Genetics – the study of heredity
Heredity – how traits are passed from parent to offspring
A man by the name of Gregor Mendel was curious as to how traits were passed from parent to child.
– He did his own mathematical experiments with pea plants .
– For all of his work, he is known as the “ Father of Genetics .”

Mendel decided to use pea plants for the following reasons:
– The plants were small
– They were easy to grow
– They were inexpensive
– They produced a lot of offspring in a short time

He also liked to use pea plants because they were easy to pollinate . A single plant had both male and female parts on the same flower.
– The stamen is the male part (holds sperm)
– The pistil is the female part (holds eggs)

Mendel studied 7 traits

First, Mendel created a Parental (P) Generation of tall & short purebred plants.
– Purebreds will only produce offspring like themselves .
– Tall purebred plants only produce tall offspring.
– Short purebred plants only produce short offspring.

Step 1 : Mendel crossed a purebred tall plant with a purebred short plant by cross pollination . This meant dusting the pollen of one flower onto the pistil of a different flower.
– All the offspring came out TALL !
– He called this generation the
F
1 generation.
– Mendel was thoroughly confused .
– Shortness had somehow disappeared !

Step 2 : Mendel crossed two of the tall plants from the F
1 generation by self pollination . This meant dusting the pollen of one flower onto the pistil of the same flower.
– ¾ of the plants were Tall and ¼ were Short!
– He called this generation the
F
2 generation .
– Mendel was now thoroughly frustrated .
– Shortness had reappeared!

P
Step 1
Step 2
F
1
? = All Tall!
? =
¾ Tall & ¼ Short!
F
2

Mendel concluded that parents pass traits to their offspring via things called “factors”.
– We now know that the factors Mendel was talking about are called genes .
– Genes are pieces of your DNA .
– Genes control all your traits .

Mendel also concluded that there are different forms of the same gene.
– Different forms of a gene are called alleles
– Everyone has 2 alleles for a single gene
– One allele comes from mom , one from dad

Dominant allele
– The allele that always shows when present
– Represented by a
Capital letter
–
THINK!
– What allele can we use to represent Tallness?
T
Recessive allele
– The allele that is masked by the dominant one
– Only shows up if the dominant allele is NOT present
– Represented by a Lower-case letter of the dominant trait
– THINK!
– What allele can we use to represent shortness?
t
Homozygous for a trait
– 2 of the same alleles for a gene
Heterozygous for a trait
– 2 different alleles for a gene

Phenotype
– What an organism looks like ; physical appearance
–
THINK!
– What do the following organisms look like?
• TT =
• Tt =
• tt =
Tall
Tall
Short
Genotype
– The 2 alleles an organism possesses
– Think of it as the combination of letters
– THINK!
– What are the genotypes for the following:
• Tall =
TT or Tt
• Short = tt

P F
1
TT tt Tt Tt Tt Tt
F
2
Tt Tt TT Tt Tt tt