Question

4B. Sweet potatoes may be long, round or oval, and they may be orange, white or yellow. You cross a long, white variety with a round, orange one and obtain an oval, yellow Fl. The F2 shows 9 phenotypic classes as follows: Long, orange Long, yellow Oval, orange Oval, yellow Long, white Round, yellow Round, white Oval, white Round, orange a) Provide a genetic explanation for these results. (2 marks) b) Define alleles and show genotypes for the P generation and the Fl. (3 marks) e) Predict the genotypic and phenotypic proportions in the progeny of a cross between a long, yellow sweet potato and an oval. yellow one. Use the notation A_ for example, to symbolize both AA and Aa. (5 marks)

Answer 1

A)GENETIC EXPLANATION FOR OBTAINED RESULTS:

According to bateson and punnett such result is obtained because by combination of homozygous recessive genes(llww-round orange) and homozygous dominant(LLWW-long white) producing a new heterozygous gene (LlWw-oval yellow),thus these genes here do not determine themselves in the development of character but modify the character determined by a basic gene.These genetic interpretation is an example of Non epistatic inter allelic genetic interaction.i.e in some cases two pairs of determine same phenotype but assorted independently,produce new phenotypes by mutual epistatic interaction.

B)ALLELES:

An allele is a viable DNA (deoxyribonucleic acid) coding that occupies a given locus(position)on a chromosome.Most genes have two alleles,a dominant allele and a recessive allele.

GENOTYPES FOR

P GENERATION: AAWW X aaww

F1 GENERATION: AaWw

GAMETES: AW,Aw,aW,aw

C)CROSSING OF LONG YELLOW AND OVAL YELLOW:

GENOTYPE PROPORTION:1/8 AAWW - 2/8 AAWw - 2/8 AaWw - 1/8 AaWW - 1/8 AAww - 1/8 Aaww

PHENOTYPE PROPORTION: 1 long white: 2 long yellow: 2 oval yellow: 1 oval white: 1 long orange: 1 oval orange.