CHROMOSOMAL DISORDERS

You have just learned what makes up chromosomes, and how chromosomes divide to make gametes (through meiosis) and body (somatic) cells (through mitosis). You will now look at problems that may occur in the chromosomes during the division process and how these problems affect individuals.

A mutation is any change in the structure or amount of genetic material. In other words, a mutation is any change in the DNA of a cell. Now we will look at some types of chromosomal mutations.

Quick Review

To fully understand the mutations that will be discussed, a good understanding of previous vocabulary is needed.

Chromosome

Chromosomes are thread-like structures located inside the nucleus of animal and plant cells. Each chromosome is made of protein and a single molecule of deoxyribonucleic acid (DNA). Passed from parents to offspring, DNA contains the specific instructions that make each type of living creature unique.

Homologous Chromosome

one of a pair of chromosomes that match up at meiosis and are identical in morphology and arrangement; a chromosome with the same gene sequence as another, each derived from one parent

Karyotype

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The chromosomes of a cell, usually displayed as a systematized arrangement of chromosome pairs in descending order of size.

Meiosis

A form of cell division happening in sexually reproducing organisms by which two consecutive nuclear divisions (meiosis I and meiosis II) occur without the chromosomal replication in between, leading to the production of four haploid gametes (sex cells), each containing one of every pair of homologous chromosomes (that is, with the maternal and paternal chromosomes being distributed randomly between the cells).

n (haploid & diploid)

There are two types of cells in the body - haploid cells and diploid cells. The difference between haploid and diploid cells is related to the number of chromosomes that the cell contains.

Diploid cells contain two complete sets (2n) of chromosomes.

Haploid cells have half the number of chromosomes (n) as diploid - i.e. a haploid cell contains only one complete set of chromosomes.

Nonhomologous Chromosome

Chromosomes that are not members of the same pair. The chromosome containing dissimilar genes that do not pair during meiosis.

Sister chromatids

Two identical strands joined by a common centromere as a result of a chromosome that duplicated during the S phase of the cell cycle.

Chromosomal Mutations
Involves one chromosome			Involves two chromosomes
Duplication	Inversion	Deletion	Insertion	Translocation
A piece or section of chromosome is copied and added to the same chromosome.	A section of chromosome is reversed and inserted back into the same location on the same chromosome.	A section of a chromosome is missing or was not copied, resulting in a loss of genetic material.	A section of chromosome is inserted or added to a nonhomologous chromosome.	A section of one chromosome switches position with a section from a nonhomologous chromosomes.

Chromosomal Mutations

Involves the number of chromosomes.

Nondisjunction

Failure of homologous chromosomes or sister chromatids to separate during meiosis or mitosis.

Chromosomal Mutation Conditions

Aneuploidy is a condition in which the number of chromosomes is not an exact multiple of the haploid number of a particular species. It involves any change in the number of individual chromosomes rather than an entire set of chromosomes. In other words, having an extra chromosome or being short a chromosome. Remember each diploid cell should have two of each type of chromosome. Aneuploidy will result in monosomy or trisomy.

Monosomy is a condition in which there is one of a homologous chromosome instead of two.

Monosomy

(Human Karyotype – No “Y”)

Trisomy is a condition in which there is three of a homologous chromosome instead of two.

Trisomy (Human Karyotype – Extra #21)

Polyploidy is a condition in which a cell has more than two sets of chromosomes (diploid number). Having three sets of chromosomes is called triploid, four sets is tetraploid, etc.

Polyploidy (Human Karyotype – Triploid)

Mosaic is a condition in which some of the cells of an organism have different numbers of chromosomes from other cells in that organism. For example, a human with mosaicism may have some cells with the normal 46 chromosomes and other cells, within that human, with 47 chromosomes.

Genetic Disease

Unit 13 Worksheet Chromosomal Disorders

UNIT VOCABULARY REVIEW

Click on the Quizlet icon below to access the quizlet.com vocabulary flash cards. Review the vocabulary before completing your assessment.

Now answer questions 1 through 20.