Problem 8 - Biology

Question

Which of the following cells is haploid? (a) primary oocyte (b) oogonium (c) secondary oocyte (d) corpus luteum (e) follicle cell

Step-by-Step Solution

Answer

The secondary oocyte is haploid.

Step 1: Understand Haploid vs Diploid

Haploid cells contain a single set of chromosomes, denoted as \(n\), which is half the number of chromosomes found in diploid cells. Diploid cells contain two sets of chromosomes, denoted as \(2n\). Only certain stages in the lifecycle of gametes, such as during meiosis, are haploid.

Step 2: Evaluate Each Option

Review each type of cell to determine its ploidy:- Primary oocyte (a): These cells are part of oogenesis and are diploid (\(2n\)).- Oogonium (b): This is an early stage in the formation of egg cells and is also diploid (\(2n\)).- Secondary oocyte (c): Formed during meiosis, when the primary oocyte completes the first meiotic division, it becomes a secondary oocyte, which is haploid (\(n\)).- Corpus luteum (d): This is a structure formed from the follicle after ovulation and is made of diploid cells.- Follicle cell (e): These surround the oocyte and are diploid.

Step 3: Draw Conclusion

The only cell from the list of options that is haploid is the secondary oocyte. It is the result of meiosis I and contains a single set of chromosomes (\(n\)).

Key Concepts

Ploidy

Ploidy refers to the number of sets of chromosomes found in the nucleus of a cell. It is an important concept in genetics because it determines the chromosomal makeup and how cells will divide and function.
In general, ploidy levels can be categorized as:

• Haploid (n): Cells with a single set of chromosomes. These are usually found in gametes—sperm and egg cells—which unite during fertilization to form a diploid zygote.
• Diploid (2n): Cells containing two complete sets of chromosomes, one from each parent. Most body cells (somatic) are diploid.

Haploid cells are crucial for sexual reproduction as they ensure that when two gametes fuse, the resultant zygote has the correct number of chromosomes. Understanding ploidy is essential for identifying different life cycle stages of reproductive cells.

Meiosis

Meiosis is a specialized type of cell division that reduces the chromosome number by half, resulting in the production of haploid cells. This process is critical in sexual reproduction, ensuring genetic diversity among offspring.
Meiosis occurs in two main stages:

• Meiosis I: This is the reductional division where homologous chromosomes are separated. The primary oocyte undergoes this division and forms two daughter cells, including the haploid secondary oocyte.
• Meiosis II: Resembles mitosis where the sister chromatids are separated. In the female reproductive system, this step results in one mature egg and additional polar bodies.

Meiosis ensures that the number of chromosomes remains constant through generations and also introduces genetic variation through mechanisms like crossing over and independent assortment. The secondary oocyte is a vital product of meiosis, especially in oogenesis.

Oogenesis

Oogenesis is the process of forming female gametes, or egg cells, in the ovary. It starts before birth and continues with each menstrual cycle.

• Oogonium: An early stage cell in this process, it is diploid and undergoes mitosis to produce a primary oocyte.
• Primary Oocyte: These are diploid cells arrested at prophase I of meiosis until puberty. They resume meiosis in response to hormonal signals.
• Secondary Oocyte: Formed after the first meiotic division, it is haploid and only completes meiosis II if fertilization occurs.
• Corpus Luteum: Although not a part of the cell differentiation, it is an essential structure formed after ovulation that secretes hormones to support early pregnancy.

Oogenesis is a complex process involving both meiotic and hormonal changes to ensure that a mature, viable egg is released and ready for potential fertilization each cycle.