Genetics: Cell Cycle & Mitosis

Flashcards testing core concepts of genetics, cell nucleus structure, cell cycle stages, mitotic phases, cytokinesis, and chromosome counting based on Lecture 1.

What is genetics?

Genetics is the science that seeks to understand, explain, and ultimately exploit the phenomenon of heredity, including the transmission of biological characteristics, its mechanism, and its variation.

What is the primary function of the cell nucleus?

It acts as the control center of the cell by protecting DNA from damage, maintaining gene integrity, regulating gene expression, and storing information needed for the cell to grow, reproduce, and function.

What are the structural features and barrier functions of the nuclear membrane?

It is a double membrane with inner and outer layers separated by $10 - 50\,\text{nm}$ that isolates nuclear contents from cytoplasm and prevents free diffusion of macromolecules between the nucleoplasm and cytoplasm.

What family of proteins makes up the main components of the nuclear pore complex?

Nucleoporins, which are a family of $50\text{ to }100$ proteins that allow free movement of small molecules and ions while requiring active transport by carrier proteins for larger molecules.

What is the function of the nucleolus?

To transcribe ribosomal RNA ($\text{rRNA}$) and combine it with proteins to form almost-complete ribosomes.

What is the difference between euchromatin and heterochromatin?

Euchromatin is the less compact form of DNA containing genes frequently expressed by the cell, whereas heterochromatin is the more compact form containing DNA that is infrequently transcribed.

What is the central dogma of biology?

The essential biological process by which genetic information stored in DNA gets transferred to the rest of the cell: $\text{DNA} \rightarrow \text{RNA} \rightarrow \text{Protein}$.

What protein structures bind to the centromere to attach spindle microtubules during cell division?

Kinetochores, which are two protein discs bound to a specific DNA sequence located within the centromere region.

How are chromosomes categorized based on centromere position?

They are classified into Telocentric, Acrocentric, Submetacentric, and Metacentric based on the placement of the centromere relative to the short arm ($p$) and long arm ($q$).

What are homologous chromosomes?

Chromosome pairs of the same length, centromere position, and gene order for the same characteristics at corresponding loci, making them similar but not identical.

How do sex chromosomes determine biological sex in humans?

Males possess $XY$ sex chromosomes (heterogametic), whereas females possess $XX$ sex chromosomes (homogametic).

What is a karyotype?

A karyotype is the particular array of the complete set of nuclear chromosomes in a species or organism, describing chromosome count and microscopic appearance.

What are the two main division events involved in cell division?

Nuclear Division (Karyokinesis) and Cytoplasmic Division (Cytokinesis).

What are the key functional differences between mitosis and meiosis?

Mitosis occurs in somatic or meristematic cells producing 2 identical daughter cells with exact DNA copies, while meiosis occurs in germ cells producing 4 cells each with half the parent DNA amount.

What main processes occur during the $G_1$, $S$, and $G_2$ stages of Interphase?

In $G_1$, cell growth and active RNA/protein synthesis occur. In $S$, DNA replicates and histones are synthesized. In $G_2$, essential mitotic components (such as spindle fiber proteins) are synthesized.

What occurs during the $G_0$ phase of the cell cycle?

The nucleus remains in a non-dividing resting stage designated for cells that undergo cell differentiation rather than further division.

What key cellular changes mark Prophase of mitosis?

Chromatin condenses into distinct chromosomes ($2n$ duplicated chromosomes per nucleus), the mitotic spindle forms, the nuclear envelope disintegrates, and nucleoli disappear.

What key events occur during Metaphase of mitosis?

Chromosomes reach maximum contraction, line up along the equator (metaphase plate) of the cell, and connect to a fully established bipolar mitotic spindle.

What occurs during Anaphase of mitosis?

Centromeres divide longitudinally, and separated sister chromatids migrate as daughter chromosomes toward opposite poles ($2n$ single chromosomes per pole).

What events characterize Telophase of mitosis?

Spindle fibers disappear, daughter chromosomes arrive at opposite poles, nuclear envelopes reform around each set ($2n$ single chromosomes per nucleus), and nucleoli reappear.

How does cytokinesis take place in plant cells?

Golgi vesicles and ER gather at the cell equator to form a cell plate, which develops into the middle lamella and primary cell wall to complete cytoplasmic division.

For a plant cell with $2n = 20$, what are the chromosome and chromatid numbers during Anaphase of mitosis?

The chromosome count is $40$ and the chromatid count is $40$.

For a plant cell with $2n = 20$, what are the chromosome and chromatid numbers during Metaphase of mitosis?

The chromosome count is $20$ and the chromatid count is $40$.