Question

In a species of plant, the alleles for the tall stem is dominant to short. The two alleles for leaf colour, giving green or white in the homozygous condition are codominant, producing variegated leaves in the heterozygote.

A plant with tall stems and green leaves was crossed with a plant with short stems and variegated leaves. The offspring from this cross consisted of plants with tall stems and green leaves and plants with tall stems and variegated leaves with a ratio of 1 :1. Construct a genetic diagram to explain this cross.

Accepted Answer

In the given example, the tall (T) plant is dominant over the short (t) plant. The leaf colour green (G) and white (g) shows codominance that is both have an expression on the phenotype in in heterozygous condition. The cross given is between the plant with tall stems and green leaves and plant with short stems (tt) and variegated leaves. The green leaves show homozygous (GG) and variegated leaves show heterozygous condition (Gg). The tall stem may be homozygous or heterozygous. The offspring of this cross consist of plants with tall stems only. If any of the offspring show recessive phenotypic character (short stem), then it must mean that the tall stems has an allele for short stems. Here, none of the offspring have short stems, so the tall plant is homozygous for tall stems alleles (TT). The cross is given below:

The homozygous tall and green plant produces only one type of gametes and short and variegated plant produces two types of gametes. The resultant offspring show a 1 : 1 phenotypic ratio.

Mary Jones, Richard Fosbery, Dennis Taylor and, Jennifer Gregory Solutions for Chapter: Inheritance, Exercise 9: Questions

Mary Jones Biology Solutions for Exercise - Mary Jones, Richard Fosbery, Dennis Taylor and, Jennifer Gregory Solutions for Chapter: Inheritance, Exercise 9: Questions

Questions from Mary Jones, Richard Fosbery, Dennis Taylor and, Jennifer Gregory Solutions for Chapter: Inheritance, Exercise 9: Questions with Hints & Solutions

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