Question

A heterozygous individual has a ____ for a trait being studied. a. pair of identical alleles b. pair of nonidentical alleles c. haploid condition, in genetic terms

Short answer

The correct answer is b. A heterozygous individual has a pair of nonidentical alleles for a trait being studied.

Step-by-step solution

Understand the terms

In genetics, the term 'heterozygous' refers to an individual having two different alleles for a specific gene or trait.

Analyze given options

To solve the problem, review what each option means: - Option a, 'pair of identical alleles', describes a 'homozygous' individual, not a heterozygous one. - Option b, 'pair of nonidentical alleles', correctly describes a heterozygous individual. - Option c, 'haploid condition, in genetic terms', does not relate to heterozygous, as haploid refers to cells with a single set of chromosomes.

Select the correct answer

Based on the definitions and the given options, the correct choice for a heterozygous individual is the one with nonidentical alleles.

Key concepts

Heterozygous

The term "heterozygous" is an important concept in genetics and refers to having two different alleles for a specific gene. Alleles are different versions of a gene that can lead to variations in a particular trait. For example, in the case of a simple flower color gene, one allele might code for red petals and another for white.
Heterozygous individuals have one allele inherited from each parent, and because these alleles are different, they might express a dominant trait if one allele is dominant over the other. This means that even though they carry two different genetic instructions, the observable trait could be determined by just one of the alleles if it masks the effect of the other. This situation is often used in Mendelian inheritance to explain how traits can skip generations and make predictions about offspring traits.

Alleles

Alleles are the different forms of a gene found at the same place, or locus, on a chromosome. Think of a chromosome as a long thread that carries genetic instructions, much like a guidebook for building an organism. Each guidebook can have variations in its instructions depending on the alleles present.

• Alleles can be either dominant or recessive. A dominant allele masks the presence of a recessive allele, and is usually represented by a capital letter, like 'A'.
• Recessive alleles only express their traits when a dominant allele is not present, and are symbolized by lowercase letters, like 'a'.
• An organism's observable traits (phenotype) depend on the combination of alleles (genotype) it possesses.

In genetics, understanding alleles is crucial because they are the fundamental units of heredity that help us predict genetic variations and inheritance patterns.

Homozygous

"Homozygous" is another key term when discussing genetics. This condition occurs when an individual has two identical alleles for a particular gene. Unlike heterozygous individuals, homozygous individuals have either two dominant alleles or two recessive alleles at a given gene locus.
For example:

• An individual with two dominant alleles for a trait (AA) is said to be homozygous dominant.
• Conversely, an individual with two recessive alleles (aa) is homozygous recessive.

Homozygosity often results in a consistent expression of a trait, as there is no competing allele in the genetic makeup to alter the phenotype. Because they carry identical alleles, predictions about trait inheritance can be quite straightforward in homozygous individuals.

Chromosomes

Chromosomes are structures within cells that hold an organism's entire set of genetic information. Each chromosome is made up of DNA—and they are like volumes in a library, each with pages (genes) that tell specific stories (traits of an organism).
Chromosomes come in pairs, and humans typically have 23 pairs for a total of 46. They contain many genes, and each gene may have different alleles, contributing to the genetic diversity in a population. Here's the breakdown:

• One chromosome of each pair is inherited from the mother and the other from the father.
• The 23rd pair of chromosomes determines biological sex: two X chromosomes make a female, while an X and a Y make a male.
• Abnormalities in chromosome number or structure can lead to genetic disorders.

By understanding chromosomes, we can see how traits are inherited and how genetic conditions can be passed from one generation to the next. This knowledge is fundamental in fields ranging from medicine to evolutionary biology.