Gregor Mendel &

Basic Genetic Principles

Who is Gregor Mendel?

• Austrian Monk that experimented with pea plants.

• He discovered the basic principles of genetics.

Pea Plants

• Pollination occurs easily within the flower.

• Relatively short life cycle (2-3 weeks).

• Have 7 characteristics with contrasting forms.

Pollination

• Movement of pollen between sexual parts of flowers.

• Self Pollination – pollination that occurs within one flower.

• Cross Pollination – movement of pollen from one flower to another.

7 different traits of pea plants

• Seed shape – round/wrinkled

• Seed color – yellow/green

• Seed coat color – colored/white

• Pod shape – inflated/constricted

• Pod color – green/yellow

• Flower position – axial/terminal

• Stem length – long/short

Mendel’s 1st Experiment

• Mendel created pure–bred pea plants of each characteristic.

Ex. Tall/Short, Green seeds/Yellow seeds.

• He crossed these plants together (P1 or Parent generation).

• Offspring: ALL TALL! (F1 generation).

Mendel’s 1st LawLaw of Dominance

• When organisms with contrasting traits are crossed, only the Dominant trait appears in the offspring.

Mendel’s 2nd Experiment

• Mendel took those F1 generation plants and crossed them.

• F2 generation results: 3 TALL, 1 SHORT = 3:1 phenotypic ratio.

• 1 TT, 2 Tt, 1 tt =1:2:1 genotypic ratio

Mendel’s 2nd LawLaw of Segregation

• Factors occur in pairs and separate during gamete formation only to recombine again during fertilization.

Vocabulary

• Dominant gene – gene that prevents the expression of another. Ex. Brown hair – represented with a capital B.

• Recessive gene – gene that is not expressed, it is usually hidden by a dominant gene. Ex. Blond hair – represented with a lower case b.

• Allele – dominant and recessive forms of genes.

• Genotype – genetic makeup of an organism regarding its characteristics.(TT, Tt, tt)

• Phenotype – physical appearance of an organism. (Tall/Short)

• Heterozygous – have 2 different alleles for a particular charateristic. (Ex. Tt = a heterozygous tall plant)

• Homozygous – have the same alleles for a particular characteristic. (Ex. TT = a homozygous tall plant & tt = a homozygous short plant)

• Hybrid – Common term for heterozygous. Ex. Tt

• Monohybrid Cross – Cross between two parents that deals with only one trait.

• Dihybrid Cross – Cross between two parents dealing with two different traits.

• Incomplete dominance – Blending, when both traits express themselves.

• Sex linked traits – Involves genes that are located on the X chromosome.

Figure 10.13

Figure 10.13

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Mendel's law of independent assortment of alleles

• Alleles of different genes are assorted independently of one another during the formation of gametes.

• Mendel determined this law by crossing plants containing two different traits. (Ex. True breed round & yellow seeded plants (RRYY) with true breed wrinkled & green seeds (rryy)

Figure 10.7

Figure 10.7

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