5.2 Meiosis and Genetic Diversity
4 min read•december 17, 2022
Caroline Koffke
Haseung Jun
Caroline Koffke
Haseung Jun
There are a few key concepts within meiosis that contribute to genetic diversity. Remember that diversity is the key to life. When all else fails, focus on diversity in your answers for the AP exam. Some key contributors to genetic diversity in meiosis are the concepts of , , and .
Crossing Over
is an incredibly important process that takes place during the first round of cellular division in meiosis.
During this process, share genetic material. Remember that are two different versions of the same chromosome. For instance, chromosome 2 might have the gene for eye color. Each individual has two versions of chromosome 2, one from mom and one from dad. One version might have a for eye color, and the other might have a .
During the process of , exchange parts of their chromosome at the same location, therefore, not adding or subtracting genes, just exchanging versions of the gene.
A more specific example of is shown below:
Image courtesy of WikiMedia Commons.
This exchange of genetic material leads to numerous possibilities for the separation of chromosomes and the resulting daughter cells. This can also be seen at the end of the diagram shown in section 1.
Independent Assortment
refers to the way that chromosomes line up for both the first and second rounds of division in meiosis. In the example below, there is a 50% chance that both blue versions of the chromosomes will line up on the same side, as shown by possibility 1. There is a 50% chance that a blue and a red version of each chromosome will line up on the same side, as shown by possibility 2.
Depending on the original orientation of these chromosomes, different daughter cells will form. This can be shown by the four unique combinations of chromosomes shown in the row of gametes.
Image courtesy of BioNinja.
The random alignment of chromosomes during contributes to an immense amount of variation. The amount can be quantified using the following formula:
For humans, results in 2^23, or 8,388,608, unique egg or sperm that one individual can produce. This does not include the variation that and contribute as well.
Random Fertilization
simply means that there is a random chance that each egg and sperm will join one another. There are potentially thousands of sperm that can fertilize the one mature egg, and the genetics in each of them is distinct. The specific sperm that joins the specific egg for each fertilization is random, meaning that the same two parents are not going to produce the same child twice.
Nondisjunction
There is a special type of "genetic diveristy" which involves meiotic errors 😨. Though not ideal with meiosis, creates cells with too many or too little chromosomes. This can happen if the chromosomes failed to separate properly during or II.
Image Courtesy of Labster Theory
If happens during meiosis I, the all of the resulting will have abnormal amounts of chromosomes. If happens during meiosis II, only two are affected. The other two will have the normal amount, n, but the other two will either have one extra or one less.
When a gamete is produced with abnormal number of chromosomes, they often end in miscarriages or genetic defects. A prime example of is Down sydrome. Individuals with have an extra copy of the 21st chromosome, so they would be the example of the n+1 situation.
Image Courtesy of CMDSS
Ending Notes
Remember, there are 3 factors of genetic diversity that College Board focuses on: , , and . The sole purpose of meiosis is creating genetic variation, so these three are crucial to understand in order to understand the purpose of meiosis. Chances are, you'll see a question about genetic variation on a FRQ.
is a meiotic error which causes most genetic defects. Depending on when the happened, you'll have 4 or 2 that have too many or too little chromosomes.
Key Terms to Review (12)
Anaphase I
: Anaphase I is a phase of meiosis where homologous chromosomes separate and move towards opposite poles (ends) of the cell.Anaphase II
: Anaphase II is the stage in meiosis II where the sister chromatids, now individual chromosomes, separate and move towards opposite poles of the cell.Crossing Over
: Crossing over is a process that occurs during meiosis where two chromosomes pair up and exchange segments of their genetic material. This leads to a mix of parental traits in offspring, contributing to genetic diversity.Dominant Allele
: A dominant allele is an allele that expresses itself fully in an organism's appearance and masks the effect of any recessive allele present at the same locus on its homologous chromosome.Down Syndrome
: Down Syndrome is a genetic disorder caused when abnormal cell division results in an extra full or partial copy of chromosome 21.Haploid Cells
: Haploid cells are cells that contain only one set of chromosomes. In humans, these would be sperm or egg cells.Homologous Chromosomes
: Homologous chromosomes are pairs of chromosomes - one from each parent - that are similar in shape, size, and gene content. They pair up during meiosis before being separated into different gametes.Independent Assortment
: Independent assortment is a principle stating that genes for different traits can segregate independently during the formation of gametes.Metaphase
: Metaphase is a stage in both mitosis and meiosis during which all chromosomes align at the center (equator) of the cell before being separated into two new cells.Nondisjunction
: Nondisjunction occurs when chromosomes fail to separate properly during meiosis, resulting in gametes with an abnormal number of chromosomes.Random Fertilization
: Random fertilization is the concept that each sperm and egg combination is unique due to independent assortment and crossing over during meiosis, leading to a vast number of potential genetic combinations in offspring.Recessive Allele
: A recessive allele is a version of a gene that does not express itself when paired with a dominant allele. It only shows its effect if two copies are present in the organism's genetic makeup.5.2 Meiosis and Genetic Diversity
4 min read•december 17, 2022
Caroline Koffke
Haseung Jun
Caroline Koffke
Haseung Jun
There are a few key concepts within meiosis that contribute to genetic diversity. Remember that diversity is the key to life. When all else fails, focus on diversity in your answers for the AP exam. Some key contributors to genetic diversity in meiosis are the concepts of , , and .
Crossing Over
is an incredibly important process that takes place during the first round of cellular division in meiosis.
During this process, share genetic material. Remember that are two different versions of the same chromosome. For instance, chromosome 2 might have the gene for eye color. Each individual has two versions of chromosome 2, one from mom and one from dad. One version might have a for eye color, and the other might have a .
During the process of , exchange parts of their chromosome at the same location, therefore, not adding or subtracting genes, just exchanging versions of the gene.
A more specific example of is shown below:
Image courtesy of WikiMedia Commons.
This exchange of genetic material leads to numerous possibilities for the separation of chromosomes and the resulting daughter cells. This can also be seen at the end of the diagram shown in section 1.
Independent Assortment
refers to the way that chromosomes line up for both the first and second rounds of division in meiosis. In the example below, there is a 50% chance that both blue versions of the chromosomes will line up on the same side, as shown by possibility 1. There is a 50% chance that a blue and a red version of each chromosome will line up on the same side, as shown by possibility 2.
Depending on the original orientation of these chromosomes, different daughter cells will form. This can be shown by the four unique combinations of chromosomes shown in the row of gametes.
Image courtesy of BioNinja.
The random alignment of chromosomes during contributes to an immense amount of variation. The amount can be quantified using the following formula:
For humans, results in 2^23, or 8,388,608, unique egg or sperm that one individual can produce. This does not include the variation that and contribute as well.
Random Fertilization
simply means that there is a random chance that each egg and sperm will join one another. There are potentially thousands of sperm that can fertilize the one mature egg, and the genetics in each of them is distinct. The specific sperm that joins the specific egg for each fertilization is random, meaning that the same two parents are not going to produce the same child twice.
Nondisjunction
There is a special type of "genetic diveristy" which involves meiotic errors 😨. Though not ideal with meiosis, creates cells with too many or too little chromosomes. This can happen if the chromosomes failed to separate properly during or II.
Image Courtesy of Labster Theory
If happens during meiosis I, the all of the resulting will have abnormal amounts of chromosomes. If happens during meiosis II, only two are affected. The other two will have the normal amount, n, but the other two will either have one extra or one less.
When a gamete is produced with abnormal number of chromosomes, they often end in miscarriages or genetic defects. A prime example of is Down sydrome. Individuals with have an extra copy of the 21st chromosome, so they would be the example of the n+1 situation.
Image Courtesy of CMDSS
Ending Notes
Remember, there are 3 factors of genetic diversity that College Board focuses on: , , and . The sole purpose of meiosis is creating genetic variation, so these three are crucial to understand in order to understand the purpose of meiosis. Chances are, you'll see a question about genetic variation on a FRQ.
is a meiotic error which causes most genetic defects. Depending on when the happened, you'll have 4 or 2 that have too many or too little chromosomes.
Key Terms to Review (12)
Anaphase I
: Anaphase I is a phase of meiosis where homologous chromosomes separate and move towards opposite poles (ends) of the cell.Anaphase II
: Anaphase II is the stage in meiosis II where the sister chromatids, now individual chromosomes, separate and move towards opposite poles of the cell.Crossing Over
: Crossing over is a process that occurs during meiosis where two chromosomes pair up and exchange segments of their genetic material. This leads to a mix of parental traits in offspring, contributing to genetic diversity.Dominant Allele
: A dominant allele is an allele that expresses itself fully in an organism's appearance and masks the effect of any recessive allele present at the same locus on its homologous chromosome.Down Syndrome
: Down Syndrome is a genetic disorder caused when abnormal cell division results in an extra full or partial copy of chromosome 21.Haploid Cells
: Haploid cells are cells that contain only one set of chromosomes. In humans, these would be sperm or egg cells.Homologous Chromosomes
: Homologous chromosomes are pairs of chromosomes - one from each parent - that are similar in shape, size, and gene content. They pair up during meiosis before being separated into different gametes.Independent Assortment
: Independent assortment is a principle stating that genes for different traits can segregate independently during the formation of gametes.Metaphase
: Metaphase is a stage in both mitosis and meiosis during which all chromosomes align at the center (equator) of the cell before being separated into two new cells.Nondisjunction
: Nondisjunction occurs when chromosomes fail to separate properly during meiosis, resulting in gametes with an abnormal number of chromosomes.Random Fertilization
: Random fertilization is the concept that each sperm and egg combination is unique due to independent assortment and crossing over during meiosis, leading to a vast number of potential genetic combinations in offspring.Recessive Allele
: A recessive allele is a version of a gene that does not express itself when paired with a dominant allele. It only shows its effect if two copies are present in the organism's genetic makeup.
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