Download Genetics PowerPoint #1 - Petal School District

GENETICS
LESSON 2: MENDEL’S LAWS OF
HEREDITY
“I Can” Statements
• I can explain the difference between
heterozygous and homozygous.
• I can explain the difference between
dominant and recessive.
• I can explain the law of dominance.
• I can explain the difference between purebred
and hybrid.
• I can explain the difference between genotype
and phenotype.
A dominant allele is one
whose trait always shows up in
the organism when the allele is
present. It blocks another
genetic factor.
Ex. Dimples
A recessive allele is blocked,
or covered up, whenever the
dominant allele is present.
Ex. No dimples
Dominant and recessive traits are represented by
using letters.
•Dominant traits are represented by capital
letters.
•Recessive traits are represented by lower case
letters.
The law of dominance states that the dominant
allele will ALWAYS be expressed WHEN
PRESENT.
Example: P = purple flower
p = white flower
PP = purple flower / purebred
Pp = purple flower / hybrid
pp = white flower / purebred
Purebred (True-bred)—An organism that
always produces offspring with the same
form of a trait as the parent. Also known
as homozygous.
“same”
In Mendel’s experiments,
P stood for the parent generation,
F1 stood for the first generation, and
F2 stood for the second generation.
Hybrid—An organism that has two different
alleles for a trait. ALSO known as
heterozygous.
Homozygous—an organism that has 2
identical alleles for a trait
Example– PP – homozygous for purple flower
pp– homozygous for white flower
Heterozygous—an organism that has two
different alleles for a trait
Example – Pp – heterozygous for purple flower
***there cannot be a hetero white***
Phenotype—physical make-up of an organism
***you can actually see phenotype***
Ex. -- purple or white.
Genotype—genetic make-up of an organism
***you cannot see genotype***
Ex. -- PP, Pp, pp