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This lesson explains the concept of homologous chromosomes. It includes key vocabulary, illustrations, and explanations. It also addresses the process of chromosome separation. A brief quiz is also included.

Hiding on Chromosomes

Have you ever heard that certain features skip generations? For example someone with blue eyes may have two parents with brown eyes but a grandparent with blue eyes.

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Or two black colored cats may produce white kittens. How and why does this occur?Part of the answer is because most organisms have homologous chromosomes. Homologous chromosomes contain the same gene sequences, but may have different versions of those genes. A gene is the segment of DNA that codes for a specific feature, such as eye color. For a better understanding, let’s start with the basics.

Studying Life

Of the various courses I teach, my current favorite is called Accelerated Biology.

It’s essentially like any introductory biology course, but due to its accelerated nature, we’re able to move quickly and cover more detail on certain topics. One such topic is genetics. We’ll study genetics from a multitude of angles.

But a specific focus is on chromosomes. Chromosomes are tightly coiled structures containing most of the DNA inside living organisms. This DNA is important because it provides the information necessary to build living organisms.

Genetic Differences

Chromosome number varies between species. For example, turkeys have 80 chromosomes; dogs have 78, mosquitoes only 6, and the black mulberry plant has a whopping 308! Humans on the other hand contain 46 chromosomes (23 pair). Below is an illustration for your reference.

Homologous Chromosomes
Homologous Chromosomes

In the picture above, each chromosome is paired with another similar chromosome. These pairings are the homologous chromosomes discussed above. It is important to remember that homologous chromosomes contain the same gene sequences.

For this reason, they appear identical.See the pattern of black and white bands in the photo? Those represent the different genes. You can clearly see how the band patterns in homologous chromosomes are similar.

Making Copies

When cells prepare to divide, they must replicate their chromosomes. This ensures that each new cell contains the same genetic information as the original cell. Following replication, your chromosomes take on a slightly altered appearance.

Below is an image to assist in understanding.

Homologous Chromosomes After Replication
Homologous Chromosomes After Replication

Notice how each homologous pair is now X shaped. This is because they are attached to their sister chromatid. Sister chromatid are copies of the original chromosome. Eventually, this copy will be removed during mitosis and passed into a new cell.

Mitosis is the process of dividing the nucleus of a cell. It is a multistep process that produces two identical daughter cells, each containing 46 chromosomes.

Lesson Summary

The DNA found in our chromosomes controls our physical appearance. Chromosomes are tightly coiled structures containing the DNA of living organisms. Each person contains 46 chromosomes that are split into 23 pair. Each pair are known as homologous chromosomes.

Homologous chromosomes are alike in appearance, pair during mitosis, and contain identical gene sequences. Genes are segments of DNA that code for specific traits. Mitosis is the process of cellular division. During mitosis, sister chromatid are separated into new cells. Sister chromatid are genetic replicas of original chromosomes.

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