Mendel's Genetics:
Gregor Mendel lived from 1822-1884 and was known as the Father of Genetics for his extreme contributions to the knowledge of genetics. By the 1890’s, better microscopes were invented to allow various biologists like Mendel discover the basic facts of sexual reproduction and cell division. The focus of the study of genetics was then changed to actually comprehending what actually happens in the transfer of the traits inherited from parents to the children. During this time many biologists had concluded on various theories that explained heredity, but all were incorrect. Although he himself was too incorrect, Mendel was the only biologist to get the idea on the right track. Mendel’s ideas were finally recognized in 1900, even though they were published in 1866. By this time, Mendel had already died.
Early in Mendel’s adult life, Mendel spent being unimportant and unrecognized as he researched basic genetics and taught high school students math, physics, and Greek in the Czech Republic. After this, and later in his life, he became very involved in his monkhood and became his monastery’s abbot, quitting his scientific work. However, before he became the monkhood leader, he would research genetics and the basic principles of heredity by studying pea plants. These conclusions he also could use to describe the basic mechanisms of heredity amongst people and animals because these mechanisms were basically the same for all complex life forms. Mendel discovered that certain traits in the Pisum sativum (pea plant) were quite evident. He discovered that a few certain traits showed up in the offspring of the original plants, without any mixing of the parent characteristics.
It is very important to understand that in this example, the original parent pea plants were pure-bred for their individual seed color. That is to say that one parent was homozygous yellow and the other was homozygous green. The first generation was a mixture of the yellow and green genes, yet all of the seed colors were yellow because that is the dominant gene. In the f2 generation, there was a green seed because the gene was still passed onto the next generation. This is because in the first generation (f1) the offspring's genotype was “YG” because each of the parent plants were purebred yellow and green. Therefore, each of the babies received both of the genes. The reason all of them turned out to be yellow was because of the yellow gene being dominant and overpowering the green gene. However, the green gene is still passed on to the next generation because it makes up that new parent’s genotype. This allows the next plant to have a possibility of being green (if of course the other parent has a green, recessive gene). Mendel’s observations from the many experiments led him to conclude:gst people and animals because these mechanisms were basically the same for all complex life forms. Mendel discovered that certain traits in the Pisum sativum (pea plant) were quite evident. He discovered that a few certain traits showed up in the offspring of the original plants, without any mixing of the parent characteristics. He concluded seven various traits that were easily recognized:
One important observation was that these traits did not show up in the offspring plants with intermediate forms. This was extremely important because it proved that the leading theory in biology, that inherited traits blend from generation to generation, was incorrect. This was the only known theory to explain the reason that children did not look exactly like their parents. This theory was very popular in the 19th century and was called the “blending theory.” Also, Charles Darwin proposed another wrong theory to explain inheritance, but it was equally as incorrect. His theory was known as “pangenesis” and proposed that the hereditary “particles” in our bodies were affected by the things that we do during our lifetime. As events occur in our lives, our hereditary “particles” change. He thought that then, these altered particles migrated through the blood to our reproductive cells and then could be inherited by your children. This was merely a variation of Lamarck’s again incorrect belief of “inheritance of acquired characteristics.”
Mendel chose to experiment with the pea plants because they grew very easily in large amounts and their reproduction was easily manipulated. This is because pea plants have both female and male reproductive parts. This allows the plants to reproduce by either self-pollinating or by cross-pollinating with another plant. Mendel was able to successfully cross-pollinate purebred plants with particular traits with others and discern various observations concerning the outcome over various generations. These experiments were the base of his conclusions about genetic inheritance nature.
When cross-pollinating the pea-plants, Mendel noticed many things. First, he noticed that the plants either produced yellow or green pea seeds and found that the first offspring generation always had yellow seeds even though he cross-bred a yellow and a green plant. Although, he also noticed that in the second offspring generation, he noticed that there was a 25% chance that there would be a green seed too, along with the 75% chance of yellows. Mendel cross-pollinated a yellow pea plant and a green pea plant, but for some reason, in the first generation, all of the offspring were yellow. Once these matured, one of the first offspring had another generation of pea plants and there was a 3:1 ratio of yellow to green plants. There were three yellow plants and one green plant. This also occurred in later generations where Mendel realized that this was the basic regularity of the inheritance of basic mechanisms. After this, Mendel came to three important conclusions:
It is very important to understand that in this example, the original parent pea plants were pure-bred for their individual seed color. That is to say that one parent was homozygous yellow and the other was homozygous green. The first generation was a mixture of the yellow and green genes, yet all of the seed colors were yellow because that is the dominant gene. In the f2 generation, there was a green seed because the gene was still passed onto the next generation. This is because in the first generation (f1) the offspring's genotype was “YG” because each of the parent plants were purebred yellow and green. Therefore, each of the babies received both of the genes. The reason all of them turned out to be yellow was because of the yellow gene being dominant and overpowering the green gene. However, the green gene is still passed on to the next generation because it makes up that new parent’s genotype. This allows the next plant to have a possibility of being green (if of course the other parent has a green, recessive gene). Mendel’s observations from the many experiments led him to conclude:
Early in Mendel’s adult life, Mendel spent being unimportant and unrecognized as he researched basic genetics and taught high school students math, physics, and Greek in the Czech Republic. After this, and later in his life, he became very involved in his monkhood and became his monastery’s abbot, quitting his scientific work. However, before he became the monkhood leader, he would research genetics and the basic principles of heredity by studying pea plants. These conclusions he also could use to describe the basic mechanisms of heredity amongst people and animals because these mechanisms were basically the same for all complex life forms. Mendel discovered that certain traits in the Pisum sativum (pea plant) were quite evident. He discovered that a few certain traits showed up in the offspring of the original plants, without any mixing of the parent characteristics.
It is very important to understand that in this example, the original parent pea plants were pure-bred for their individual seed color. That is to say that one parent was homozygous yellow and the other was homozygous green. The first generation was a mixture of the yellow and green genes, yet all of the seed colors were yellow because that is the dominant gene. In the f2 generation, there was a green seed because the gene was still passed onto the next generation. This is because in the first generation (f1) the offspring's genotype was “YG” because each of the parent plants were purebred yellow and green. Therefore, each of the babies received both of the genes. The reason all of them turned out to be yellow was because of the yellow gene being dominant and overpowering the green gene. However, the green gene is still passed on to the next generation because it makes up that new parent’s genotype. This allows the next plant to have a possibility of being green (if of course the other parent has a green, recessive gene). Mendel’s observations from the many experiments led him to conclude:gst people and animals because these mechanisms were basically the same for all complex life forms. Mendel discovered that certain traits in the Pisum sativum (pea plant) were quite evident. He discovered that a few certain traits showed up in the offspring of the original plants, without any mixing of the parent characteristics. He concluded seven various traits that were easily recognized:
- Flower Color- purple or white
- Flower Position- axial or terminal
- Stem Length- long or short
- Seed Shape- round or wrinkled
- Seed Color- yellow or green
- Pod Shape- inflated or constricted
- Pod Color- yellow or green
One important observation was that these traits did not show up in the offspring plants with intermediate forms. This was extremely important because it proved that the leading theory in biology, that inherited traits blend from generation to generation, was incorrect. This was the only known theory to explain the reason that children did not look exactly like their parents. This theory was very popular in the 19th century and was called the “blending theory.” Also, Charles Darwin proposed another wrong theory to explain inheritance, but it was equally as incorrect. His theory was known as “pangenesis” and proposed that the hereditary “particles” in our bodies were affected by the things that we do during our lifetime. As events occur in our lives, our hereditary “particles” change. He thought that then, these altered particles migrated through the blood to our reproductive cells and then could be inherited by your children. This was merely a variation of Lamarck’s again incorrect belief of “inheritance of acquired characteristics.”
Mendel chose to experiment with the pea plants because they grew very easily in large amounts and their reproduction was easily manipulated. This is because pea plants have both female and male reproductive parts. This allows the plants to reproduce by either self-pollinating or by cross-pollinating with another plant. Mendel was able to successfully cross-pollinate purebred plants with particular traits with others and discern various observations concerning the outcome over various generations. These experiments were the base of his conclusions about genetic inheritance nature.
When cross-pollinating the pea-plants, Mendel noticed many things. First, he noticed that the plants either produced yellow or green pea seeds and found that the first offspring generation always had yellow seeds even though he cross-bred a yellow and a green plant. Although, he also noticed that in the second offspring generation, he noticed that there was a 25% chance that there would be a green seed too, along with the 75% chance of yellows. Mendel cross-pollinated a yellow pea plant and a green pea plant, but for some reason, in the first generation, all of the offspring were yellow. Once these matured, one of the first offspring had another generation of pea plants and there was a 3:1 ratio of yellow to green plants. There were three yellow plants and one green plant. This also occurred in later generations where Mendel realized that this was the basic regularity of the inheritance of basic mechanisms. After this, Mendel came to three important conclusions:
- The inheritance of each trait is determined by the “factors” or “units” (genes) that are passed on to descendents unchanged
- Individual inherits one such unit from each parent for each trait
- A trait may not show up in an individual, but can still be passed onto the next generation for the characteristic to then be obtained.
It is very important to understand that in this example, the original parent pea plants were pure-bred for their individual seed color. That is to say that one parent was homozygous yellow and the other was homozygous green. The first generation was a mixture of the yellow and green genes, yet all of the seed colors were yellow because that is the dominant gene. In the f2 generation, there was a green seed because the gene was still passed onto the next generation. This is because in the first generation (f1) the offspring's genotype was “YG” because each of the parent plants were purebred yellow and green. Therefore, each of the babies received both of the genes. The reason all of them turned out to be yellow was because of the yellow gene being dominant and overpowering the green gene. However, the green gene is still passed on to the next generation because it makes up that new parent’s genotype. This allows the next plant to have a possibility of being green (if of course the other parent has a green, recessive gene). Mendel’s observations from the many experiments led him to conclude:
- The Principle of Segregation- Segregation of alleles in the production of sex cells (to the left)
- The Principle of Independent Assortment- Traits are transmitted to the offspring independently (below)
- The Principle of Dominance- Both recessive and dominant traits are passed down to the offspring, but the dominant trait in the genotype results as the phenotype (bottom left)
All three of these principles are similar because they describe the way the pea plants give the hereditary traits to their offspring. In the Principle of Segregation, Mendel said that the allele pairs of the genotypes of the pea plants separate in the formation of gametes. He also concluded that they would randomly reunite in fertilization. In the Principle of Individual Assortment, Mendel stated that during the transmission of traits to the offspring from the parent, the allele pairs divide independently in the gamete formation. This causes the traits to be given to the offspring independently of one another.
In the Principle of Dominance, which is considerably different than these two, Mendel stated that the dominant trait in a genotype will overpower the recessive one and therefore, will become the phenotype. In this law, you have to notice that (referring to the picture below) even though there is purebred yellow and a purebred green pea pods that breed together, only the green pods' phenotypes remain evident. This is due to the Law of Segregation and Mendel's new discovery of the Law of Dominance. In the Law of Segregation, Mendel stated that each allele is separated and form new gametes. This is true because if you take that example, gg x GG (gg- Yellow Pod, and GG- Green Pod) and try to figure out the possible gametes, Gg is the only one! This makes it evident that even with the Law of Segregation, the Law of Dominance is prominent. Whichever allele is dominant in the genotype is the one that will be seen as the phenotype.
Aside from these principles, many modern textbooks seem to forget to include that Mendel’s theory actually proved Lamarck’s theory of the inheritance of acquired characteristics wrong. This theory was described in the Early Theories of Evolution. Although this was a major discovery, Mendel rarely receives credit for this because his work was very unpopular until very long after Lamarck’s ideas were used very often and were believed to be correct.
Aside from these principles, many modern textbooks seem to forget to include that Mendel’s theory actually proved Lamarck’s theory of the inheritance of acquired characteristics wrong. This theory was described in the Early Theories of Evolution. Although this was a major discovery, Mendel rarely receives credit for this because his work was very unpopular until very long after Lamarck’s ideas were used very often and were believed to be correct.
Meiosis:
Meiosis is a process of cell division that produces sperm cells and egg cells that contain 1/2 the number of chromosomes as the body cells of their parents. There are several stages of meiosis that occur in this order:
1. Prophase I
2. Metaphase I
3. Anaphase I
4. Telophase I
5. Prophase II
6. Metaphase II
7. Anaphase II
8. Telophase II
Important Info:
1. Each gamete is a combination of the parents' traits in a unique form and because of this, we have so many types and variations in sexual reproduction
2. The sex cells each have 1/2 the chromosomes needed to conceive a child or offspring, which is why a sperm cell and an egg cell are needed
3. The crossing over of traits can occur in prophase I (which creates more offspring variations)
4. Meiosis involves two divisions, not one
Meiosis is just like the Law of Separation-
-the gametes come together in fertilization
-more variations are created as a result of this
1. Prophase I
2. Metaphase I
3. Anaphase I
4. Telophase I
5. Prophase II
6. Metaphase II
7. Anaphase II
8. Telophase II
Important Info:
1. Each gamete is a combination of the parents' traits in a unique form and because of this, we have so many types and variations in sexual reproduction
2. The sex cells each have 1/2 the chromosomes needed to conceive a child or offspring, which is why a sperm cell and an egg cell are needed
3. The crossing over of traits can occur in prophase I (which creates more offspring variations)
4. Meiosis involves two divisions, not one
Meiosis is just like the Law of Separation-
-the gametes come together in fertilization
-more variations are created as a result of this
How Does All of This Affect the Twins' Situation?:
Referring to Mendel’s Law of Segregation, the twins having children might be affected in several ways. Surprisingly, even though the twins each have the exact same DNA which would technically make their children siblings, the kids would not look exactly alike as their cousins. In Mendel’s Principle of Separation, it says that the various alleles that are responsible for a certain trait split up and separate until fertilization of an egg and a sperm. Therefore, unless the parents were purebred in every single genotype of a trait, the kids would each have a possibility of looking different because of the recessive genes. Aside from the obvious gene parts of this, environmental factors play a major role in how a child’s traits are. Even though each parent grew up in the same household as their sibling, there are distinct, unique characteristics about each person. This will influence the way their children behave and how they look. For example, if one family moves away from the same area they grew up in, the two families have a higher chance in being different than one another because of two different settings they live in. No two people are exactly alike, even if they are twins. This is because different things affect people and how they are emotionally, physically, and mentally.
In the University of Western Ontario, new research has been conducted, analyzing the differences between identical twins. Shiva Singh, a Molecular geneticist has been working with Dr. Richard O’Reilly, a psychiatrist to see if identical twins or monozygotic twins are the exact same genetically. Using the common disease, schizophrenia, the two used a pair of identical and monozygotic twins, one with the disease, and the other without it, to see if the other would develop it overtime as well. Before this research, it was believed that if one twin developed the disease, the other would have a 100% chance of developing it too. However, this is not the case. If one twin does develop the disease, the other just has a 50% chance of developing the disease as well, proving that in monozygotic twins, their genetic makeup is not identical, or the disease involves non-genetic effects. Concluding, that the twins are not the exact same person. This would make the children not exactly alike either. Their parents are not the same, so neither would each new family member, just like every ordinary family. The difference between any average family and these two families is that the cousins will look remarkably similar, yet not identical.
The Law of Dominance will affect how the children look because of the dominant and recessive traits that are handed down from generation to generation. Each parent has the same genotype for each trait as their sibling and each of those traits has their own dominant features. This causes the children to have a higher chance of inheriting the dominant genes more than the recessive genes which will cause the children to look alike, even though they are cousins. There is a small possibility that some of the cousins will inherit the recessive genes that each parent carries around, but that is a small chance because the dominant trait typically blocks out the recessive one. Even though the children will look similar, they will not look exactly the same because of the possibility of this.
In the University of Western Ontario, new research has been conducted, analyzing the differences between identical twins. Shiva Singh, a Molecular geneticist has been working with Dr. Richard O’Reilly, a psychiatrist to see if identical twins or monozygotic twins are the exact same genetically. Using the common disease, schizophrenia, the two used a pair of identical and monozygotic twins, one with the disease, and the other without it, to see if the other would develop it overtime as well. Before this research, it was believed that if one twin developed the disease, the other would have a 100% chance of developing it too. However, this is not the case. If one twin does develop the disease, the other just has a 50% chance of developing the disease as well, proving that in monozygotic twins, their genetic makeup is not identical, or the disease involves non-genetic effects. Concluding, that the twins are not the exact same person. This would make the children not exactly alike either. Their parents are not the same, so neither would each new family member, just like every ordinary family. The difference between any average family and these two families is that the cousins will look remarkably similar, yet not identical.
The Law of Dominance will affect how the children look because of the dominant and recessive traits that are handed down from generation to generation. Each parent has the same genotype for each trait as their sibling and each of those traits has their own dominant features. This causes the children to have a higher chance of inheriting the dominant genes more than the recessive genes which will cause the children to look alike, even though they are cousins. There is a small possibility that some of the cousins will inherit the recessive genes that each parent carries around, but that is a small chance because the dominant trait typically blocks out the recessive one. Even though the children will look similar, they will not look exactly the same because of the possibility of this.
This Law of Independent Assortment helps explain as to why there is a possibility that the children of each family will not look exactly alike. In this law, Mendel concluded that each individual allele for a trait independently create a pair for trait at fertilization, just like in the Law of Separation. Referring to meiosis, a type of cell division, the parent genotypes each split and then came together, creating a “mixture” of each parent’s genotype. This law created an explanation of how there such a diversity in the genotype of the offspring compared to the genotype of the parent. Each offspring inherits a dominant and recessive gene from the parent. Although a gene may be recessive, there is still a possibility that the child may have a phenotype of that recessive gene, depending on what kind of genotype the other parent has. This will allow each child each family has to possibly look different because of the recessive genes that play a part in the child’s genotype. Using the example shown in the video, each mother has blonde hair, a recessive gene. For this particular example, we will use “bb” to explain their genotype. Also in this example, each father had brown hair, a dominant gene. For this example, we will use “BB or Bb” to explain their genotype. Referring to the first example to the right, we can see that in each child’s genotype, both of the parents’ genotypes are involved in it. Although, the brown hair is shown as the phenotype because it is the dominant gene. Now, referring to the example to the left, we can see that each child inherits a mixture of both parents’ genotypes. Although they are not all identically the same, like the first example, each genotype is still a mixture of each parental genotype to make different possibilities.