Genetics Chapter on Dominance and Segregation

Study Notes

Law of Dominance states that in hybrid organisms, only one trait appears while the other remains hidden; the dominant trait is expressed, while the recessive trait is not.
Law of Segregation explains that traits segregate independently during hybrid crossing, leading to predictable inheritance ratios established by Mendel, which can sometimes show incomplete dominance.

Average fertile man produces approximately 200 million sperm weekly; average fertile woman produces around 400,000 eggs every 28 days.
Fertilization occurs when a single sperm penetrates the egg, forming a zygote protected by a thick wall to prevent further sperm entry, solidifying the genetic combination.
Each parent contributes an equal number of chromosomes to the child, with sperm releasing chromosomes that replicate through meiosis, resulting in 23 pairs of chromosomes in germ cells.

Genes, located on chromosomes and invisible under the microscope, act as hereditary carriers capable of duplication.
Genes control cell processes that shape tissue development and function in pairs to determine specific physical traits and characteristics.
The law of dominance and recessiveness guides which traits manifest in offspring.

Heredity is the genetic transmission of characteristics from parents to offspring in organisms.
Genetics is the biological field that studies heredity mechanisms.

Dominant traits exemplify phenotypic expression (e.g., brown eyes, curly hair).
Recessive traits remain unexpressed in presence of dominant traits (e.g., blue eyes, straight hair).
Examples:
- Dominant: Brown eyes, Normal sight, Extra fingers.
- Recessive: Blue eyes, Night blindness, Normal number of fingers.

Homozygous refers to identical alleles for a trait, while heterozygous refers to different alleles.
Eugenics focuses on improving species heredity through selective breeding.
Euthenics emphasizes improvement through environmental regulation.

Mendel conducted genetic experiments on plant inheritance, laying the groundwork for heredity study through his observations.

Law of Unit Characters states traits are transmitted as distinct, individual entities.

Immature egg cells in ovaries are surrounded by germinal epithelium from birth.
Fertilized eggs undergo cell division; complete splits produce identical twins, while incomplete division results in Siamese twins.
Fraternal twins arise from two separate eggs fertilized independently.

Development is a continuous change process from origin to maturity, encompassing structural and functional changes.
Growth usually refers to quantitative changes, while development focuses on qualitative transformations.
Maturation is an aging-related process that excludes effects of practice; for instance, birds fly when wings mature, regardless of practice.