Studies like the one described in question AP12.1 were...

Studies like the one described in question AP12.1 were carried out by Morgan and Sturtevant beginning in 1911. The discovery of linkage was made by Bateson and Punnett in 1900. They crossed a true-breeding purple (P) plant with long seeds (L) with a true-breeding red (r) plant with round seeds (l). They then performed a self-cross between the $\mathrm{F}_{1}$ generations. They obtained the $\mathrm{F}_{2}$ data shown below. A. Use the symbols $\mathrm{P}, \mathrm{p}, \mathrm{L},$ and 1 to construct a representation of the $\mathrm{F}_{2}$ genotypes and complete the second column in the table. B. Complete the fourth column of the table above by recording the values of the predicted numbers of plants with each genotype. C. Apply a c' test at the 95$\%$ confidence level to evaluate the claim that these data confirm linkage. The definition of the statistic $\chi^{2}=\sum \frac{(o-e)^{2}}{e}$ and this table are provided in the AP Biology Exam. D. At first, Bateson and Punnett did not see that these genes are located on the same chromosome and proceeded to measure the linkage distance between them, taking the first step toward creating a gene map. Justify the selection of data and the procedure from which data could be collected that would have provided the necessary evidence to confirm linkage and recombination.

Studies like the one described in question AP12.1 were carried out by Morgan and Sturtevant beginning in 1911. The discovery of linkage was made by Bateson and Punnett in 1900. They crossed a true-breeding purple (P) plant with long seeds (L) with a true-breeding red (r) plant with round seeds (l). They then performed a self-cross between the $\mathrm{F}_{1}$ generations. They obtained the $\mathrm{F}_{2}$ data shown below.
A. Use the symbols $\mathrm{P}, \mathrm{p}, \mathrm{L},$ and 1 to construct a representation of the $\mathrm{F}_{2}$ genotypes and complete the second column in the table.
B. Complete the fourth column of the table above by recording the values of the predicted numbers of plants with each genotype.
C. Apply a c' test at the 95$\%$ confidence level to evaluate the claim that these data confirm linkage. The definition of the statistic $\chi^{2}=\sum \frac{(o-e)^{2}}{e}$ and this table are provided in the AP Biology Exam.
D. At first, Bateson and Punnett did not see that these genes are located on the same chromosome and proceeded to measure the linkage distance between them, taking the first step toward creating a gene map. Justify the selection of data and the procedure from which data could be collected that would have provided the necessary evidence to confirm linkage and recombination.

Key Concepts

Genetic Linkage

Genetic linkage refers to the tendency of genes that are located close to each other on the same chromosome to be inherited together. This phenomenon occurs because linked genes do not assort independently during meiosis, which can result in deviations from the expected Mendelian ratios. Understanding linkage is crucial for analyzing inheritance patterns and for mapping the relative positions of genes on chromosomes.

Recombination

Recombination is the process by which homologous chromosomes exchange segments during meiosis, leading to new combinations of alleles. The frequency of recombination between two genes is used as an indicator of the physical distance between them on a chromosome, providing critical data for gene mapping and for studying the relationship between linked genes.

Chi-square Test

The Chi-square test is a statistical method used to compare observed data with expected outcomes based on theoretical models, such as Mendelian inheritance. In genetic studies, it helps determine whether deviations from expected ratios are due to random chance or suggest underlying factors like linkage, thereby providing evidence for or against the hypothesis of independent assortment.

Punnett Squares and Genotype Representation

Punnett squares are a tool used in genetics to predict the outcome of crosses by diagramming the possible allele combinations from parental genotypes. Representing genotypes using symbols allows for systematic analysis of offspring ratios, which is essential for identifying deviations from expected Mendelian ratios that may indicate phenomena like linkage or recombination.

Gene Mapping

Gene mapping is the process of determining the relative positions of genes on a chromosome using data from crosses, such as recombination frequencies. This technique provides a visual representation of gene order and distances, making it possible to understand the physical relationships and linkage between genes, which in turn influences their patterns of inheritance.

Transcript

00:01 Hello, everyone.

00:01 Today i will be helping you with the 20th problem of the chapter 13 problem set.

00:07 And so i'm just going to do them in order of what they ask from a to d.

00:12 So a is asking you to use the symbols of p, big p, little p, big l, and little l to construct a representation of the f2 genotypes and complete the column in the second table.

00:27 So instead of copying the table over here, i'm just going to be label them one to four, and that will be representative of the rose.

00:38 So basically what you want to know is that, so you have, so in the question, it says they cross a true breeding purple plant with long seeds with a true breeding red plant with round seeds.

00:55 They then performed a self cross between the f1 generation.

01:00 So if you know the f generation is a self -cross, so you know that that is going to turn into p, r, and then big l, and little l.

01:12 So, i mean, what i like to do this type of stuff, the different types, you can write them out, like, every single one.

01:21 But usually how i do it is, for example, 1, when you know that it's going to be a certain one, which is purple long, and you know that purple is going to be dominant over it, so you're going to have p.

01:32 Leave this one open for either a bigger p or an r, and then big l, for either a little l right here or big l, and it just leaves the possibility open.

01:40 Then you have purple round, so again it's here, but since it's round, it's recessive, so you know both of those.

01:46 And then you have three, which is red round, so you know this is rr, red long, and then you have big l and then an open space and then you have red round which is two rs and then two little ls so i hope so this one so a is done now and now you have b which is asking you to uh complete the predicted and expected plants so if they are unleaked they would think nine to three to three to one and so when you have nine to three to one this is the ratios that they get from the total that they'd expect so i just do nine divided by sixteen the you you get the percentage and then you'd multiply that by the 69 .52...

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