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Chapter 6: Problem 14

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?

Short Answer

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Answer: The karyotypes of these chrysanthemums share the feature of having chromosome counts in sets of 9, indicating they are polyploid organisms. A variety with 27 chromosomes is sterile because it is a triploid organism, having three copies of each chromosome, which leads to irregular distribution of chromosomes during meiosis and the production of non-viable gametes.

Step by step solution

01

Observe the given numbers of chromosomes

Notice that all given numbers of chromosomes in these chrysanthemums are multiples of a basic set of 9: \(18 = 9 \times 2\), \(36 = 9 \times 4\), \(54 = 9 \times 6\), \(72 = 9 \times 8\), and \(90 = 9 \times 10\).
02

Describing the varieties genetically

Since all these varieties have chromosome counts that are multiples of 9, we can say that these varieties are polyploid. Polyploidy is a condition where an organism has more than two sets of chromosomes.
03

Identifying the karyotype feature

The common feature among the karyotypes of these varieties is that they contain a multiple of the basic set of 9 chromosomes. In other words, these karyotypes have chromosomes in sets of 9.
04

Explaining the sterility of 27-chromosome variety

The variety with 27 chromosomes can be represented as \(9 \times 3\). Since 3 is an odd number, this variety is a triploid organism, meaning it carries three copies of each chromosome. Triploid organisms are usually sterile because they cannot produce viable gametes due to irregular distribution of chromosomes during meiosis. In a triploid organism, the chromosomes cannot pair evenly during meiosis, leading to uneven distribution of genetic material and non-viable gametes. As a result, the 27-chromosome variety is sterile.

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Most popular questions from this chapter

Review the Chapter Concepts list on page \(99 .\) These all center on chromosome aberrations that create variations from the "normal" diploid genome. Write a short essay that discusses five altered phenotypes that result from specific chromosomal aberrations.

A boy with Klinefelter syndrome \((47, \mathrm{XXY})\) is born to a mother who is phenotypically normal and a father who has the X-linked skin condition called anhidrotic ectodermal dysplasia. The mother's skin is completely normal with no signs of the skin abnormality. In contrast, her son has patches of normal skin and patches of abnormal skin. (a) Which parent contributed the abnormal gamete? (b) Using the appropriate genetic terminology, describe the meiotic mistake that occurred. Be sure to indicate in which division the mistake occurred. (c) Using the appropriate genetic terminology, explain the son's skin phenotype.

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?

Human adult hemoglobin is a tetramer containing two alpha (a) and two beta ( \(\beta\) ) polypeptide chains. The \(\alpha\) gene cluster on chromosome 16 and the \(\beta\) gene cluster on chromosome 11 share amino acid similarities such that 61 of the amino acids of the \(\alpha\) -globin polypeptide ( 141 amino acids long) are shared in identical sequence with the \(\beta\) -globin polypeptide \((146\) amino acids long. How might one explain the existence of two polypeptides with partially shared function and structure on two different chromosomes? Include in your answer a link to Ohno's hypothesis regarding the origin of new genes during evolution.

Contrast the fertility of an allotetraploid with an autotriploid and an autotetraploid.
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