# data[].attributes.body
Video to teach "nondisjunction" in Meiosis

# data[].attributes.attachment_link.readable_text
What is Nondisjunction in Meiosis?

All of your body cells, except eggs and sperm cells, have two sets of 23 chromosomes, for a total of 46 chromosomes. Having two sets of chromosomes is called diploid and designated as 2n. Eggs and sperm cells are called gametes, and they have only one set of 23 chromosomes, which is called a haploid, or n. When two haploid gametes (one egg and one sperm cell) fuse during fertilization, a diploid cell is produced. This diploid cell has one set of chromosomes from the egg and one set of chromosomes from the sperm cell. This diploid cell will divide and develop into a baby.

Meiosis is the process of creating haploid gametes from a diploid cell. If everything goes smoothing during meiosis, chromosomes will be separated and distributed evenly to produce four haploid gametes. However, sometimes chromosomes do not separate properly. This is called nondisjunction and results in gametes with either too many or too few chromosomes. In humans, nondisjunction becomes more common the older one gets.

Production of Normal Gametes

To get ready for meiosis, a diploid germ cell must first undergo DNA replication. This process duplicates every strand of DNA so that there are two copies of every chromosome. The two copies are called sister chromatids and are attached to each other. Once DNA replication is complete, two rounds of chromosomal divisions take place, one each in meiosis I and meiosis II. During meiosis I, homologous chromosomes pair up, line up, and then are split apart.

Homologous chromosomes are those that are the same size and carry the same genes. You get one from your mom and one from your dad. In human diploid cells, there are 23 pairs of homologous chromosomes. After meiosis I, two cells are present, each with 23 different chromosomes that are still in duplicate as sister chromatids.

Both the cells produced in meiosis I undergo meiosis II. During this round, chromosomes line up and sister chromatids are pulled apart into two sets. Now, a total of four haploid cells are present. The pulling apart of either homologous chromosomes or sister chromatids is called disjunction and occurs during anaphase of meiosis I or meiosis II, respectively.

Nondisjunction Produces Abnormal Gametes

Sometimes during anaphase, chromosomes will fail to separate properly. Remember, this is called nondisjunction. This can happen either during meiosis I or meiosis II.

If nondisjunction occurs during anaphase I of meiosis I, this means that at least one pair of homologous chromosomes did not separate. The end result is two cells that have an extra copy of one chromosome and two cells that are missing that chromosome. In humans, n + 1 designates a cell with 23 chromosomes plus an extra copy of one for a total of 24 chromosomes. n - 1 designates a cell missing a chromosome for a total of only 22 chromosomes in humans.

If nondisjunction occurs during anaphase II of meiosis II, it means that at least one pair of sister chromatids did not separate. In this scenario, two cells will have the normal haploid number of chromosomes. Additionally, one cell will have an extra chromosome ( n + 1) and one will be missing a chromosome ( n - 1).

Fertilization with Abnormal Gametes

If one of these abnormal gametes undergoes fertilization, then a baby with an abnormal number of chromosomes in its cells could be born. Trisomy is the condition of having 3 copies of one chromosome type. It is designated as 2n + 1 because the cell has the normal two sets of each 23 types of chromosomes plus an extra copy of one chromosome. Monosomy is the condition of having only 1 copy of a chromosome and is designated as 2n - 1.

# data[].attributes.attachment_link.keywords[]
nondisjunction in meiosis: definition & examples - video & lesson transcript | study.com

# data[].attributes.attachment_link.title
Nondisjunction in Meiosis: Definition & Examples - Video & Lesson Transcript | Study.com

# data[].attributes.attachment_link.description
All of your body cells, except eggs and sperm cells, have two sets of 23 chromosomes, for a total of 46 chromosomes. Having two sets of chromosomes is called diploid and designated as 2n . Eggs and sperm cells are called gametes, and they have only one set of 23 chromosomes, which is called a haploid, or n .

# data[].attributes.headline
November 15                        JOIN Quizlet class

# data[].attributes.subject
November 15                        JOIN Quizlet class

# data[].attributes.body
To join the class, first set up a quizlet account.

# data[].attributes.attachment_link.description
Start studying SAT II Biology - Ecology. Learn vocabulary, terms, and more with flashcards, games, and other study tools.

# data[].attributes.body
Practice 20 minutes . November 15

# data[].attributes.attachment_link.description
The security system for this website has been triggered. Completing the challenge below proves you are a human and gives you temporary access.

# data[].attributes.attachment_link.description
Big Idea 1: Evolution. Natural Selection, Phenotypic impact of Natural Selection, Random Processes, Core Processes, Evolutionary history, Extinction, Repoductive Isolation, Orgin of Life, and Scientific Evidence.

# data[].attributes.body
The website will score your work

# data[].attributes.attachment_link.title
Test: SAT II Biology - Ecology | Quizlet

# data[].attributes.attachment_link.description
Quizlet is a lightning fast way to learn vocabulary.

# data[].attributes.headline
November 15                  Barron's Biology Test Prep

# data[].attributes.subject
November 15                  Barron's Biology Test Prep

# data[].attributes.body
click on this link to register and take a TIMED practice test.

# data[].attributes.attachment_link.title
Barron's Online SAT Subject Tests - Biology Practice Exam

# data[].attributes.attachment_link.description
SAT Subject Test - Biology Online Test - FREE from Barron's with purchase of SAT Subject Test - Biology book

# data[].attributes.body
CollegeBoard SAT Biology practice

# data[].attributes.attachment_link.readable_text
Jump-Start Your Practice

Taking the SAT Subject Test in either Biology Ecological or Biology Molecular can help you indicate to colleges that you are interested in focusing on science. The Biology Subject Test assesses your understanding of the major concepts of biology typically learned in high school and is an excellent way to showcase your achievements.

Start practicing online with general Biology questions

The Biology Ecological (Biology-E) test leans more toward biological communities, populations, and energy flow.

Start practicing online with Biology-E questions

The Biology Molecular (Biology-M) test is more geared toward biochemistry, cellular structure and processes, such as respiration and photosynthesis.
Start practicing online with Biology-M questions
Video Lessons from Khan Academy

Use the free Khan Academy ® lessons in this playlist to study for both the Biology Ecological and Biology Molecular Subject Tests.

Test Basics

60 of the 80 questions are common to both Biology E and M, followed by 20 specialized questions for each section.

Important Notes

Getting Ready for the Test

Additional Things to Know

How to Choose between Biology-E (Ecological) and Biology-M (Molecular)

Take Biology E if you feel more comfortable answering questions about biological communities, populations, and energy flow.

Take Biology M if you feel more comfortable answering questions about biochemistry, cellular structure and processes, such as respiration and photosynthesis.

Indicate choice of Biology E or Biology M by filling in the appropriate circle on your answer sheet for the test you have chosen to take on test day. You must indicate Biology E or Biology M on your answer sheet on test day for the test to be scored correctly

You cannot take both tests on the same test date, but you can take them on two different test dates.

Please note that this test reflects what is commonly taught in high school. Due to differences in high school classes, it's likely that most students will find questions on topics they're not familiar with. This is nothing to worry about. You do not have to get every question correct to receive the highest score (800) for the test. Many students do well despite not having studied every topic covered.

# data[].attributes.attachment_link.description
Taking the SAT Subject Test in either Biology Ecological or Biology Molecular can help you indicate to colleges that you are interested in focusing on science. The Biology Subject Test assesses your understanding of the major concepts of biology typically learned in high school and is an excellent way to showcase your achievements.

# data[].attributes.headline
ALBERT Learn anything through interactive practice

# data[].attributes.subject
ALBERT Learn anything through interactive practice

# data[].attributes.attachment_link.title
AP Biology - Osmosis and the Chicken and the Egg

# data[].attributes.attachment_link.description
Three chicken eggs are placed in distilled white vinegar for a period of thirty­-six hours until the shells have been removed, leaving behind only the membrane covering. Once the shell has been removed, each egg is then weighed. One of the decalcified eggs is placed in ${500}\text{ ml}$ of distilled water.

# data[].attributes.body
MCUs for science

# data[].attributes.body
Collaboration Tool