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Definition of a gene
A piece of DNA that can be found on a specific location
on a chromosome. Code for traits.
Genes & Alleles
Gene/
allele
Different
versions of a
gene are
called alleles.
Alleles- Different forms of the same gene.
This is an
allele for
blue eye
color.
Homologous
chromosomes
This is an
allele for
brown eye
color.
Genes and alleles
These are alleles of
the same gene- eye
color. Notice they
are on the same
location on the pair
of homologous
chromosomes.
What are homologous chromosomes?
• A pair of matching chromosomes in an organism, with one being
inherited from each parent.
Homologous chromosomes
are the same size and
structure. They carry the
same genes in the same
locations, however the gene
pairs may be different
versions from one another.
Homologous Pairs of Chromosomes
w/different allele combinations
Homozygous
genes/alleles
Homozygous
genes/alleles
Heterozygous
genes/alleles
Homologous Pairs of Chromosomes
One from dad and one from mom
Gene location on the chromosome. Genes are found
in pairs.
A pair of alleles. Sometimes they are the same &
sometimes they are different. Homologous
chromosomes are similar but not necessarily identical.
Each carries the same genes in the same order, but the
alleles for each trait may not be the same.
Three pairs of alleles. These code for the same
version of the gene.
Human Karyotype
A karyotype is
the number,
size, and
shape of
chromosomes
in an
organism.
Genotype
Phenotype
The genetic makeup of an The specific visible
organism.
characteristics of an
organism.
Karyotype
Entire chromosome
pattern of an organism or
species of organisms.
Homozygous vs heterozygous traits review
Key Concepts:
• A homozygous trait is made up of two of the same
alleles. Homozygous genotypes = HH, ii, bb, EE.
• A heterozygous trait is made of two different alleles.
Heterozygous genotypes = Hh, Ii, Bb, Ee
Dominant vs Recessive Traits
• A dominant trait is one that shows up in the
phenotype even though only one dominant allele
is present in the genotype. Dominant genotypes
are TT, Tt or RR, Rr.
• A recessive trait must have both of its alleles in
order to show up in the phenotype. Examples
include tt, rr, ee.
Dominant vs Recessive Examples
Dominant- even with only
one capital B.
Recessive- is masked even if only one
dominant allele is present
Punnett Squares and Probability
• Probability- the measure of the chance that the event will occur
as a result of an experiment.