Assisted Reproduction, Genetics, and Heredity Concepts
Assisted Reproductive Technologies
In Vitro Fertilization (IVF)
In vitro fertilization is a technique where the union of an egg and sperm occurs in a laboratory. The resulting pre-embryo is then deposited in the patient’s uterus. This can be done using the patient’s own eggs or donated eggs. In either case, eggs are extracted from the woman’s body via ovarian puncture. Once obtained and treated, both the eggs and sperm are combined for fertilization. The patient receives hormonal treatment to prepare the uterus for pre-embryo implantation. Not all obtained eggs will successfully fertilize. When fertilization occurs, the egg will have two pronuclei, leading to a zygote. On the third day, the selected pre-embryos are transferred into the uterine cavity using a catheter. Two to three days after the transfer, the pre-embryo can implant in the endometrium of the uterus, where its development will continue normally.
Intracytoplasmic sperm injection (ICSI) is a specialized form of IVF where a single sperm is injected directly into the egg’s cytoplasm using a microneedle.
Artificial Insemination
Artificial insemination involves the introduction of previously treated semen into a woman’s uterus.
Recombinant DNA and Genetic Theories
Recombinant DNA
Recombinant DNA consists of fragments of DNA from different sources. These fragments are cut using enzymes called restriction endonucleases. These enzymes recognize specific DNA sequences and cut at precise locations. The resulting fragments have cohesive or ‘sticky’ ends that are complementary to other ends cut by the same enzyme. This allows fragments from different origins to join, creating recombinant DNA.
Pangenesis
Pangenesis is a theory that suggests every organ in the body produces gemmules that travel through the blood to the reproductive organs of offspring. If changes occur in the organs, the gemmules would also change.
Germplasm
The germplasm theory, developed by Weismann, proposes that the germplasm is self-perpetuating and determines the formation of the entire body. It establishes a continuity across generations without modification. Changes in the germplasm would result in changes throughout the body.
Mendelian and Post-Mendelian Inheritance
Mendelian Inheritance
Mendel selected seven characteristics for his experiments, including seed color and shape. He crossed purebred pea plants that differed in one characteristic.
- Hereditary factors are stored in pairs within gametes.
- These factors come from both parents and combine in the new individual without mixing when reproductive cells are formed.
Mendel’s laws govern the transmission of characteristics from one generation to the next:
- Law of Uniformity: The dominant trait is expressed, while the recessive trait is masked.
- Law of Segregation: Hereditary factors separate during gamete formation, leading to new combinations.
- Law of Independent Assortment: Characteristics are transmitted independently. This law is only true when genes are located on different chromosomes.
Post-Mendelian Inheritance
In 1900, three scientists rediscovered Mendel’s work. His laws were extended to animals. It was later learned that hereditary factors are not structures within cells. In 1916, it was demonstrated that genes are located on chromosomes. Genes located on different chromosomes are transmitted independently, while those on the same chromosome are transmitted together. Sometimes, recombination or exchange of fragments occurs between homologous chromosomes, joining genes that were previously separated. The instructions for life are stored in the cell nucleus. Each chromosome has two versions for the same trait. Within these chromosomes are genes that determine every characteristic of the organism. These genes, located on chromosomes, are passed from parents to offspring. In 1944, Avery showed that DNA, not protein, contains genetic information.