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Gregor Mendel
- The father of genetics
- -mid 19th C.
- -pea plants
Austrian monk & naturalist
Wasn't truely recognized for his work until decades after his death
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Mendel's Main inferences
- Basic units of genetics are material elements
- These elements come in pairs
- these elements (today called genes) retain their characteristics through many generations
- these element (gene) pairs separate during gamete formation
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Mendel's Experimental subjects
- PEA PLANTS:
- capable of self-pollination
therefore can be cross pollinated
peas: seeds in the ovary
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Phenotype
Physiological features
Example: color, size, etc.
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Genotype
Genetic makeup
Technically codes for proteins
(phenotype is controlled by its genotype)
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Alleles
one of the alternative forms of a single gene
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Cross pollination
- P generation: parent (started with "true breeding" parents)
- F1 = first fillal generation
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F1 generation self-pollination..
- 3:1 ration, yellow: green seeds
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Dominant
- an allele that is expressed in the heterozygous condition
- (uppercase lettter)
- Example:
- heterozygous peas (Yy) the yellow was the portion that showed.
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Recessive
- An allele that is not expressed in the heterozygous condition
- (lower case letter)
- Example:
- heterozygous peas (Yy) the green is the recessive because you cannot see it
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Three Genotypes yield Two phenotypes
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Chromosomes and Phenotypes
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Punnett Squares
Give expected phenotypic and genotypic ratios of offspring
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Law of Segregation
Differing characteristics in organisms result from two genetic elements (alleles) that separate in gamete formation
- -Each gamete only gets one of the two alleles
- -homologous chromosomes separate during Metaphase I of meiosis
- -this is how Yy could never give rise to yy
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Law of independent assortment
Genes for different characters are passed on independently of each other
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Incomplete Dominance
- Heterozygote phenotype is intermediate beetween either of the homozygous phenotypes
- (Mendel's rules do not apply to all intstances of inheritance)
EXAMPLE: the cross of a RR red snapdragon with an rr white snapdragon results in a Rr pink snap dragon...why isn't this blending?
ANSWER: beause the characteristics Rr is STILL there and can be passed down to later generations. Also there isn't enough pigment of the dominant red color to color the entire flower.
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Codominance
- 2 alleles are equally dominant
- -Each has different phenotypic effects
- -both effects expressed in organisms heterozygous for that gene
- EXAMPLE: blood type in humans
- -3 different alleles: A, B, and O
- -A and B are codominant (think blood type AB)
- -O is recessive
(blood type is based on the surface glycolipids..)
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Multiple Alleles
When 3 or more alleles of the same gene exist in a population
NOTE: no single person can have more than two alleles for a gene...but a population can have multiple variants
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Polygenic Traits
- Inheritance of a genetic character that is determined by the interaction of multiple genes
- -each gene has a small, additive effect on trait
- -more common than traits governed by single genes
- -display "continuous variation"
EXAMPLES: skin color, hair color, eye color, height. etc.
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Gene-Environment Interactions
Effects of genes can vary greatly depending on environment.
Environmental factor: any external influnce that is favorable or unfavorable for the development of a trait in an organism.
- EXAMPLE: Hydrangeas
- depending on the pH of the soil (acidic or basic) will determine the color of the hydrangeas
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Pleiotropy
Single gene influences multiple phenotypic traits
- EXAMPLE: Fragile X Syndrome
- -break on X chromosome which can cause:
- Mental retardation, abnormally long face, large ears, large testicles.
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