Question

QUESTION 5 A researcher is attempting to determine the inheritance pattern exhibited by the ales for shell colour of freshwater snails. The trait is known to be controlled by alleles at a single locus; one for brown and completely dominant to allele for yellow. A mating between a brown-shelled snail and a yellow-shelled snail, both from pure breeding lines, produced progeny that are brown-sheiled. F2 consisted of 27 yellow and 23 brown snails. inheritance pattern exhibited by the alleles for Based on the 1:1 F2 ratio predicted by the researcher, calculate and interpret the X2 value of these data. a) (4 marks) b) Based on the correct 3:1 ratio, calculate and interpret the X value for these data. (4 marks) c) Suggest what can the researcher do to improve this experiment. (2 marks)

It saids there the "Brown and completely dominant TO allele for yellow" . what does that means? brown is dominant? becuz if we further read, it saids the two pure allele produce brown. (all brown??) please help me solve this question

Answer 1

Brown is compleletly dominant over the yellow .

Dominance is the trait that is visible and expressed in all the offsprings . there are several types of pattern of inheritance of dominant allele . complete dominance phenotype of the heterozygote is completely dominant than the other phenotype of the homozygous dominant.

incomplete dominance ;

the phenotype of the offspring is intermediate between the the phenotypes of thetwo homozygotes zygotes .the two traits appear to be blended .they produce intermediate product .

codominance;

co dominance is similar to the incomplete dominance but there is no dominant allele .phenotypic expression is different.if it is heterozygote the both the allele are equally expressed .

the above expression of the brown allele to the yellow is an example of the Psudominance ,the relationship between the two allele appear to be completely dominant .inheritance of the recessive traits appear to be dominant . the pattern of the inheritance where in which single recessive allele is inherited but it is expressed .this kind of inheritance may appear in the autosomal recessive traits and sex lnked traits . whenever there is a mutation in the domianat allele deletion,then offspring appear to be homozygous and recessive . so in our example the yellow allele is a psudodomiance expressive trait and appear to be domianant whenever the brown allele is mutated or deficient