Answer to Question #159718 in Genetics for asia

Question

Hi,

could you please help me answer this question on genetic.

In a different species of plant, bell shaped flower is dominant to tube shaped flower and the gene controlling this trait is inherited in normal Mendelian fashion. Flower colour can be either red, white, or in combination pink. The two genes are not linked.

Give a reasoned explanation for the simultaneous transmission of characteristics, the possible outcomes of crossing a heterozygous bell flowered plant with pink flowers, and a tube flowered plant with white flowers. You should also clearly identify the phenotypic combinations that are not possible from this cross. 

Many thanks in advance!  

Answer 1

In a different species of plant, the bell-shaped flower is dominant to tube-shaped flower and the gene controlling this trait is inherited in normal Mendelian fashion. Flower color can be either red, white, or in combination pink. The two genes are not linked.

Give a reasoned explanation for the simultaneous transmission of characteristics, the possible outcomes of crossing a heterozygous bell flowered plant with pink flowers, and a tube flowered plant with white flowers. You should also clearly identify the phenotypic combinations that are not possible from this cross.

Solution:

Let`s name the dominant (bell shape) and recessive (tube shape) alleles of flower shape gene "B" and "b" respectively. B completely dominates b according to the task. Let`s name the dominant (red color) and recessive (white color) alleles of flower color gene "R" and "r" respectively. R incompletely dominates r according to the task, so the combination Rr leads to the pink color of flowers. R is dominant to r because if they define color they rather code proteins that are involved in pigment synthesis. The lack of pigment causes the white color of the flower. The lack of pigment is rather due to the disfunctional product of gene (in that case r allele) transcription. But if there is at least one allele (in that case R) that codes functional product, the flower would have pigment and so wouldn`t have recessive trait.

P: BbRr (bell-shaped pink flower) x bbrr (tube-shaped white flower)

F1:

BbRr - bell-shaped pink flower (25%)

Bbrr - bell-shaped white flower (25%)

bbRr - tube-shaped pink flower (25%)

bbrr - tube-shaped white flower (25%)

Tube- or bell-shaped red flowers are the phenotypic combinations that are not possible from this cross. Red color can be achieved only by a combination of two R alleles, but it`s impossible because one of the parents lacks the R allele.

Answer:

The possible outcomes of crossing a heterozygous bell-flowered plant with pink flowers, and a tube flowered plant with white flowers: bell-shaped pink flowers, bell-shaped white flowers, tube-shaped pink flowers, tube-shaped white flowers.

Tube- or bell-shaped red flowers are the phenotypic combinations that are not possible from this cross.