Drosophila geneticists made the first genetic maps. They claimed that the gene loci that they mapped “behaved mathematically as though they were in linear order” in the genetic material. They did not claim that these loci were actually physically located in a line along the chromosome. 1. Given what was known about chromosomes and the genetic material at that time, are these statements correct? Why or why not?

Drosophila geneticists made the first genetic maps. They claimed that the gene loci that they mapped “behaved mathematically as though they were in linear order” in the genetic material. They did not claim that these loci were actually physically located in a line along the chromosome. 1. Given what was known about chromosomes and the genetic material at that time, are these statements correct? Why or why not?

Human Heredity: Principles and Issues (MindTap Course List)

11th Edition

ISBN:9781305251052

Author:Michael Cummings

Publisher:Michael Cummings

Chapter6: Cytogenetics: Karyotypes And Chromosome Aberrations

Section: Chapter Questions

Problem 1QP: Analyzing Karyotypes 1. Originally, karyotypic analysis relied only on size and centromere placement...

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In an electrophoretic gel across which is applied a powerful electrical alternating pulsed field, the DNA of the haploid fungus Neurospora crassa (n = 7) moves slowly but eventually forms seven bands, which represent DNA fractions that are of different sizes and hence have moved at different speeds. These bands are presumed to be the seven chromosomes. How would you show which band corresponds to which chromosome?
The size of one copy of the human genome is approximately 3 billion base pairs, and it contains about 27,000 genes organized into 23 chromosomes. Human chromosomes vary in size. What would you predict is the size of the average chromosome? Assuming that genes are spread evenly among chromosomes, how many genes does an average human chromosome contain?
Colchicine is a chemical mutagen that inhibits the spindle formation and prevents anaphase, which retains the cell’s single restitution nucleus (doubled chromosome number). Suppose that an onion (2n=16) is subjected to three consecutive rounds of colchicine treatment, what will be the resulting chromosome number of the treated onion?
The garden pea (Pisum sativum) is normally a diploid and has 7 chromosomes in one set (in other words, n = 7). Use this information to answer the following questions: a. How many centromeres would be in a cell of a tetraploid pea plant? ______ b. How many total chromatids would be in a cell of a tetraploid pea plant in metaphase of mitosis? _______ c. How many total chromosomes would be in a cell of a pea plant that is monosomic for a single chromosome?
Variations in Chromosome NumberAneuploidy Describe the process of nondisjunction and explain when it takes place during cell division.
Analyzing Karyotypes 1. Originally, karyotypic analysis relied only on size and centromere placement to identify chromosomes. Because many chromosomes are similar in size and centromere placement, the identification of individual chromosomes was difficult, and chromosomes were placed into eight groups, identified by the letters A to G. Today, each human chromosome can be readily identified. a. What technical advances led to this improvement in chromosome identification? b. List two ways this improvement can be implemented. c. What clinical information does a karyotype provide?
Domesticated sheep cells have a total of 54 chromosomes (versus 46 chromosomes in human cells). (a) How many separate DNA molecules are present in a sheep liver cell at the end of the G1 phase? (b) How many separate DNA molecules are present in the daughter cells after meiosis I in the ovary of the sheep? (c) How many separate DNA molecules are present in the daughter cells after meiosis II in the ovary of the sheep?
The genes dumpy wings (dp), clot eyes (cl), and apterous wings(ap) are linked on chromosome II of Drosophila. In a series of twopoint mapping crosses, the genetic distances shown below weredetermined. What is the sequence of the three genes? dp–ap 42dp–cl 3ap–cl 39
The size of one copy of the human genome is approximately 3 billion base pairs, and it contains about27,000 genes organized into 23 chromosomes.a. Human chromosomes vary in size. What wouldyou predict is the size of the average chromosome?b. Assuming that genes are spread evenly amongchromosomes, how many genes does an averagehuman chromosome contain?c. About half of the DNA in chromosomes containsgenes. How large (in base pairs) is an averagehuman gene?
. With regards to the grasshopper testes experiment, diakinesis is an ideal stage to determine chromosome number due to the degree of condensation of the chromosomes? Count the chromosomes at this stage. Does it represent a diploid or a haploid number?
In a human genetic study, a family with five phenotypicallynormal children was investigated. Two children were “homozygous”for a Robertsonian translocation between chromosomes19 and 20 (they contained two identical copies of the fusedchromosome). They have only 44 chromosomes but a completegenetic complement. Three of the children were “heterozygous”for the translocation and contained 45 chromosomes,with one translocated chromosome plus a normal copy of bothchromosomes 19 and 20. Two other pregnancies resulted instillbirths. It was later discovered that the parents were firstcousins. Based on this information, determine the chromosomecompositions of the parents. What led to the stillbirths? Whywas the discovery that the parents were first cousins a key pieceof information in understanding the genetics of this family?
The genes dumpy (dp), clot (cl), and apterous (ap) are linked on chromosome II of Drosophila. In a series of two-point mapping crosses, the following genetic distances were determined. What is the sequence of the three genes? dp–ap 42 dp–cl 3 ap–cl 39