Mendel and His Pea Plants Mendel and His
- Slides: 35
Mendel and His Pea Plants
Mendel and His Pea Plants Gregor Mendel • Austrian • Recommended to enter an abbey by his physics teacher • Becoming a friar allowed Mendel to continue his studies in various science fields without having to pay for it • Mendel was interested in astronomy, physics, meteorology, beekeeping, and selective breeding
Mendel and His Pea Plants What is selective breeding? Selective breeding is agriculture! It is breeding plants or animals for specific traits. • pest resistant corn • stronger oxen • sheep with thicker wool Can you think of others? People have been doing selective breeding for thousands of years.
Mendel and His Pea Plants wild wheat we eat wild corn
Mendel and His Pea Plants Mendel started his selective breeding experiments with mice. However, the head of the abbey was not happy about using and breeding animals. So Mendel switched to pea plants.
Mendel and His Pea Plants It was a great decision! Pea plants are glorious little plants! • Reproduce quickly • Have easily observed traits • Have DISTINCT traits – The traits are “this” OR “this. ” There are no ranges. For example, peas are either green or yellow … not green, yellowish-green, greenish-yellow, or even chartreuse.
Mendel and His Pea Plants Another great reason to use pea plants is you can control which plants are reproduced. pollen (sperm cells) pistil For plants to reproduce, pollen needs to get to a plant’s pistil. Plants can do this themselves. This is selfpollination. Or you can take pollen from one plant and put it on the pistil of another. This is called cross-pollination.
Mendel and His Pea Plants Mendel started with true-breeding plants • Offspring are the same as the parent • What you start with is what you get True-breeding plants self-pollinate
Mendel and His Pea Plants Word Definition a plant that Trueproduces breeding offspring with traits that are like the parents Picture
Mendel and His Pea Plants Mendel allowed some plants to self-pollinate. Some plants he cross-pollinated. Why did Mendel cross-pollinate? Cross-pollination introduces VARIATION!
Mendel and His Pea Plants Word Definition when the pollen of one Crossplant reaches pollination the pistil of a flower on a different plant Picture
Mendel and His Pea Plants In daughter generations (the offspring), Mendel was collecting data for what things LOOKED like. What something looks like is the phenotype.
Mendel and His Pea Plants Word Definition how a trait appears or is Phenotype expressed (what it looks like) Picture blue flower
Mendel and His Pea Plants But what makes something look a certain way? What gave Mendel yellow peas or white flowers? Genotypes! We inherit two sets of chromosomes – one from each parent. On each chromosome, there are genes that code for phenotypes. You inherit one gene from your mother and one gene from your father. These different forms of the genes are called alleles. The combination of these alleles is your genotype.
Mendel and His Pea Plants Word Definition Gene section of a chromosome that has genetic information for one trait Picture
Mendel and His Pea Plants Word Definition Picture blue flower Allele different forms of a gene brown flower
Mendel and His Pea Plants Word Definition the two alleles that control the Genotype phenotype of a trait Picture Gg for green peas
Mendel and His Pea Plants For certain phenotypes – like those measured by Mendel in the pea plants – you only need those two alleles to code for what something looks like. Those two alleles make the genotype for that specific phenotype. Let’s look at what Mendel did with his true-breeding plants when he looked at pea color…
Mendel and His Pea Plants Mendel bred a true-breeding pea plant that produced green peas with a true-breeding pea plant that produced yellow peas. Then he bred two pea plants to create a 2 nd generation. + 2 nd generation + Wait! What? !?
Mendel and His Pea Plants • To figure why this happened with the phenotypes, we need to look at the plants’ genotypes. • In pea plants, green peas are the dominant genotype. This means that it is also the more common phenotype seen. • A dominant genotype means that will be the genotype that “wins. ” This is the trait that is expressed in the phenotype. • If either pea plant gives its offspring a green pea gene (the dominant one), then the peas will be green.
Mendel and His Pea Plants Word Definition allele that Dominant blocks another allele and is trait expressed in the phenotype Picture green pea color is dominant to yellow
Mendel and His Pea Plants That makes the yellow pea color recessive. Recessive genes are more rare, and they create less frequently seen phenotypes. For something to show a recessive phenotype, it needs two of the recessive genes. Why? Because if it had one recessive gene and one dominant gene, the dominant gene would be expressed in the phenotype.
Mendel and His Pea Plants Word Recessive trait Definition Picture allele that is blocked by another allele yellow peas are recessive
Mendel and His Pea Plants Let’s look at the genotypes of the pea colors. This is a Punnett Square. It allows us to easily see ratios of offspring for simple genotypes.
Mendel and His Pea Plants You place the genotypes of each parent on the top and the left sides of the square. Let’s start with the true-breeding plants from our example: one plant that only produces green peas and another that produces only yellow peas. G G We are looking at green vs. yellow. Since green is dominant, we will use a “G” for green and “g” for yellow. Always use capital letters for the dominant allele.
Mendel and His Pea Plants We know the genotype of the plants that produce yellow peas. Yellow peas are a recessive genotype. So the two gg alleles would be _______. Remember, we use the code based on the dominant genotype, so lowercase “g” g g means yellow. If the genotype were Gg, what color G would the peas be? green, because there is a dominant allele (G) G
Mendel and His Pea Plants Now, we separate the alleles. Remember, we get one set of genes from our father and one from our mother. Let’s distribute! Do it the same way every time so it becomes a habit. g g G G G
Mendel and His Pea Plants Now, the other set of genes. Dominant alleles are always listed first. g g G Gg Gg
Mendel and His Pea Plants These are the genotypes from the first daughter generation. What are the phenotypes? g Gg G G green pea Gg green pea g Gg green pea What is the frequency of the genotypes? Gg appears 4 out of 4 times, or 100%.
Mendel and His Pea Plants What if we take two daughter plants from the first generation and cross them? • What are the genotypes for the mother and father plants? Gg • What are the phenotypes for the peas? green • What do you think will happen?
Mendel and His Pea Plants Fill out the Punnett Square for the second generation. Careful where you fill in! G g G G G g g g
Mendel and His Pea Plants Fill out the Punnett Square for the second generation. Careful where you fill in! G g GG Gg Gg gg
Mendel and His Pea Plants What are the phenotypes for the genotypes inherited? G GG G g green pea Gg green pea gg yellow pea What is the frequency of the genotypes? GG appears 1 out of 4 times, or 25%. Gg appears 2 out of 4 times, or 50%. gg appears 1 out of 4 times, or 25%.
Mendel and His Pea Plants How many different phenotypes are produced? Two – green pea and yellow pea How many different genotypes are produced? Three – GG, Gg, and gg Name the dominant genotype(s): GG and Gg What about recessive? gg
Mendel and His Pea Plants Exit question: Finish this Punnett Square. G g g g
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