Transcript Mendel & His Pea Plants

Mendelian Genetics
Mendel & His Pea Plants
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 & His Pea Plants
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
Mendel & His Pea Plants
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
Mendel’s Experiments
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.
Mendel’s Experiments
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 F1 generation.
– Mendel was thoroughly confused.
– Shortness had somehow disappeared!
Mendel’s Experiments
Step 2: Mendel crossed two of the tall plants from
the F1 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 F2 generation.
– Mendel was now thoroughly frustrated.
– Shortness had reappeared!
Let’s Recap
P
F1
Step 1
? = All Tall!
F2
Step 2
? = ¾ Tall & ¼ Short!
Mendel’s Conclusion
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’s Conclusion
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
Learning Terminology
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
Learning Terminology
Phenotype
– What an organism looks like; physical appearance
– THINK! – What do the following organisms look like?
• TT = Tall
• Tt = Tall
• tt = 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
Let’s Recap: Write the Genotypes
P
F1
TT
tt
Tt
Tt
Tt
Tt
F2
Tt
Tt
TT
Tt
Tt
tt