(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 B can exist both in homozygous and heterozygous forms.
(b) Complete the table below by naming the classes of vertebrates in their evolutionary trend and giving one example each of the classes.
| Classes of vertebrate | One example |
Explanation
(a)(i) Independent Assortment of Genes; is the random selection of genes during meiosis to produce gametes, where the genes separate/segregate so that only one of a pair is found in any one gamete. In the dihybrid inheritance in heterozygote the pairs of alleles are found on different pairs of chromosome, Only four types of gametes are produced in approximately equal numbers.
(ii) Blood grouping in humans; Is determined by three alternative genes/alleles A, B and O. A person can only possess two alleles of the genes on a pair of homologous chromosomes. Gene O is recessive to both genes A and B which are dominant/co-dominant and possess antigen A and B in the red blood cells hence it is possible to have blood group A as AA (homozygous) or AO (heterozygous) and blood group B as BB or BO, Blood group O can only exist genotypically as OO and does not possess antigen A or B in the red blood cells or in the homozygous recessive state.
(b) Classes of Vertebrates in their Evolutionary Trend;
| Class of Vertebrates | One Example |
| Pisces/Osteichthyes/Chondricthyes | Tilapia; Tuna, Salmon, Shark, Dogfish, Catfish, Skate, Ray |
| Amphibia | Frog/Toad |
| Reptilia | Snake, Crocodile, Tortoise, Turtle, Lizard, Wall Gecko |
| Aves | Dove, Pigeon, Parrot, Weaver Bird, Hawk, Eagles, Domestic Fowl |
| Mammalia | Human, Monkeys, Rat, Rabbit/Guinea pig |