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• “Father of Genetics”
• Famous for pea plant
studies
• Mendel studied seven
pea plant traits
• Results shaped our
understanding of genetics
What is Genetics?
• Genetics: Study of heredity
• Heredity: passing of traits
from parent to child
• Patterns of relatedness can
help predict offspring
characteristics
Mendel’s 7
traits studied
Pure Breeding Purple & White Flowers
Parent Generation (P)
Mendel crossed a purple
flower with a white flower.
Result:
100% offspring were purple
(even though one parent was white)
1st Generation (F1)
Mendel crossed 2 F1 purple
flowers.
Result:
75% purple flowers,
25% white flower
(3:1 ratio)
Each trait had a 3:1
ratio. No way that
can be a
coincidence!
Mendel’s First Law/Law of Segregation
• Organisms inherit 2 copies of each
gene
• One from each parent
• Organisms donate only 1 copy of
each gene in their gametes.
• Two copies of each gene separate
during gamete formation.
• Genes are pieces of DNA that
create proteins:
– located on chromosomes
– inherited from parents
– come in dominant & recessive
forms (alleles)
– Ex: Flower color
• Purple allele (dominant)
• White (recessive)
• Letters used to abbreviate alleles
– Dominant Allele = Capital letter
– Recessive Allele = Lowercase
letter
• Defined: Genetic makeup of an organism
• Homozygous dominant: combination of two dominant alleles
(PP)
• Heterozygous: combination of one dominant, one recessive allele
(Pp)
• Homozygous recessive: combination of two recessive alleles (pp)
• Defined: Physical appearance of a gene
• Example:
Purple
What’s the phenotype of a flower that is PP genotype? __________
Purple
What’s the phenotype of a flower with Pp genotype? ___________
White
What’s the phenotype of a flower with a pp genotype? __________
Genetics Vocabulary Review
Choices:
1) YY
2) Tall
3) Yy
4) SS
5) yY
6) gg
7) Smooth
8) Green
9) TT
10) Dwarf
Which choice(s) are examples of:
Genotypes?
1, 3, 4, 5, 6, 9
Phenotypes?
2, 7, 8, 10
Homozygous genotypes?
1, 4, 6, 9
Heterozygous genotypes?
3, 5
Homozygous recessive genotypes?
6
Homozygous dominant genotypes?
1, 4, 9
Cross a homozygous dominant yellow (YY) plant with
a homozygous recessive green (yy) plant
Key
Y = yellow
y = green
100%
Probability of growing a yellow plant? _____________
0%
Probability of growing a homozygous recessive plant? ____________
0%
Probability of growing a homozygous dominant plant? ____________
Cross a heterozygous dominant yellow (Yy) plant with a
heterozygous dominant yellow (Yy) plant
Key
Y = Yellow
y = green
50%
Probability of growing a heterozygous plant? ________
25%
Probability of growing a green plant? ________
25%
Probability of growing pure yellow? _________
Review
1) How are dominant alleles expressed? Recessive?
2) Which of the following are genotypes? Phenotypes?
TT Green yY Pp Purple gg Smooth
3) Which of the following are heterozygous genotypes?
TT Green yY Pp Purple gg Smooth
4) Genes may often be found in two forms (dominant and recessive). What are
these alternate forms of a gene called?
5) Genes are segments of DNA found on _______________.
6) If item A is found in a 2:1 ratio compared to item B, what percentage is item A?
7) If item A is found in a 4:1 ratio compared to item B, what percentage is item A?
8) Cross a heterozygous tall with a homozygous recessive short pea plant. List the
genotypes in a Punnett square.
What’s the probability of growing a tall plant?
What’s the probability of growing a homozygous dominant plant?
What’s the probability of growing a homozygous recessive plant?