Download Dominant Recessive

Chapter 9
Genetics
9.1 The Work of Gregor Mendel
• Mendel – crossed pea plants to study and
understand genetics
– Most pea plants self pollinate (true breeding)
– Mendel forced plants to cross pollinate (have 2
plants)
– Studied 7 traits of pea plants pg 176.
– Took the plants that had different traits and
crossbreds them (hybrids)
The F1 Cross
• First Filial (parent cross, produce the F1,
then cross the F1 making an F2)
– Law of segregation: Segregation of alleles
occurs during the formation of gametes, sex
cells.
– Pg 177
– Law of Independent Assortment – factors for
individual characteristics are not connected.
Assort independently of each other.
Came to 2 conclusions after the
breeding
1. Genes, segment of DNA, occurs in pairs,
controll heredity. Visual form called
alleles. (noted as “factors”)
2. Found that some of the alleles are
dominant and some are recessive.
1. Dominant trait always uppercase (TT, Tt)
2. Recessive always lowercase (tt)
9.2 Probability and Punnett
Squares
• Punnett square – table representation of
crossing alleles
– TT or tt – homozygous – same alleles
– Tt – heterozygous – different alleles
– Phenotype – physical look, all tall (TT, Tt) have
same phenotype.
– Genotype – based on alleles. (TT, and Tt) are
different now.
Probability
• Penny = ½ = .50
• A cross results in 787 pink flowers and 277
white flowers. If we cross the same P
generation, the probability will be the
same)
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Dominant
Curled Up Nose
Clockwise Hair Whorl
Can Roll Tongue
Widow's Peak
Facial Dimples
Able to taste PTC
Earlobe hangs
Middigital hair (fingers)
No hitchhiker's thumb
Tip of pinkie bends in
Oval face
Cleft chin
Broad eyebrow
Separated eyebrows
Long eyelashes
Almond eyes
Freckles
Wet-type earwax
Left thumb on top of
interlocking fingers
Recessive
Roman Nose
Counter-clockwise Hair Whorl
Can't Roll Tongue
No Widow's Peak
No Facial Dimples
Unable to taste PTC
Earlobe attaches at base
No middigital hair
Hitchhiker's thumb
Pinkie straight
Square face
no cleft chin
Slender eyebrow
Joined eyebrows
Short eyelashes
Round eyes
No freckles
Dry-type earwax
Right thumb on top of
interlocking fingers
Punnett Squares pg 182
Homozygous x homozygous
Homozygous x heterozygous
• AA x Aa
Hetero x hetero
Summary of Mendel’s Principles
pg 272
• Some alleles are neither dominant nor recessive, and
many traits are controlled by multiples alleles or
multiple genes.
• Incomplete Dominance – when one allele is not
necessarily dominant (red and white flowers produce
pink)
• Codominance – both alleles contribute to the
phenotype.
• Multiple alleles – within the population of the species
there are more than just 2 types of alleles. Coloration
in Rabbits
• Polygenic Traits – having many genes, traits controlled
by 2 or more genes. Skin color in humans.
• Incomplete
Dominance
• We'll use "F" for the flower color allele.
FR = allele for red flowers
FW = allele for white flowers red x white ------> red & white spotted flowers
FRFR x FWFW ----> 100% FRFW
Codominance
• Problems
Explore Punnett Squares!!
• http://www.geocities.com/CapeCanaveral/
Hall/1410/lab-B-19.html
Dihybrid cross – two traits