2. Review - Simple Mendelian Genetics
Dominant gene
covers other allele
• Ss or SS genotype
yields smooth coat
Recessive gene is
only expressed
when dominant
allele is not
inherited
• ss genotype
yields long coat
3. Lethal Allele Combinations
The yellow fur color allele is
dominant (Y)
• however, it's only expressed in
heterozygous Yy mice
Homozygous dominant (YY)
mice never appear (they die
before birth)
Homozygous recessive (yy)
mice are white
Even though the fur color Y is
dominant, the lethal allele is
considered recessive because
it only appears in the
homozygous YY genotype.
4. Incomplete Dominance
Heterozygotes (CRCW) express
an intermediate phenotype
(pink)
Instead of overpowering one
another, both traits are
partially expressed
Flower color traits separate
again during meiosis and can
be seen in the F2 generation
5. Codominance
The inheritance of ABO • Two alleles are dominant
blood groups demonstrates • Type A and Type B
codominant inheritance • (Type O is recessive)
• Both phenotypes are
expressed in the
heterozygote (Type AB)
6. Codominance
B = black
X W = white
What would the
genotype of each
of these chickens
have to be?
7. Multiple Alleles
The ABO blood type is an example of a trait that has more
than just two different alleles (A, B, and O)
Most genes have multiple alleles (different forms of the same gene)
• hair, eye, and fur color genes all have many different alleles
• multiple alleles usually exhibit some sort of incomplete dominance
8. Polygenic Traits
The control of a trait by more
than one gene
• Skin color is controlled by at
least 6 genes
Each gene product is
additive to the others
The hallmark of a polygenic
trait's phenotype expression
is:
• A bell curve distribution
• A continuous distribution
9. The Human Genome Project
In the 1950's, scientists
were first able to view a
set of human
chromosomes
In 2003, scientists
finished mapping the
human genome
Now every gene of
each human
chromosome is know
by location and trait
11. Sex Chromosomes
The X and Y chromosomes determines gender
X + Y = BOY X + X = GIRL
The mother always donates an X chromosome.
Why?
The father gives either an X (female) or a Y (male).
12. Sex-Linked Recessive Inheritance
The pattern of
inheritance still follows
Mendel's predictions
Genes found on the
X chromosome:
• Hemophilia
• Color blindness
Males are more often
affected than females
because they inherit
only one X chromosome
13. Pedigree
Pedigrees help track
the appearance of
one trait (or disease)
• Very useful for
determining the
type of inheritance
Does the whirling trait
appear to be sex-linked?
Are there multiple alleles for
the whirling trait?
Is it recessive or dominant?
16. Autosomal Dominant Inheritance
Genes on non-sex chromosomes are autosomes
• Huntington’s disease is an autosomal dominant trait
• It only take one copy of the Huntington gene to have the disease
Some individuals in every generation are affected
regardless of gender
This pedigree
shows the affected
individuals of each
generation as a
black circle or square
18. Environmental Influences
Genes are often influenced by
environmental factors
• leaf & stem size is dictated by genes, but
also affected by sunlight
• black fur color genes can be "turned on"
by changes in temperature
• conditions such as baldness can be
triggered by hormones (internal environment)
• both men and women
inherit baldness genes,
but the gene is only expressed
when exposed to high levels of
testosterone
19. Different levels of hormones affect the thickness and length of
horns in bighorn sheep, even though their genotype is identical.
Diet, exercise, and other environmental factors have been
proven to influence the expression of genes causing
heart disease, diabetes and other serious illnesses.
Exposure to chemicals during
pregnancy and early infancy can
trigger severe genetic abnormalities.
20. Abnormal Chromosome Number
many miscarriages this zygote has 3
copies of a
are the result of chromosome instead
extra or missing of 2
chromosomes due instead of a
to nondisjunction homologous pair,
there is a trisomy
21. Trisomy 13 - also known as Patau's
Syndrome
An individual with full
trisomy 13 at age 7 years
(survival beyond the first
year is uncommon).
He is deaf and legally blind
If Adam and Eve did not have all three blood type alleles, then there must have been a mutation creating the O allele while the human race was still very small and before humans dispersed across the globe. Whether the origin of blood type O was in Adam and Eve at Creation or whether it arose as a mutational event that took place shortly before or after the Flood, it strongly supports that all humans today are descendants of two individuals or a small group of people that eventually populated the globe. Both scenarios are consistent with the biblical model of human origins.
Chickens also display codominance in their feather color. Instead of gray feathers from a black/white hybrid, both black AND white feathers are expressed.
Probable # of genes responsible is around 40! additive = not clearly dominant/recessive, and not equally codominant either, but each gene contributes a degree of pigment that combines to produce a variety (or full spectrum) of skin color
Each gene of every human chromosome is now know by location and trait.
So who determine's a baby's sex? The Father!
sex-linked recessive trait
multiple incomplete dominant alleles
Trisomy 13, also called Patau syndrome, is a chromosomal condition associated with severe intellectual disability and physical abnormalities in many parts of the body. Individuals with trisomy 13 often have heart defects, brain or spinal cord abnormalities, very small or poorly developed eyes (microphthalmia), extra fingers and/or toes, an opening in the lip (a cleft lip) with or without an opening in the roof of the mouth (a cleft palate), and weak muscle tone (hypotonia). Due to the presence of several life-threatening medical problems, many infants with trisomy 13 die within their first days or weeks of life. Only five percent to 10 percent of children with this condition live past their first year. Trisomy 13 occurs in about 1 in 16,000 newborns. Although women of any age can have a child with trisomy 13, the chance of having a child with this condition increases as a woman gets older.
Down syndrome is a genetic disorder that includes a combination of birth defects, including some degree of mental retardation, characteristic facial features and, often, heart defects, visual and hearing impairment, and other health problems. The severity of all of these problems varies greatly among affected individuals. Down syndrome is one of the most common genetic birth defects, affecting approximately one in 800 to 1,000 babies. In this country, there are more than 350,000 individuals with Down syndrome, according to the National Down Syndrome Society. Life expectancy among adults with Down syndrome is about 55 years, though average lifespan varies. The name "Down syndrome" comes from the physician, Dr. Langdon Down, who first described the collection of findings in 1866. It was not until 1959 that the cause of Down syndrome (the presence of an extra #21 chromosome) was identified.
