Understanding Species, Genetics, and Mitosis: Key Biological Concepts
Understanding Species and Biological Variation
A species is a group of organisms that can reproduce with each other and whose offspring are fertile.
Key Characteristics
The characteristics that allow us to distinguish one individual from another are called characters.
- Discontinuous variation: Occurs if the character can be used to divide the members of one species into two or more distinct groups.
- Continuous variation: Occurs if the differences between individuals are very small and gradual.
Hereditary vs. Acquired Characters
- Hereditary characters: Transmitted generation after generation, although they may not appear in every generation.
- Acquired characters: Not transmitted to offspring.
Genetics and Karyotypes
The genetic information responsible for the character of a new individual is located in the nucleus of the egg cell. The set of chromosomes in a cell or individual is called a karyotype.
Human Karyotyping
- Men: 44 chromosomes form 22 pairs, but the 23rd pair is formed by two different chromosomes: the X chromosome and the Y chromosome.
- Women: The two chromosomes of each pair are homologous. In the 23rd pair, both are X chromosomes.
Chromosomes, Genes, and the Genome
Chromosomes are the support of genetic information. The portion of a chromosome that carries the information for a character is called a gene, and the complete set of genes of an individual or species is known as the genome.
The Process of Mitosis
Mitosis consists of four distinct phases:
- Prophase: Chromatin, which was scattered, condenses and the chromosomes become visible.
- Metaphase: Chromosomes, now short and thick, arrange themselves in a central plane.
- Anaphase: The centromere of each chromosome splits, and the chromatids separate.
- Telophase: Once at the respective poles, the daughter chromosomes are surrounded by a new nuclear membrane, completing the division of the nucleus.
Mitosis ensures that the nuclei of daughter cells receive a set of chromosomes identical to the stem cell. The duplication of genetic material occurs prior to cell division, ensuring that daughter cells receive equal copies during the cell cycle.