Download CH 8 Cellular Reproduction

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CHAPTER NINE
Patterns of Inheritance
I. Mendelian Genetics
♦ 1866 Gregor Mendel published paper on
“Discrete heritable units”
- work on peas rejected two common theories
of Inheritance:
1. “Pangenesis” (Hippocrates theory)
(all acquired traits of adult migrate to
gametes)
2. Blending Hypothesis (early 19th century)
(heritable traits from each parent blend in
young)
- Choose peas: trace 7 traits w/ 2 distinct forms
of each trait (2 alleles)
Self-fertilize OR
Cross-fertilize
True-breeding Varieties
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II. Monohybrid Crosses
♦ track inheritance of a single trait
♦ 4 Mendelian Hypotheses:
1. Different forms of a gene exist (allele)
2. Ea. Organism carries 2 copies (diploid)
3. Gametes only carry 1 copy (haploid) due to
Law of Segregation
Homozygous
Heterozygous
4. Forms may differ in expression:
Dominant
vs
Recessive
- Solving Mendelian Inheritance:
P generation x P generation
F1 generation
x F1
F2 generation
Organisms described in two ways:
1. Phenotype
2. Genotype
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PUNNETT SQUARE:
- visually shows principle of
Independent Assortment
- 4 Steps to Solving:
1. Determine P generation genotypes (diploid)
2. Determine Gametes (haploid)
3. Cross gametes in square to yield offspring
(diploid)
4. Summarize
P Generation __________
__________
Gametes ___ ___
___ ___
Solve:
RULES OF PROBABILITY:
- Rule of Multiplication
Product of each event ½ * ½ = ¼
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III. Dihybrid Cross
- track inheritance of two traits
- 4 Steps to solving:
1. Determine P generation genotypes (diploid)
2. Determine Gametes (haploid)
FOIL method
3. Cross gametes in square to yield offspring
(diploid)
4. Summarize
P Generation __________
__________
Gametes ___ ___ ___ ___ ___ ___ ___ ___
Solve:
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IV. Pedigrees
- family genetic history illustrated, allows one to
deduce pattern of inheritance and Carriers
Ο = Female
= Male
Patterns of Inheritance:
1. Simple Dominant/Recessive:
AUTOSOMAL RECESSIVE:
Albinism, deafness, unattached ear lobes
Cystic fibrosis
(inflicts 1/1800 caucasian, 1/25 carriers)
AUTOSOMAL DOMINANT:
Extra digits, webbed digits, tongue rolling,
dimples, achondroplasia (dwarfism),
Alzheimer’s, Huntington’s
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2. Incomplete Dominance:
(intermediate phenotypes)
Red x White = pink
Coat color (cats, cows),
hypercholesterolemia, flower colors
3. Multiple Alleles
(more than 2 alleles in population)
ABO Blood of humans (+ codominance)
Phenotype
A
B
AB
O
Genotype
AA, AO
BB, BO
AB
OO
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4. Pleiotropy
(one trait affects more than one character)
Albinism and eye orientation in Siberian
tigers, Sickle cell anemia
5. Polygenic
(additive effect of 2 or more genes on a
single trait)
Skin/Hair/Eye colors & height in humans
SEX-CHROMOSOMES
6. Sex-Linked
X-Linked = colorblindness, hemophilia, heart-valve
defect, MS, Fragile X syndrome
Y-Linked = SRY gene (gonads) Hypertrichosis