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Biology: Genetics, Reproduction, and Biotechnology - Mitosis, Meiosis, and the Cell Cycle

Grade 8IB

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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The Cell Cycle consists of two main phases: Interphase (which includes G1G_1, SS (DNA Synthesis), and G2G_2 stages) and the M-phase (Mitosis and Cytokinesis).

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Mitosis is the process of nuclear division in somatic cells, resulting in two genetically identical daughter cells, maintaining the diploid (2n2n) chromosome number.

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The stages of Mitosis are Prophase, Metaphase (chromosomes align at the equator), Anaphase (sister chromatids separate), and Telophase (two new nuclei form).

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Meiosis is a reduction division that occurs in germ cells to produce gametes (sperm and egg). It reduces the chromosome number from diploid (2n2n) to haploid (nn).

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Genetic variation in meiosis is achieved through 'crossing over' during Prophase I and 'independent assortment' during Metaphase I.

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Biotechnology utilizes the principles of the cell cycle for processes like cloning (producing genetically identical copies via mitosis) and stem cell therapy.

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DNA replication occurs during the SS phase of interphase, ensuring that each new cell receives a complete set of genetic instructions.

📐Formulae

Total cells after n mitotic divisions=2n\text{Total cells after } n \text{ mitotic divisions} = 2^n

Diploid number=2n\text{Diploid number} = 2n

Haploid number=n=2n2\text{Haploid number} = n = \frac{2n}{2}

Surface Area to Volume Ratio=SAV\text{Surface Area to Volume Ratio} = \frac{SA}{V}

💡Examples

Problem 1:

A human skin cell contains 2n=462n = 46 chromosomes. If this cell undergoes mitosis, how many chromosomes will be present in each of the daughter cells?

Solution:

46 chromosomes46 \text{ chromosomes}

Explanation:

Mitosis is an equational division. The parent cell replicates its DNA once and divides once, ensuring that each daughter cell retains the full diploid (2n2n) number of chromosomes, which is 4646 in humans.

Problem 2:

Calculate the total number of cells produced from a single parent cell after it completes 66 successive mitotic divisions.

Solution:

26=64 cells2^6 = 64 \text{ cells}

Explanation:

In mitosis, the number of cells doubles with every division. Using the formula 2n2^n, where n=6n=6: 2×2×2×2×2×2=642 \times 2 \times 2 \times 2 \times 2 \times 2 = 64.

Problem 3:

A fruit fly has a diploid number of 2n=82n = 8. How many chromosomes will be found in its sperm cell after meiosis?

Solution:

n=4 chromosomesn = 4 \text{ chromosomes}

Explanation:

Meiosis is a reduction division. Gametes (like sperm cells) are haploid (nn), meaning they contain half the number of chromosomes of a somatic cell. 82=4\frac{8}{2} = 4.