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