Transcript Chapter 14 Notes

AP Biology
Mendel used the scientific approach to identify two laws of
inheritance
 Known
as the “Father of
Genetics”
 Experimented with pea
plants to develop
principles of genetics
• In the 1800s… before
anyone even knew:
 what DNA was, let alone how it
worked (1940s-1950s)
 What meiosis was or how it
worked (1870s-1880s)
 Knew
some “factor”
caused organisms to
have “characters” like
their parents
 Now we call them genes
and traits
P generation –
true breeding
F1 generation –
heterozygous
F2 generation –
3:1 ratio; recessive
trait reappears
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Dominant: gene that is always expressed if present
Recessive: gene that only expressed when 2 copies are
inherited
Homozygous/True-breeding/Pure: two of the same allele (ex:
BB, bb)
Heterozygous/Hybrid: two different alleles (ex: Bb)
Phenotype: physical appearance of an organism (based on its
genes)
Genotype: genetic makeup of an organism (letters)
P generation: parent generation (Mendel – true-breeding
plants)
F1 generation: first generation made from crossing P generation
F2 generation: second generation made from crossing
F1generation
 Law
•
•
of Segregation
Two alleles of a gene
separate during
meiosis
Each parent can give
one of each
homologous
chromosome (one
copy of each gene) to
offspring
 Law
•
•
of Independent Assortment
Each allele pair segregates into gametes
independently of other pairs (random)
How homologous chromosomes align in
metaphase I
 Monohybrid
crosses cross 1 trait
• Ex: pea color
• F2 generation shows
3:1 ratio
 Dihybrid
crosses cross 2
traits at once
• Ex: pea color and
shape
• F2 generation
shows 9:3:3:1
ratio
The laws of probability govern Mendelian inheritance
 Rule
of Multiplication
• Probability that independent events will occur in
sequence
• Look for “and”
 Rule
of Addition
• Probability that events will occur mutually
exclusive of each other
• Look for “or”
 Bozeman
Probability in Genetics:
Multiplication & Addition Rules
Inheritance patterns are often more complex than predicted by
simple Mendelian genetics
 Complete
dominance
(as shown in Mendel’s
pea plants)
• Dominant is always
expressed over recessive
• Recessive only shows if
both alleles are recessive
• RR = purple; Rr = purple;
rr = white
 Mendel
was lucky – most inheritance
follows other patterns…
 Let’s look at the exceptions to the norms
 One
allele is not
completely dominant
over another
 Heterozygous
organisms display a
blend between both
phenotypes
 Example:
snapdragons
 Alleles
do NOT blend
 Both traits show in heterozygous organism
• Both alleles expressed dominantly
• Neither allele is recessive
 Ex:
roan cattle
 Many
genes have
more than 2 alleles
 Examples:
• human blood type
• fur color in rabbits
 Multiple
genes affect single phenotype
 Ex: skin color, height
• The more dominant alleles inherited, the darker
the skin, taller the offspring
 DNA
isn’t the only factor that influences a
phenotype
 Environment can influence genes too
 In reality, phenotype is a combination of an
organism’s genes, environment, as well as
other factors
 Examples:
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Temperature
Light
Moisture
Minerals
Nutrients
 Snowshoe hare
• Genes code for pigments that give its hair a
brownish-grey color called agouti.
• However, during cold winter months the alleles
for pigment production are turned-off and the
hare appears white in color.
• In this case temperature regulates the
expression of the coat color alleles.
 Himalayan rabbits
• Genotype ch/ch should produce black pigments in
their hair.
 when the rabbit’s body temperature is above 37 o C, the ch
alleles are turned-off and the rabbit’s hair appears white
 if the rabbit’s body temperature falls below 37 o C, black
pigments will appear in the rabbit’s hair
 Hydrangeas
• flower coloration is subject to the pH of the soil in
which the hydrangea bush is growing.
 In acidic soil, the flowers pink pigments are produced.
 In basic soil, blue pigmentation is produced in flowers.
Many human traits follow Mendelian patterns of inheritance
 Analyze
inheritance of traits through
family relationships
 Autosomal
recessive
 Defective chloride channels in cells
leads to build up of mucus in pancreas,
lungs, digestive tract, etc.
 Autosomal
recessive
 Fatal neurological/brain degeneration
beginning at around 6 months of age
 Autosomal
recessive
 Causes abnormally shaped red blood
cells, leads to anemia, clots
 Autosomal
 Dwarfism
dominant
 Autosomal
dominant
 Progressive degeneration of
brain/nervous system
 Late onset (age 35-45)
 Fetal
testing
• Amniocentesis
• Chorionic villus
sampling
• Blood testing
 Newborn
screening
• Blood analysis for
genetic disorders