Let us Assess

1. Are basic building blocks of DNA and RNA the same? Explain.

Ans:

The basic building blocks of DNA and RNA are not entirely the same, though they share some similarities. DNA and RNA are made up of nucleotides but have different sugars and nitrogen bases. DNA and RNA share the following components within their nucleotides: A sugar molecule, A phosphate group, and Nitrogen bases. The main difference lies in the sugar; ribose sugar is in RNA, and deoxyribose is in DNA. In the case of nitrogen bases, uracil is in RNA instead of thymine in DNA. Most of the RNAs have a single strand, but DNA is double-stranded.

2. Analyse the statements and choose the appropriate one.

i) F1 has similarity with both the parents.

ii) F1 has no similarity with any of the parents’ characters but is intermediate to them.

iii) F1 has similarity with one of the parents
a) i - Dominance, ii - Incomplete dominance, iii - Co-dominance
b) i - Incomplete dominance, ii - Dominance, iii - Co-dominance
c) i - Co-dominance, ii - Incomplete dominance, iii - Dominance
d) i - Dominance, ii - Co-dominance, iii - Incomplete dominance

Ans: c) i - Co-dominance, ii - Incomplete dominance, iii - Dominance

3. Which of the following is contributed by organisms that reproduce sexually, to their offspring?

a) All genes

b) Half of their genes

c) One fourth of their genes
d) Double the number of genes

Ans: b)Half of their genes

4. A tall pea plant with purple flowers (dominant character) is crossed with a dwarf plant with white flowers.

a) Illustrate the dihybrid cross of these and write the F2 ratio.

b) Did characters that differ from the parents appear in the F2 generation? Why?
c) If both the genes are not assorting independently, how does it affect the F2 ratio?

The phenotypic ratio of F2 generation is 9:3:3:1

b) New combinations of characters that differ from those of the parent plants emerge in the F2 generation. This occurs because the genes responsible for plant height and flower color assort independently during meiosis, resulting in varied combinations of alleles being transmitted to the offspring.

c) If the genes for plant height and flower color do not assort independently, the expected F2 ratio will deviate from the typical 9:3:3:1 ratio.

5. How does dominance, co-dominance and incomplete dominance differ from one another?

Dominance

The dominant allele completely masks the trait of the recessive allele.

Co-dominance

Both alleles exhibit their traits at the same time.

Incomplete dominance

A dominant allele cannot entirely hide the trait of the recessive allele.

6. Different phenotypic ratios are obtained in monohybrid and dihybrid cross. Why? What does it indicate about the inheritance of characters?

A monohybrid cross involves crossing individuals that differ in only one trait. When two heterozygous individuals are crossed, the resulting offspring will exhibit a phenotypic ratio of 3:1. A dihybrid cross simultaneously examines the inheritance of two traits. When two heterozygous individuals are crossed, the offspring will display a 9:3:3:1 phenotypic ratio.

The different phenotypic ratios observed in monohybrid and dihybrid crosses indicate that a pair of alleles in an organism does not influence the separation of another pair of alleles.

7. Even though a gene responsible for certain characters has more than two alleles, why does that particular gene have only two alleles in an individual?

Even though a gene responsible for a particular trait might have multiple alleles in a population, each individual only carries two alleles for that gene. This is because in humans, each chromosome in every pair of chromosomes is inherited from each parent, and each chromosome carries one allele for each gene.

8. Although the DNA possesses all genetic information for protein synthesis, RNA is also required for protein synthesis. Why?

While DNA holds all the genetic information for protein synthesis, RNA is essential for this process because it serves as a messenger to carry the information from DNA to ribosomes, where protein synthesis occurs. mRNA is formed from a specific nucleotide sequence(gene) in DNA with the help of various enzymes. The mRNA contains messages for protein synthesis. tRNAs (transfer RNA) carry specific amino acids to the

ribosome based on the message in the mRNA that has reached the ribosome from the nucleus. The rRNAs (ribosomal RNA), part of ribosomes, combine amino acids to make protein.

9. How do co-dominance and multiple allelism function in the determination of blood groups in the ABO blood grouping in human beings? Explain.

In ABO blood grouping, multiple allelism and co-dominance work together to determine the four blood types A, B, AB, and O. Three alleles IA, IB and i determine the blood group in humans. Since more than two alleles are there in the gene that determines the blood group in human beings, ABO blood grouping is a perfect example of multiple allelism. Co-dominance occurs when IA and IB are both expressed, resulting in the AB blood type.

10. All ova formed in females contain one type of sex-determining

chromosome. Why?

In humans, all ova contain an X chromosome because females have two X chromosomes (XX), and during meiosis, only one of these X chromosomes is passed on to each egg cell. The sex chromosome X or Y from males determines the sex of the offspring.