Section 6-4
“Traits &
Genes”
Write everything that is
underlined
6.4 Traits, Genes, and Alleles
KEY CONCEPT
Genes encode proteins that produce a
diverse range of traits
6.4 Traits, Genes, and Alleles
Important Vocabulary Terms for You to Know
Please make a chart or table at the top of your notes for these
vocabulary terms:
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•
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Gene
Allelle
Homozygous
Heterozygous
Genome
Genotype
Phenotype
Dominant
Recessive
6.4 Traits, Genes, and Alleles
A. The same gene can have many versions
1. A gene is a piece of DNA
that tells a cell to make a
certain protein
• Each gene has a locus,
a specific position
on a pair of
homologous chromosomes
6.4 Traits, Genes, and Alleles
2. An allele is an alternative form of a gene
-Each parent donates one allele for every
gene
• Pea plants have 2
alleles for shape - they
receive one from each
parent
• For shape, there is a
wrinkled allele and a
round allele
6.4 Traits, Genes, and Alleles
B. Genes influence the development of
traits
• All of an organism’s genetic
material is called the genome
• A genotype refers to the actual
genes
• A phenotype is the physical
expression of a trait
6.4 Traits, Genes, and Alleles
C. Genotype:
1. The gene combination of an
organism
• It consists of 2 alleles
• For example:
– Pure dominant, 2 dominant genes
– Pure recessive, 2 recessive genes
– Hybrid, 1 dominant and 1 recessive
gene
6.4 Traits, Genes, and Alleles
D. Phenotype:
1. The way an organism
looks
• No matter what genes are
present, phenotype of a
tall pea plant is tall and a
short pea plant is short
6.4 Traits, Genes, and Alleles
– 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
2. Dominant alleles are
represented by
uppercase letters
3. Recessive alleles by
lowercase letters
6.4 Traits, Genes, and Alleles
Think fast!!!
• Determine if the following is genotype or phenotype.
– A horse with white stockings
– A pink rose that was bred from a white rose and
red rose
– A pig that has super heavy muscling
6.4 Traits, Genes, and Alleles
E. Mendel’s observed traits
1. Dominant traits: covers up the other
traits
2. Recessive traits: traits that
“disappear”
3. Rule of Dominance: When a
dominant trait is present the
recessive trait is hidden
6.4 Traits, Genes, and Alleles
How’s it related????
• You have 4 minutes and 25 seconds to draw a concept
map to show (with words, chart, or a concept map) how
these terms are related.
– Gene
– Genotype
– Phenotype
– Allelle
– Dominant traits
– Recessive traits
6.4 Traits, Genes, and Alleles
• Most traits occur
in a range and do
not follow simple
dominantrecessive
patterns
6.4 Traits, Genes, and Alleles
F. The Law of Independent Assortment:
• Genes for different traits are
inherited independently of
each other
• When you have 2 or more
different traits they are not
“stuck” together
6.4 Traits, Genes, and Alleles
Example (for your genetics book)
• Seed types of Parents:
• Wrinkled, yellow
• Round, green
• You can get offspring with:
• Wrinkled, green seeds
• Or Round, yellow seeds