|Genetics for beginners|
Behavioral genetics is also known as behavior genetics. Behavior can also be classified into two types which are: a. Overt behavior (behavior that is readily available to be observed. For example, singing, jumping etc.) and b. Covert behavior (behavior that is not readily observable e.g. memory in the brain, thinking, brainstorming, homeostasis etc.).
What is behavioral genetics shall unfold in this article by first introducing the study of genetic characteristics, which is captured in the field of study called genetics. Gene is the unit of heredity that is, the basic or fundamental structure into which the physiological makeup of an individual organism can be traced.
Naturally, gene itself is structural and functional. By structural, it means it has constituents and by functional, it means it performs some functions. A gene codes for a particular trait…for example, blue eye (trait) is expressed by the gene that codes for it. Another example is leukocyte which some of its properties coded by the genes located in a part of the chromosome no 6.
By gene code, it simply means the complementary base pairing of gene bases as exemplified diagrammatically in the chain of nucleotides such as the bases (Adenine-Thymine, Cytosine-Guanine), Deoxyribose sugar, and the phosphate group.
Conventionally, the base codes are the genetic codes. That is to say, Adenine, Thymine (Uracil in the case if RNA which usually lacks thymine), Cytosine and Guanine. The codes are the set of instructions needed in order that protein might be formed which in turn serve as a prerequisite to body growth and development.
Gene and DNA
Gene as explained already as the unit of heredity and that it has structure but what really makes up the structure of the gene? The answer is, the chemical make-up, Deoxyribonucleic acid (DNA). The gene is better explained by using the DNA, its chemical structure and also by further breaking it down to its components.
Better still, in a diagrammatic or schematic way as to elucidate or clarify the structure itself.
Related: Current issues in Genetics
DNA, Gene and Chromosome
These three concepts of genetics should not be misrepresented. To make a clear distinction, they should not be used interchangeably although they are most likely talked about as a unity so that one does not exist without the existence of the others. Wonder how and why? Yes, this is because of the perfect relationship between them all.
A chromosome is a thread-like structure into which the genes (multiple numbers of them) are located. Genes themselves are the basis of protein formation.
In other words, without the genes that have the nucleotides (in form of codes), protein can never be formed. In a more rational and logical sense, DNA replication that is necessary for the increase of somatic cells (body cells) can never be. Without protein and protein too can never be formed without the existence of DNA in the first place.
Looking into the above diagram closely, it is evident that the DNA is molecular and as such, a tiny structure, in fact, a micro one. So minute! It is so amazing how the chromosome capable of containing into folds such a massive amount of genes.
The DNA is made up of a double helix which twists into each other. In-between the double helix is located other elements that form the rungs of the ladder. The DNA is thus a molecular structure of double helix integrating the nucleotides.
1 base codes,
2 deoxyribose sugar,
3 phosphate group
Alleles are nothing ambiguous or vague at all. They are the alternative forms of a gene, the variants of a gene. In fact, the diverse forms in which genes can manifest. For example, some genes code for height, therefore we say a tall person has acquired the gene for tallness. Height in this regard can be in two forms either tallness or shortness. Tallness and shortness in this case are the alleles.
Remember from the definition of an allele as the alternative forms of a gene (height). In most cases, we do not refer to allele, we refer to the gene. This is simply because of the fact that alleles are only being used for the purpose of analysis clarification and the crossing of traits or when using Punnet’s square to calculate the genetic probability of offspring(s) inheritance of the said trait. For Height in this example, the schematic view of its allele is T and t so that the uppercase letter “T” represents tallness and the lower case letter “t” represent shortness.
Types of allele
a. Single allele e.g. skin color
b. Multiple alleles e.g. the ABO system of blood group
Punnet Square for Genetic Probabilities
How and why do we test for the chance of inheriting a dominant or recessive gene? The probability is to ascertain at least in part whether the resultant zygote or offspring would carry a particular trait.
The result of the calculation is normally exhibited in genotypic ratio and phenotypic ratio this can be done by using the traditional Mendelian crossing method or the Punnet’s square method. Before going into the Punnet’s square or any crossing at all’ it is important to first note the pattern of gene transmission, patterns of inheritance and sex determination.
Patterns of Gene Transmission
How are genes transmitted from parents to their offspring? This is, of course, a question related to the genetic transmission which follows the pattern of the works of genetics and reproductive mechanisms.
By genetic mechanisms, it entails genetic processes such as gene replication. By reproduction, it entails the release or matured egg from the ovary to the fallopian tube of the female reproductive system, the sperm cell moves from the male gonad to the genitalia and then into the vagina and of course to the uterus, and finally, the fallopian tube where fertilization of the ovum takes place when the acrosome (head) of the sperm cell breaks the egg and eventually result in the zygote development within two weeks. Both reproduction and gene replication encompass the process of cell division (meiosis and mitosis).
Meioc Meiotic Cell Division
|Meiosis in action during cell division|
– Meiosis is a cell division specific to the formation of gametes ( egg cells and sperm cells)
– It halves the 46 chromosomes into a haploid set of chromosomes which means 23 so that a matured sperm cell or an ovum can produce additional numbers of the cell using itself as a precursor i.e. as a basis for the formation of the new cells.
– In order that multiple numbers of sperm cells or egg cells can be produced, replication of genes and chromosomes has to take place at first.
– Each sex cell contains 23 number of chromosomes that when the process of fertilization takes place, 46 chromosomes are produced in the resulting zygote.
– The 23rd chromosome is usually the sex chromosome which is X for females and Y for males. Here comes the phenomenon called sex determination of the resulting zygote/offspring.
– The division of sex cell results in 4 daughter cells per cycle because 23 which is the haploid number of chromosome in every sex cells replicate to become 46 and this 46 further divide into two halves so that we have 23, 23 chromosomes each for each sex cell (note that we now have 2 sex cells). These 23, 23 each is further replicated into 46, 46 which will soon divide again into 23, 23, 23, and 23 per cycle.
– If the sex cell is an egg, it is no doubt that we will definitely have X as its 23rd chromosome. For a sperm cell, it is a double chance that is, the 23rd chromosome could be an X or a Y. If during fertilization, the sperm cell that has an X chromosome fertilizes an egg, then we can expect a female offspring but if it is Y sperm that fertilizes the constant X egg, then we can expect a male offspring.
Mitosis in summary
|Mitosis in in action during cell division|
Mitosis follows almost the same pattern of meiosis (see meiosis) but differs in some number of ways:
– Mitosis is specific to somatic cells (body cells)
– Mitosis does not produce 4 daughter cells per cycle of cell division but rather produce 2 daughter cells per cycle. As it is evident in meiosis, the process of gene replication starts it.
– Mitosis may follow meiosis in order that zygote might be able to multiply their cells and therefore forms the parts of the body because mitosis is concerned with ‘soma’ (body) growth and development.
– This process goes on throughout lifespan where there is a gradual increase in size and height of the organism. Cells form and are organized into tissues which in turn organize into organs which in turn organize into systems.
Gene expression is simply the way genes become manifest to produce a trait. This is, however, a simplified or layman term of this phenomenon for the purpose of understanding.
In order for this to occur, genes must go through the process of replication. In the somatic cell, the gene is capable of self-replication that is, it can replicate itself so that there would be an effectual increase in the number of cells from the existing cells.
When in this case, an existing gene is used as a precursor that is, the basis or the information needed to be copied to from whatever new cells. It usually involves the formation of protein which is body-building in nature.
This is simply the reproduction of gene from the existing ones. It is different from gene cloning; cloning is the making of the exact copy of an organism through laboratory manipulations.
In gene replication, there is usually a process called transcription.
Transcription is the process by which the double helical strands of the DNA structure unfolds i.e. untwist. Each helix is further unzipped and the codes in the base pairing are copied into each other thereby resulting in more number of genes even as the process goes further. An enzyme usually starts the process and another enzyme ends it.
The formation of protein follows two processes;
This is the manufacture of protein which takes place at the ribosome in the cytoplasm of a cell. The information for determining the correct sequence of amino acids is carried to the ribosome by mRNA and the amino acids are brought to the correct position in the ribosome by the transferRNA.
Why does DNA have to transcribe? Why then use of mRNA and not carry the codes directly by itself to the ribosome in the cytoplasm? This is because genetically, DNA structure is too big to leave the nucleus so it needs to send a messenger (mRNA) because it is a single strand that can leave the nucleus.
It is this mRNA that carries the genetic codes instead. The codes are the bases: adenine, thymine, cytosine, guanine, and uracil (for mRNA-remember it replaces thymine but also note that the precursor code can be thymine).
The ribosome in the cytoplasm reads these codes in codons that is, in threes up to 64 and assembles the appropriate amino acids that match the codes. The amino acids are actually the free amino acids in the body which are broken- down proteins of the proteinous food (e.g. egg, beans) that we eat.
– mRNA uses uracil in place of thymine
– DNA serves as a template for mRNA
– The codes in the DNA are copied when the ‘start’ enzyme polymerase initiates the process and another enzyme ends it.
– Formation of protein follows the matching of the appropriate codes in three group of codes e.g. AUC ( Adenine, Uracil, Cytosine) up to about 64. These codes themselves do not form the protein but rather, they are the information needed by the ribosome to group three or more amino acids together which give rise to an amino acid chain called polynucleotide chain. The stop signal is initiated by a stop enzyme that terminates the process and thereby resulting in the polynucleotide chain into a newly formed protein just immediately.
List of 20 Different Amino Acids
4. ASPARTIC ACID
7. GLUTAMIC ACID
Pattern of Inheritance
The pattern in which traits are inherited follows the process of gene transmission. It includes concepts like;
ii. Incomplete dominance
c. Polygenic inheritance
d. Epigenic inheritance
This is a situation whereby a gene usually called dominant gene is the gene that is expressed in a particular trait.
a. Co-dominance is when two alleles for the same traits are equally expressed e.g. a black and white goat, a green and white leaf.
b. Incomplete dominance is the blending of two traits coming from the two parents e.g. the blending of red and green flower gave rise to a’ pink flower’ according to the Mendelian geneticist.
on the other hand is the gene that is masked or not expressed in a particular trait. For example,’Tt’ for height. Here ‘T’ is dominant over
‘t’, so ‘T’ alone is expressed but nevertheless, ‘t’ can still be transferred from parents to their offspring.
This is when a single trait is a direct result of the combinations of two or more genes that express that trait such as height.
From the word epigenetics, ‘epi’ means ‘outside of’ or ‘beyond’. This means beyond genetics. Logically, some traits can be acquired without the influence of the gene.
The concepts of phenotype and genotype
a. Genotype: is the genetic endowment of an organism .e.g. blood, colour of the skin, hair colour, certain diseases group etc.
b. Phenotype: is the obvious or visible characteristic as a result of the genotype and its interaction with the environment. For example, the colour of the skin, an individual’s shoe size, sounds of your voice.
Mutation is an alteration of the gene structure. It can occur as a physiological process i.e. when they are internal or inherent in the organism. They can also occur as environmental process i.e. environmental influences such as X-ray, nutrition etc.
Mutation of gene is usually the cause of;
a. Chromosomal abnormalities
i. Mongolism (Down’s syndrome),
ii. Turner’s syndrome
iii. Klinifelter’s syndrome
iv. Super male syndrome
v. Criduchat’s syndrome (cat’s cry)
b. Gene-linked abnormalities
ii. Cystic fibrosis
iii. Huntington’s disease
iv. Some cancers, e.g. breast and gastric cancers
v. Diabetes mellitus
c. Sex-linked abnormalities
i. Colour blindness
Behavioral genetics is the branch of genetics that seeks to understand the interaction or relationship between behavior, gene, and the environment in both human and animal. For further readings on this particular topic, search https//en.m.wikipedia.org/wiki/Behavioural_genetics, www.nature.com/scitable/topicpage/behavioural-genomics-29093
Research Frontiers in Behavioral Genetics
– Twins studies
– Adoption studies
– Reared together or reared apart
– Gene-environment interaction
– Gene-environment correlation
– Shared and non-shared environment
– Cloning and its methods such as: Intra-cytoplasmic-sperm-injection (ICSI), Invitro Fertilization (IVF)
– Cloning methods using certain animals as case studies e.g. Dolly the sheep, Cumilina.
– Mitosis and meiosis
– Human Genome project
I. Ross and Wilson Anatomy and Physiology 11th edition (www.rossandwilson.com). Pg. 427-436.
II. Oxford medical dictionary
III. Collins English dictionary
IV. Readings in Psychology. Edited by D.C. Uguru-Okorie