Biology: Sexual Reproduction and Meiosis

Study Notes

Many organisms pass genes to offspring through sexual reproduction, which begins when two gametes unite to form a genetically unique embryo.
The embryo grows into an adult, passing genetic information to its own offspring.

Meiosis produces haploid gametes with one copy of each chromosome from diploid germline cells with two copies of each chromosome.
Meiosis consists of two cell division events: Meiosis I and Meiosis II.

Before meiosis, cells pass through interphase, G1, S, and G2 stages.
During S phase, DNA is duplicated, forming sister chromatids that remain attached until Meiosis II.

Meiosis I results in two unique daughter cells with half the DNA of the parent germline cells.
Prophase I involves DNA condensation, chromosomal synapsis, and crossing over, making each pair of sister chromatids unique.
Metaphase I involves the alignment of synapsed chromosomes at the equator of the cell.
Anaphase I involves the separation of homologous chromosomes to the two poles of the cell.
Telophase I and cytokinesis result in two daughter cells.

Meiosis II is similar to Mitosis, with no synapsis or crossing over.
Prophase II involves chromosome condensation, nuclear envelope breakdown, and spindle apparatus formation.
Metaphase II involves the alignment of chromosomes at the equator of the cell.
Anaphase II involves the separation of sister chromatids as microtubules shorten.
Telophase II and cytokinesis result in four unique haploid cells (gametes).

Two gametes, one from each parent, fuse to form a diploid embryo that grows through many cycles of Mitosis.

Sexual reproduction allows organisms to pass genes to their offspring, resulting in genetically unique individuals.
This process begins with the fusion of two gametes to form a unique embryo, which grows into an adult and passes its genetic information to its own offspring.

Meiosis is a process that produces haploid gametes with one copy of each chromosome from diploid germline cells with two copies of each chromosome.
Meiosis consists of two consecutive cell division events: Meiosis I and Meiosis II.

Before meiosis, cells undergo interphase, consisting of G1, S, and G2 stages.
During the S phase, DNA is duplicated, resulting in sister chromatids that remain attached until Meiosis II.

Meiosis I results in two unique daughter cells, each with half the DNA of the parent germline cells.
Prophase I involves DNA condensation, chromosomal synapsis, and crossing over, making each pair of sister chromatids unique.
Metaphase I involves the alignment of synapsed chromosomes at the equator of the cell.
Anaphase I involves the separation of homologous chromosomes to the two poles of the cell.
Telophase I and cytokinesis result in two daughter cells.

Meiosis II is similar to Mitosis, with no synapsis or crossing over.
Prophase II involves chromosome condensation, nuclear envelope breakdown, and spindle apparatus formation.
Metaphase II involves the alignment of chromosomes at the equator of the cell.
Anaphase II involves the separation of sister chromatids as microtubules shorten.
Telophase II and cytokinesis result in four unique haploid cells (gametes).

The fusion of two gametes, one from each parent, results in a diploid embryo that grows through many cycles of Mitosis.
This diploid embryo contains genetic information from both parents.

A person consumes around 1-2.7 kilograms of food per day, equivalent to over 365 kilograms per year and 28,800 kilograms in a lifetime.
The digestive system consists of ten specialized cells and is one of the most complex systems in the human body.

The digestive tract is a winding tube with a surface area of approximately 30-40 square meters, equivalent to half a tennis court.
The tract is responsible for breaking down food into nutrients and energy.

Salivary glands produce around 1.5 liters of saliva per day, which breaks down carbohydrates into simpler forms using the enzyme amylase.
The food then enters the esophagus, a 25-centimeter-long tube, where it is propelled towards the stomach by muscular contractions.

The stomach is a sac-like structure that secretes digestive enzymes and acids to break down proteins and fats.
Hormones produced by the stomach lining stimulate the pancreas, liver, and gallbladder to produce digestive enzymes and bile.

After 3 hours in the stomach, the partially digested food enters the small intestine, where most nutrient absorption takes place.
The liver releases bile into the small intestine to break down fats, and pancreatic enzymes break down proteins and carbohydrates.
The walls of the small intestine are lined with finger-like projections called villi, which increase the surface area for absorption.

The remaining waste products, including fiber, water, and dead cells, enter the large intestine, also known as the colon.
The body absorbs most of the remaining fluids, and the leftover waste is formed into a soft, stool-like consistency called feces.
The feces are stored in the rectum until they are eliminated through the anus.