Genetics Terminology and Mendelian Crosses Practice
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1. Explain what you understand by the following terms:
(a) Genotype
(b) Phenotype
(c) Test cross
(d) Linkage
(e) Crossing-over
(f) Polyploidy
2. Explain why the following are considered suitable organisms for use in genetic experiments:
(a) Garden peas
(b) Drosophila Melanogaster
3. What are the causes of genetic variations in living organisms?
4. In human beings, the ability to roll the tongue depends on the presence of a dominant gene. Construct diagrams to show the genotype and phenotype of the parental generation, the $F_1$ generation and the gametes of a cross between homozygous tongue roller and a non-roller.
5. On the basis of Mendel’s hypothesis and observations, predict the results from the following crosses in garden peas:
(a) A tall homozygous dominant variety crossed with a dwarf variety.
(b) Selfing the offspring (progeny) from the cross in (a) above.
(c) The progeny from the cross in (a) crossed with the original dwarf parent variety.
6. (a) State Mendel’s first law of inheritance.
(b) How would you explain this law?
7. A tall garden pea plant crossed with a dwarf plant produces offspring of which about half are tall and the other half are dwarf. What are the genotypes of the parents?
8. In an experiment, a variety of garden peas having a smooth seed coat was crossed with a variety having a wrinkled seed coat. All the seeds obtained in the $F_1$ generation had a smooth coat. The $F_1$ generation was selfed.
The total number of $F_2$ generation was 7324.
(a) Using appropriate letter symbols, work out the genotypes of the $F_1$ generation.
(b) From the information above, work out the following for the $F_2$ generation:
(i) Genotypic ratio.
(ii) The total number of wrinkled seeds.
(iii) Phenotypic ratio.
9. In the four O'clock plant, red flower colour is determined by a gene represented as R and white flower colour by a gene represented as W. The heterozygous plant is pink flowered. If a red flowered plant is crossed with a white flowered plant, what will be
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Step by Step Written Solution
In this video, we will solve problem number eight, which involves a monohybrid cross of garden peas focusing on seed coat texture.
Genetics: Monohybrid Cross Analysis
The problem states that a variety with a smooth seed coat was crossed with a wrinkled variety. All offspring in the first filial generation had smooth coats.
Given Data
- Parent 1: Smooth seed coat
- Parent 2: Wrinkled seed coat
- F1 Generation: All Smooth ($7324$ individuals)
Since all F1 offspring are smooth, we can conclude that smooth is the dominant trait and wrinkled is recessive. Let is use capital S for smooth and lowercase s for wrinkled.
For part A, let's work out the genotypes of the F1 generation. The homozygous dominant smooth parent produces S gametes, and the wrinkled parent produces s gametes.
Part (a): F1 Genotypes
So, the F1 generation consists entirely of heterozygous individuals with the genotype big S little S. Because smooth is dominant, they all appear smooth.
Now for part B, we self-pollinate the F1 generation to produce the F2 generation. This means crossing Ss with Ss.
Part (b): F2 Generation Analysis
Let's use a Punnett square to determine the genotypic results.
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