
White
wwYy
Yellow
wwyy
Green
Punnett Square
30
31. WY Wy wY wy
WY WWYY
White
WWYy
White
WwYY
White
WwYy
White
Wy WWYy
White
WWyy
White
WwYy
White
Wwyy
White
wY WwYY
White
WwYy
White
wwYY
Yellow
wwYy
Yellow
wy WwYy
White
Wwyy
White
wwYy
Yellow
wwyy
Green
Punnett Square
31
32. WY Wy wY wy
WY WWYY
White
WWYy
White
WwYY
White
WwYy
White
Wy WWYy
White
WWyy
White
WwYy
White
Wwyy
White
wY WwYY
White
WwYy
White
wwYY
Yellow
wwYy
Yellow
wy WwYy
White
Wwyy
White
wwYy
Yellow
wwyy
Green
Punnett Square for F2
Phenotypic ratio of F2 generation is White: Yellow: Green = 12:3:132
34. 34
In this gene interaction, the dominant allele of one gene
produces a phenotypic effect
The dominant allele of the other gene does not produce any
phenotypic effect
But when it is present with dominant allele of the first
gene, it modifies the phenotypic effect produced by the
first gene
C A
C A
C ACA CA
36. 36
The coat colour of mice is control by two genes C and A
C alone determine black colour but due to supplementary
effect of A the colour is become black
C_A_
37. 37
When only gene C is homozygous recessive albino mice
are produce
cc_ _
A alone has no effect
C_ aa
38. 38
Mating between black mice of identical genotype produced
offspring as follows; 14 Gray, 47 Black and 19 Albino.
1. What epistastic ratio is approximated by these offspring?
2. What are the phenotypes of the parents and offspring?
39. 39
CA Ca cA ca
CA CCAA
Black
CCAa
Black
CcAA
Black
CcAa
Black
Ca CCAa
Black
CCaa
Gary
CcAa
Black
Ccaa
Gray
cA CcAA
Black
CcAa
Black
ccAA
Albino
ccAa
Albino
ca CcAa
Black
Ccaa
Gray
ccAa
Albino
Ccaa
Albino
Punnett Square for F2
Phenotypic ratio is Black: Gray: Albino= 9: 3: 4