(a) Explain four causes of damage to maize during storage.
(b) Two heterozygous tall plants, Tt, were crossed in an experiment. Using a genetic diagram, (i) show the possible offspring that could result from the cross. (ii) determine the:
1. genotypic ratio of the offspring:
2. phenotypic ratio of the offspring.
(c) State Mendel’s first and second laws of inheritance.
(d) Mention two forage grasses.
Explanation
(a) Explanation of causes of damage to maize during storage (i) High humidity - High humidity often leads to mould formation, thus reducing the quality of maize
(ii) Pests -The presence of pests reduces the quality of maize - Pests reduces the quantity of maize - Reduces the viability of seeds; thus the germination rate
(iii) Pathogens - The presence of moulds and other fungi reduces the quality of stored maize
(iv) Heat generated during storage - This enhances the formation of moulds, thus reducing the quality of maize.
(v) Poor Storage Structure - Leaking roof allows water to get into the stored maize; thus leading to mouldiness - Allows infestation of pests and pathogens
(b)(i) Possible offspring that could result from the cross
(ii)1. Genotypic ratio of the offspring 1:2:1
2. Phenotypic ratio of the offspring 3:1
(c) Menders laws of inheritance - First law (Law of segregation of genes) Genes occur in pairs and are transmitted independently from one generation to another Second law (Law of independent assortment of genes) Genes for different traits are sorted separately from one another such that the inheritance of one trait is not dependent on another
(d) Forage grasses - Guinea grass/Panicum maximum - Stubborn grass/Eleusine indica - Elephant grass/Pennisetum purpureum -Southern gamba grass/Andropogon tectorum - Rhodes grass/Chloris gay ana -Bermuda grass/Bahana grass/Cynodon dactylon -Spear grass/lmperata cylindrica -Carpet grass/Axonopus compressus -Kikuyu grass/Pennisetum clandestinum -Northern gamba grass/Andropogon gayana - Giant star grass/Cynodon plectostachyus