Genetics Notes PDF

## EDITED BY JUDE EZEJIOFOR AMADI ### Haploid = N ### Diploid = 2N A gene is a unit that specifies a particular trait. ### Chromosome Associations: Thomas Hunt Morgan Thomas Hunt Morgan, an American geneticist, carried out research on the fruit fly *Drosophila melanogaster* because it can be eas...

## EDITED BY JUDE EZEJIOFOR AMADI ### Haploid = N ### Diploid = 2N A gene is a unit that specifies a particular trait. ### Chromosome Associations: Thomas Hunt Morgan Thomas Hunt Morgan, an American geneticist, carried out research on the fruit fly *Drosophila melanogaster* because it can be easily and economically cultured in large numbers in the laboratory. It produces a new generation every 10-12 days. ### F2 Mixture of Tall and Dwarf - Tall to dwarf - 3:1 ### Principle of Segregation States that the characteristics of an organism are determined by internal factors (genes) which occur in pairs. ### Principle of Independent Assortment: States that any one of a pair of characteristics may combine with either one of another pair. ### Chromosome The physical structure of a genome composed primarily of nucleic acid with structural proteins. ### Chromatid Chromosomes are double-stranded structures in eukaryotic cells. Chromatid refers to each of the two identical strands of a duplicated chromosome while they remain attached by their shared centromere. ### Chromatin This is used to refer to dispersed (irregular strands of chromosomes) present in the nucleus during interphase. ### Gene arrangement Can be arranged by chromosomal deletions, inversions and translocations. ### Translocations When part of a chromosome breaks off and attaches to a non-homologous chromosome, it can cause Down Syndrome (translocation of chromosomes 14 and 21). ### Inversion A segment of a chromosome is cut out and reversed. ### Modern Genetics #### Branches of Genetics - **Breeding genetics**: Science aimed at improving the hereditary makeup of cultivated plants. - **Cytogenetics:** A hybrid field from cytology and genetics. - **Population genetics:** The study of genetics in relation to Cytology. - **Ecological genetics:** The study of genetic variations within and between populations. - **Molecular genetics:** The study of gene structure and function at the molecular level. - **Human genetics:** The study of genetic variation in humans. - **Medical genetics:** The study of genetic diseases. ### Genetic tests Are used to diagnose certain disorders, e.g., hemochromatosis and chromosomal disorders such as Down syndrome and Turner syndrome. ### Genetic Screening Is used to counsel parents about the risks of passing on a genetic disorder to their offspring. ### Pharmacogenomics Science dealing with how genetic variation affects the response to drugs. ### Mendel and the Laws of Heredity - Mendel was born in Moravia in 1822 and used the garden pea plant, *Pisum sativum*, to study the seven basic characteristics: - Length of the stem - Shape of seed - Color of seed - Shape and color of the pod - Position and color of the flower ### Allele: Homozygous dominant Eg AA (homozygous dominant) ### Recessive: The allele which influences the appearance of the phenotype only in the presence of another identical allele is said to be recessive, for example 'a' (homozygous recessive). ### Codominance Conditions where two or more alleles do not show complete dominance or recessiveness due to the failure of any allele to be dominant in the heterozygous condition. ### Hybrids These are the progeny of a cross between genetically unlike parents or individuals. ### Pureline A group of individuals with similar genetic backgrounds is referred to as pure line or strain or breed. ### First Filial (F1) Generation This refers to the generation produced by crossing homozygous parental stocks. ### Second Filial (F₂) Generation This refers to the generation produced by crossing two (F1) organisms. ### Lethal Alleles These are genes which lead to death when they manifest in the phenotype. They may be dominant or recessive. ### Multiple Alleles A single characteristic may appear in several forms controlled by three or more alleles, for example coat color in mice and blood groups in humans. ### Background of Genetics - **1760:** Joseph Kolreuter carried out the first work on artificial hybridization using two species of tobacco plants. His offspring was a blend of the two parents in respect to many characteristics. ### Gene The basic unit of inheritance of a characteristic. - **DNA:** Sugar + Phosphate + Nitrogenous bases ### Nitrogenous Bases: - Adenine (A) - Guanine (G) - Thymine (T) - Cytosine (C) ### Chromosome: Thread-like structures in the nucleus which carry the genes. ### Homologous Chromosomes - A pair of chromosomes that are similar in form and function. ### Allele: One of a number of alternative forms of a gene responsible for determining characteristics. ### Zygote: A single cell formed as a result of the union of a male sex cell with a female sex cell during sexual reproduction. It contains a diploid number of chromosomes. ### Gamete: Mature sex or reproductive cell, which takes part in sexual reproduction. It contains a haploid number of chromosomes ### Genotype: Refers to the genetic constitution of an individual. ### Phenotype: Refers to the observable characteristics of an individual, resulting from the interaction between the genotype and the environment. ### Dominant: The allele which influences the appearance of the phenotype when in the presence of an alternate allele is said to be dominant.