genetics. gregor mendel: father of genetics genetics: study of heredity heredity: passing traits...
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Genetics
Gregor Mendel: Father of Genetics
Genetics: study of heredity
Heredity: passing traits from parent to offspring
Used peas to study heredity
Why Peas?
1. Several Traits 2. Control mating 3. Small, grow easily, and matures
quickly
Alleles: Different versions of a geneEx: White and Purple Flowers
Mendel’s Experiment
Monohybrid Cross: One pair of contrasting traits. Ex: Mating a plant with purple flowers with white
flowers
True-breeding: All offspring would have only one form of the trait Ex: Purple-flowering plant only has purple-
flowered offspring
Mendel’s Experiments
Vocabulary
Dominant: Expressed in appearance (A)
Recessive: Not noticeable in appearance (a)
Homozygous: AA or aa
Heterozygous: Aa
More Vocabulary
Genotype: Genetic make up (ex: Pp)
Phenotype: Appearance (ex: Purple flowers)
Laws of Heredity Law of Segregation
The two alleles for a trait separate when gametes are formed
Law of Independent Assortment Alleles of different genes separate independently of
each other during meiosis
Law of Segregation
Separation of alleles into separate gametes
50% chance that one allele will go into a gamete
Law of Independent Assortment
Punnett Square
Ratios
Test Cross
Dihybrid Cross: Cross that involve two traits
Incomplete DominanceIncomplete Dominanceandand
CodominanceCodominance
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Incomplete DominanceIncomplete Dominance
F1F1 hybridshybrids have an appearance somewhat inin betweenbetween the phenotypesphenotypes of the two parental varieties.
Example:Example: snapdragonssnapdragons ( (flowerflower))red (RR) x white (rr)
RR = red flowerRR = red flower rr = white flower
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R
R
r r
Incomplete DominanceIncomplete Dominance
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RrRr
RrRr
RrRr
RrRr
RR
RR
rr
All Rr All Rr == pink pink(heterozygous pink)(heterozygous pink)
produces theproduces theFF11 generation generation
r
Incomplete DominanceIncomplete Dominance
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CodominanceCodominance
Two alleles are expressed (multiple Two alleles are expressed (multiple alleles) in heterozygous individuals.alleles) in heterozygous individuals.
Example: blood typeExample: blood type
1.1. type Atype A = I= IAAIIAA or I or IAAii 2.2. type Btype B = I= IBBIIBB or I or IBBii 3.3. type ABtype AB = I= IAAIIBB
4.4. type Otype O = ii= ii
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Codominance ProblemCodominance Problem
Example: homozygous male Type B (IBIB)
x heterozygous female Type A (IAi)
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IAIB IBi
IAIB IBi
1/2 = IAIB
1/2 = IBi
IB
IA i
IB
Another Codominance ProblemAnother Codominance Problem
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• Example:Example: male Type O (ii) x female type AB (IAIB)
IAi IBi
IAi IBi
1/2 = IAi1/2 = IBi
i
IA IB
i
Sex-linked TraitsSex-linked Traits
Traits (genes) located on the sex Traits (genes) located on the sex chromosomeschromosomes
Sex chromosomes are X and YSex chromosomes are X and YXX genotype for femalesXX genotype for femalesXY genotype for malesXY genotype for malesMany sex-linked traits carried on Many sex-linked traits carried on
X chromosomeX chromosome24
Sex-linked TraitsSex-linked Traits
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Sex ChromosomesSex Chromosomes
XX chromosome - female Xy chromosome - male
fruit flyeye color
Example: Eye color in fruit Example: Eye color in fruit fliesflies
Sex-linked Trait ProblemSex-linked Trait ProblemExample: Eye color in fruit flies (red-eyed male) x (white-eyed female)
XRY x XrXr
Remember: the Y chromosome in males does not carry traits.
RR = red eyedRr = red eyed rr = white eyedXY = maleXX = female
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XR
Xr Xr
Y
Sex-linked Trait Solution:Sex-linked Trait Solution:
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XR Xr
Xr Y
XR Xr
Xr Y
50% red eyed female
50% white eyed male
XR
Xr Xr
Y
Female CarriersFemale Carriers
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