How certain characteristics are transmitted from one generation to another


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Rules of Mendelian Genetics

Mendel''s Law is the study about how a certain characteristics are transmitted from one generation to another in an organism. This study was derived from an Austrian monk, Gregor Mendel (1822 'C 1884) who is considered as the father of genetics. He believed that natural laws such as those that govern inheritance could be explained as mathematical relationships. In his experiments, Mendel used ordinary pea plants to study the traits, he pair these pea plants with considering the control over each reproduction to prevent the pea plant from self fertilizing. The traits that are being observed are the colour of a plant''s flower, the location on the plant, the shape and colour of the pea pods, the shape and colour of the seeds and the length of the plant stems. Pea plants are used because they are easily available and can be manipulated in large amount within a short period of time. (Starr, Evers & Starr, 2010)

Mendel''s approach for his experiment was to transfer pollen from the stamen (which is the male reproductive organ that contains male sex cells) and to the pistil (the female sex cell which contain female reproductive organs) of another pea plant. In the first experiment, he took two pea plants with true breeding variant; one with round seed and another with wrinkled seed. The offspring that were produced in the first generation (F1 generation) had all round seeds. This shows that the pea plant will only take the dominant trait that is the round seeds. Next, Mendel crossed two of the F1 generation plant together, he obtained a result of 75% of the plant is round seeds whereas 25% of the pea plants are wrinkled seeds. Based on this result, a ratio of approximately 3:1 will be deduced for the traits in F2 generation. As a result of these experiments, Mendel was able to state three generalizations about the way characteristics are transmitted from one generation to the next in pea plants. (Science Clarified, 2010).

From this pea plants experiment, Mendel derived 3 theories that support on genetic inheritance

? Mendel's first principle of genetics, the law of segregation states that the sex cell of a plant or animal may contain one factor (allele) for different traits but not both factors needed to express the traits. Each offspring, however, would only display the characteristics of one parent and not a blend of the two different characteristics of the parents.

? Mendel's second principle of genetics, the law of independent assortment states that characteristics are inherited independently from other characteristics. Any trait in a generation is independent of other traits if the parents of the generation have two or more traits that vary from each other.

? Mendel's third principle, principle of dominance states that each inherited characteristic is determined by two heredity genes, one from each parent which determines whether a gene will be dominant or recessive. This means that the trait of one parent must be dominant over the trait of the other parent, and so the dominant trait would be displayed by the offspring. (Minnesota State University, 2010; Nigel, D. P.,2006 ).

Introduction to traits of family

There have been variations in different characteristic in my family genes. The variations of the genes are mainly caused by inheritance from my parents who carry a genotype of certain traits; this trait is passed on from one generation to another. The dominant allele of the traits of the genotype would be the phenotype of the offspring. I have chosen to look into the appearance of one-sided dimples and blood types in my family genes.

Cheek dimples occur when the muscles underneath the surface of the skin are shorter than the skin on top, so when you smile, the muscle pulls the skin at its attachment point, thus folding the top skin as it is pulled back. Chin dimples are actually a cleft chin in which the bones do not fuse completely and the outer skin lies on top of the cleft bone, revealing the structure underneath. In most cases, facial dimples appear on the cheeks, and they are typically not visible until someone smiles. However, some people only have a dimple on one side; this physical trait can actually be rather endearing (Smith, S. E., 2010). The look of dimples can also vary; as an inherited trait, unusual dimples can be passed on through multiple generations of a family. Dimples occurrence can be relatively related to genetic inheritance, dimples are dominant trait that will be pass on from the parents (K-show, 2008). If you inherit the genes for dimples, there may be other factors during your development that could lengthen the muscles, or allow full closure of the cleft chin.

Next, all humans can be typed for the ABO blood group. There are four principal types: A, B, AB, and O. There are two antigens and two antibodies that are mostly responsible for the ABO types. The specific combination of these four components determines an individual's type in most cases (Dennis O'Neil, 2010). Every individual inherits one blood type allele from each their biological mother and their biological father. Based on the alleles of a person, the blood group genotype of the person can be determined. The O allele is the recessive allele amongst the blood group alleles. A person with blood group A can have either IA IA or IA IO as their genotype. Type B blood is produced when an individual has either genotype IB IB or IB IO. Genotype IO IO results in type O blood while type AB blood results from genotype IA IB (Windelspecht, 2007).


Based on the phenotype occurrence in my family, I have come out with a research based on the traits on genotypes in my family. In this research, I''ve taken consideration of the variation in traits from my parents and siblings; my brother and sister.

One-sided dimples

In my family, my father carries the gene of one-sided dimple, my mother do not contain dimple, my sister contains one-sided dimple and my brother and me do not contain dimple. Based on the data I had collected, a pedigree chart is drawn to illustrate the traits in my family.

Figure 1 : pedigree chart on one-sided dimple of my family

Since one-sided dimple is considered to be an autosomal dominant traits. From this pedigree chart illustrated above, my father have a phenotype of one-sided dimples, he would be either be carrying a homozygous dominant (DD) or heterozygous dominant (Dd) genotypes. On the other hand, my mother would be carrying the homozygous recessive (dd) genotype. My sister also carries the one-sided dimple trait; therefore she also be either having the genotype of DD or Dd. My brother and I do not have dimples, therefore why we would have carried the dd trait.

Since, allele of our genes can''t be seen; therefore we could only predict which of the possibility outcome the genotype of each individual belongs to. Based on the different possible allele, I have built a Punnet''s square to list out all the possibility outcomes of the genotypes outcome of the offspring from my parents depending on which genotype my parent possesses.

D d

d Dd dd

d Dd dd



Dd Dd

d Dd Dd

( ii )

( i ) ( ii )

Figure 2 : Punnet square based on parents genotype?

Based on the Punnet square ( i ), the possibility of homozygous dominant allele is being used. From this point of view, the outcome of a mixture of DD and dd would result in a Dd gamete. Therefore, based on the result, the offspring produced would be heterozygous dominant (Dd). The probability of the offspring produce by my parents to be heterozygous dominant would takes up 100%, this means that there would not be any possibilities of any offspring not having one-sided dimples. In addition, no offspring would also me homozygous dominant to one-sided dimples.

On the other hand, in Punnet square ( ii ), heterozygous dominant (Dd) allele is being used, the possibility outcome of allele from the combination of Dd and dd would result in a Dd or dd offspring. The probability of a heterozygous dominant (Dd) gamete would be 50%, whereas the probability of the homozygous recessive (dd) gamete would also be 50%. There would not be any homozygous dominant offspring with one-sided dimple being produced.

After analysing both the Punnet square, I came to conclusion that that my family follows the genotype of Punnet square ( ii ). This is because in my family, among the siblings, we have a variation between having one-sided dimples and not having dimples. Therefore, from the possibility of Punnet square ( i ), all the offspring would have dimples. Nevertheless, in my family, my brother and I do not have dimples whereas my sister have one-sided dimple. So, it can be said that the possibilities in Punnet square ( ii ) would be much more accurate. It shows that there are variations between gametes which have and have not got one-sided dimples. This could clearly explains why the occurrence of one-sided dimples only on my sister.

Blood type

A blood test had been carried out to determine our blood type in my family. From the result, it is shown that my father is tested to be blood group O, my mother is tested to be blood group A, my brother is tested to be blood group O, my sister is tested to be blood group A and lastly I am tested to be blood group O. Based on the data I had collected, a pedigree chart is drawn to illustrate the traits in my family.

Figure 3 : Pedigree chart of blood group in my family

From the pedigree chart, my father has blood group O, the possible genotypes for his allele would be IoIo. This would also apply to my brother and I, we both also contain the possible genotype allele of IoIo. On the other hand, my mother has blood group A, the possible genotypes for her allele would be IAIA or IAIO. My sister also has blood group A, she would also have the possible genotypes for her allele is IAIA or IAIO.

By sorting out the possible genotypes in the allele, the data will be analysed into a Punnet table for a clearer outlook on all the possibilities from the combination of both the genotypes from my parents. The Punnet square will show the different combination that will result in a variation of offspring.








( i ) ( ii )

Figure 4 : Punnet square based on parents genotype

Based on the Punnet square ( i ), the genotypes of my father''s allele is IOIO , whereas my mother''s possible genotype is stated as IAIA . The outcome of this mixture results in the possibility of an offspring with only IOIA, which is blood group A. The probability of the offspring becoming a blood group A would then be 100%. None of them would be of blood group O.

In Punnet square ( ii ) the genotype of my father''s allele is IOIO, whereas my mother''s possible genotype is IAIO . The possible genotypes of the offspring produced by this combination of alleles will be genotype IOIO and genotype IAIO. The offspring could have a variation of blood type O or blood type A. The possibility of getting blood type O is 50% and the possibility of getting blood type A is also 50%.

After analysing both the Punnet square, I can conclude that my family follow the genotypes as stated in Punnet square ( ii ). This is because in my family, among the siblings, we have a variation between blood group A and blood group B. Therefore, from the possibility of Punnet square ( i ), all the offspring would result in having blood group O. Nevertheless, in my family, my sister has blood group A whereas my brother and I have blood group O. So, it can be said that the possibilities in Punnet square ( ii ) would be much more accurate. It shows that there are variations between gametes which have the different group type. This could clearly explain why the occurrence in variance of different blood type within different people.



The study of Mendel''s Law leads us to enhance more on our genetic inheritance. Knowing our inheritance may help us to study a large range of different traits; like hair colour, iris colour, dimples, and eyes. We will be able to notify and recognize the different genetic variation, which will also help in preventing certain disorder from spreading through reproduction. A few of the disorder that are genetically inheritance are like Down''s syndrome, Turner syndrome, sickle-cell anemia, colour blindness and haemophilia. Prevention towards this kind of disorder will widely safe many misfortune life of infants.

Mendel''s Law do not only emphasis on human trait, it is used in many agricultural field to improve the production of crops. The seeds of the corn plant is modified and paired genetically to improve its taste, colour, quantity and quality. These seed are being paired to obtain better traits from different types of fruits. The seasonal fruits can be planted all year round now, the fruits are mostly seedless; all these are from the discovery of genetic inheritance.

Not only that, Mendel''s law had also helped me in this research regarding the genotype of different traits in my family. For one-sided dimples, I''ve found out from the Punnet square that, my father is heterozygous dominant pairing with my mum with homozygous recessive that will result in a mixture of heterozygous dominant and homozygous recessive offspring. For the blood type, I''ve found that my father is is IOIO, whereas my mother''s possible genotype is IAIO.

In conclusion, Mendel''s law can be used to illustrate inheritance traits; the Punnet''s square can help us visualize all the genotype of the traits. This enables us to learn our genotypes based on our phenotypes shown, that is the one-sided dimple and blood type. It is important for us to study and understand our patterns of inheritance.

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