The dorsal pigment pattern of frogs can be either 'leopa...

Question

The dorsal pigment pattern of frogs can be either 'leopard' (white pigment between dark spots) or 'mottled' (pigment between spots appears mottled). The trait is controlled by an autosomal gene. Males and females are selected from pure-breeding populations, and a pair of reciprocal crosses is performed. The cross results are shown below.

Cross 1: P₁: Male leopard x male mottled
F₁: All mottled
F₂: 70 mottled, 22 leopard
Cross 2: P₁: Male mottled x female leopard
F₁: All mottled
F₂: 50 mottled, 18 leopard

Propose two different genetic crosses that would allow you to determine the genotype of one mottled frog from the F₂ generation.

Accepted Answer

Hi, everybody. Welcome back. Here's our next question. If you cross a red eyed, which is big, a little a Drosophila and a white eyed, little, a little a Drosophila. What is the resulting Jenna typical ratio of the offspring? And we see we have four answer choices with three numbers in the ratio. So first let's recall, we're looking for a gene, a typical ratio. So ratio of the actual genetic um makeup of the animals, not fanatic. So we're not looking for the red eyed or white eyed, but whether genotype is and we're going to write that in the form homocide is dominant to heterosexuals to homosexuals, recessive. So that's the order of our three numbers. So let's just drop our simple punnett square. We just got um of our cross here and we're just looking at one gene here, one trait. So we just have our simple four boxes here. So here's our red eyed hetero zegas parent big a little a and then we have a wide eyed homos, I guess, recessive parent, little a little a. So we can just fill in our pendant square and we see that we only see two Jenna types. Um There are no homeless, I guess dominant offspring, which makes sense since our wide eyed parent cannot pass on that dominant allele. So our first number should be zero and that's actually going to lead us to eliminate choice a where the first number is one choice be where it's too and choice, see where it's one right away. So we actually consume in our answer without doing anything else. Choice, the 0 to 2 to two. But if we want to be thorough, we can just look at our punnett square to confirm that indeed. Um We then have of our offspring, two out of four will be hetero sickos and two out of four homesickness recessive. So again, across the red eyed heterocyclic Drosophila with a wide eyed Drosophila, the resulting Jenna typical of the offspring is choice D zero to, to, to, to see you in the next video.

Key Concepts

Autosomal Inheritance

Reciprocal Crosses

Phenotypic Ratios in F₂ Generation

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