Theoretical Genetics Terminology (Genotypes (The homologous chromosomes…
Theoretical Genetics Terminology
1 DNA molecule with associated proteins (eukaryotic cells)
A segment of a DNA molecule that codes for a specific polypeptide chain = a gene
Other definition: A specific base pair sequence on a chromosome
Basic module of inhereitance
One can follow specific genes from one generation to the next and thus display the probability of genotype and phenotype ratios. Either one uses punnet grids or derive from calculations.
An individuals PHENOTYPE is not only defined by the GENOTYPE (NATURE) but also a product of internal and external conditions/ environments (NURTURE) effect on genetic expression. That could be physical cues or influenced epigenetics
PHENOTYPE: External and internal characteristics (physiology, anatomy, mental conditions) and behaviours.
Examples of such include: 1. The shape of ones nose and amount of facial hair (nature) 2. Skin pigmentation (nature) can be affected by sunlight (nurture) 3. Height- we are born with genetic pre-disposition for a maximum and minimum height (nature) but it is our diet (supply and content - nurture) that will decide the actual height attained.
Behaviours: 1. Innate: Genetically determined e.g. instincts, reflexes. 2. Learnt: pre-requisite is genetically determined i.e complex nervous system (nature) but what is preformed and how is dictated by the surrounding (nature)
Humans: 46 chromosomes / 23 pairs. The pairs consist of two homologous chromosomes where one was received from an egg (maternal) and one from a sperm (paternal).
The homologous chromosomes carry the same genes and for a sexual reproductive organism each gene has a double. These are called ALLELES.
Genes = Characteristics e.g to have eye colour
Alleles = Traits e.g. which eye color
Placement of genes/alleles is called their loci (sing. locus)
Alleles display different capacity of expression
Dominant: Allele is always expressed
Represented with capital letter e.g. D
Recessive: Only expressed if a dominant are absent e.g. seen between X and Y chromosomes where the male only has one set-up of genes. For autosomal chromosomes an individual needs two recessive for it to be expressed.
Represented with versal letter e.g. d
Co-dominant: Will be expressed independently of another co-dominant. E.g. blood type AB. Sometimes it can give rise to an intermediate expression i.e. mix between the co-dominant alleles e.g. petal colours.
Represented with same capital letter for the gene and a superscript capital letter displaying the allele
Homozygotic: If the gene is represented by two of the same allele
Heterozygotic: If the gene is represented by two different alleles
Heterozygotic: i.e. one dominant and one recessive
Phenotypes are often described in words but can also be displayed using the letters used for the involved alleles adding a tidle (-) on top of the letters
Red = R and White = r
For R (-): genotype is unknown, it can either be a heterozygotic or dominant homozygotic condition the causes the phenotype
For r (-): the genotype is known. Always a recessive homozygotic condition otherwise it would not be expressed.
Mendelian ratios: The same as the phenotypic ratio seen in offspring after breeding
In a population there may be MULTIPLE ALLELES for a gene but an individual can only have two of them. E.g. For the ABO system of blood types there are three alleles. Two co-dominant: IA and IB and one recessive i.
MENDELIAN genetics / hypothesis
Characteristics are inherited from both parents
Characteristics (later = genes) comes in version (later = gene)
The versions (alleles) have different capacity of expression. Dominant vs. recessive
The version (alleles) are segregated into different packages (later = gametes, egg and sperm) before reproduction and delivered into the offspring
Compare with Meiosis 1: At Anaphase 1 the homologous pairs (the maternal and the paternal) are separated and places in separate cells