(a) Explain briefly; (i) independent assortment of genes (ii) the reason blood group O in humans can only exist in homozygous form while blood groups A and ...

Answer Details

(a)

(i) Independent assortment of genes refers to the way that different genes for different traits are inherited independently of each other. This means that the inheritance of one gene does not influence the inheritance of another gene. This is because each gene is located on a separate chromosome, and during meiosis, each chromosome pair segregates independently of other pairs. Therefore, the distribution of one gene to a gamete does not influence the distribution of another gene.

(ii) Blood group O in humans can only exist in a homozygous form (OO) because it is recessive to both blood group A and B. Blood group A and B are codominant, meaning that they can be expressed in both homozygous and heterozygous forms. For example, someone with blood group A can have the genotype AA or AO, while someone with blood group B can have the genotype BB or BO. However, since blood group O is recessive, it can only be expressed in the homozygous form (OO) since the presence of one dominant allele (A or B) will always result in the expression of that dominant allele.

(b)

The table above shows the classes of vertebrates arranged in their evolutionary trend, starting from the most primitive to the most advanced.

• Agnatha refers to jawless fish, and the lamprey is an example of this class.
• Chondrichthyes refers to cartilaginous fish, such as sharks.
• Osteichthyes refers to bony fish, such as trout.
• Amphibia refers to animals that live both on land and in water, such as frogs.
• Reptilia refers to animals that lay eggs on land and have dry, scaly skin, such as crocodiles.
• Aves refers to birds, and an example of this class is the pigeon.
• Mammalia refers to animals that have mammary glands and hair, and humans are an example of this class.

By understanding the different classes of vertebrates and their characteristics, we can better understand the diversity of life on Earth and how different species have evolved over time.