12. Red-flowering snapdragons are homozygous for allele R^1....

12. Red-flowering snapdragons are homozygous for allele $R^{1}$. White-flowering snapdragons are homozygous for a different allele $\left(R^{2}\right)$. Heterozygous plants $\left(R^{1} R^{2}\right)$ bear pink flowers. What phenotypes should appear among first-generation offspring of the crosses listed? What are the expected proportions for each phenotype? a. $R^{1} R^{1} \times R^{1} R^{2}$ b. $R^{1} R^{1} \times R^{2} R^{2}$ c. $R^{1} R^{2} \times R^{1} R^{2}$ d. $R^{1} R^{2} \times R^{2} R^{2}$ (In cases of incomplete dominance, alleles are usually designated by superscript numerals, as shown here, not by the uppercase letters for dominance and lowercase letters for recessiveness.

12. Red-flowering snapdragons are homozygous for allele
$R^{1}$. White-flowering snapdragons are homozygous for a different allele $\left(R^{2}\right)$. Heterozygous plants $\left(R^{1} R^{2}\right)$ bear pink flowers. What phenotypes should appear among first-generation offspring of the crosses listed? What are the expected proportions for each phenotype?
a. $R^{1} R^{1} \times R^{1} R^{2}$
b. $R^{1} R^{1} \times R^{2} R^{2}$
c. $R^{1} R^{2} \times R^{1} R^{2}$
d. $R^{1} R^{2} \times R^{2} R^{2}$
(In cases of incomplete dominance, alleles are usually designated by superscript numerals, as shown here, not by the uppercase letters for dominance and lowercase letters for recessiveness.

Key Concepts

Genotype-Phenotype Relationships

Understanding the relationship between genotype and phenotype is fundamental in genetics. Genotypes represent the genetic makeup of an organism, while phenotypes represent the expressed traits. This relationship is particularly important in cases of incomplete dominance, where the phenotype of heterozygotes is a blend of the traits associated with each allele.

Incomplete Dominance

Incomplete dominance is a form of inheritance where the heterozygous genotype results in a phenotype that is intermediate between the phenotypes of the two homozygous genotypes. This is different from complete dominance, where one allele completely masks the other in heterozygotes.

Homozygosity

Homozygosity refers to the condition in which an organism possesses two identical alleles for a particular trait. In genetics, this concept is important because crossing individuals with homozygous genotypes can produce predictable and uniform phenotypic outcomes.

Heterozygosity

Heterozygosity occurs when an organism has two different alleles for a particular gene. This condition can lead to varied phenotypes depending on the type of interaction between the alleles, such as the intermediate phenotype observed in incomplete dominance.

Punnett Square Analysis

The Punnett square is a diagrammatic tool used to predict the genotype and phenotype ratios of offspring from a particular cross. It allows geneticists to visualize how alleles from each parent combine and to calculate the probability of inheriting certain traits.

Transcript

00:01 So the question that we're looking at involves across between snapdragons of different colors, and their color of their flower depends on their genotype.

00:11 So we have red snapdragons, which are homozygotes for allele r1.

00:16 We have white snapdragons, which are homozygotes for allele r2.

00:21 And we have pink snapdragons who are heterozygotes.

00:31 So they have both allele r1 and r2, but because they're heterozygotes and they have both alleles, their flower color is pink.

00:44 Um, so for our first cross that we're looking at, is a cross between a homozygous parent and another heterozygous parent.

00:56 So to solve this, we just make a point it's square.

01:01 Um, and we'll have parent one at the top and parent two at the side.

01:06 So we just separate each parent into, by which alleles are contributing to the cross.

01:13 So the parent one will contribute two r1 alleles, and parent two will contribute one r1 allele, and one r2 allele.

01:22 And just by going down and going across and filling up each box in the table, you can see what the genotype of the resulting offspring from this cross will be.

01:34 So one fourth of the offspring will be r1r1, the other fourth will also be r1r1.

01:47 The third offspring is the cross.

01:50 Another fourth will be r1r2.

01:55 And the last fourth will also be r1r2.

01:59 So we can see that half the offspring will be homozygous for the r1 allele.

02:07 Let's say half will be red, r1, r1.

02:14 And the other half will be heterozygotes.

02:18 They'll have, they'll be pink, and they'll have the genotype r1 r2.

02:26 Um, so the second cross that we're looking at is a cross between two homozygose parents, but they will be homozygous for the different alleles.

02:45 So again we just make our planet square...