Genetics The Puzzle of Heredity
What is Genetics? • Genetics is the scientific study of heredity.
Who is Gregor Mendel? • Austrian Monk • Experimented repeatedly with garden peas • Kept careful records based on NUMBERS
Why peas? • Easy to grow • Produce abundant offspring • SELF-FERTILIZE • CROSS-FERTILIZE
Pea’s characteristics • Mendel studied 7 different pea characteristics. • We will look at flower color.
The experiment • Mendel allowed peas to self-fertilize for several generations.
The Experiment • The resulting offspring were true-breeding. • They produced only one form of a trait. Purple flowers produced purple flowers and white flowers produced white flowers.
The Experiment • Mendel named these plants the P generation. • P stands for parental.
The Experimental • Mendel then took pollen from a white flower plant and allowed it to fertilize a purple flower plant.
The Experiment • He collected and grew the resulting seeds.
The Experiment • All of resulting plants from these seeds produced only purple flowers. • Mendel named this the F1 generation. • F stands for filial.
The Experiment • Mendel allowed the F1generation to self-fertilize. • He grew the seeds from these plants.
The Experiment • In addition to white flowers, purple flowers appeared. • Mendel named this generation the F2generation.
The Experiment • Mendel discovered the ratio of purple flowers to white flowers was 3:1.
Conclusions • Parents transmit information about traits to their offspring. • Mendel called these factors.
Conclusions • The purple factor is represented by a P. • Capital letter • The white factor is represented by a p. • Lower case letter
Conclusions • Each individual has 2 factors for each trait. • One factor comes from each parent.
Conclusions • Possible factor combinations for flower color are: • PP • Pp • pp
Conclusions • Organisms possessing the same factors for a trait are homozygous. • PP • pp
Conclusions • Organisms possessing different factors for a trait are heterozygous. • Pp
Conclusions • Some factors are “stronger” than other factors. • These are called dominant factors.
Conclusions • Dominant factors are represented by a capital letter. • The dominant factor is expressed. • It can be seen
Conclusions • Some factors are weaker than others. • These are called recessive. • They are represented by a lower case letter.
Conclusions • Purple flowers are dominant to white flowers. • White flowers are recessive.
Conclusions • The phenotype refers to an organism’s appearance.
Conclusions • The genotype is all of the factors or genes an organism possesses.
Conclusions • Today we know Mendel’s factors were actually genes.