On a remote Pacific island there are Kumquat trees with quan

On a remote Pacific island there are Kumquat trees with quantitative genes that allow the trees to bear enormous fruit. One strain of tree bears \"huge\" 20 pound kumquats. Another strain bears \"normal\" 4 pound fruit (still very large!). Assume that this trait (fruit weight) is controlled by 4 gene loci. From a cross between the \"huge\" and \"normal\" strains, what weight fruit will the progeny have? 12 16 10 4 18 Following our simplified model of polygenic inheritance, what is the contribution per allele? 1 2 4 6 10 If the F_2 generation were produced, what proportion of the offspring would you expect to produce 14 pound fruits? 1/16 128/256 56/256 47/128 1/256 When two 12 pound F_2 trees were crossed they produced offspring which all produced 12 pound fruit. However, when these offspring were crossed randomly, the fruit produced weighted from 4 to 20 pounds. What can you say about the possible genotypes of the original F_2 trees?

Solution

Weight of the fruit is controlled by 4 polygenes. Suppose dominant alleles of these loci we mark as \"A\", and the recessive alleles as \"a\". The weight of the fruit of dominant homozygous genotype \"AAAA\" is equal to 20 pond, and for recessive homozygous genotype \"aaaa\" is equal to 4 pond. If four recessive alleles gives us 5 pond, then one allele gives us 1 (4/4 = 1). And one dominant allele gives us 5 ponds (20/4 = 5). Thus we can say that each dominant allele increases the weight by 4 pond (5 - 1 = 4). Then theweight of the tree with three dominant alleles will be equal to 16 ponds (20 - 4 = 16), with two - 12 ponds (16 - 4 = 12), and with one will be equal to 8 pond (12 - 4 = 8). If you cross rabbits with genotypes \"DDDD\" and \"dddd\", then all the hybrids of first generation will have 12 pond (\"DdDd\").

Answer 12 pond