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Chapter 8: Problem 15

The primrose, Primula kewensis, has 36 chromosomes that are similar in appearance to the chromosomes in two related species, \(P .\) floribunda \((2 n=18)\) and \(P .\) verticillata \((2 n=18)\) How could \(P .\) kewensis arise from these species? How would you describe \(P .\) kewensis in genetic terms?

Short Answer

Expert verified
Answer: Primula kewensis could potentially arise from Primula floribunda and Primula verticillata through a process called allopolyploidy, where the two species hybridize and their chromosomes are doubled, resulting in a new species with a higher chromosome count than its parental species. Primula kewensis can be described in genetic terms as an allopolyploid species derived from Primula floribunda and Primula verticillata with a diploid count of 2n = 36, which could be a result of 18 chromosomes originating from each parent species and then duplicated in the hybrid offspring during speciation.

Step by step solution

01

Understand how many chromosomes are present in each species

Primula kewensis has 36 chromosomes, while both Primula floribunda and Primula verticillata have 18 chromosomes each. We need to figure out how a species with 36 chromosomes could arise from two species with 18 chromosomes each.
02

Determine how chromosomes could double during speciation

A possible way for this to happen is through a genetic event called allopolyploidy. Allopolyploidy occurs when two species hybridize, and their chromosomes are doubled, resulting in a new species with a higher chromosome count than its parental species. In this example, Primula kewensis could potentially be a hybrid species derived from both Primula floribunda and Primula verticillata due to an allopolyploidy event that doubled the chromosome count in the hybrid offspring.
03

Describe Primula kewensis in genetic terms

Primula kewensis, in genetic terms, could be described as an allopolyploid species derived from Primula floribunda and Primula verticillata. Its diploid count is 2n = 36, which could be a result of 18 chromosomes originating from each parent species, and then the chromosomes were duplicated in the hybrid offspring during speciation.

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Most popular questions from this chapter

Certain varieties of chrysanthemums contain \(18,36,54,72,\) and 90 chromosomes; all are multiples of a basic set of nine chromosomes. How would you describe these varieties genetically? What feature do the karyotypes of each variety share? A variety with 27 chromosomes has been discovered, but it is sterile. Why?

Drosophila may be monosomic for chromosome \(4,\) yet remain fertile. Contrast the \(\mathrm{F}_{1}\) and \(\mathrm{F}_{2}\) results of the following crosses involving the recessive chromosome 4 trait, bent bristles: monosomic IV, bent bristles \(\times\) diploid, normal bristles; monosomic IV, normal bristles \(\times\) diploid, bent bristles.

Contrast the genetic composition of gametes derived from tetrads of inversion heterozygotes where crossing over occurs within a paracentric versus a pericentric inversion.

A couple planning their family are aware that through the past three generations on the husband's side a substantial number of stillbirths have occurred and several malformed babies were born who died early in childhood. The wife has studied genetics and urges her husband to visit a genetic counseling clinic, where a complete karyotype-banding analysis is performed. Although the tests show that he has a normal complement of 46 chromosomes, banding analysis reveals that one member of the chromosome 1 pair (in group \(A\) ) contains an inversion covering 70 percent of its length. The homolog of chromosome 1 and all other chromosomes show the normal banding sequence. (a) How would you explain the high incidence of past stillbirths? (b) What can you predict about the probability of abnormal- ity/normality of their future children? (c) Would you advise the woman that she will have to bring each pregnancy to term to determine whether the fetus is normal? If not, what else can you suggest?

Having correctly established the \(\mathrm{F}_{2}\) ratio in Problem 18 , predict the \(\mathrm{F}_{2}\) ratio of a "dihybrid" cross involving two independently assorting characteristics (e.g., \(\mathrm{P}_{1}=W W W W\) AAAA \(\times\) wwwwaaaa).
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