- Factors in phenotypic variations
Factors in phenotypic variation consist of: Variation in phenotype (Vp); Variation in phenotypes caused by genetic variation (Vg); Variation of phenotype caused by environment (Ve); Variation in phenotype caused by interaction of genotype and environment (Vgxe). In addition to the above factors, phenotypic variation is also influenced by effects of genotype on phenotypes.
- Additive genetic variation formula shows that Va is influenced by phenotypes (p), additive (a) and dominance (d). As population evolves, the values of p, a, and d change. Consequently, Va value also changes. Based on the narrow sense heritability formula, change in Va value will influence the narrow sense heritability. Therefore, we can expect changes in narrow sense heritability, as the population evolves.
- A) Broad sense heritability will be an appropriate means for quantifying phenotypic variation due to genetic variation. Broad sense heritability is a proportion of variation due to genetic variation (Vg) and variation in phenotypes (Vp).
B) Zero value of narrow sense heritability shows that additive genetic variation (Va) is zero. This suggests that there is no genetic variation inherited directly. Meanwhile, 20% broad sense heritability shows that 20% of phenotype variation is attributed to genetic variation. Based on these results, it would be incorrect to conclude that variations in phenotypes have no genetic basis. Broad sense heritability shows that 20% of phenotype variation is due to genetic variation, and the narrow sense heritability suggests that the variation is not directly inherited. The source of genetic variation may come from factors other than hereditary (e.g. mutations, epistatic, etc.).
- Phenotypic response to selection indicates a function of broad sense heritability. Selection is an external force that works against or for specific genetic variations in broad sense heritability. Selection does not influence how the trait is directly inherited in narrow sense heritability. Therefore, phenotype response to selection is more applicable to the broad sense heritability rather than to narrow sense heritability.
- The table shows that the difference in stigma exertion is due to higher proportion of additive genetic variance (Va) in Krumms population compared to that in CERA population. This is inferred from high narrow sense heritability value of Krumm population compared to the value in CERA population. This also implies that there are more additive factors that are directly inherited within Krumm’s population.
- A) Corolla width in 2000 shows that the direct selection (0.005) is impeded by indirect selection (-0.336) resulting in -0.332 in total response to selection.
B) Flower numbers in 2000 shows that the direct selection (0.670) is improved by indirect selection (0.011) resulting in the total response to selection at 0.681.
- Intron acts as a separator between exons that aids the creation of so many different m RNA transcripts. Due to its position between exons, intron can potentially prevent frameshift mutation by blocking (preventing) exons from recombining with non-coding region of the DNA prior to mRNA transcription.
- Rate of evolution is influenced by two factors consisting of expression level of protein and protein dispensability (based on gene knock out experiment). In addition to these factors, protein interaction is also suspected to influence the rate of evolution.
- Selective sweep is fixation of beneficial allele that causes simultaneous fixation of allele physically close to the site of beneficial allele. The beneficial alleles may be rare alleles that would normally occur in low frequency under neutral condition. Therefore, the statement is true because in selective sweep the rare alleles occur in a higher frequency than expected under neutral model. This is proven by Tajima’s D statistic that shows excess of rare alleles (value of -2.20) where the probability of such excess is 0.002.
- A) Silent changes correspond to synonymous substitution. They cause changes in nucleotides, but do not cause changes in amino acid.
B) Pattern of substitution in human shows adaptive pattern where the ratio of non-synonymous substitution (dn) is greater than the synonymous ones (ds). Value of dn/ds in human from Figure 2 is 2/0, which is greater than 1; thus showing an adaptive (positive) pattern.
