Transcript Genetics
Genetics
Power point number 2
Definitions
Genotype – the genetic makeup of an
organism
Example: Bb or BB
Phenotype – the physical trait that an
organism develops
Example: Brown eyes or blue eyes
Di-hybrid Crosses
Used when 2 different traits are involved in the
same cross
Results in 16 possible offspring
When the number of offspring are large enough,
the phenotype ratio is 9:3:3:1
(DD : DR : RD : RR)
Di-hybrid Cross Example
Example: Cross an individual heterozygous for brown
hair and brown eyes with an individual recessive for
blond hair and blue eyes. What possible offspring will
result?
Practice
Practice Worksheet
Codominance
Both alleles contribute to the phenotype
of the organism
Occurs in chickens black and white
feathers give a speckled black and
white feathered chicken
Polygenic traits
The exhibited trait is controlled by two
or more genes
Example: wide range of skin color in
humans because it is controlled by
more than 4 different genes
Incomplete Dominance
When one allele is not completely
dominant over another
Example: Crossing a red and white 4
o’clock plant (Mirabilis) gives a pink
flower
Sex linked traits
Sex-Linked Genes
Genes on the X and Y chromosome
Called sex-linked because the X and Y
determine sex of an individual
100 genetic disorders have been mapped
to the X chromosome
Sex-Linked con’t
Sex linked genetic disorders are more
common among men b/c men only
have one X.
Recessive alleles on the X will be
expressed in males
Sex-Linked con’t
Genetic Disorders
Colorblindness
Hemophilia
Duchenne Muscular Dystrophy
Male Pattern Baldness
Sex Linked con’t
Colorblindness
About 1 in 10 men (most common redgreen)
About 1 in 100 women
Sex-linked genes are passed from Fathers
to daughters and then may show up in
sons of those daughters
Sex-Linked
Hemophilia
Protein necessary for normal blood clotting
is missing
About 1 in 10,000 males
People can bleed to death from minor cuts
and may suffer internal bleeding from
bumps or bruises.
Sex-linked con’t
Duchenne Muscular Dystrophy
Progressive weakening and loss of skeletal
muscle
Rarely live through early adulthood
About 1 in 3000 males
Sex linked con’t
Male Pattern Baldness
Fathers give to daughters who are carriers
Daughters pass trait to son
Sex Linked Trait
Example
Color Blind father crosses with a
Homozygous dominant mother
XcY and XCXC
Color Blind father and heterozygous
mother
XcY and XCXc