8.1

1. What one-word term is defined as a scientist who studies chromosomes microscopically?

cytogeneticist

2. Staining eukaryotic chromosomes is useful because it makes it possible to a. distinguish chromosomes that are similar in size and centromeric locations. b. identify changes in chromosome structure. c. explore evolutionary relationships among different species. d. do all of the above.

d

5. A gene is located on the short arm of chromosome 4 in region 1, subregion 3. How is this information conveyed in shorthand notation?

4p13

Giemsa staining

A type of stain used for G banding of chromosomes.

karyotype

An organized presentation of the condensed chromosomes from a somatic cell of an organism.

E7. What is a G band? Discuss how G bands are useful in the analysis of chromosome structure.

Answer: A G band is a dark band on a chromosome that has been stained with Giemsa. The pattern of G bands on chromosomes can be used to distinguish chromosomes from each other even if their sizes and centromere locations are very similar. Banding patterns are also used to detect changes in chromosome structure.

genetic variation

Genetic differences among members of the same species or between different species.

4. What stain (one word) is used to produce chromosomes with G-banding?

Giemsa

G bands

Staining patterns on chromosomes produced by using Giemsa stain.

2. What does it mean if a gene is located on the p arm of a chromosome?

Because the centromere is never exactly in the center of a chromosome, each chromosome has a short arm and a long arm. For human chromosomes, the short arm is designated with the letter p (for the French, petit)

2. Which one of the following is NOT a commonly used method to classify and identify chromosomes? A. Centromere location B. Relative size C. Telomere location D. Banding patterns E. All of the above are commonly used methods.

C

telocentric

Centromere is at one end of the chromosome

metacentric

Centromere is at the middle of the chromosome.

acrocentric

Centromere is significantly off center but not at the end of the chromosome

submetacentric

Centromere is slightly off center.

2. Use the terms listed below to correctly explain concepts, assigned figures, and specified end-of-chapter questions. Genetic variation Allelic variation Chromosome variation Cytogenetics Centromere Metacentric Submetacentric Acrocentric Telocentric Short arm (p) Long arm (q) Giemsa staining G bands Karyotype

If there are differences in genetic material between members of same species or between two different completely different species the organisms are thought to have a genetic variation. If genetic variation happens within same species we call it allelic variation. However different species are observed to have chromosomal variations such as different number of chromosomes, different nr. of genes or alterations in genetic material . Cytogenetics is a study that compares the chromosomes of members of same species or different species at microscopic level to find differences between the species and to find the reference chromosomes. Centromere is a segment of DNA that holds the sister chromatids together. If centromere is located in the middle it is called metacentric, if is slightly away from the middle is submetacentric, if it is away from center but not at the end is called acrocentric, if is at the end is called telocentric. The shorter side of the chromosome is called p for petite, the larger side is called q bcs of alphabetical order. Giemsa staining is used to observe differences in chromosomes of same size and same centromere location. Giemsa staining produces darker bands if the region is more compact and the g bands shown absorb the dye. A karyotype is a microgram that shows the chromosomes in order of their appearance and their sizes from largest size to the smallest as well as the banding patterns. It looks at the chromosomes within a cell in their standard order.

short arm p

Part of a eukaryotic chromosome designated as "p".

long arm q

Part of a eukaryotic chromosome designated as "q".

centromere

Segment of eukaryotic chromosomal DNA that serves as an attachment site for the kinetochore.

Fig 8.1 why is it useful to stain chromosomes?

The staining of chromosomes results in banding patterns that make it easier to distinguish chromosomes that are similar in size and have similar centromere locations.

cytogenetics

The study of chromosomes at the microscopic level.

1. Describe the characteristics that are used to classify and identify chromosomes.

The three most commonly used features are: location of the centromere, size, and banding patterns that are revealed when the chromosomes are treated with stains. Location of centromere are 1. metacentric- if centromere is located right in the middle, submetacentric- if centromere slightly off but close to middle, acrocentric- if centromere is far from the middle but also not at the end, telocentric- centromere is at the end of sisterchromatids. Sizes - smaller nr. = larger size, in humans chromosome 1-3 large, chromosomes 21-22 smallest, chromosome 23 no nr. bcs sex chromosomes carry letters XY or XX. Staining- different types of staining. Giemsa staining - uses mild heat or proteolytic enzymes that partially digest chromosomal proteins- if giemsa dye staining the band shows very dark= very compact. Prometaphase less compacted so more bands than metaphase which is more compacted.

chromosome variation

Variation in chromosome composition or number.

allelic variation

Variation within a specific gene.

3. Describe the general appearance of a human karyotype

When preparing a karyotype, the chromosomes are aligned with the short arms on top and the long arms on the bottom. By convention, the chromosomes are numbered roughly according to their size, with the largest chromosomes having the smallest numbers. For example, human chromosomes 1, 2, and 3 are relatively large, whereas 21 and 22 are the two smallest. An exception to the numbering system involves the sex chromosomes, which are designated with letters (for humans, X and Y).Though the mechanism of staining is not completely understood, the dark bands are thought to represent regions that are more tightly compacted. As shown in Figure 8.1c and d, the alternating pattern of G bands is a unique feature for each chromosome. In the case of human chromosomes, approximately 300 G bands can usually be distinguished during metaphase. A larger number of G bands (in the range of 800) can be observed in prometaphase chromosomes because they are less compacted than metaphase chromosomes. Figure 8.1d shows the conventional numbering system that is used to designate G bands along a set of human chromosomes. The left chromatid in each pair of sister chromatids shows the expected banding pattern during metaphase, and the right chromatid shows the banding pattern as it would appear during prometaphase.

1. A chromosome that is metacentric has its centromere a. at the very tip. b. near one end, but not at the very tip. c. near the middle. d. at two distinct locations.

c

3. A chromosome whose centromere is in the middle is classified as ______ (one word) and if the centromere is located at the end of a chromosome it's classifed as ______ (one word). Enter the two words separated by one space.

metacentric telocentric

1. Describe the centromere location for each of the following terms: submetacentric, telocentric, acrocentric, and metacentric.

submetacentric- slightly away from center but close to center, telocentric- at the end of chromosome, acrocentric- significantly away from center but not at the end, metacentric- near the middle