How do scientists study traits? Objective: I can describe how genetic information is passed on to influence traits.

The study of heredity started with the work of Gregor Mendel and his pea plant garden Mendel was an Austrian Monk that lived in the mid 1800’s

All the traits observed were one trait or the other. There was no blending of traits.

Most scientists of the time thought that inheritance was a blending of traits or an equal mixing of traits. What do you think the offspring will look like?

Mendel didn’t observe the blending of traits.

Mendel's Experiment How are traits inherited? Mendel Crossed pea plants with specific traits. To answer specific questions. How is plant height inherited? How is seed color inherited? How is seed shape inherited?

Mendel's Experiment

Mendel noted that the size of pea plants varied. He cross-bred these pea plants to find some surprising results. What do you think the results of this cross will be? Make a prediction.

Mendel’s cross between tall pea plants yielded all tall pea plants. His cross between small pea plants yielded all small pea plants. Mendels’ cross between tall pea plants and small pea plants yielded all tall pea plants. X = x = X =

Mendel then crossed these second generation tall pea plants and ended up with 1 out 4 being small. This is a 1:3 ratio. x =

Mendel's Discoveries. After repeating his experiments he came up with some conclusions. - There must be 2 factors for each trait. - 1 factor causes them to be tall - 1 factor that causes them to be short.  One factor is dominant over the other.

Chromosomes Chromosomes come in pairs. Chromosomes have more than 1 form of a gene. These forms are called Alleles.

X T t Cross Parents Offspring Alleles for plant height T=tallness (Dominant) t=shortness (Recessive) Allele combinations TT = _____________ Tt = _____________ tt = _____________

Expressed Traits A combination of alleles determines how the trait will express. Example: Pea plants can be tall or short. Alleles for plant height T=tallness (Dominant) t=shortness (Recessive) Allele combinations TT = _____________ Tt = _____________ tt = _____________ X

Some traits are more dominant than other traits. Tallness is dominant over shortness. TT= Tallness Tt= Tallness tt= shortness Alleles for plant height T=tallness t=shortness

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How do scientists today explain Mendel's Discoveries? BARF Reading activity.