Transcript Chap 11 PowerPoint Notes

Observable Patterns of
Inheritance
Edited by: R. LeBlanc, M.S.
Mountain Pointe High School
2012
Starr/Taggart’s
Biology:
The Unity and Diversity of Life,
Chapter 11
9e
Tom Cruise
Charles Barkley
What do Charles
Barkley and Tom
Cruise have in
common? (hint:
check out their
ears).
Gregor Mendel
Joan Chen
Fig. 11.1, p. 174
Terms Used in Genetics
 Genes
 Alleles
 Hybrid
 Homozygous
 Heterozygous
 Dominant
 Recessive
 Genotype
 Phenotype
 Generations
P, F1, F2
Plant Reproductive Organs
Plant Reproductive Terms
carpel stamen
GAMETES - the male or female sex cells. In plants, the sperm is the
male sex cell (found in pollen grains), and the ovule (egg) is the female
sex cell.
PISTIL – female reproductive structure.
STAMEN – male reproductive structure.
FERTILIZATION- the uniting of the male and female gametes within
the flower.
POLLINATION - The transfer of pollen from the anther to the pistil,
usually by wind, water, or insects.
CROSS-POLLINATION - transferring the pollen from one plant to
another plant.
Mendel identified seven traits in his garden peas
that were easily studied:
SEED SHAPE
round
wrinkled
SEED COLOR
yellow
green
POD SHAPE
inflated
wrinkled
POD COLOR
green
yellow
FLOWER COLOR
purple
white
FLOWER POSITION
axial
terminal
STEM LENGTH
tall
dwarf
He carefully isolated pure
breeding varieties before
experimenting with
crosses between different
varieties.
Mendel’s Insight Into
Patterns of Inheritance
Mendel’s
Experimental
Approach
Garden pea plant
Cross pollination
What are the
advantages of SELF
cross pollination?
What is the
advantage of using
pea plants?
How did Mendel
control his
experiments?
Mendel’s Experiment
 Mendel concluded that each organism has two factors
(alleles) for each trait.
 He performed crosses with seven different pairs of traits
(for example, pure-breeding purple-flowered plants
crossed with pure-breeding white-flowered plants). In
every case he found that one trait disappeared from the F1
generation only to reappear in the F2 generation plants!
 This is explained by the Rule of Dominance which will be
demonstrated in the next two examples:
Mendel’s Theory of Segregation
Monohybrid cross
Gene segregation
What do you notice about the alleles of both
parents?
What do the letters A & a stand for? (the font
of the letters)
What are diploid gamete cells? Haploid?
Why are the final gamete cells haploids?
What does the fertilized zygote traits
represent? (check the alleles)
Probability and Punnet Squares
A possibility of outcomes and crosses
Test crosses
Unknown genotype crossed with homozygous
recessive
Mendel’s Monohybrid Cross
Pure White Flower
Pure Purple Flower
What traits (genotype) do F1 offspring have?
Mendel’s Monohybrid Cross
What percentage of
the second
generation are
purple? White?
What % are pure
purple? White?
If you planted four
first generation seeds
, how many of these
seeds will be purple
flowers in the 2nd
generation?
Chapter 9
Section 1 Mendel’s Legacy
Mendel’s Conclusions
Trait Studied
SEED SHAPE
Dominant
Form
Recessive
Form
F2 Dominant-toRecessive Ratio
5,474 round
1,850 wrinkled
2.96:1
SEED COLOR
6,022 yellow
2,001 green
3.01:1
POD SHAPE
882 inflated
299 wrinkled
2.95:1
POD COLOR
428 green
152 yellow
2.82:1
FLOWER COLOR
705 purple
224 white
3.15:1
FLOWER POSITION
651 long stem
207 at tip
3.14:1
To get the ratios
on the right to all
be approximately
equal, what do
we know about
the P1 plants?
What do you
notice about the
number of plants
studied?
How did Mendel
decide which of
the traits were
dominant?
Recessive?
Why aren’t the
ratios exactly
3:1?
STEM LENGTH
787 tall
277 dwarf
2.84:1
Fig. 11.5, p. 178
Independent Assortment
http://www.biology.arizona.edu/mendelian_genetics/mendelian_genetics.html
Use the website above for practice genetics problems.
TRUEBREEDING
PARENTS:
purple
flowers,
tall
x
white
flowers,
dwarf
AABB
GAMETES:
AB
aabb
AB
ab
AaBb
F1 HYBRID
OFFSPRING:
ab
What are the phenotype ratios of all the
offspring resulting from the cross of these
2 parents? Genotype?
ALL F1 OFFSPRING: PURPLE TALL
GENOTYPE: AaBb
What about the phenotype ratio of the
offspring of the F2 generation?
9 : 3 : 3: 1
In-text, p. 180
AABB
purpleflowered
tall parent
(homozygous
dominant)
AB
aabb
whiteflowered
dwarf parent
(homozygous
recessive)
ab
X
F1 OUTCOME: All F1 plants purple-flowered, tall
(AaBb heterozygotes)
AaBb
AaBb
meiosis, gamete formation
1/4
AB
1/4
Ab
1/4
aB
1/4
ab
1/4
AB
1/4
Ab
1/4
aB
1/4
ab
ADDING UP THE F2 COMBINATIONS POSSIBLE:
1/16
1/16
1/16
1/16
9/16 or 9 purple-flowered, tall
AABB AABb AaBB AaBb
1/16
1/16
1/16
1/16
AABb AAbb AaBb Aabb
1/16
1/16
1/16
3/16 or 3 purple-flowered, dwarf
3/16 or 3 white-flowered, tall
1/16 or 1 white-flowered, dwarf
1/16
AaBB AaBb aaBB aaBb
1/16
1/16
1/16
1/16
AaBb Aabb aaBb aabb
Possible outcomes of cross-fertilization
Fig. 11.9, p. 181
Theory in Modern Form
Independent Assortment
Gametes require genes independently
of how other pairs of genes were sorted
out
Variety of Offspring
INCOMPLETE DOMINANCE
A cross where one
allele does not
completely hide or
mask the other
producing a blended
appearance in the
phenotype.
Example: In
snapdragons, pure red
crossed with pure
white produce pink!
CODOMINANCE
 Two non-identical
alleles of a pair
specify two
different
phenotypes yet
one cannot mask
the other and both
are expressed .
Multiple Alleles
 More than two alleles
in a population for a
given trait.
 Example: human
blood types.
 3 alleles: A,B,O.
 What do the letters A,
B & O stand for?
 A & B stand for a type
of protein found on
the surface of RBC
and i stands for the
lack of this protein.
Multiple Effects
of Single Genes
Pleiotropy.
The expression of a
single gene can
influence two or
more traits.
Sickle Cell Anemia.
What do you notice
about the physical
effects of having
sickle cell anemia?
*Refer to the next slide
HbA = Normal Red Blood Cells
HbS = Sickle Cell Red Blood Cells
To develop the full effects of Sickle Cell Anemia you need to be Homozygous for this trait.
Fig. 11.12, p. 183
Interactions Between
Gene Pairs
Epistasis
(When 1 gene pair influences other gene pairs with their
combined activities producing some effect on phenotype)
Fur color in mammals
(Melanin produces fur color)
Melanin production
(influenced by an enzyme produced from the alleles from another
gene)
Albinism
(the absence of melanin)
Comb shape in chickens (see the example in
the next slides)
Epistasis Problem: Cross a Rose Comb (RRpp) chicken with a Pea (rrPP) Comb
chicken. What will be the phenotype ratio of the off-spring? Cross this F1
generation. (R = Rose Comb; P = Pea Comb; RP = Walnut Comb; and rp = Single
Comb)
P:
RRpp
(rose comb)
X
rrPP
(pea comb)
F1:
RrPp
(all walnut comb)
X
F2:
9/16 walnut
(RRPP, RRPp, RrPP, or RrPp)
3/16 rose
(RRpp or Rrpp)
3/16 pea
(rrPP or rrPp)
1/16 single
(rrpp)
ROSE COMB
PEA COMB
SINGLE COMB
comb
WALNUT COMB
NOTE: Sometimes interaction between 2 gene pairs results in a phenotype that neither pair can
produce alone. Comb shape in chickens can result in 4 types depending on the interactions of 2 gene
pairs (R & P)
Fig. 11.15, p. 185
What causes this Albino snake??????
In some individuals the 2 genes mentioned earlier do NOT interact, causing another gene to effect
coloration. At gene ‘C’, a gene at another gene locus, is responsible for the enzyme called tyrosinase,
one of many enzymes responsible for the production of melanin. An individual with one of the
dominant alleles (CC or Cc) can make the functional enzyme. If two recessive alleles (cc) are present,
melanin production is interfered with resulting in ALBINISM.
Fig. 11.14, p. 185
Epistasis Problem: Cross homozygous Black Lab with a Gold Lab (bbee) What
would be the off-springs phenotype ratio of a cross between 2 F1 generation offspring? List the different genotypes of each phenotype represented?
Black
Golden
Brown
B = BLACK
b = BROWN
E = Full deposit
ee = Reduced Deposit produces
a Golden color (in B or b)
The alleles of one gene
specify an enzyme for
melanin production
while an allele on
another gene is
responsible for the
deposit of melanin in the
hairs of the organism.
(BBEE; BBEe; BbEE; BbEe)
(bbEE; bbEe)
(BBee; Bbee; bbee)
Less Predictable
Variation in Traits
 Camptodactyly (A
rare genetic abnormality the
affects both the shape and the
movement of fingers. This can
be caused by improper enzyme
production.)
 Continuous
variation (A range of
small differences in the
phenotypes of individuals)
Eye color
Height
Eye Color:
-iris (eye color) is beneath the
cornea.
-Color: a cumulative outcome
of a number of gene products
-Melanin production affects
color.
-Dark eyes = increased
amounts of melanin.
Continuous Variation:
-Different pairs of genes
(alleles) interact to produce
and deposit melanin.
-Eye color seems to be
Continuous; from
Black ------------- Blue
(+ melanin
- melanin)
-Brown eyes = less melanin.
-Light brown/hazel = even less
-Gray/green/blue = very little
melanin, so these wave
lengths of light are reflected
back to the observer.
Fig. 11.16, p. 186
Examples of Environmental
Effects on Phenotypes
Himalayan Rabbit & Siamese Cat
Less melanin in warm body regions. Heat
makes enzyme in melanin production pathway
less active
Hydrangea color
Color ranges from blue to pink, depending on
acidity of soil
In Conclusion
 Gene is unit of information about a
heritable trait
 Mendel provided indirect evidence of
dominant and recessive genes
 F1 offspring form monohybrid crosses
AA x aa -----> Aa
 Crosses from F1 result in F2 offspring with
phenotypes having a 3:1 ratio
In Conclusion
 Theory of segregation states that genes of
each pair segregate during meiosis and
wind up in different gametes
 Dihybrid crosses result in 9:3:3:1
phenotypic ratio
 Theory of Independent Assortment states
that gene pairs independently sort out into
different gametes regardless of other gene
pairs of other chromosomes
In Conclusion
 Four factors influence gene expression
Degrees of dominance
Products of pairs of genes may interact
One gene may effect two or more traits
Environment