Mendel's Experiments - Online Tutor, Practice Problems & Exam Prep

Gregor Mendel's experiments with self and cross fertilization in pea plants established foundational concepts in genetics. Self fertilization involves one parent, producing true breeding offspring with identical phenotypes, while cross fertilization involves two parents, leading to hybrid offspring with varied phenotypes. Mendel identified dominant and recessive traits through these methods, discovering that yellow peas are dominant over green. He categorized generations into parental (P), first filial (F1), and second filial (F2), allowing for systematic tracking of inheritance patterns and genetic variation.

Mendel's Experiments

In this video, we're going to continue to talk about Gregor Mendel's experiments. Gregor Mendel used two different types of fertilization or gamete fusion in his experiments, using either just one or two parent organisms. The very first type of fertilization that Gregor Mendel used in his experiments is self-fertilization. As its name implies, the organism is going to be fertilizing itself. It only involves one parent organism. Self-fertilization is when Gregor Mendel would apply pollen from a male organ to a female organ on the same plant. Therefore, this only involves one parent organism, and the organism would be fertilizing itself, hence it's called self-fertilization.

Now, the second type of fertilization that Gregor Mendel used in his experiments is cross-fertilization. Unlike self-fertilization, cross-fertilization requires two parent organisms. There's going to be a cross of gametes between these two organisms. In cross-fertilization, Gregor Mendel would cross pollen or apply pollen from a male organ to a female organ on different plants. Again, this is going to require two parent organisms.

If we take a look at our example down below, we can better distinguish between self-fertilization and cross-fertilization. Over here on the left-hand side, notice that we're only showing you one single plant here, and this is going to be self-fertilization. You can take pollen from the male organ and transfer it to the female organ on the same exact plant, which would be self-fertilization. Now over here on the right, notice that we're showing you cross-fertilization because we're showing you two plants. Notice that pollen from the male organ of one plant is being transferred to the female organ on a different plant, and this is called cross-fertilization.

Moving forward in our course, when you see this arrow going across the two different plants, that's going to represent cross-fertilization. And when you see arrows that loop back onto itself, that's going to represent self-fertilization. Moving forward in our course, we'll talk more about Gregor Mendel's self-fertilization experiments and his cross-fertilization experiments. So, I'll see you all in our next video.

Self-Fertilization Experiment: True-Breeding vs. Hybrid Plants

In this video, we're going to introduce Gregor Mendel's self-fertilization experiment, which helped him distinguish between true-breeding and hybrid plants. True breeding is highly linked to homozygous plants, and Gregor Mendel called true-breeding plants plants that would self-fertilize and produce offspring with the same phenotype as the original parent. Now hybrids, on the other hand, are highly linked to heterozygous organisms. And Gregor Mendel called hybrid plants plants that upon self-fertilization would produce offspring with mixed phenotypes that are not always the same as the original parent. Monohybrids are just a term that refers to organisms that are heterozygous for just one specific trait or gene, and that's because the root mono means one. So again, monohybrids are heterozygous for one specific trait or gene. If we take a look at our image down below, we can better distinguish between true-breeding pea plants and hybrid pea plants.

Notice over here on the left what we're showing you are true-breeding pea plants. Notice that we have over here on the left a homozygous dominant plant, that has 2 dominant alleles, two capital Ys. Notice that this homozygous dominant plant is being self-fertilized, meaning that it is fertilizing itself. And in that scenario, we essentially have a homozygous dominant being crossed with the same exact homozygous dominant. So, we have two capital Ys as the gametes across the top and the sides of our Punnett square. And, of course, this creates organisms that have the same exact genotype and phenotype as the original parent. This is why all of the offspring are going to be yellow, and that means that this is part of true breeding. Now, on the right-hand side of true breeding, we're showing you a homozygous recessive plant that is green. Notice that this homozygous recessive plant is being self-fertilized, so we're having a homozygous recessive cross with another homozygous recessive, which is itself. And, of course, that's going to create offspring that are all homozygous recessive, all green offspring. All of the offspring have the same phenotype as the original parent, which means that this is another example of true breeding.

However, what Gregor Mendel noticed is that sometimes when he crossed yellow plants, they did not create true-breeding results. And so, over here, notice that this is showing the hybrid plants. The hybrid plants turns out, are heterozygous, meaning that they have one dominant allele and one recessive allele. And even though they have a recessive allele, you can't tell just by visually looking at them because the recessive allele is being masked or hidden by the dominant allele. And so this plant appears yellow just as the homozygous dominant one would appear yellow. However, when you self-fertilize this hybrid plant over here, what you get are results that are different than the true-breeding results. And what you end up getting, of course, when you fill in this Punnett square, you get the homozygous dominant here, you get a heterozygous here, you get another heterozygous here, and of course, you get a homozygous recessive in this last box. And so what you get is a mixture of offspring with the hybrids, and that's what we're showing you down here is that some of the offspring are going to be green. So you get a mixture of offspring and that is how these hybrids were identified.

Mendel's discoveries using self-fertilization intrigued him. He became fascinated by this. So what he began to do is cross-fertilization experiments using pea plants where he would again take pollen from one male plant and transfer that pollen to pollinate or fertilize another, a plant of the female organ of a different plant. This here concludes our introduction to Gregor Mendel's self-fertilization experiments and how he was able to distinguish between true-breeding plants that produce organisms that have the same exact phenotype as the parent, from hybrid plants that created a mixture of offspring upon self-fertilization. We'll be able to get some practice with this as we move forward in our course, and then we'll talk about cross-fertilization experiments. So I'll see you guys there.

Cross-Fertilization Experiment: Dominant vs. Recessive Alleles

In this video, we're going to introduce Gregor Mendel's cross-fertilization experiment, which helped him distinguish between the dominant and the recessive alleles. And so Gregor Mendel discovered dominant and recessive traits when he cross-fertilized yellow pea plants with green pea plants. And so when analyzing the offspring of crossing yellow and green pea plants, he noticed that he always found yellow peas in every scenario where he crossed yellow with green pea plants. He would always find yellow. And so this told him that the yellow color must be the dominant trait if it's always showing up in every scenario where he crosses a yellow and a green plant. But then Gregor Mendel also realized that sometimes he would find a mixture of phenotypes where he would find yellow and green offspring. Yet Gregor Mendel never found all green offspring when he crossed yellow and green pea plants. This information revealed to him that since he never got all green offspring, the green trait must be the recessive trait.

Now, once again, sometimes, when Mendel found a mixture of phenotypes, that gave Mendel a clue that some of the yellow pea plants are going to be heterozygotes, and that they have one copy of the allele for each of these traits. And so if we take a look at our image down below, we'll be able to see Gregor Mendel's cross-fertilization experiments. Here on the left-hand side, he is crossing a homozygous dominant yellow plant, with a homozygous recessive green plant. And of course, when you set up the Punnett square for this, you'll put the gametes of one parent on one side of the square, so we'll put the capital Y's over here. And you'll put the gametes of the other parent on the top of the square, so we'll put the lowercase y's here at the top.

And of course, when you complete the Punnett square, what you'll realize here is that you're going to have a capital Y and a lowercase y, and that'll be the same for all 4 of the squares in the Punnett square. And so all of them are going going to be heterozygotes, and heterozygotes all come out yellow. And so, when Gregor Mendel did these cross-fertilization experiments, crossing yellow with green, often he would just get all yellow offspring. But then sometimes when he crossed yellow with green pea plants, he wouldn't get all yellow offspring. This is because it turns out that the yellow plants he was crossing were hybrids or heterozygous, and the homozygous recessive green plants were still homozygous recessive.

And so of course, when you fill out the Punnett square here, what you get is that the capital Y is going to be brought all the way across. The lowercase y here will be filled in at the top, and then down below here you have all lowercase y's. And so when he crossed a heterozygous yellow plant with a homozygous recessive green plant, what he saw was a mixture of offspring. He would get 50% yellow and 50% green. And so, once again, the fact that he never got all green when he crossed the yellow and green pea plants told him that the green must be the recessive pea color. And of course, the fact that he always got yellow no matter how he crossed yellow with green told him that the yellow color must be the dominant p color. And again, he was able to get a clue that heterozygous plants existed when he saw this mixture of offspring. And so this video concludes our introduction to Gregor Mendel's cross-fertilization experiments, and we'll be able to get some practice applying the concepts that we've learned as we move forward in our course. So I'll see you all in our next video.

Mendel crossed a pea plant with yellow peas with a pea plant with green peas. All of the offspring created from this cross has yellow peas. What must be true about the parent plants of this cross for this to occur?

• A. The parent with green peas was heterozygous for pea color.
• B. The parent with green peas was homozygous recessive for pea color.
• C. The parent with yellow peas was heterozygous for pea color.
• D. The parent with yellow peas was homozygous dominant for pea color.
• E. A and C.
• F. B and D.

You cross a pea plant with yellow peas (Yy) and a pea plant with green peas. How many unique genotypes are possible for pea color in the offspring? How many unique phenotypes are possible for pea color in the offspring?

• A. 2 unique genotypes; 2 unique phenotypes.
• B. 3 unique genotypes; 2 unique phenotypes.
• C. 2 unique genotypes; 1 unique phenotype.
• D. 1 unique genotype; 1 unique phenotype.

Generations of Mendel’s Plants

In this video, we're going to talk about the generations of Mendel's plants. Gregor Mendel standardized the naming system of generations to track inheritance patterns. There are three generations that you all should be familiar with. The very first generation is the parental generation, commonly abbreviated as the P generation. This is the original set of individual plants that are mated, or the parents, if you will.

The second generation that you all should know is the first filial generation or, in other words, the F₁ generation. The first filial generation is the offspring of the P generation. The word filial is related to children; thus, this generation is the children of the parental generation. Last but not least, we have the second filial generation or the F₂ generation. This generation is the offspring of the F₁ generation plants.

Let's take a look at our image down below to get a better idea of these generations. Notice here in our first block, we're showing you the P generation, which is the original set of parents that are mated. Here, what we have is a homozygous dominant pea plant being crossed with a homozygous recessive pea plant. When you set up their gametes on a Punnett square, like what you see here, and you fill in the Punnett square, what you're going to get are heterozygous individuals in each of these squares, representing a heterozygous genotype. The individuals inside of this Punnett square represent the F₁ generation.

That leads us to the next part: the F₁ generation, the first filial generation, the children of the parental generation. Because these offspring are all heterozygous, we can either self-fertilize a single heterozygous individual or cross-fertilize two heterozygous individuals. Either way, we're going to have heterozygous alleles of the gametes across the top. When we fill this in, what we will have is one homozygous dominant, two heterozygous, and one homozygous recessive; these are the possibilities of the offspring. So, these squares within here represent the F₂ generation.

The F₂ generation, as you can see here, includes three yellow and one green possibility among the four. The generations are referred to as the P generation, F₁ generation, and F₂ generation. This concludes our introduction to the generations of Mendel's plants, and we'll be able to get some practice applying this as we move forward in our course. So, I'll see you all in our next video.

In the study of genetics the offspring of the parental generation is referred to as the:

• A. Phenotype
• B. P generation.
• C. F1 generation.
• D. F2 generation.

Here’s what students ask on this topic:

What are the key differences between self fertilization and cross fertilization in Mendel's experiments?

In Mendel's experiments, self fertilization involves a single parent organism, where pollen from the male organ fertilizes the female organ on the same plant. This method produces true breeding offspring with identical phenotypes to the parent. Cross fertilization, on the other hand, requires two parent organisms. Pollen from the male organ of one plant is transferred to the female organ of a different plant. This method results in hybrid offspring with varied phenotypes. These differences allowed Mendel to study inheritance patterns and distinguish between true breeding and hybrid plants.

How did Mendel distinguish between true breeding and hybrid plants?

Mendel distinguished between true breeding and hybrid plants through self fertilization experiments. True breeding plants, which are homozygous, produce offspring with the same phenotype as the parent when self fertilized. For example, a homozygous dominant yellow pea plant (YY) will always produce yellow offspring. Hybrid plants, which are heterozygous, produce offspring with mixed phenotypes. When a heterozygous yellow pea plant (Yy) is self fertilized, the offspring can be yellow or green, as shown by the Punnett square: 1 YY, 2 Yy, and 1 yy. This mixture of phenotypes indicated the presence of hybrid plants.

What did Mendel discover about dominant and recessive traits through cross fertilization?

Mendel discovered dominant and recessive traits by cross fertilizing yellow and green pea plants. He observed that crossing a homozygous dominant yellow plant (YY) with a homozygous recessive green plant (yy) always produced yellow offspring (Yy), indicating that yellow is the dominant trait. When he crossed heterozygous yellow plants (Yy) with green plants (yy), he found a mixture of yellow and green offspring, but never all green. This confirmed that green is the recessive trait. These observations helped Mendel understand how dominant and recessive alleles interact in inheritance.

What are the P, F1, and F2 generations in Mendel's experiments?

In Mendel's experiments, the P generation refers to the parental generation, which is the original set of plants that are mated. The F1 generation, or first filial generation, consists of the offspring of the P generation. These offspring are typically heterozygous if the P generation plants were homozygous for different traits. The F2 generation, or second filial generation, is the offspring of the F1 generation. When F1 plants self fertilize or cross fertilize, the F2 generation exhibits a 3:1 ratio of dominant to recessive phenotypes, revealing the inheritance patterns of the traits studied.

How did Mendel use Punnett squares in his experiments?

Mendel used Punnett squares to predict the genotypes and phenotypes of offspring from his breeding experiments. By placing the gametes of each parent along the top and side of the square, he could fill in the squares to show all possible combinations of alleles. For example, crossing a homozygous dominant yellow plant (YY) with a homozygous recessive green plant (yy) results in all heterozygous yellow offspring (Yy). This tool allowed Mendel to visualize and quantify the inheritance patterns, leading to his discovery of dominant and recessive traits and the ratios of different phenotypes in the F2 generation.