Identifying Causes of Linkage Disequilibrium
Linkage disequilibrium (LD) describes the situation where specific alleles at different genetic loci are inherited together more often than would be expected by chance. This non-random association is influenced by several factors. Analyzing the options provided helps identify the primary drivers of LD:
-
Option 1: Low recombination rate between loci
A low recombination rate between two loci means that the alleles at these loci are less likely to be separated during meiosis (crossing over). Consequently, alleles that are initially associated tend to be passed down together through generations, maintaining or increasing linkage disequilibrium. This is a significant factor contributing to LD.
-
Option 2: High recombination rate between loci
Conversely, a high recombination rate facilitates the independent assortment of alleles. It frequently breaks down any existing associations between alleles at different loci, thus tending to decrease linkage disequilibrium over time. Therefore, a high recombination rate is not a cause of LD.
-
Option 3: Natural selection
Natural selection can directly influence linkage disequilibrium. If certain combinations of alleles (haplotypes) confer a survival or reproductive advantage, natural selection will favor these combinations. This selection pressure increases the frequency of advantageous haplotypes, leading to increased LD between the loci involved.
-
Option 4: Polyploidy
Polyploidy refers to having more than two complete sets of chromosomes. While polyploidy can alter allele frequencies and potentially influence recombination patterns, it is not considered a direct or primary cause of linkage disequilibrium between two specific loci compared to factors like recombination rate and selection. Its effect on LD is complex and indirect.
Conclusion on Linkage Disequilibrium Factors
Based on the analysis, the factors that can cause or contribute to linkage disequilibrium between alleles at two loci are:
- A low recombination rate between the loci.
- Natural selection favoring specific allele combinations.
Therefore, the correct options are A (Low recombination rate between loci) and C (Natural selection).
Important Questions from Natural selection
Aphids feed on both alfalfa and clover plants. A researcher collected and reared different genotypes of aphids from separate alfalfa and clover fields. He then measured the fecundity of both aphid groups when fed on each of the two host plants. The figure summarizes the performance of aphid groups originating from alfalfa (dashed) or clover (solid).
Which one or more of the following situations does the figure depict?- Which one or more of the following conditions is/are necessary for the evolution of increased nectar production in an insect-pollinated plant via natural selection?
There are two species, X and Y, with abundances $x$ and $y$, respectively. Species X has growth rate $\alpha$, and species Y has growth rate $\beta$. Assume that the sum of the species abundances is constant over time, i.e., $x + y = 1$. Let $x$ and $y$ follow the rate equations:
$$\frac{dx}{dt} = \alpha x - \varphi x,$$
$$\frac{dy}{dt} = \beta y - \varphi y,$$ where $\varphi$ is the average species fitness.
Which one of the following options correctly represents the expression for $\varphi$?The figure illustrates the soil zinc tolerance of the grass species Anthoxanthum along a transect from inside a mine to the middle of a pasture outside the mine.
Which one or more of the following processes explain(s) the observed pattern of zinc tolerance in this grass species?A researcher estimates the relationship between reproductive success ($N$, number of offspring) and horn length ($H$, in cm) in a wild goat as
$N = 40 – 2.2H + 0.04H^2$
Horn length typically varies from 10 cm to 50 cm in this species. Which one of the following graphs correctly represents this relationship?
