Transmission Genetics Notes PDF

II-Transmission genetics Dr. Marina Fathy  Theories of genetics Old theory : - The inherited traits transmitted from different parts of parents to their progeny by concentration of these traits in some manner into the gamete then to the progeny....

II-Transmission genetics Dr. Marina Fathy  Theories of genetics Old theory : - The inherited traits transmitted from different parts of parents to their progeny by concentration of these traits in some manner into the gamete then to the progeny. Dr. Marina Fathy  Weismann theory :- Differentiated between germplasm (reproductive cell ) and somatoplasm (other body cell ) and considered the inherited trait transmitted through germplasm which not affected by what happen in somatoplasm. This theory is reason to accept Mendel law. Dr. Marina Fathy  Mendelian/Classical genetics Gregor Johann Mendel is called ( the father of genetics ) as he put the foundation of genetics science 19th century. Dr. Marina Fathy Dr. Marina Fathy Dr. Marina Fathy Dr. Marina Fathy ✔ He concluded that characters pass from one generation to the other. But what about disappearance of the trait from one complete generation ? Mendel said that some genes are always expressed irrespective of the other ( dominant , recessive ). Representation by symbols :- P purple colored flower p white colored flower P1 Ꝗ Ơ PP × pp G1 P p F1 Pp dominant recessive enough to express the trait Dr. Marina Fathy  P2 Ơ Ꝗ Pp × Pp G2 P p P p F2 PP Pp Pp pp Have at least one dominant Both are recessive gene this explain each of No gene to dominate the trait as a them are purple result the plant express the recessive trait. Dr. Marina Fathy  Terms in genetics : - Gene : the information containing unit. Locus : location of gene on chromosome. Allele : different forms of gene. Genotype : all genes posed by individual ( present in individual ). genetic make up that can’t be observed. set of genes that give rise to a particular trait. External Phenotype : the result of gene product that expressed in a given environment. Internal Physical expression of the genes giving rise to a particular trait. Observable as color , length. Measurable as blood groups. Dr. Marina Fathy o Homozygous ( pure ) : two alleles are identical. may be homozygous dominant ( AA ) or homozygous recessive ( aa ). give one type of gametes. o Heterozygous ( hybrid ) ( carrier ) : two alleles are different ( Aa ). give two types of gametes. o Dominant : genes which are always expressed. o Recessive : genes which are always suppressed and expressed only in homozygous form. Dr. Marina Fathy  Laws of genetics 1) First law ( law of segregation ) : The genetic trait controlled by genes which exist in pair of alleles , during gametic formation the two alleles of each gene separated or segregated from each other so each gamete contain only one allele from each pair. Ex :- P2 Ơ × Ꝗ Ơ tall plant × Ꝗ dwarf Tt Tt plant P1 T T tt G2 t T t T T t G1 F2 TT Tt Tt tt Genotypic ratio 1 : 2 : 1 F1 Tt Phenotypic ratio 3 tall : 1 dwarf 100% tall plant Dr. Marina Fathy  N.B The cross involving one character at a time is called monohybrid cross. Ratio obtained from monohybrid cross is called monohybrid ratio. Dr. Marina Fathy  From previous example , if we have tall plant ( genotype may be TT or Tt ) How could we know the genotype of this plant ? Dr. Marina Fathy  Monohybrid test cross Mating unknown individual with homozygous recessive one to know the genotype of the parent & know how many kinds of gametes produced by it. Ex.1 T_ tall tt dwarf if P1 Ơ Ꝗ P1 Ơ Ꝗ TT × tt Tt × tt G1 T t G1 T t t F1 Tt F1 Tt tt 100% tall 50% tall 50% dwarf Dr. Marina Fathy Dr. Marina Fathy Thank you Dr. Marina Fathy