Observable Patterns of Inheritance
Starr/Taggart’s Biology:
The Unity and Diversity of Life, 9e
Chapter 11
Edited by: R. LeBlanc, M.S.
Mountain Pointe High School
2012
Fig. 11.1, p. 174
Tom Cruise Charles Barkley
Gregor Mendel Joan Chen
What do Charles Barkley and Tom Cruise have in common? (hint: check out their ears).
Terms Used in Genetics
Genes Alleles Hybrid Homozygous Heterozygous Dominant Recessive Genotype Phenotype Generations
P, F1, F2
Plant Reproductive Organs
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.
Plant Reproductive Terms
Mendel identified Mendel identified sevenseven traits in his garden peas traits in his garden peas that were easily studied:that were easily studied:
SEED SHAPESEED SHAPE
SEED COLORSEED COLOR
POD SHAPEPOD SHAPE
POD COLORPOD COLOR
FLOWER COLORFLOWER COLOR
FLOWER POSITIONFLOWER POSITION
STEM LENGTHSTEM LENGTH
roundround wrinkledwrinkled
yellowyellow greengreen
inflatedinflated wrinkledwrinkled
greengreen yellowyellow
purplepurple whitewhite
axialaxial terminalterminal
talltall dwarfdwarf
He carefully isolated He carefully isolated pure pure breedingbreeding varieties before varieties before
experimenting with experimenting with crosses between different crosses between different
varieties.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 crossesTest 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?
ChapterChapter 9 9
Mendel’s Conclusions
Section 1 Mendel’s Legacy
Trait Studied Dominant Form
Recessive Form
F2 Dominant-to- Recessive Ratio
SEED SHAPE
SEED COLOR
POD SHAPE
POD COLOR
FLOWER COLOR
FLOWER POSITION
STEM LENGTH
2.96:1
3.01:1
2.95:1
2.82:1
3.15:1
3.14:1
2.84:1787 tall 277 dwarf
651 long stem
207 at tip
705 purple 224 white
152 yellow428 green
299 wrinkled882 inflated
6,022 yellow 2,001 green
5,474 round 1,850 wrinkled
Fig. 11.5, p. 178
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?
Independent Assortment
In-text, p. 180
AABB aabb
x
AaBb
AB AB ab ab
TRUE-BREEDING PARENTS:
GAMETES:
F1 HYBRID OFFSPRING:
purple flowers, tall
white flowers,dwarf
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
http://www.biology.arizona.edu/mendelian_genetics/mendelian_genetics.html
Use the website above for practice genetics problems.
Fig. 11.9, p. 181
aB
AB
AB
abAb
Ab
aB
ab
1/4
1/4
1/4
1/4
1/4 1/4 1/4 1/4
AB ab
AABBpurple-
floweredtall parent
(homozygousdominant)
aabbwhite-
flowereddwarf parent(homozygous
recessive)
F1 OUTCOME: All F1 plants purple-flowered, tall(AaBb heterozygotes)
X
meiosis, gamete formation
AaBb AaBb
Possible outcomes of cross-fertilization
AaBb aabbAabb aaBb
AABB AABb AaBB AaBb
AABb AAbb AaBb Aabb
AaBb aaBB aaBbAaBB
1/161/161/161/16
1/161/161/161/16
1/161/161/161/16
1/16 1/16 1/16 1/16
ADDING UP THE F2 COMBINATIONS POSSIBLE:
9/16 or 9 purple-flowered, tall
3/16 or 3 purple-flowered, dwarf
1/16 or 1 white-flowered, dwarf
3/16 or 3 white-flowered, tall
Theory in Modern Form
Independent Assortment
Gametes require genes independently of how other pairs of genes were sorted out
Variety of Offspring
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!
INCOMPLETE DOMINANCE INCOMPLETE DOMINANCE
CODOMINANCECODOMINANCE
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
Fig. 11.12, p. 183
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.
Interactions Between Gene Pairs
Epistasis
Fur color in mammals
Melanin production
Albinism Comb shape in chickens (see the example
in the next slides)
(When 1 gene pair influences other gene pairs with their combined activities producing some effect on phenotype)
(Melanin produces fur color)
(influenced by an enzyme produced from the alleles from another gene)
(the absence of melanin)
Fig. 11.15, p. 185
WALNUT COMB
9/16 walnut(RRPP, RRPp, RrPP, or RrPp)
ROSE COMB
3/16 rose(RRpp or Rrpp)
PEA COMB
3/16 pea(rrPP or rrPp)
SINGLE COMB
1/16 single(rrpp)
RRpp(rose comb)
rrPP(pea comb)
RrPp(all walnut comb)
comb
P:
F2:
F1:X
X
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)
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)
Fig. 11.14, p. 185
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.
What causes this Albino snake??????
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.
B = BLACK b = BROWNE = Full deposit ee = Reduced Deposit produces a Golden color (in B or b)Black Golden Brown
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 off-spring? List the different genotypes of each phenotype represented?
(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
Fig. 11.16, p. 186
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.
-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.
Continuous Variation:
-Different pairs of genes (alleles) interact to produce and deposit melanin.
-Eye color seems to be Continuous; from
Black ------------- Blue
(+ melanin - melanin)
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
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