Two genes control color in corn snakes as follows: O-B-...

Two genes control color in corn snakes as follows: $O-B-$ snakes are brown, $O$ - $b b$ are orange, oo $B$-are black, and $o o b b$ are albino. An orange snake was mated to a black snake, and a large number of $\mathrm{F}_1$ progeny were obtained, all of which were brown. When the $\mathrm{F}_1$ snakes were mated to one another, they produced 100 brown offspring, 25 orange, 22 black, and 13 albino. a. What are the genotypes of the $\mathrm{F}_1$ snakes? b. What proportions of the different colors would have been expected among the $\mathrm{F}_2$ snakes if the two loci assort independently? c. Do the observed results differ significantly from what was expected, assuming independent assortment is occurring? d. What is the probability that differences this great between observed and expected values would happen by chance?

Two genes control color in corn snakes as follows: $O-B-$ snakes are brown, $O$ - $b b$ are orange, oo $B$-are black, and $o o b b$ are albino. An orange snake was mated to a black snake, and a large number of $\mathrm{F}_1$ progeny were obtained, all of which were brown. When the $\mathrm{F}_1$ snakes were mated to one another, they produced 100 brown offspring, 25 orange, 22 black, and 13 albino.
a. What are the genotypes of the $\mathrm{F}_1$ snakes?
b. What proportions of the different colors would have been expected among the $\mathrm{F}_2$ snakes if the two loci assort independently?
c. Do the observed results differ significantly from what was expected, assuming independent assortment is occurring?
d. What is the probability that differences this great between observed and expected values would happen by chance?

Key Concepts

Gene Interaction and Epistasis

This concept refers to how two or more genes can interact to affect a single trait. In such interactions, the effect of one gene can mask or modify the effect of another gene, leading to phenotypes that are not simply additive. Epistasis is essential for understanding complex traits where the combination of alleles across different loci results in unique phenotypic outcomes.

Allelic Dominance and Recessiveness

Dominance and recessiveness describe the relationship between alleles at a single gene locus, where dominant alleles mask the expression of recessive alleles in heterozygotes. This principle is fundamental in predicting phenotypes from genotypes, especially in cases where multiple alleles interact, and helps explain why certain phenotypes only appear when alleles are homozygous.

Independent Assortment

Independent assortment is a principle of Mendelian genetics stating that alleles of different genes segregate into gametes independently of each other. This concept is crucial for predicting the distribution of genotypes and phenotypes in the offspring, assuming that the genes are located on different chromosomes or are far apart on the same chromosome.

Punnett Square and Expected Genotypic/Phenotypic Ratios

The use of Punnett squares allows for a systematic prediction of the genotypic and phenotypic ratios of offspring from a given genetic cross by considering all possible combinations of parental gametes. This method helps in determining the expected outcomes when genes assort independently and are influenced by dominance, recessiveness, and gene interactions.

Chi-Square Test for Goodness-of-Fit

The chi-square test is a statistical tool used to compare observed counts of phenotypes with expected counts derived from genetic predictions. It determines whether deviations between observed and expected ratios are due to random chance or indicate a significant departure from hypothesized genetic models, such as those assuming independent assortment.

Transcript

00:01 In order to answer this question, let's talk about inheritance.

00:02 It says an albino corn snake is crossed with a normal -colored corned snake.

00:06 The offspring are all normal -colored.

00:08 When the first -generation progeny are crossed among themselves, they produce 32 normal -colored snakes and thin albino snakes.

00:17 So in the f2, you got 32 normal color.

00:24 Remember that normal color is dominant, and includes the homozygous dominant plus the hymone.

00:32 Heterozygos, okay, and you get 10 albino.

00:36 Albino is homo -sego recessive, remember.

00:39 So you have a total of 42.

00:41 So in order to get or to know if there is only one gene involved, you have to find a frequency for normal color in the f2.

00:47 And you do that by dividing this number by the total that is 42.

00:51 And if you divide 32 by 42, you get approximately 0 .76.

00:56 And if you do the same here, 10 divided by 42, 10 divided by 42, it is equal to.

01:02 0 .24 approximately.

01:04 Okay.

01:05 So these two frequencies are very similar to the f2 of two heterocycos.

01:11 For example, in this case, what is happening is that you're crossing a homocylus domino in the parental generation, okay? an albino -corn snake is crowed with a normal color corn snake.

01:22 In this case, the parent is homosecigous domino, and the second parent is homosecicis.

01:26 And from this cross, you're going to get that the first generation is going to be, all of them are going to be heterocylus.

01:31 And when you perform an intercross between the f1, you're going to get the following cross.

01:39 That is like this in order to produce the ff2.

01:41 So you get the following panel in a square that is like this...

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