Question

Match each example with the best description. dihybrid cross monohybrid cross homozygous heterozygous a. \(b b\) b. \(A a B b \times A a B b\) c. \(A a\) d. \(A a \times A a\)

Short answer

a. Homozygous, b. Dihybrid cross, c. Heterozygous, d. Monohybrid cross.

Step-by-step solution

Understand the Definitions

First, we need to understand what each term means. A dihybrid cross is a genetic cross using two traits with two alleles each. A monohybrid cross involves one trait with two alleles. Homozygous refers to having two of the same allele, like 'AA' or 'bb', while heterozygous means having two different alleles, like 'Aa'.

Match 'a. bb'

We are looking for a description for 'bb'. Since 'bb' consists of the same alleles, it fits the definition of homozygous. Therefore, 'a. bb' matches 'homozygous'.

Match 'b. Aa Bb × Aa Bb'

In the cross 'Aa Bb × Aa Bb', we see two pairs of alleles for two different traits, which corresponds to a dihybrid cross. So, 'b. Aa Bb × Aa Bb' matches with 'dihybrid cross'.

Match 'c. Aa'

The pair 'Aa' contains two different alleles. According to our definitions, this is heterozygous. Thus, 'c. Aa' matches with 'heterozygous'.

Match 'd. Aa × Aa'

The cross 'Aa × Aa' involves a single trait with different alleles. This matches the description of a monohybrid cross. Hence, 'd. Aa × Aa' corresponds with 'monohybrid cross'.

Key concepts

Dihybrid Cross

A dihybrid cross is a type of genetic cross that involves two different traits. Each trait has two alleles, or variations, that can pass from parent to offspring. This kind of genetic cross allows for the study of how different genes interact with each other during inheritance. In a dihybrid cross, typically, the parents are heterozygous for both traits. For example, if we have two traits such as flower color and plant height, each parent might have alleles represented as RrYy, where 'R' and 'r' stand for dominant and recessive alleles for flower color, and 'Y' and 'y' for plant height. The focus is on the phenotypic ratio, which traditionally follows a 9:3:3:1 pattern in offspring of heterozygous hybrids. The dihybrid cross is an excellent way to explore the principle of independent assortment. This principle states that alleles for different traits are distributed to sex cells (& and subsequently offspring) independently of one another.

Monohybrid Cross

A monohybrid cross focuses on a single trait involving two alleles. This type of genetic cross helps you observe how one particular characteristic is inherited from one generation to the next. Typically, one of the parents in a monohybrid cross is homozygous dominant (e.g., AA) while the other is homozygous recessive (e.g., aa). The offspring, in this case, would be heterozygous (e.g., Aa). When two heterozygous individuals (Aa) are crossed, the possible genotypes of the offspring follow a 1:2:1 ratio — one homozygous dominant (AA), two heterozygous (Aa), and one homozygous recessive (aa). The resulting phenotypic ratio often appears as 3:1, where three offspring show the dominant trait and one shows the recessive trait. This cross helps understand the basic mechanism of Mendelian inheritance and is an entry point into more complex genetic studies.

Homozygous

"Homozygous" refers to the condition wherein an organism carries two identical alleles for a specific trait. This can occur in both dominant and recessive forms. - **Homozygous Dominant:** This occurs when both alleles for a trait are dominant, represented by, for instance, 'AA'. - **Homozygous Recessive:** This involves both alleles being recessive, such as 'bb'. Homozygous conditions often lead to predictable trait expression, because there is no genetic variation for that trait. In cases like a homozygous recessive condition, the recessive characteristic will only appear if both alleles are recessive. This clarity in predicting traits plays a critical role in genetics, especially in breeding and predicting genetic disorders.

Heterozygous

Heterozygous describes the genetic condition where an organism possesses two different alleles for a given trait. This often results in dominance expression of one allele over the other. For instance, if 'A' is dominant and 'a' is recessive, a heterozygous genotype (Aa) would express the dominant trait. The recessive trait wouldn't show unless both alleles were recessive (aa). This type of genetic makeup provides a richer genetic diversity within a population as it allows for carrier states — where organisms may not show a trait (like a genetic disease) but can pass it on to offspring. Heterozygous conditions are key in understanding how traits are inherited and predicting potential offspring genotypes, especially in the formation of hybrid vigor, where heterozygosity can lead to individuals being more robust than their homozygous counterparts.