(HER) Mendel's Law of Genetics Lesson

Mendel's Law of Genetics

Can an organism's surroundings or environment have any effect on the genes that determine its physical and behavioral traits? Nature refers to the innate qualities of an organism such as genetics. Nurture refers to the care provided by parents or environmental influences that can lead to development of an organism. Do you think nature or nurture has a greater influence on how our genes are expressed? Mendel's paper was about the outcome of the experiments he conducted in the monastery garden to study the inheritance of certain traits in pea plants. Mendel studied the following characteristics of pea plants:

  • Stem height (tall or short)
  • Flower position (terminal which is near the top of the stem or axial which is at the stem's side)
  • Flower color (purple or white)
  • Seed color (yellow or green)
  • Pod color (green or yellow)
  • Pod shape (inflated and smooth or constricted and pinched)
  • Seed shape (round or wrinkle)
  • Seed coat color (gray or white)

 

Mendel's seven characters Table Image, description below

See description of diagram Links to an external site.

 

Mendel's experiments consisted of three main steps.

  • allowed the peas to self-pollinate until true breeding took place.
  • cross-pollinated two varieties from P generation. Offspring= F1 generation.
  • F1 generation bred. Offspring= F2. Monohybrid cross is 1 gene with 2 alleles.

First, he obtained purebred pea plants so that he could observe a specific trait. These plants were self-pollinated. This occurs when the pollen and pistil from within the same pea plant are used in reproduction. It took many generations to develop purebred pea plants. These purebred pea plants were the P1 or the parental generation. Mendel used a method called cross-pollination to mate a purebred tall with a purebred short pea plant and all of the offspring were tall. The tall plants from that cross were called the F1 generation.

Mendel Pea Plants, see description below

See description of diagram Links to an external site.

 

Why were all the offspring tall especially when one parent was short? What happened to the trait for shortness? Mendel got the same results each time he crossed a tall purebred with a short purebred plant. All of the offspring had the same phenotype.   The pea plants from the F1 generation were tall. The third step in Mendel's experiments consisted of self-pollinating the offspring from the F1 generation. The trait for shortness reappeared. About ¼ of the pea plants were short and ¾ of the pea plants were tall. This mixture of tall and short pea plants was called the F2 generation.

Mendel performed many experiments to study the other traits of pea plants. The results and observations were the same. Round seeds were produced in the F1 generation when Mendel crossed purebred round seeds with purebred wrinkle seeds. Mendel concluded that factors contain the information in a plant that determines a certain trait. Those factors are now known as genes. Mendel believed that the plants inherited genes from each parent. One of those genes is more powerful or dominant. Although the weaker gene's trait is not expressed, it is still present in the organism and it can be passed on to the next generation. Mendel also proposed that the paired genes for each trait segregate or separated during gamete formation. The offspring will get half of its genes from one parent and the other half from the other parent during sexual reproduction.

Using several animated sequences, this video below (adapted from the Dolan DNA Learning Center) demonstrates the principle of dominance, which is fundamental to modern genetics. By crossing two pea plants, each pure-bred for a given trait like pea color, we learn why only the dominant trait—in this case, yellow pea color—appears in any and all offspring. We also learn why some offspring in subsequent generations exhibit the recessive trait—green—even though this may not have been apparent in the previous generation.

 

Watch the following presentation to learn more.

 

 

In the following video, Biologically Speaking: Genetics and Heredity, we explore the history of genetics, and learn how traits are passed from one generation to another. Dominant and recessive traits are described, as well as the differences between pure and hybrid traits. These are illustrated through use of the Punnett square. We see the composition of DNA and its role in reproduction. The processes of mitosis and meiosis are colorfully detailed - with emphasis on the division and infinite variety of genetic material. The program explains how mutations occur, and about the present and possible future role of genetic engineering in such fields as agriculture and medicine. The video also examines humankind's responsibility to carefully weigh not only the probable benefits but also the possible consequences of future developments in this exciting scientific domain. The video is approximately 16 minutes long. Pause the video when necessary to make notes.

 

Watch the following presentation.

 

 

[CC BY 4.0] UNLESS OTHERWISE NOTED | IMAGES: LICENSED AND USED ACCORDING TO TERMS OF SUBSCRIPTION