ACT Science Practice Test - 4 - online test

Inherited Disorders

Inherited disorders can arise when chromosomes behave abnormally during meiosis. Chromosome disorders can be divided into two categories: abnormalities in chromosome number and chromosomal structural rearrangements. Because even small segments of chromosomes can span many genes, chromosomal disorders are characteristically dramatic and often fatal.

The isolation and microscopic observation of chromosomes forms the basis of cytogenetics and is the primary method by which clinicians detect chromosomal abnormalities in humans. A karyotype is the number and appearance of chromosomes, and includes their length, banding pattern, and centromere position. To obtain a view of an individual’s karyotype, cytologists photograph the chromosomes and then cut and paste each chromosome into a chart, or karyogram, also known as an ideogram (Figure 13.5).

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Figure 13.5 This karyotype is of a female human. Notice that homologous chromosomes are the same size, and have the same centromere positions and banding patterns. A human male would have an XY chromosome pair instead of the XX pair shown. (credit: Andreas Blozer et al)

In a given species, chromosomes can be identified by their number, size, centromere position, and banding pattern. In a human karyotype, autosomes or “body chromosomes” (all of the non–sex chromosomes) are generally organized in order of size from largest (chromosome 1) to smallest (chromosome 22). (The X and Y chromosomes, the 23rd pair, are not autosomes.) However, chromosome 21 is actually shorter than chromosome 22. This was discovered after the naming of Down syndrome as trisomy 21, reflecting how this disease results from possessing one extra chromosome 21 (three total). Not wanting to change the name of this disease, scientists retained the original numbering system. The chromosome “arms” projecting from either end of the centromere may be designated as short or long, depending on their relative lengths. The short arm is abbreviated p (for “petite”), whereas the long arm is abbreviated q(because it follows “p” alphabetically). Each arm is further subdivided and denoted by a number. For example, locus 3 on the short arm of chromosome 21 is denoted 21p3. Using this naming system, locations on chromosomes can be described consistently in the scientific literature.

Anne is a geneticist interested in autosomal and sex-linked genetic disorders. She conducted a study where she gathered all genetic disorder patient files from all hospitals throughout her country. She was interested in documenting the percentage of people in each study group who were affected by genetic disorders and what type of disorder they had. Each patient file included a karyotype of the patient’s genetic make-up.

Case Study 1

Anne has a table in her office that serves as a quick reference to the various autosomal disorders that were researched.

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Case Study 2

Anne has another table in her office that serves as a quick reference guide to the various sex-linked disorders that were researched.

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Science lesson Science Practice Test - 4 exam questions 1 questionAnne is organizing the karyotypes of patients with autosomal genetic disorders. Use the information in the attached passage to determine the syndrome of the patient with the karyotype shown in the attached image.

DiGeorge syndrome

Patau syndrome

Williams syndrome

Down syndrome

In the attached image, the pair of chromosomes that is affected by the syndrome is #13. In Patau’s syndrome, the karyotype contains extra genetic material from this pair of chromosomes, causing development problems such as cognitive disability and physical abnormalities.

Consult the attached reading passage. If the sex chromosome of a patient is XXXXY, the patient is a _________ and has the ________ syndrome.

female, Klinefelter

female, Triple X

male, Triple X

male, Klinefelter

The XXXXY chromosome is observed in patients with Klinefelter syndrome. It is produced by an extra X chromosome and affects only males, causing them to develop hypogonadism and infertility.

What percentage of patients in the Edwards study group (detailed in the attached passage) were affected with Edwards syndrome?

20%

50%

40%

250%

In the Edwards study group, 20 out of 50 patients were affected with Edwards syndrome. To calculate the percentage of patients with this syndrome, the following formula is use

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Which of these syndromes does not affect males?

Down

All of these syndromes can affect both males and females.

Angelman/Prader-Willi

Warkany

The listed syndromes affect chromosomes that are not sex-linked. That is why they are called autosomal genetic disorders. The word “autosomes” refers to the 22 pairs of chromosomes that are not sex-linked, while the sex-linked pair of chromosome is called “allosome.” Autosomal genetic disorders can affect both males and females, while allosomal genetic disorders affect only a specific sex.

Which is the least common syndrome from table 1 in the attached passage?

Jacobsen

Miller-Dieker/Smith-Magenis

Cat Eye

DiGeorge

The least common syndrome is the one with the lowest percentage of patients that have it. To calculate the percentage the following formula is use

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The syndrome with the lowest percentage is Jacobsen syndrome, which affects 5% of the patients in the study group.

Anne has a karyotype that is incomplete. She had spilled coffee on the karyotype by mistake, which blurred the images of the chromosomes at two positions on the karyotype. Anne knows that the patient of this karyotype has the Cat Eye, Wolf-Hirschhorn, and Turner syndrome. Which image in the attached visual would the complete karyotype look like?

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Cat Eye syndrome affects the 22nd pair of chromosomes by adding extra genetic material. Wolf-Hirschhorn syndrome affects the 4th pair of chromosomes by removing part of the genetic material. Turner syndrome affects the sex-linked chromosome (the 23rd pair of chromosomes) by removing one X chromosome. The karyotype that shows all three of these changes is karyotype C.