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Chapter 6.3 & 6.4
 Traits
are characteristics
that are inherited.

Ex. Right handed or left?
 Genetics
is the study of
biological inheritance
patterns and variation.
 Gregor Mendel showed that
traits are inherited as
discrete units. (alleles)
 Mendel’s Research that lead
to today’s theories…….
•
Mendel used pea plants to research and discover genetics.
– First he bred 2 purebred purple plants (P Generation)
Results: 100% purple offspring
Mendel controlled the
fertilization of his pea plants
by removing the male parts,
or stamens.
He then fertilized the female
part, or pistil, with pollen from
a different pea plant.
– Then he bred a purebred Purple to a purebred White
(2 P generation)
Results: 100% purple offspring (F1 Generation)
– Then he bred 2 F1 generation (purples)
Results: 75% Purple, 25% White (F2 Generation)
•
Mendel drew three important conclusions.
– Traits are inherited as discrete units. (alleles)
– Organisms inherit two copies of each gene, one from each parent.
– The two copies segregate
during gamete formation.
– The last two conclusions are
called the law of segregation.
purple
white
A
gene is a piece of DNA that directs a cell to make
a certain protein.
 Each gene has a locus, a
specific position on a pair of
homologous chromosomes.
 An
allele is any alternative form of a gene
occurring at a specific locus on a chromosome.

Example: Dominant hand – Right or left
•
– Each parent donates one
allele for every gene.
– You have 2 alleles for every
gene
We use letters to symbolize
alleles
– Example: BB, Bb, or bb
– The same letter represents
that gene


Homozygous – When you have two alleles that are the
same. (AA or aa)
Heterozygous - When you have two alleles that are
different (Aa)
•
•
A genotype refers to the makeup of a specific set of genes.
– Your alleles that you inherited
A phenotype is the physical expression of a trait.
– What you see
• Yes you have more very important Vocab to learn
– A dominant allele is expressed as a
phenotype when at least one allele is
dominant.
– A recessive allele is expressed as a
phenotype only when two copies are
present.
– Dominant alleles are represented by
uppercase letters; recessive alleles by
lowercase letters.
•
Tips when doing genetics
– You can use any letter you want
– Avoid letters like C, S, P, X, etc b/c their big letter looks the same as
the little letter and it looks VERY confusing
– When working with a one trait use one letter
Example: Eye Color is B and b NOT B and g
The different letter represents another trait
What is the genotype for a Red cow?
What is the phenotype for Bb?
What is the phenotype of a cow that is heterozygous?
What is the phenotype of a cow that is homozygous dominant?