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Q3.14. Flower color in sand blossoms (Linanthus parryae) is controlled largely by a single gene with two alleles. Individuals with genotype BB or Bb are blue; individuals with genotype bb are white. Sand blossoms grow in patches in the desert. Some patches have only blue individuals, some have only white, and some are mixed. Based only on this information, which explanation below is plausible?

The difference among patches is due to natural selection. Blue individuals have higher reproductive success in some patches, white plants have higher success in some patches, and the two colors do equally well in some patches.

The difference among patches is due to the founder effect. Some patches were founded by homozygous blue individuals, some patches by white individuals, and some patches by individuals carrying both alleles.

The difference among patches is due to genetic drift. Particularly if population size in a patch is small, one color or the other might be lost simply as a result of chance events, such as drought or herbivory.

All of the above explanations are plausible.

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Deanna Hettinger
Deanna HettingerLv2
28 Sep 2019

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Related questions

1). Thyroid hormone (TH) has been identified as one of the factors promoting phenotype development in the Mexican axolotl salamander. Which of the following statements regarding the impact of TH is FALSE?

A). Axolotls maturing in water with high concentration of TH (thyroxine; T4) metamorphose into a terrestrial form.

B). A genome-wide scan of both the axolotl and its sister species found a large reduction in the number of mRNA transcripts that regulate the production of TH.

C). Adding TH (thyroxine; T4) to the water in which axolotl individuals are reared causes them to remain in a larval stage.

D). Most salamander species produce a burst of TH when they move from water to land.

2).What would be an appropriate evolutionary explanation of the fact that the ordering of some homeotic genes (such as Hox genes) on vertebrate chromosomes parallels the ordering of homeotic genes on fruit fly chromosomes?

A). The similarity is a coincidence, not documented in other invertebrates and largely a result of random mutations.

B). Homeotic genes show that insects and vertebrates are closer relatives than the traditional classification system indicates.

C). Homeotic genes of different animal lineages might be ordered in a similar fashion, yet their sequences are completely different.

D). The similar ordering of homeotic genes in animals, both vertebrate and insect, is due to ancient homology.

3). Which of the following correctly defines "homeotic genes"?

A). Homeotic genes encode proteins that control the cellular environment in a differentiated cell tissue.

B). Homeotic genes are DNA sequences that turn off, but not on, the expression of other genes and are controlled by "master-switch" genes.

C). Homeotic genes are "master-switch" genes that control other genes in a set sequence and thereby affect cell size, shape, division, and the positioning of the cells within the organism.

D). Homeotic genes are DNA sequences that turn on, but not off, the expression of other genes and are controlled by "master-switch" genes.

4). Which of the following is NOT considered a type of heterochrony (change in the rate and timing of development)?

A). hypermorphosis

B). acceleration

C). neoteny

D). ontogeny

5). How does the dominance theory explain why the heterogametic sex is at a disadvantage in Haldane's rule?

A). Beneficial dominant alleles will never be fully expressed in hybrids as they only carry one copy of the sex chromosome that carries the allele.

B). If a dominant allele has a negative effect on the fitness of hybrids, it will always be expressed in the heterogametic hybrids that possess that allele because they only need one copy of the respective sex chromosome.

C). If a recessive allele linked to a sex chromosome has a negative effect on the fitness of hybrids, that allele will always be expressed in the heterogametic hybrids that possess that allele because they only have one copy of the sex chromosome that carries the allele.

D). If a recessive allele linked to a sex chromosome has a positive effect on the fitness of hybrids, that allele will never be expressed in the heterogametic hybrids that possess that allele because they only have one copy of the sex chromosome that carries the allele.

6). In a hypothetical flowering plant species, one population evolves a different response to environmental stimuli and begins to bloom significantly later in the season than nearby populations. What type of reproductive isolating mechanism would this be?

A). hybrid sterility

B). postzygotic

C). prezygotic

D). gametic incompatibility

7). In a study of red spruce trees and black spruce trees, scientists found that the red spruce was living in a smaller geographic area and had much less genetic variation than the black spruce. They proposed that the red spruce might have arisen from a southern population of black spruce, which became geographically isolated from other black spruce populations at some point during the Pleistocene glaciations. What is this an example of?

A). allopatric speciation with the vicariance model

B). sympatric speciation

C). allopatric speciation with the peripheral isolate model

D). sympatric speciation with the ring species model

8). Which of the following defines Haldane's rule and its predictions?

A). If among hybrid offspring one sex is absent, rare, or sterile, that sex is always male.

B). If among hybrid offspring one sex is absent, rare, or sterile, that sex is always female.

C). If among hybrid offspring one sex is absent, rare, or sterile, that sex is heterogametic (has two different sex chromosomes).

D). If among hybrid offspring one sex is absent, rare, or sterile, that sex is homogametic (has two of the same sex chromosomes).

8.) Which of the following statements best explains secondary reinforcement?

A). If the reproductive isolating mechanisms that developed during the geographic isolation are strong but the hybrids have higher fitness than the parent species, then the speciation process will cease.

B). If the reproductive isolating mechanisms that developed during the geographic isolation are somewhat weak but the hybrids between two populations have lower fitness, then the speciation process may continue.

C). If the reproductive isolating mechanisms that developed during the geographic isolation are sufficiently weak as to allow free interbreeding across reunited populations, then the speciation process will halt and a single species will remain.

D). When geographic isolation comes to an end, two populations always complete the divergence process and become separate species.

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