Question

8. Refer to the following information to answer Questions 8 and 9.

A certain species of grasshopper can have red stripes, yellow stripes, or red and yellow stripes. An RR grasshopper has red stripes, an YY grasshopper has yellow stripes, and an RY grasshopper has red and yellow stripes.
Which type of inheritance is this an example of?

(Points : 3)
Aincomplete dominance
B sex-linked inheritance
C codominance
D recessive inheritance


9. A grasshopper with red stripes mates with a grasshopper with yellow stripes. What ratio would you expect to see in the phenotypes of their offspring? (Points : 3)
A2 with red stripes: 2 with yellow stripes
B 1 with red stripes: 2 with red and yellow stripes: 1 with yellow stripes
C all with red stripes
D all with yellow and red stripes


10. Which of the following best describes the relationship between a gene and an allele? (Points : 3)
AA gene is a variant of an allele.
B An allele is a variant of a gene.
C A gene is always dominant to an allele.
D A gene is always recessive to an allele.


11. Which of the following is the best physical description of a gene? (Points : 3)
A A gene is a specific segment of DNA on a chromosome.
B A gene consists of all of the DNA on a chromosome.
C A chromosome is a segment of a gene.
D Genes carry many chromosomes.


12. Suppose you cross a true-breeding blue flower with a true-breeding yellow flower. In the next generation, all of the flowers are blue. What does this outcome tell you about the allele for blue flowers? (Points : 3)
A The blue allele is dominant to the yellow allele.
B The blue allele shows incomplete dominance.
C The blue allele is sex-linked
D The blue allele is recessive to the yellow allele.

Answer 1

8
codominance
9
all with yellow and red stripes
10
An allele is a variant of a gene.
11
A gene consists of all of the DNA on a chromosome.
12
The blue allele is dominant to the yellow allele.

Answer 2

Answers:

8. Option C codominance.

9. Option D all with yellow and red stripes.

10. Option B An allele is a variant of a gene.

11.. Option A A gene is a specific segment of DNA on a chromosome.

12. Option A The blue allele is dominant to the yellow allele.

Explanation :

1. When the pair of alleles of a given gene fully express themselves in a heterozygous condition and the phenotype corresponding to each of the alleles is visible in the progeny, this is known as codominance.

Since the progeny has both red and yellow stripes the given situation is a case of codominance.

2. According to the question, the following cross is made:

Red stripes X yellow stripes

RR X YY-----> RY RY RY RY

Since the alleles are codominant, all the progenies will have yellow and red stripes.

3. Alleles are defined as the alternative forms of a given gene which are found on the same position on the chromosome. A given gene can have two or more alleles.

Thus, an allele is a variant of a gene.

4. A chromosome is a thread like structure found in the nucleus of all eukaryotic cells and it is made up of deoxyribonucleic acid (DNA).

The functional segment of the DNA on the chromosome which codes for a functional molecule is known as the gene.

5.

• A dominant allele is the one which expresses itself and thus dictates the phenotype of the individual in both homozygous and heterozygous condition.

• A recessive allele is the one which only expresses itself in the absence of dominant allele, that is in homozygous condition.

On crossing true breeding yellow and blue flowers we get the following results :

YY X BB----> YB YB YB YB

Since, in the heterozygotes YB the phenotype is blue color this means that allele for blue color is dominant over yellow color.