Biology Of Heredity (Genetics)-Transmission And Expression Of Characteristics In Organisms
A) Hereditary Variations: Characters that can be transferred from parents to offsprings-from generation to generation like skin colour, eye and hair, blood group, sickle cell, shape of face and nose
Genetics is the branch of biology that deals with the science of heredity. Heredity is the transfer of characteristics from one generation to the next. It is the reason why offspring resemble their parents. For instance, we know that a tall mother and a tall father are liable to have children that are tall.
It as well explains why cats constantly give birth to kittens and never puppies. Geneticists (scientists who study genetics) are interested in finding out two things regarding this observation.
First, what is there in the cells of a person’s body that signals the body to become tall instead of short? Second, how are the signals for “tallness” transferred from parent to offspring, from one generation to the next?
The process of heredity takes place in the midst of every living thing including animals, plants, bacteria, protists and fungi. The study of heredity is known as genetics and scientists that learn heredity are called geneticists.
Through heredity, living things take over traits from their parents. Traits are physical characteristics. You bear a resemblance to your parents due to the fact that you inherited your hair and skin color, nose shape, height, and other traits from them.
Cells are the fundamental unit of structure and function of every living thing. Small biochemical structures inside every cell known as genes transmit traits from one generation to the other.
Genes are made of a chemical known as DNA (deoxyribonucleic acid). Genes are strung jointly to structure long chains of DNA in structures referred to as chromosomes.
Genes are similar to blueprints for building a house, apart from the fact that they bear the plans for building cells, tissues, organs, and bodies. They have the instructions for manufacturing the thousands of chemical building blocks in the body.
These building blocks are known as proteins. Proteins are made of smaller units known as amino acids. Differences in genes give rise to the building of diverse amino acids and proteins.
These differences give rise to individuals that possess various traits like hair color or blood types.
A gene offers only the prospective for the development of a trait. The way this potential is achieved depends partially on the interaction of the gene with other genes. But it as well depends partly on the environment.
For instance, a person may have a genetic tendency toward being overweight. But the person’s real weight will depend on such environmental factors like the kinds of food the person eats and the amount of exercise that person does.
The history of Genetics
Humans have known about hereditary characteristics for thousands of years. That knowledge has been used for the improvement of domestic plants and animals. Until the late nineteenth century, however, that knowledge had been obtained through trial-and-error experiments.
The contemporary science of genetics started with the pioneering work of the Austrian monk and botanist Gregor Mendel (1822–1884).
Words you may come across and their meaning
DNA (deoxyribonucleic acid): Molecules that make up chromosomes and on which genes are situated.
Dominant gene: The state or genetic trait that will constantly convey itself when present as part of a pair of genes in a chromosome.
Gene: A section of a DNA molecule that carries instructions for the formation, functioning, and transmission of specific traits from one generation to another.
Heredity: The transfer of characteristics from parents to offspring.
Nucleotide: A group of atoms that exists in a DNA molecule.
Proteins: Large molecules that is crucial to the structure and functioning of all living cells.
Recessive gene: The state or genetic trait that can put across itself only when two genes, one from both parents, are available and act as a kind of code for creating the trait, but will not articulate itself when paired with a dominant gene.
Triad: This is as well referred to as codon; group of three nucleotides that carry a particular message for a cell.
Through heredity, variations demonstrated by individuals can build up and cause a number of species to evolve. The study of heredity in biology is known as genetics, which includes the field of epigenetic.
In humans, eye color is an example of an inherited characteristic: characteristics transferred from parents to offspring. An individual might inherit the “brown-eye trait” from one of the parents. Inherited traits are restricted by genes and the complete set of genes within an organism’s genome is known as its genotype.
The entire set of observable traits of the structure and behavior of an organism is called its phenotype. These traits arise from the interaction of its genotype with the environment. As a result, a lot of aspects of an organism’s phenotype are not inherited.
For instance, suntanned skin comes from the interaction between a person’s phenotype and sunlight; thereby, suntans are not transferred to people’s children.
Nevertheless, a few people auburn more easily than others, as a result of differences in their genotype: a conspicuous example is people with the inherited trait of albinism, who do not auburn at all and are very sensitive to sunburn.
Heritable traits are transferred from one generation to the other through DNA, a molecule that encodes genetic information. DNA is a longpolymer that is made up of four types of bases, which are exchangeable.
The sequence of bases along a specific DNA molecule specifies the genetic information: this is equivalent to a sequence of letters spelling out a passage of text.
Prior to the cell division through mitosis, the DNA is copied, so that every one of the resultant two cells will inherit the DNA progression.
A segment of a DNA molecule that specifies a particular functional unit is known as a gene; different genes have different progressions of bases.
Within cells, the long strands of DNA form condensed structures known as chromosomes.
Organisms inherit genetic material from their parents in the form of homologous chromosomes, containing a unique amalgamation of DNA progressions that code for genes.
The definite location of a DNA sequence within a chromosome is referred to as a locus. If the DNA sequence at a specific locus varies between individuals, the diverse forms of this sequence are known as alleles.
DNA sequences can alter through mutations, giving rise to fresh alleles. If a mutation takes place within a gene, the fresh allele may have effect on the trait that the gene controls, changing the phenotype of the organism.
Although this simple correspondence between an allele and a trait works in a few cases, the majorities of traits are more compounds and are restricted by multiple interacting genes within and among organisms.
Developmental biologists recommend that composite interactions in genetic networks and communication among cells can result to heritable variations that may underlay a number of of the mechanics in developmental plasticity and canalization.
B) Mendel Works In Genetics: Mendelian Traits, Mendelian Law And Mendelian Experiment
Mendelian laws of inheritance are statements about the manner specific characteristics are transmitted from one generation to another in an organism. The laws were derived by the Austrian monk Gregor Mendel (1822–1884) as a result of experiments he carried out in the period from about 1857 to 1865.
For his experiments, Mendel made use of ordinary pea plants.
Among the traits that Mendel examined were the color of a plant’s flowers, their position on the plant, the shape and color of pea pods, the shape and color of seeds, and the length of plant stems.
Mendel’s experiment was to transfer pollen (which is composed of male sex cells) from the stamen (the male reproductive organ) of one pea plant to the pistil (female reproductive organ) of a second pea plant.
As a plain example of this sort of experiment, presume that one takes pollen from a pea plant with red flowers and makes use of it to fertilize a pea plant with white flowers.
What Mendel intended to find out is what color the flowers would be in the offspring of these two plants. In a second series of experiments, Mendel examined the changes that took place in the second generation.
That is, assuming two offspring of the red/white mating (“cross”) are themselves mated. What color will the flowers be in this second generation of plants?
As a result of his experiments, Mendel was able to come out with three generalizations about the way characteristics or traits are transmitted from one generation to the next in pea plants.
Words you ought to Know
Allele: One of two or more forms a gene may exist in.
Dominant: An allele whose expression overshadows the effect of a second form of the same gene.
Gamete: A reproductive cell.
Heterozygous: A state in which two alleles for a given gene differ from each other.
Homozygous: A state in which two alleles for a given gene are the same.
Recessive: An allele whose effects are covered in offspring by the dominant allele in the pair.
Mendel’s first law: The Law of Segregation
Mendel’s law of segregation explains what occurs at the alleles that constitute a gene during formation of gametes. For instance, suppose that a pea plant is composed of a gene for flower color in which the two alleles code for red.
One way to symbolize that condition is to write RR, which indicates that both alleles (R and R) code for the color red. An additional gene might possess a diverse combination of alleles, as in Rr.
In this situation, the symbol R stands for red color and the r for “not red” or, in this situation, white. Mendel’s law of segregation says that the alleles that constitute “a gene” break up from each other, or segregate, during the formation of gametes.
That law can be represented by simple equations, like:
RR → R + R or Rr → R + r
Mendel’s second Law: Law of independent assortment
Mendel’s second law-the law of independent assortment refers to the fact that any plant contains a lot of different kinds of genes. One gene determines the colour of the flower, a second gene determines length of stem, a third gene determines shape of pea pods, and so on.
Mendel observed that the manner in which alleles from dissimilar genes divide and then recombine is unconnected to other genes. That is, assuming that a plant contains genes for color (RR) and for shape of pod (TT).
Then Mendel’s second law says that the two genes will segregate independently, as shown below:
RR → R + R and TT → T + T
Mendel’s third law: Dominance
Mendel’s third law takes care of issue of dominance. Assuming that a gene is composed of an allele for red color (R) and an allele for white color (r).
What colour will the flower of the final plant take? Mendel found out that in every pair of alleles, one is more likely to be expressed than the other.
In other words, one allele is dominant and the other allele is recessive.
In the example of an Rr gene, the flowers produced will be red for the fact that the allele R is dominant over the allele r.
MENDELIAN LAWS OF INHERITANCE