Mendel's Law of Segregation

Mendel's Law of Segregation

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Mendel's Law of Segregation is one of three laws that make up Mendelian genetics. The other two are the Law of Dominance and the Law of Independent Assortment. The Law of Segregation explains that gene pairs split apart to form individual gametes. These gametes combine to create offspring. This law is important because it helps explain two key biological processes: gametogenesis and genetics.

Explaining Mendel's Law of Segregation

Mendel's Law of Segregation is one of three laws that make up Mendelian genetics. The other two laws are the Law of Dominance and the Law of Independent Assortment. The Law of Dominance explains that when an organism is a heterozygote, it will express the phenotype of the dominant allele. The Law of Independent Assortment states that alleles of different genes are inherited independently of one another. This means that inheriting an allele on one gene doesn't affect your ability to inherit any allele on another gene.

Mendel's Law of Segregation

Mendel's Law of Segregation tells us that during meiosis, a diploid organism packages each allele individually when making its gametes. Gametes are sex cells that an organism uses to reproduce and create offspring. In humans, sperm is the male gamete, and eggs are the female gamete. This law ensures that each allele pair for a gene is separated and not packaged together into gametes. This process is important because when two gametes (one from the mother and one from the father) combine, they create an organism with a standard pair of alleles but with more genetic diversity.

Definitions in Mendel's Law of Segregation

To fully understand Mendel's Law of Segregation, it is essential to understand some key terms in reproduction, gametogenesis, and genetics.

Gametogenesis is the process of gamete formation, which requires meiosis. A diploid organism has two sets of chromosomes, with examples including humans, mammals, and most animals. In contrast, haploid organisms, such as male bees, male ants, and male wasps, have only one set of chromosomes.

A chromosome is a long strand of DNA that contains all the genes and genetic information of an organism. Diploid organisms have two pairs of each gene, with one set of chromosomes inherited from their mother and the other set from their father during reproduction and gamete fusion.

Meiosis is the process that enables the formation of gametes in sexual reproduction. It begins with a somatic, diploid cell, and involves two rounds of cell division to produce four haploid daughter cells.

Somatic cells are any cells in the body that are not gametes, such as heart cells, eye cells, and toenail cells. Gametes, on the other hand, are the cells that perform reproduction and include egg cells and sperm cells. The classification of cells as either somatic or gametes holds for all species, not just

Example of Mendel's Law of Segregation

Mendel's Law of Segregation can help us understand and explain many phenomena related to reproduction, genetics, and the inheritance of traits, including genetic diseases. Most genetic diseases are inherited in a recessive pattern, which means that the allele causing the disease has no effect if paired with a normal allele that codes for a normal phenotype. However, two copies of the recessive allele are needed, along with a mutated allele, for the disorder to appear in offspring.

Using Mendel's Law of Segregation, we can determine the probability of offspring inheriting the recessive allele and developing the disease. For example, if two parents are carriers of a recessive genetic disorder, such as cystic fibrosis, each has a 50% chance of passing the recessive allele to their offspring. If both parents pass the recessive allele to their child, the child will have the disorder.

Mendel's Law of Segregation explains why most offspring will be normal, as it ensures that each allele pair for a gene is separated and packaged individually into gametes. This process creates genetic diversity in offspring while also reducing the likelihood of inheriting.


Effects and symptoms of hemochromatosis
Effects and symptoms of hemochromatosis

Let's use the disorder hemochromatosis to study this. Hemochromatosis is a disorder of iron storage where too much iron is stored in places like the pancreas, the skin, the liver, the heart, and the joints (Fig. 1).

This excessive iron storage causes a syndrome called "Bronzed Diabetes", which is what it sounds like - a person has diabetes and has very tan, bronze-colored skin. They also have a really big heart (cardiomegaly), a big liver (hepatomegaly), painful joints, and sometimes neurological or brain problems.

Hemochromatosis has an autosomal recessive pattern of inheritance. Autosomal chromosomes are the non-sex chromosomes. In humans, the sex chromosomes are X and Y (Fig. 2).

The X and Y chromosomes of mammals, literally look like an X and a Y
The X and Y chromosomes of mammals, literally look like an X and a Y

Performing a Punnett square for the cross between two carriers of the hemochromatosis gene (Rr) can help us understand the possible outcomes for their offspring.

The Punnett square (Fig. 3) shows that each parent can produce two types of gametes, one with the normal allele (R) and the other with the hemochatosis allele (r). The offspring inherit one allele from each parent to determine their genotype.

The possible outcomes for the offspring are as follows:

  • 25% chance of inheriting two normal alleles (RR) and having a normal phenotype.
  • 50% chance of inheriting one normal allele and one hemochromatosis allele (Rr) and being a carrier like their parents. They will have a normal phenotype but are at risk of passing on the hemochromatosis allele to their own offspring.
  • 25% chance of inheriting two hemochromatosis alleles (rr) and having the disorder.

These outcomes follow the principles of Mendelian inheritance, specifically the Law of Dominance, Segregation, and Independent Assortment. The Law of Dominance states that the normal allele is dominant over the hemochromatosis allele, meaning that individuals with one normal allele will have a normal phenotype. The Law of Segregation explains how the parents package their alleles equally and randomly into gametes. The Law of Independent Assortment explains how inheriting one allele does not affect the offspring's ability to inherit other alleles at different genes.

Rr x Rr cross
Rr x Rr cross

We can see that 50% of offspring will have Rr genotype like both their parents, 25% will have RR genotype, and the last 25% will have rr genotype (Fig. 4).

Rr Carrier Mother x Rr Carrier Father and Offspring
Rr Carrier Mother x Rr Carrier Father and Offspring

Errors in gene or chromosome segregation can lead to genetic disorders and chromosomal disorders. These errors often occur during meiosis, the process of cell division that produces haploid gametes with half the number of chromosomes as the parent cell. There are two main types of errors: aneuploidy and polyploidy.

Aneuploidy occurs when there is an addition or subtraction of individual chromosomes, resulting in an abnormal number of chromosomes from what is standard for the organism. For example, a human with Down syndrome has an extra copy of chromosome in of 47 chromosomes instead of the usual 46. Aneuploidy can occur due to errors in meiosis, such as non-disjunction, where chromosomes fail to separate properly during cell division.

Polyploidy occurs when there is an addition of chromosome sets, resulting in an abnormal number of chromosomes from what is standard for the organism. This can occur naturally in some plant species, but it is rare in animals. Polyploidy can also occur due to errors in meiosis, such as the failure of chromosomes to separate during cell division.

Both aneuploidy and polyploidy can lead to various genetic and chromosomal disorders, including developmental abnormalities, intellectual disabilities, and cancer. It is important to understand the principles of Mendelian inheritance and meiosis to identify and diagnose these disorders.

Cancer Cells:

Yes, cancer cells often exhibit abnormal ploidy or chromosomal changes, which can contribute to their ability to grow and divide uncontrollably. For example, cancer cells may lose a whole chromosome or gain an extra copy of a chromosome, resulting in aneuploidy. These chromosomal changes can disrupt normal gene expression and alter the function of proteins involved in cell growth and division.

In some cases, aneuploidy can confer a selective advantage for cancer cells, allowing them to evade normal mechanisms of cell growth control and proliferate more rapidly. Aneuploidy can also lead to changes in the expression of genes involved in metabolism, DNA repair, and other cellular processes, which can contribute to the development and progression of cancer.

Overall, understanding the role of chromosomal changes in cancer development is an important area of research, as it can help to identify new targets cancer and our mechanisms this

Down Syndrome:

Down syndrome is a genetic condition due to aneuploidy at chromosome number 21. Instead of having a pair of chromosome 21's, individuals with Down Syndrome have three chromosome 21's. Hence, Down Syndrome is also called Trisomy 21 (Fig. 5).

Down Syndrome Karyotype
Down Syndrome Karyotype

Polyploid Plants:

Many cultivated plants are polyploid. We bred them to be this way; this is not a diseased state for them. Polyploid plants often have bigger, more bountiful yields (Fig. 6). Some examples of this include species of wheat, peanuts, strawberries, and coffee!

Fig. 6: Polyploid Strawberry. Texas Gateway.

Double Y Males:

We all know the genotype for the female sex is XX, and that of the male sex is XY. But the term double Y males refers to people with the genotype XYY. This genotype is often due to errors in meiosis and leads to this state of aneuploidy. The symptoms of this disorder are not usually drastic, but often these individuals are tall!

Mendel's Law of Segregation - Key Takeaways Mendel's Law of Segregation is a part of the trio of laws that make up Mendelian genetics. The other two laws in Mendelian genetics are the law of dominance and the law of independent assortment. Mendel's Law of Segregation states that alleles are packaged individually into gametes in a diploid organism. Mendel's Law of Segregation describes what happens during gametogenesis in mammals. During gametogenesis, meiosis occurs, leading to a somatic diploid cell producing haploid gametes. Errors in the segregation of alleles can lead to aneuploidy and polyploidy. Aneuploidy can be seen in chromosomal and genetic conditions like Down Syndrome.


Mendel's Law of Segregation

What is Mendel's law of segregation?

Mendel's Law of segregation is the second law of Mendelian inheritance.

What does Mendel's law of segregation state?

It states that when a diploid organism is making its gametes it packages each allele individually.

Which or what is not true according to Mendel's law of segregation?

It is not true that we inherit two alleles together. The truth is that we inherit alleles individually from both our parents, and then the maternal one and the paternal one combine to form an allele pair.

What is Law of segregation also known as? Explain why it is called so?

The law of segregation is also known as the law of purity of gametes. It is called this because alleles segregate or separate individually into gametes, so the gametes purely contain just one allele of a gene pair.

What is segregated in Mendel's law of segregation?

Alleles of a gene pair are segregated in Mendel's Law of segregation.

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