In minks, wild types have an almost black coat. Breeders...

In minks, wild types have an almost black coat. Breeders have developed many pure lines of color variants for the mink-coat industry. Two such pure lines are platinum (blue gray) and aleutian (steel gray). These lines were used in crosses, with the following results: a. Devise a genetic explanation of these three crosses. Show genotypes for the parents, the $\mathrm{F}_{1},$ and the $\mathrm{F}_{2}$ in the three crosses, and make sure that you show the alleles of each gene that you hypothesize for every $\operatorname{mink}$ b. Predict the $\mathrm{F}_{1}$ and $\mathrm{F}_{2}$ phenotypic ratios from crossing sapphire with platinum and with aleutian pure lines.

In minks, wild types have an almost black coat. Breeders have developed many pure lines of color variants for the mink-coat industry. Two such pure lines are platinum (blue gray) and aleutian (steel gray). These lines were used in crosses, with the following results:
a. Devise a genetic explanation of these three crosses. Show genotypes for the parents, the $\mathrm{F}_{1},$ and the $\mathrm{F}_{2}$ in the three crosses, and make sure that you show the alleles of each gene that you hypothesize for every $\operatorname{mink}$
b. Predict the $\mathrm{F}_{1}$ and $\mathrm{F}_{2}$ phenotypic ratios from crossing sapphire with platinum and with aleutian pure lines.

Key Concepts

Allelic Dominance and Interactions

Allelic dominance describes the relationship between different alleles of the same gene, where one allele can mask the expression of another in heterozygous individuals. In cases where multiple alleles or interacting genes are involved, such as in the expression of coat color, a dominance hierarchy might exist. This hierarchy, along with potential epistatic interactions, explains the variety of phenotypes observed in the offspring of different crosses.

Mendelian Inheritance

Mendelian inheritance is the basic framework for understanding how traits are passed from parents to offspring through discrete units called genes. It involves principles such as segregation, where each parent contributes one allele for each trait, and independent assortment, meaning that alleles of different genes are distributed to gametes independently. This concept is used to predict the outcome of crosses, such as F1 and F2 generations, based on the genotypes of the parents.

Genotype and Phenotype

The genotype refers to the genetic makeup of an organism—its specific alleles for a particular gene or genes—while the phenotype is the observable expression of that genotype, such as coat color. This distinction is essential in genetic crosses because knowing the genotype allows one to predict the phenotype under given dominance relationships between alleles.

Pure Breeding (True-Breeding) Lines

Pure breeding lines are populations where individuals are homozygous for particular traits. In such lines, when individuals are crossed, all offspring display the same phenotype, which makes these lines ideal for genetic analysis and for predicting outcomes in crosses. They serve as a starting point for establishing the genetic basis of variations, as seen in distinct coat colors.

F1 and F2 Generation Crosses

The F1 generation is the first filial generation produced by crossing individuals from two pure breeding lines, and they typically exhibit uniform phenotypes if one allele is completely dominant. The F2 generation, produced by intercrossing F1 individuals, displays a variety of phenotypes whose ratios can be predicted with Punnett squares based on expected segregation and independent assortment of alleles. This analysis is fundamental in determining the underlying genetic mechanisms.

Transcript

00:04 The wild type is a black fur color, but breeders have produced two additional colors.

00:13 One is called platinum, which is a blue gray, and the other is called an allusion, which is a steel gray.

00:26 And so if we look at answering a part, we can use the provided information in the crosses.

00:31 So there were three crosses, and the parents for the first cross were wild type crossed with platinum, and the f -1s were all wild type.

00:46 And then the f -2, f -1 by f -1 produced 18 wilds and five platyms.

00:58 In the f -i, i'm sorry, in cross -2, the parents were wild -type crossed with allusion.

01:07 The f -1s were all wild, and the f -2s were 27 wild to 10 allusion.

01:17 And lastly, the third cross was a platinum mink crossed with an allusion mink.

01:26 Again, the f1 was all wild type.

01:30 And then in the f2, we had 133 wild, 41 platinum, 46 allusion, and we had a new color, sapphire, and there were 17 of those.

01:52 And so if we look at these data, what we can start to see, and i'm going to make some notes for you so we can tackle this problem, is that in cross one, wild type was dominant to platinum.

02:07 In cross two, wild type is dominant to illusion.

02:12 And in cross three, sapphire is your double recessive.

02:17 And so here we know that there's a dominance hierarchy.

02:20 Wild type is dominant to platinum.

02:23 Wild type is dominant to allusion and both of them are dominant or i'm sorry all three of them are dominant to sapphire which is a double recessive and i know this because in the f2 of cross three there's a nine to three three to one ratio of phenotypes so they are nine wild type three platinum three illusion and only seven or one sapphire and so we have a nine three three one ratio there in crosses one and two they indicate that we have a dominance hierarchy cross three gives us a little more insight because the way to get a nine to three three to one ratio when breeding two parents that are pure breeding or true bread that means that there's two genes involved and that those two genes have multiple alleles.

03:29 Because we can produce wild type, we can produce platinum, we can produce sapphire, and we can produce allusion.

03:37 And so we know that based on that third cross, that we have two genes and that these two genes have multiple alleles.

03:51 Now we have enough information to answer the question.

03:55 So what i'm going to do is i'm going to back up and just use the information that i've written for you.

04:01 So if we let, we know there's two genes.

04:06 So for cross one, the wild type, and remember, these have to be true breeding or we wouldn't get these ratios in the f2.

04:13 So this true breeding parent is big a, big a, big b, big b, because there's two genes with multiple alleles for wild type.

04:22 And that is crossed with a platinum individual.

04:24 And remember platinum is recessive to wild type.

04:28 It must be that they're two little a's, big b, big b...

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