Question

10) An orchid breeder is simultaneously trying to improve three important traits: leaf color [green (G) leaves are dominant to white leaves (gg)]; flower color [red flowers (R) are dominant to white flowers (r)]; and stem length [long stems (L) are dominant to short stems (l)]. This breeder is trying to create an orchid that has white leaves, red flowers, and short stems.

Plants with the following genotypes are available: Plant 1: ggrrLL Plant 2: GGRRll Plant 3: GgRrLl

(i) What cross or self would produce the highest frequency of the desired progeny? .

(ii) What is the frequency of the desired progeny in this cross?

Answer 1

3 traits of orchid given are :

leaf color = G = Dominant = green ; g = recessive = white(gg).

Flower color = R = Dominant = Red ; r = recessive = white (rr).

Stem length = L = Dominant = long ; l = recessive = short ( ll).

Breeder wants to create orchid that has --- white leaves = gg ; Red flowers = RR or Rr ; and short stems = ll.

Available Genotypes of plant are : 1) ggrrLL 2)GGRRll 3)GgRrLl

Ans 1) what cross or self would produce the highest frequency of desired progeny that is white leaves Red flowers short stems = gg R_ ll ----> _ = R or r.

Plant 1 -- ggrrLL.

A) If we self this plant, Gametes = grL ; we will get only one kind of progeny = ggrrLL = all white leaves white flower and long stem. Not as desired one. So, will not self this plant.

B) if we cross it with plant 2 = GGRRll , Gametes = GRl and of plant 1 = grL.

Progenies = GgRrLl = Green leaves Red flowers and long stem.

Not as desired one. So, will not cross these.

C) if we cross plant 1 with plant 3 = GgRrLl = Gametes = GRL, gRL, grL, grl, GrL, Grl, GRl, gRl. And Gametes from plant 1 = grL.

Cross :

	grL	phenotys
GRL	Gg Rr LL	green red long
gRL	gg Rr LL	white red long
grL	gg rr LL	white white long
GrL	Gg rr LL	green white long
Grl	GG rr Ll	green white long
GRl	Gg Rr Ll	green red long
gRl	gg Rr Ll	white red long
grl	gg rr Ll	white white long

Result = none of the progeny is of desired one.

Plant 2 --- GGRRll.

A) self cross this plant, Gamete = GRl.

Progenies = GGRRll = green red short.

Not the desired one.

B) cross with plant 3 ( with plant 1 is already done in plant 1 cross). Plant 3 = Gg Rr Ll.

We can cross by using Punnett Square and also by monohybrid cross and multiply method.

Using monohybrid cross and multiply method.

1) GG (plant2) X Gg ( plant 3)

	G	G
G	GG	GG
g	Gg	Gg

All green leaves orchid = 4/4

2) RR (plant 1) X Rr (plant 3)

	R	R
R	RR	RR
r	Rr	Rr

All Red flower orchid = 4/4

3) ll (plant 1) X Ll (plant 3)

	L	l
l	Ll	ll
l	Ll	ll

2/4 = long stem ; 2/4 = short stem

White leaf = 0 ; Red flower = 4/4 ; short stem = 2/4

Progenies = 0 * 4/4 * 2/4 = 0.

None with desired progeny.

Plant 3 -- Gg Rr Ll

A) self cross plant 3. Using monohybrid cross and multiply method.

1) Gg X Gg

	G	g
G	GG	Gg
g	Gg	gg

3/4 = green leaves ; 1/4 = white leaves.

2) Rr X Rr

	R	r
R	RR	Rr
r	Rr	rr

3/4 = Red flower ; 1/4 = white flower

3) Ll X Ll

	L	l
L	LL	Ll
l	Ll	ll

3/4 = long stem ; 1/4 = short stem

White leaves = 1/4 ; Red flower = 3/4 ; short stem = 1/4. --------> desired plant

Progenies = 1/4 * 3/4 * 1/4

= 3/64

3 progenies with desired orchid traits

The self between Plant 3 (GgRrLl) will produce highest desired progeny.

ans 2) the frequency of desired progeny in this ( plant3 self ) cross is = 3/64.