4. Gregor Mendel
Born in 1822 in
Czechoslovakia.
Became a monk at a
monastery in 1843.
Taught biology and
had interests in
statistics.
Also studied at the
University of Vienna
5. Mendel continued
After returning to the
monastery he
continued to teach and
worked in the garden.
Between 1856 and
1863 he grew and
tested over 28,000 pea
plants
6. Mendel’s Peas
Easy to grow.
Easily identifiable traits
Can work with large numbers of samples
7. Genes and dominance
Trait : a characteristic
Mendel studied seven of these traits
After Mendel ensured that his true-breeding
generation was pure, he then crossed plants
showing contrasting traits.
He called the offspring the F1 generation or
first filial.
8. What did Mendel conclude?
Inheritance is determined by factors passed
on from one generation to another.
Mendel knew nothing about chromosomes,
genes, or DNA. Why?
These terms hadn’t yet been defined.
9. Mendel’s “factors”
The ‘factors” that Mendel mentioned were
the genes.
Each gene has different forms called alleles
Mendel’s second principle stated that some
alleles are dominant and some are recessive.
10.
11. Punnett Square
Developed by
Reginald Punnett.
A diagram used to
show the probability
or chances of a certain
trait being passed from
one generation to
another.
12. Reading Punnett squares
Gametes are placed above and to the left of
the square
Offspring are placed in the square.
Capital letters (Y) represent dominant
alleles.
Lower case letters (y) represent recessive
alleles.
14. Homozygous = when an organism possesses
two identical alleles. ex.
YY or yy
Heterozygous = when an organism
possesses different alleles. ex.
Yy
15. Phenotype vs genotype
Genotype
The genetic makeup
Symbolized with
letters
Tt or TT
Phenotype
Physical appearance of
the organism
Expression of the trait
Short, tall, yellow,
smooth, etc.
17. Some exceptions to Mendel’s
principles:
Some alleles are neither dominant
nor recessive.
Many traits are controlled by more
than one gene (polygenic traits)
