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 Johann Gregor Mendel                                         

is the person who figured out basic genetics in 1866 by breeding pea plants. He was an Austrian monk who crossbred pea plants that had discreet traits. He observed the distribution of these traits over several generations. Through careful experimentation and observation he formulated the rules in genetics that we use today.

This is what Mendel said:

1) Dominant alleles overpower recessive alleles. Dominant traits overpower recessive traits.

Let's say that "B" means that a cat will be BIG.

Let's say that "bb" will make a small cat.

"BB" and "Bb" cats would show the dominant phenotype. There is no difference between "Bb" and "bB".

"bb" cats show the recessive phenotype.

 

Two letters control every trait.

In class we've worked with letters like "HH", and "Tt" and "pp". Why do we always have two letters for every trait/gene in a body cell? Why are letters always found in pairs in the developing baby?

Answer: Each parent gives a letter to make up that trait. 2 factors, or 2 alleles, control every trait (hair color, number of fingers) - one letter comes from each parent.

Different forms of a gene are called alleles. Therefore, each parent gives an allele to make up a trait. Therefore a gene is made up of 2 alleles = BB or Bb or bb.

 

2) Rule of segregation: Gametes (sex cells) only receive one allele from the original gene.

3) Rule of Independent assortment: One trait will not determine the random selection of another.

 Check out how to make Punnett squares!

 

The following shows Mendel's results for breeding tall pea plants with short pea plants:

The original generation:

Tall pure-bred pea plants (TT) X short pure-bred pea plants (tt)

The next generation:

Tall, hybrid pea plants (Tt)

 

When hybrids inbreed:

Tall hybrid pea plants (Tt) X Tall hybrid pea plants (Tt)

The next generation:

75 % tall pea plants

25% short pea plants

Check out how to make Punnett squares!

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