Some individual Induce the cell to divide Stop

Some people with chromosomal disorders may have too many or too few chromosomes in their cells.

A karyotype analysis can be used to look at the number and appearance of chromosomes in individuals. Keep reading to learn more.

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What is a Karyotype?

Most living things have chromosomes, or units of genetic information, in their cells. The number and appearance of chromosomes vary among species.

A karyotype is the number, size, and shape of chromosomes in an organism. To determine the karyotype of an organism, scientists must follow these steps:

  1. Collect a cell from an individual
  2. Induce the cell to divide
  3. Stop cell division in metaphase when chromosomes are easiest to see
  4. Stain the chromosomes to make them visible
  5. View the cell under a microscope

Analysis of a Karyotype

It is often easier to understand a karyotype if a picture is taken. A karyogram is a photograph of an organism’s chromosomes, in which the chromosomes have been sorted and arranged by size.

Humans have a total of 46 chromosomes (23 from each parent), which you can see in the karyograms.

In karyograms, homologous chromosomes, or pairs of chromosomes that are the same size and shape, are grouped together. Humans have 22 of these pairs called autosomes.Autosomes are chromosomes that have genes for everything but the determination of the sex.

In humans, autosomes are numbered 1 through 22, and you have two of each number because one came from your mom and one came from your dad. Chromosome 1 is the largest, and chromosome 22 is the smallest.Autosomes only account for 44 of your total chromosomes, so what are the other two? The remaining two chromosomes in humans are called sex chromosomes because they are the ones that determine whether you are male or female. They are placed after autosomes in a karyogram.Sex chromosomes are not numbered, but instead they are given the letters X and Y.

If someone has two X chromosomes, then they will be female. If someone has an X and a Y chromosome, then they will be male.

Disorders

A karyotype analysis can be used to determine if individuals have abnormal numbers of chromosomes or abnormal-sized chromosomes. These abnormalities can be due to:

  • Nondisjunction: chromosomes did not separate in parental cells, leading to children that have too many or too few copies of chromosomes
  • Deletion: a chunk of a chromosome is missing, resulting in a shorter-than-normal chromosome
  • Duplication: parts of a chromosome are repeated, resulting in a longer-than-normal chromosome
  • Translocation: occurs when one part of a chromosome breaks off and attaches to another chromosome, resulting in one shorter and one longer chromosome

Abnormal numbers or sizes of chromosomes can lead to many genetic disorders.

Some known disorders are because of getting extra copies of the a chromosome, including Down syndrome, triple X syndrome, where a female gets an extra X chromosome, and Klinefelter syndrome, where the male gets an extra X chromosome. Some disorders occur from a missing chromosome, like Turner syndrome, when a female only gets one X chromosome, and some from translocation, like a form of leukemia, which produces abnormal white cells.

Lesson Summary

The number and appearance of chromosomes in a cell is called a karyotype.

A karyotype can only be seen and studied with a microscope. To make karyotypes easier to understand, karyograms are often made. In karyograms, homologous chromosomes are put side by side and then arranged by size.

Sex chromosomes are placed as the last pair of chromosomes. Karyotype analysis can reveal abnormalities, such as missing chromosomes, extra chromosomes, deletions, duplications, and translocations. These abnormalities can cause genetic disorders including Down syndrome, turner syndrome, Klinefelter syndrome, and fragile X syndrome.

Notes on Karyotypes

A karyogram is a photograph of the chromosomes of an organism
A karyogram
What is it? Why is it Studied?
A karyotopye is the number, size, and shape of the chromosomes in an organism Karyotypes can reveal chromosome abnormalities including: *Nondisjunction *Deletion *Duplication *Translocation

Learning Outcomes

After you’ve finished, you should be able to:

  • State what a karyotype is
  • Outline the process used to determine an organism’s karyotype
  • Define karyogram
  • Discuss some of the abnormalities that can be observed through karyotype analysis
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