Biology 1- Chapter 13 (Mendelian Genetics)

Mendel's experiment

-mendel started the experiment by mating 2 contrasting, true-breeding varieties, this was the P generation -the resulting offspring was a hybrid (F1 generation) -mendel then analyzed all of the hybrids that resulted from mating true-breeding white & true-breeding purple plants & he found that all of the hybrids (the F1 generation) had purple flower color and none of the hybrids were white -he then used F1 generation plant & self pollinated it to produce offspring's which became the F2 generation -mendel found that the white color flower which had disappeared in the F1 generation had now reappeared in the F2 generation along with the purple flower plants -he counted thousands of these offspring and found that for every purple plant the white appeared in a 3:1 ratio

discovery from mendel's experiment

-of this experiment came a very significant discovery, & that was that the white flower color had not been destroyed in the F1 generation but instead was only masked by the purple color -this white color came to be known as the recessive trait, since it was masked by the purple color -similarly, the purple color which was able to dominate itself & mask the white, came to be known as the dominant trait

Hybrid

-offspring who receives 2 traits, 1 from each parent for every character the parents have (example: an offspring flower with 1 purple color trait & 1 white color trait for the character, flower color)

True-breeding

-plants that produce offspring of the same variety when they self-pollinate

alleles

-the alternate versions of genes -for example, the gene for flower color in a pea plant exists in 2 versions or variants, purple and white. Purple or white are therefore the allele versions of the gene that is flower color -each gene resides at a specific locus on a specific chromosome

genotype

-an organisms genetic makeup -example: PP and Pp plants have the same phenotype (purple) but different genotypes

phenotype

-an organisms physical appearance -example: PP and Pp plants have the same phenotype (purple) but different genotypes

Gregor Mendel

-father of modern genetics -discovered the basic principles of heredity by studying pea plants -he did so by breeding garden peas in carefully planned experiments & studied the 7 characteristics of the plea plants: 1. Plant height 2. Pod color 3. Pod shape 4. Seed color 5. Seed shape 6. Flower position 7. Flower color

Cross-pollination

-fertilization between different plants

Same pattern of inheritance in other 6 characters

-mendel observed the same pattern of inheritance in the 6 other pea plant characters, each represented by 2 traits: 1. Plant height: Tall, short 2. Pod color: Green, Yellow 3. Pod shape: Inflated, Constricted 4. Seed color: Yellow, Green 5. Seed shape: Round, Wrinkled 6. Flower position: Axial, Terminal

Dihybrid

hybrid produced for 2 characters (pod color & pod shape)

dominant allele

in the hybrids, of the 2 different alleles that were inherited, the one that determines the organism's appearance (purple color)

Monohybrid

the hybrid offspring produced from a cross between the true breeding parents for only 1 character (such as flower color)

heterozygous

an organism that has 2 different alleles for a gene

homozygous

an organism with 2 identical alleles for a character ( & the organism, true breeding)

Advantages of pea plants for genetic study

1. pea plants have distinct heritable characters (such as flower color: purple or white, Pod shape: round or wrinkled) 2. Mating of plants can be controlled 3. Cross-pollination (fertilization between different plants) can be achieved by dusting one plant with pollen from another 4. Pea plants are capable of true-breeding(plants that produce offspring of the same variety when they self-pollinate)

dominant traits of the 7 characters of the pea plant

flower color: purple Plant height: tall seed color: yellow seed shape: round Pod color: green Pod shape: inflated (full) Flower position: Axial

recessive traits of the 7 characters of the pea plant

flower color: white Plant height: short seed color: green seed shape: wrinkled Pod color: yellow Pod shape: constricted (flat) Flower position: terminal

recessive allele

has no effect on the physical appearance (white color)

Self pollination

technique used to produce offspring from the male & female reproductive parts of the same plant (one plant acts as both male & female)