Question

Meiosis_____the parental chromosome number. a. doubles c. maintains b. halves d. mixes up

Short answer

The correct answer is b. halves.

Step-by-step solution

Understanding the Question

The question is asking about the change in chromosome number resulting from meiosis, a type of cell division that occurs in sexual reproduction. The options describe different ways in which the chromosome number could be affected.

Identify Chromosome Number Changes

During meiosis, the chromosome number is reduced. In humans, for example, the cells start with 46 chromosomes and create gametes (sperm or eggs) with 23 chromosomes.

Comparison with Given Options

Compare the process of meiosis with the provided options: doubling (which would increase the number), maintaining (keeping the chromosome number the same), having (reducing the chromosome number by half), and mixing (which refers to a combination of traits).

Selecting the Correct Option

Based on the understanding of meiosis halving the chromosome number, the correct option is b. halves.

Key concepts

Chromosome Number

Chromosome number refers to the total count of chromosomes present within a cell. In humans, normal somatic cells contain 46 chromosomes, organized into 23 pairs.

This includes 22 pairs of autosomes and one pair of sex chromosomes. Each parent contributes one chromosome per pair, hence maintaining genetic diversity through sexual reproduction.

• Importance of Chromosome Number: The correct chromosome number is crucial for normal cellular and organismal function. Divergings can lead to disorders called aneuploidies, like Down syndrome which involves an extra chromosome 21.

Every organism has a specific chromosome number. While humans have 46, other species like fruit flies have 8 and dogs 78.

Cell Division

Cell division is the process by which a cell splits into two or more daughter cells. There are two main types of cell division: mitosis and meiosis.

Both types serve distinct roles and follow different processes within an organism.

• Mitosis: In mitosis, the cell divides to produce two identical daughter cells, each with the same number of chromosomes as the parent cell. This is vital for growth, repair, and asexual reproduction.
• Meiosis: Meiosis, on the other hand, is a two-stage process, resulting in gametes with half the original chromosome number.

Meiosis is crucial for sexual reproduction, as it ensures that offspring have the same chromosome number as their parents.

Sexual Reproduction

Sexual reproduction is a biological process where new offspring are produced by the combination of genetic material from two different parents.

This mixing of genes introduces diversity within a population.

• Process: It involves the fusion of two specialized cells called gametes, which are produced by meiosis. Each gamete has half the number of chromosomes as a normal body cell.
• Advantages: Through genetic mixing, sexual reproduction increases the genetic diversity of a population, enhancing adaptability and survival.

For example, in humans, sperm (male gamete) and egg (female gamete) combine to form a zygote, restoring the diploid chromosome number.

Gametes

Gametes are the reproductive cells involved in sexual reproduction. They carry half the genetic information of typical somatic cells: in humans, this means 23 chromosomes.

These cells unite during fertilization to form a zygote, which has the full chromosome complement.

• Types of Gametes: The main types are sperm, in males, and eggs or ova, in females. Both are crucial for reproduction and are formed through meiosis.
• Formation: During meiosis, cells undergo division that results in gametes with half the parent's chromosome number. This halving is key to maintaining species-specific chromosome numbers across generations.

In flowering plants, gametes are involved in seed formation, showcasing the universality of this reproductive strategy.