Genetics Course Notes (2024-2025) PDF

COURSE n°1 Genenetics Module: Genetics Second Level LMD Academic year: 2024-2025 First course: General introduction to genetics The traits of an individual or a cell are commonly passed down from generation to generation. They are said to be hereditary. So, heredity is the...

COURSE n°1 Genenetics Module: Genetics Second Level LMD Academic year: 2024-2025 First course: General introduction to genetics The traits of an individual or a cell are commonly passed down from generation to generation. They are said to be hereditary. So, heredity is the stability of specific properties and functions of a cell, tissue, organ or individual during procreation, but this general rule has exceptions. In fact a new characters may appear in the descendances, these variations are called genotypical variations. So genetics can be defined as the study of heredity and genotypic variations. Definitions The internal structure of an individual is called genotype; however, the external appearance of a character is called phenotype. When the two factors of a genotype (two alleles) are identical, the individual is said to be homozygous for this character (pure race). However, when they are different, the individual is said to be heterozygous (hybrid). 2 factors of the same character represent 2 alleles of the same gene. An allele is dominant: if present on only one of the two homologous chromosomes (one of paternal origin, the other of maternal origin), it is able to express a character.. An allele is recessive: if its expression requires it to be present on both homologous chromosomes. Gene: a genetic information unit made up of a DNA sequence and responsible for the expression of a character.. Allele: particular form or version of a gene. Pair of alleles: the 2 variants of the same gene that occupy the same locus on the 2 homologous chromosomes. Locus: Localisation of a gene on a chromosome Genome: the set of DNA and chromosomes that make up an individual’s genetic material DNA (deoxyribonucleic acid): A double chain of nucleotides linked to each other; the fundamental substance from which genes are composed. Chromosome: A linear (or circular) arrangement of genes and other types of DNA, sometimes associated with proteins and RNA. From the organism to the genetic material Introduction to Mendelian genetics Monohybridism: the crossing of 2 individuals of the same species of purbred, having only 1 different character. Dihybridism: The crossing 2 individuals of pure breeds having 2 different characters. Polyhybridism: Several different characters Exemple of Monohybridism: Mendel’s experience: 1st step: He crossed 2 purebred of different peas by a single character which is the appearance of the seed Conclusion All F1 hybrids are similar. F1 is said to be homogeneous or uniform. 1st Mendel’s law: Uniformity of F1. 1st Mendel’s law: Uniformity of F1. Phenotypically, the wrinkled character of the 2nd parent seems to have disappeared 2nd step: He crosses 2 hybrid seeds of F1 between them, it gets a F2 formed of = 3⁄4 (75%) smooth seeds and 1⁄4 (25%) wrinkled seeds. Conclusion The wrinkled character appears again in F2, so it was present in F1, but hidden by the smooth character. We can say that the smooth character is dominant and the wrinkled character is recessive. In order to carry out the crossing in a theoretical way, we need to assign the above alleles symbols: For 1 same gene = 1 same letter of the alphabet. The dominant allele in capital letters, and the recessive allele in lower case. They are noted: Smooth: S Wrinkled: s Each gene is characterized by 2 alleles in diploid individuals (2 n chromosomes). If we take the first step of Mendel’s experiment: Parents are pure breeds, so their genotypes are: Smooth = SS and wrinkly = ss During the formation of the gametes, the 2 alleles of the couple separate through meiosis and each gamete has only 1 single allele of the parental couple. This is the second law of Mendel = Gamete Purity. 2nd Cross