Question

Dogs have a diploid chromosome number of 78 . How many chromosomes do their gametes have? a. 39 c. 156 b. 78 d. 234

Short answer

Chromosomes in dog gametes: 39 (option a).

Step-by-step solution

Understanding Diploid and Haploid

Diploid cells have two complete sets of chromosomes, one from each parent. In dogs, the diploid chromosome number is 78, meaning they have 2 sets of 39 chromosomes each.

Determine the Chromosome Number in Gametes

Gametes (sperm and egg cells) are haploid, meaning they contain only one complete set of chromosomes. To find the number of chromosomes in a gamete, divide the diploid number by 2: \( 78 \div 2 = 39 \).

Concluding the Answer

Since gametes have only one set of chromosomes, the number of chromosomes in a dog's gamete is 39. This matches option (a) 39.

Key concepts

Diploid

In biology, the term "diploid" refers to cells that contain two complete sets of chromosomes. These two sets are inherited from the organism’s maternal and paternal parents. For instance, humans have 46 chromosomes, forming 23 pairs, and hence are considered diploid organisms. Similarly, in dogs, the diploid chromosome count is 78, meaning they have 39 pairs of chromosomes.

Understanding diploid cells is vital because they make up most of the body's cellular structure, including tissues and organs. These cells undergo mitosis, a type of cell division that results in two identical daughter cells, allowing for growth and tissue repair. The diploid state ensures genetic stability throughout these processes.

Diploid cells are sometimes contrasted with haploid cells, which contain only one chromosome set, but more on those in the next section.

Haploid

Haploid cells contain just a single set of chromosomes, unlike diploid cells, which have two sets. This halved chromosome number is crucial for sexual reproduction. Haploid cells result from a special type of cell division called meiosis, serving as the foundational structure for gametes, which include sperm and egg cells.

The single set of chromosomes in haploid cells enables genetic diversity. When two gametes meet during fertilization, they form a complete diploid zygote with a full set of chromosomes—one from each parent. This contributes to the genetic uniqueness of the offspring.

Haploid cells are fundamental in maintaining stable chromosome numbers across generations. By halving during gamete formation, it ensures that when two haploid cells merge, the resulting organism will have the correct diploid chromosome count, preventing abnormalities.

Gametes

Gametes are the reproductive cells in animals and plants that facilitate sexual reproduction. In animals, gametes are referred to as sperm cells in males and egg cells (or ova) in females. These cells are always haploid, containing only a single set of chromosomes.

For example, in dogs, each gamete contains 39 chromosomes. This is half the diploid number, which is essential for ensuring that offspring have a complete set of chromosomes when gametes from each parent combine during fertilization.

Gametes play a crucial role in genetic variation. During their formation through meiosis, processes such as crossing over and independent assortment result in genetically unique gametes. This variation is a source of biodiversity and plays a role in evolution. Understanding gametes helps explain the continuation of genetic traits from one generation to the next.