Mendelian Inheritance

• Pangenesis, as suggested by Hippocrates, is the idea that "seeds" are produced by all parts of the body, which are then collected and transmitted to the offspring, causing certain traits of the offspring to resemble those of the parent.
• The "blending" hypothesis, by Kölreuter, is the idea that genetic material from the two parents blends together (like blue and yellow paint blend to make green).
• The "particulate" hypothesis is the idea that parents pass on discrete heritable units (genes).
• Predictions for recessive phenotype, known genotype: pp .
• If PP, then all offspring will be purple.
• Backcrossing is a crossing of a hybrid with one of its parents or an individual genetically similar to its parent, in order to achieve offspring with a genetic identity which is closer to that of the parent.
• Gregor Johann Mendel, considered the father of genetics, documented a particulate mechanism through his experiments with garden peas.
• Dominant phenotype, unknown genotype: PP or Pp?
• If Pp, then 1/2 of the offspring will be purple and 1/2 will be white.
• P Generation Appearance: Genetic makeup: Gametes: Purple flowers White flowers PP P Pp P
• F1 Generation Gametes: Genetic makeup: Appearance: Purple flowers Pp P p 1/2 1/2
• Because the heterozygous produces different types of gamete; one with dominant allele, another with recessive allele, both gametes must be shown here.
• Because the homozygous produces same types of gamete, only one of the gametes will be shown here.
• Mendel's laws of inheritance include the idea that Gregor Johann Mendel, an Austrian monk, conducted his landmark studies in a small 115-by-23-foot plot in the garden of his monastery.
• From 1856-1864, Mendel performed thousands of crosses and kept meticulously accurate records that included quantitative analysis.
• Mendel's work, entitled "Experiments on Plant Hybrids", was published in 1866 and was ignored for 34 years due to its publication in an obscure journal and lack of understanding of chromosome transmission.
• In 1900, Mendel's work was rediscovered by three botanists working independently: Hugo de Vries of Holland, Carl Correns of Germany, and Erich von Tschermak of Austria.
• Mendel discovered the basic principles of heredity by breeding garden peas in carefully planned experiments.
• F1 generation: The generation produced by crossing homozygous parental stocks.
• True breeding: An organism with two identical alleles for a character is said to be homozygous for the gene controlling that character.
• Genotype: The genetic constitution of an organism with respect to the alleles under consideration.
• Unlike homozygotes, heterozygotes are not true-breeding.
• Phenotypic ratio: If there are 100 of F2 seeds, how many of them will be planted with purple flowers?
• Recessive: The allele which influences the appearance of the phenotype only in the presence of another identical allele.
• Different effects of dominant and recessive alleles: An organism’s traits do not always reveal its genetic composition.
• Heterozygous: An organism that has two different alleles for a gene is said to be heterozygous for the gene controlling that character.
• F2 generation: The generation produced by crossing two F1 organisms.
• Dominant: The allele which influences the appearance of the phenotype even in the presence of an alternative allele.
• P Generation: Appearance, Genetic makeup, Gametes: Purple flowers, White flowers.
• Phenotype: The characteristics of an individual usually resulting from the interaction between the genotype and the environment in which development occurs.
• Mendel observed the same pattern of inheritance in six other pea plant characters, each represented by two traits.
• A capital letter represents a dominant allele, and a lowercase letter represents a recessive allele for example: Purple – dominant trait = P White – recessive trait = p.
• When F1 individuals self-pollinate, the F2 generation is produced.
• The probability of a couple, both are carriers for albino trait to get a child with albino is ¼.
• P Generation (true-breeding parents) produced purple flowers and white flowers.
• The hybrid offspring of the P generation are called the F1 generation.
• Phenotype ratio: ¾ healthy: ¼ cystic fibrosis means that ¾ of the offspring are healthy and ¼ are carriers.
• Genotype ratio: 1 CC: 2Cc: 1 cc means that for every 1 CC, there are 2Cc and 1 cc.
• Mendel chose to track only those characters that varied in an either-or manner.
• Mendel reasoned that only the purple flower factor was affecting flower color in the F1 hybrids.