chapter 12/13 (mitosis/meiosis, cell cycle, mendel)

What is the cell cycle?

The cell cycle is the repeating process by which cells grow, replicate DNA, and divide to form new cells, allowing for growth, repair, and reproduction.

What is the purpose of mitosis?

Mitosis ensures that when a cell divides, each new daughter cell receives an identical set of chromosomes, maintaining chromosome number from one generation of cells to the next.

What is cytokinesis?

Cytokinesis is the division of the cytoplasm following mitosis, resulting in two separate daughter cells.

What are sister chromatids?

Sister chromatids are identical copies of a chromosome that are joined together at a region called the centromere before being separated during mitosis or meiosis.

What is the difference between mitosis and meiosis?

Mitosis produces two genetically identical diploid cells for growth or repair, while meiosis produces four genetically unique haploid cells for sexual reproduction, reducing chromosome number by half.

What are the phases of the cell cycle?

The cell cycle includes M phase (mitosis and cytokinesis), G1 phase (growth), S phase (DNA synthesis or replication), and G2 phase (growth and preparation for division). Cells may also enter G0, a non-dividing resting stage.

What happens during the G1 phase?

The cell grows, performs normal metabolic functions, and prepares for DNA replication.

What happens during the S phase?

DNA is replicated, forming two identical copies of each chromosome (sister chromatids).

What happens during the G2 phase?

The cell continues to grow, produces proteins needed for mitosis, and checks for any DNA errors before division.

What happens during the M phase?

The cell undergoes mitosis (nuclear division) and cytokinesis (cytoplasmic division), forming two new cells.

What is interphase?

Interphase includes G1, S, and G2 phases; it is the period when the cell grows, duplicates its DNA, and prepares for mitosis. It does not include M phase.

What happens during prophase?

• Chromatin condenses into visible chromosomes,

• the nuclear membrane and nucleolus break down,

• spindle fibers form,

• centrioles move to opposite poles of the cell.

What happens during prometaphase?

• The nuclear envelope completely disappears,

• spindle fibers attach to chromosomes at the kinetochores,

• chromosomes begin to move toward the cell’s center.

What happens during metaphase?

• Chromosomes line up along the equator (metaphase plate) of the cell

• attached to spindle fibers from opposite poles.

What happens during anaphase?

• Sister chromatids separate at the centromere and move toward opposite poles of the cell

• becoming individual chromosomes.

What happens during telophase?

• Chromosomes de-condense back into chromatin,

• nuclear membranes reform around each set of chromosomes, and the nucleolus reappears.

• Cytokinesis often begins here.

What happens during cytokinesis in animal cells?

The cell membrane pinches inward at a cleavage furrow until the cell splits into two daughter cells, each with identical DNA.

What happens during cytokinesis in plant cells?

A cell plate forms between the two nuclei, which develops into a new cell wall separating the two daughter cells.

How do bacteria reproduce?

Bacteria reproduce asexually through binary fission, where the DNA replicates and the cell splits into two identical cells.

What are internal controls of the cell cycle?

Internal controls include

• proteins like Cyclin-Dependent Kinases (CDKs)

• Maturation Promoting Factors (MPFs) that regulate checkpoints to ensure the cell only divides when conditions are right.

What are external controls of the cell cycle?

External controls include

• growth hormones, nutrients,

• physical factors such as anchorage dependence (cells must attach to a surface to divide) and density-dependent inhibition (cells stop dividing when crowded).

What happens when cell cycle control is lost?

Loss of control leads to uncontrolled cell division and can cause cancer.

What is cancer?

Cancer is a disease caused by the loss of cell cycle control, leading to uncontrolled cell growth and division.

What are benign and malignant tumors?

Benign tumors remain localized and do not spread, while malignant tumors invade surrounding tissues and can spread to other parts of the body (metastasis).

What are oncogenes and tumor suppressor genes?

Oncogenes promote cell division and can cause cancer when overactive. Tumor suppressor genes, like p53, normally prevent uncontrolled growth but can lead to cancer when mutated or inactive.

What is the Hayflick limit?

The Hayflick limit is the number of times a normal human cell can divide (about 50–70 times) before it stops due to telomere shortening.

What are telomeres?

Telomeres are DNA sequences at the ends of chromosomes that protect genes from being lost during DNA replication. They shorten each time a cell divides.

What is telomerase?

Telomerase is an enzyme that rebuilds telomeres, allowing some cells—like stem cells and cancer cells—to divide indefinitely.

What are Blue Zones?

Blue Zones are regions of the world where people live exceptionally long lives due to a combination of genetics, lifestyle, diet, social support, and environment.

What is heredity?

Heredity is the passing of traits from parents to offspring through genes.

What is genetics?

Genetics is the scientific study of heredity and the variation of inherited characteristics.

What are genes and alleles?

Genes are segments of DNA that code for traits, while alleles are different forms of a gene that can produce variations of a trait.

What are homologous chromosomes?

Homologous chromosomes are pairs of chromosomes (one from each parent) that carry genes for the same traits in the same locations.

What is a diploid cell?

A diploid cell (2n) has two sets of chromosomes—one from each parent (46 total in humans).

What is a haploid cell?

A haploid cell (n) has one set of chromosomes (23 in humans). Gametes like sperm and egg cells are haploid.

What is a karyotype?

A karyotype is a visual display of all the chromosomes in a cell, arranged by size and shape, used to detect chromosomal abnormalities.

What is asexual reproduction?

Asexual reproduction produces offspring from a single parent without the fusion of gametes. The offspring are genetically identical clones of the parent.

What is sexual reproduction?

Sexual reproduction involves the fusion of two gametes (egg and sperm), producing genetically unique offspring and increasing genetic variation.

Why is sexual reproduction advantageous?

It increases genetic variability, which helps populations adapt to changing environments.

What is meiosis?

Meiosis is a type of cell division that reduces the chromosome number by half, creating four haploid gametes for sexual reproduction.

What are the two stages of meiosis?

Meiosis I separates homologous chromosome pairs, and Meiosis II separates sister chromatids.

What happens during Prophase I?

Homologous chromosomes pair up and exchange genetic material through crossing over, forming tetrads. This increases genetic diversity.

What is crossing over?

Crossing over is the exchange of DNA between non-sister chromatids of homologous chromosomes, creating new gene combinations.

What happens during Metaphase I?

Homologous chromosome pairs line up along the equator of the cell, and independent assortment occurs (random arrangement of maternal and paternal chromosomes).

What is independent assortment?

Independent assortment is the random distribution of homologous chromosome pairs during meiosis, leading to genetic variation in gametes.

What happens during Anaphase I?

Homologous chromosomes separate and move to opposite poles of the cell, but sister chromatids remain attached.

What happens during Telophase I and cytokinesis?

The cell divides into two haploid daughter cells, each with half the number of chromosomes, but each chromosome still has two sister chromatids.

What happens during Meiosis II?

The two haploid cells divide again, separating sister chromatids into four genetically unique haploid gametes.

How many cells are produced at the end of meiosis, and how many chromosomes do they have?

Four haploid cells are produced, each with half the original number of chromosomes (23 in humans).

Why does only one egg survive in females after meiosis?

In females, unequal division of cytoplasm results in one large egg cell and smaller polar bodies that disintegrate, ensuring the egg has enough nutrients.

What are the four main sources of genetic variation in sexually reproducing organisms?

1. Crossing Over (recombines DNA), 2. Independent Assortment (random chromosome separation), 3. Random Fertilization (which sperm meets which egg), and 4. Random Mating (who reproduces with whom).

What is the total potential number of genetic combinations in humans?

Two to the 23rd power from each parent (8.3 million combinations) can combine to produce about 70 trillion potential diploid combinations in offspring.

What is mutation?

A mutation is a change in DNA sequence and is the only source of entirely new genes. Sexual reproduction only reshuffles existing genes.