Animal Reproduction and Mating Systems

Study Notes

Breeding is based on the concept that certain characteristics are transmitted from parents to offspring.
The goal of breeding is to produce offspring that are as good as or better than their parents.

Reproduction occurs through the union of an egg (ovum) from the female parent and a sperm from the male parent.
The characteristics expressed by the offspring result from the information passed on by the parents through these gametes.

All living organisms, including plants and animals, are composed of small microscopic units of organized life called cells.
Cells are made up of protoplasm, a viscous, jellylike material, surrounded by a thin cell membrane.
Cells can be single-celled (protozoa or microbes) or composed of millions/billions of cells specialized into different groups or types performing specific functions.

All cells have two major parts: the nucleus and the cytoplasm.
The nucleus is oval-shaped, consisting of thick protoplasm in the center of the cell.
Cytoplasm is the thin, watery portion of the protoplasm surrounding the nucleus.

Chromatin is the dark-stained material present in the nucleus, visible under a microscope.
Chromatin can take different forms depending on the stage of cell activity, including chromatin granules, chromatin network, or rod-shaped bodies called chromosomes.
Chromosomes occur in pairs in diploid cells, with each pair consisting of homologous chromosomes (similar in size and shape).
Each species has a characteristic number of chromosome pairs (e.g., 30 in cattle, 27 in sheep, 30 in horses, 33 in donkeys).

During gametogenesis, one member of each homologous pair of chromosomes is passed on to each gamete.
On fertilization, the zygote receives one member of each homologous pair of chromosomes from each parent (father through sperm, mother through ovum).
The number of chromosome pairs is restored in newborn individuals.
The members of homologous chromosomes segregate and assort in all possible combinations according to the laws of chance or probability among the gametes contributed by the individual to the next generation.
Hereditary material/genes present on these chromosomes is transmitted from parents to offspring.