Download 6.4 Traits, Genes, and Alleles

6.4 Traits, Genes, and Alleles
KEY CONCEPT
Genes encode proteins that produce a diverse range
of traits.
6.4 Traits, Genes, and Alleles
(PN) The same gene can have many versions.
• 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.
Think about a house!
• A house is a physical structure
with an address that tells us
where it is located
• The locus is the address that
tells us where a gene is located
on a chromosome
6.4 Traits, Genes, and Alleles
• (PN) An allele is any alternative form of a gene occurring at
a specific locus (location/address) on a chromosome.
– Each parent donates
one allele for every
gene, so each cell has
two
– The two alleles may be
the same or different
– Homozygous describes
two alleles that are the
same at a specific locus.
– Heterozygous
describes two alleles
that are different at a
specific locus.
6.4 Traits, Genes, and Alleles
(PN) Genes influence the development of traits.
• All of an organism’s genetic material (all of your genes) is
called the genome.
• Unless you have an identical twin, you have a unique
genome that determines all of your traits.
• Some traits can be seen while others can not.
• The traits that represents your eye color can be seen.
• The traits that makeup your actual eyeball can not be seen.
• A genotype refers to the makeup of a specific set of genes.
– The genotype of a pea plant includes both of the genes that code for
flower color, even if one of them is masked
• A phenotype is the physical expression of a trait.
– The environment and genotype influence the phenotype
– A pea plant with purple flowers has a phenotype for purple flowers
6.4 Traits, Genes, and Alleles
• (PN) Symbols:
– Alleles can be represented using letters.
– Uppercase letters = dominant
– Lowercase letters = recessive
– A dominant allele is expressed
as a phenotype when at least
one allele is dominant.
Remember that dominant does not
mean better or stronger!
It is merely expressed while the
other is not!
– A recessive allele is expressed
as a phenotype only when two
copies are present.
6.4 Traits, Genes, and Alleles
• Both homozygous dominant and heterozygous genotypes
yield a dominant phenotype.
• Most traits occur in a range
and do not follow simple
dominant-recessive patterns.