Mendel’s laws

Mendel is considered the father of genetics He was a monk, biologist and botanist, born in Austria in 1822 and who died in 1884 His experiments consisted of crossing pea plants with distinct characteristics (size, seed colour,…), cataloging the results and interpreting them The experiments led him to develop his laws

Mendel’s 1 st law: law of segregation One of two principles of heredity first formulated by Mendel states that during the production of gametes the two copies of each hereditary factor [gene] segregate, so that offspring acquire one factor from each parent When a plant with two dominant alleles [genotype: DD, phenotype: pink flowers] is crossed with a plant having two recessive alleles [genotype rr, phenotype white flowers], the first generation of plants will have one dominant and one recessive allele [genotype: Dr], and they will show de characteristic of the dominant father [phenotype: pink flowers]

Mendel’s 2nd law: law of independent assortment The second of Mendel’s principles states that each member of a pair of chromosomes segregates during meiosis independently of the members of other pairs, with the result that alleles carried on different chromosomes are distributed randomly to the gametes In the second generation (bottom row) on average one of four plants will have two recessive alleles (genotype: rr) and will have the characteristic of the recessive parent [phenotype: white flowers] Three of four plants will have at least one dominant allel [genotypes: DD, Dr] and will present the characteristic of the dominant father [phenotype: pink flowers]:

Glossary EnglishDefinitionCatalà Gene Segment of DNA that is the molecular unit of heredity. It encodes the genetic information for one characteristic Gen Allele One of the alternatives forms of the same gene (for example: the gene that determines the colour of the flowers has two alleles: red and white) Al·lel Genotype An organism full hereditary information (all its genes, but we can refer to the genotype concerning one unique trait) Genotip Phenotype An organism actual observed properties. It depends on the genotype, but also on environmental factors. Fenotip Dominant It always shows, even if the individual has a single copy of the allele Dominant Recessive It only shows if the individual has two pies of the allele Recessiu Homozygous Having identical alleles for a single trait Homozigot Heterozygous Having different alleles for a single trait Heterozigot

GEP 2015/16