Download Beyond Mendel…. - OnCourse Systems

OBJ discuss the characteristics and cause of some of the
following genetic diseases and conditions
BEYOND MENDEL….
Objectives
• SWBAT describe the experiments of Gregor Medel, which led to the development of
modern genetics
• SWBAT define and apply the following genetic terms: homozygous, heterozygous,
alleles, genotypes, phenotypes, probability, monohybrid/dihybrid,
dominance/recessive, codominance, incomplete dominance, multiple alleles,
polygenic traits, sex-linked traits, test cross, pedigree
• SWBAT list and explain Mendel’s laws of inheritance, noting the exceptions to the laws
• SWBAT complete punnett squares to determine genotypic and phenotypic ratios
• SWBAT discuss the characteristics and cause of some of the following genetic diseases
and conditions: color blindness, hemophilia, male-pattern baldness, sickle cell
anemia, albinism, cystic fibrosis, tay-sachs diease, huntingtin’s disease, dwarfism
• SWBAT act as a genetic counselor to determine the probability of a couple passing a
genetic condition to offspring
• SWBAT analyze and address a bioethical issue regarding genetic engineering.
When Dominant and Recessive is too simple…real
life
• Not all genes are
dominant/recessive
• Many traits are
controlled by +2
alleles, +1 gene
Beyond Mendel
• Incomplete Dominance
• Codominance
• Multiple Alleles
• Polygenic Traits
• Sex Linked Traits
• Genetics and the Environment
Beyond Mendel
• Incomplete Dominance
• Codominance
• Multiple Alleles
• Polygenic Traits
• Sex Linked Traits
• Genetics and the Environment
Incomplete Dominance
• One allele is not completely dominant over another
• The heterozygous phenotype= mix between the two
homozygous phenotypes
• Example: a cross between a red flowered plant (RR) and a
white flowered plant (WW) produces a pink flowered plant
(RW)
Incomplete Dominance
Beyond Mendel
• Incomplete Dominance
• Codominance
• Multiple Alleles
• Polygenic Traits
• Sex Linked Traits
• Genetics and the Environment
Codominance
• Both phenotypes contribute to the phenotype of the
offspring
• Two different proteins are produced, and both are detected
• Chicken Example:
White feathers = dominant
Black feathers = dominant
offspring = checkered chickens
More Codominance
• Sickle Cell Anemia
Beyond Mendel
• Incomplete Dominance
• Codominance
• Multiple Alleles
• Polygenic Traits
• Sex Linked Traits
• Genetics and the Environment
Multiple Alleles
• Many genes have more than two alleles
• This means that more than two alleles exist in the general
population
• Example: blood type
•
•
•
•
Type A (IAIA)
Type B (IBIB)
Type AB (IAIB)
Type O (ii)
Blood Typing
Beyond Mendel
• Incomplete Dominance
• Codominance
• Multiple Alleles
• Polygenic Traits
• Sex Linked Traits
• Genetics and the Environment
Polygenic Traits
• Many genes control these traits
• Results in a wide range of phenotypes
• Example: skin color in humans is controlled by
more than four different genes
Beyond Mendel
• Incomplete Dominance
• Codominance
• Multiple Alleles
• Polygenic Traits
• Sex Linked Traits
• Genetics and the Environment
Sex-Linked Traits
• Genes found on the X or Y chromosome are called sexlinked
• Most of these genes are found on the X chromosome
• human Y chromosome is much smaller/carries only a few genes
Color-Blindness
• The X chromosome carries 3 human genes for
color vision
• In males, a defective version of any of these
will cause color-blindness
• Red-green color-blindness (1/10 American males
and 1 out of 100 females)
• Males have only one X chromosome, the X
alleles are expressed in the males, even if
they are recessive
What about the girls?
• In order for an X
chromosome gene to be
expressed in females, she
must receive two copies of
the defective allele (one on
each X chromosome)
• Since this trait is carried on
the X chromosome, it will
be passed from father to
daughter, and may appear
again in her sons
Hemophilia…
• Sex-linked trait passed on the
X chromosome
• Affects gene that helps
control blood clotting
• A recessive allele in either of
the two genes required
causes hemophilia in the
individual
Hemophilia…
• affects 1 in 10,000 males
• Small cuts can be lethal
• Can be treated by injections of
normal clotting proteins
Beyond Mendel
• Incomplete Dominance
• Codominance
• Multiple Alleles
• Polygenic Traits
• Sex Linked Traits
• Genetics and the Environment
Genetics and Environment
• Genes + Environment = trait
• Example: the height of a sunflower is determined by:
• the genes it receive
• sunlight, amount of water, and climate
• The genes - development plan
• actual plan is determined by the environment
Human Traits
• Inherited the same way that
Mendel discovered
• Tricky= biologists must identify a
trait determined by a single gene
(must also ensure that the trait is
inherited and not
environmentally influenced)
• Then study how the gene is
passed from one generation to
the next
LINKAGE AND GENE MAPS
Gene Linkage
• Certain genes linked
together (located on
same chromosome)
• Chromosomes assort
independently, not genes
Applying Mendel’s Principles
• Thomas Morgan decided to apply Mendel’s
principle of genetics
• Does this apply to animals too?
• Fruit fly
• it is small, can be kept in the lab
• reproduces quickly (1 pair can create 100
offspring)