Download Ch 9 Fundamentals of genetics

CH 9
FUNDAMENTALS OF
GENETICS
Genetics
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What is it?
 Define
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it in your notebook with a partner.
Field of biology devoted to understanding how
characteristics are transmitted from parent to
offspring
Gregor Mendel
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“Father of genetics”
Studied science and mathematics
Austrian monk mid 1800s
Researched heredity:
transmission of characteristics
from parent to offspring
Worked with pea plants
Mendel and pea plants
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Observed 7 heritable characteristics of pea plants
Trait: genetically determined variant such as color
The pea plant characters existed in two variants
Height
Flower position
Flower color
Pod color
Pod appearance
Seed texture
Seed color
Methods
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Pollination: combination of
male and female gametes
Self-pollination: same plant
Cross-pollination: different
plants
(male)
(female)
Methods
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Needed true breeding plants (pure; offspring
always had same variant of trait as parent)
Then crossed two true breeding plants for a single
trait (one of each variant; one purple flowered and
one white)
This is the P generation: true-breeding parents
Resulting generation called F1 generation
F1 self crossed to get F2 generation
3 steps in Mendel’s experiment
Results
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Observed similar frequencies of traits
Traits came out in consistent ratios of 3:1
Dominance
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Dominant traits: always observed; can mask a
recessive trait
Recessive traits: only observed when dominant trait
is not present; can be masked by dominant trait
Mendel’s factors
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Remember, Mendel didn’t know about genes.
We call mendel’s factors: Alleles
Alleles: alternative forms of a gene
Example: brown hair vs blond hair
Example: purple flowers vs white flowers
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Alleles represented by letters
Capital letter of dominant trait
Alleles for flower color in pea plants:
P = purple and p = white
P p
Mendel’s conclusions
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1.
2.
Open books to page 177. read paragraphs for
the following and rewrite the definition in your own
words.
Law of segregation
Law of independent assortment
9-2: Genetic crosses
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Genotype: genetic makeup
Consists of alleles inherited from parents
for flower color in peas there are three possible
combinations of the two alleles (P & p)
PP = purple genotype
Pp = purple genotype
pp= white genotype
phenotype
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Phenotype: organism’s appearance (physical
characteristic)
PP and Pp = purple flowers
pp= white flowers
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Homozygous: when both alleles are the same
Homozygous dominant = PP (purple)
Homozygous recessive = pp (white)
Heterozygous: when both alleles are different =
Pp (purple)
Probablity
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Likelihood a specific event will occur
Genetic crosses deal with probability
Punnett squares used to predict the possible
distribution of inherited traits in offspring
Tells potential genotypes and phenotypes of
offspring
Monohybrid cross: cross in which only ONE trait os
tracked
Punnett squares
Need genotypes of parents
1.
(PP x pp)
Draw a punnett square
Place parents alleles on either
side of square
2.
3.
1.
4.
5.
Each parent can give only one of
their two alleles to the offspring
Combine columns and rows
Count genotypes and determine
probabilities
Lets do some crosses!
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Pea color: Yellow dominant to green
Cross a homozygous dominant plant with a
heterozygous plant
What is the probability of each genotype?
What is the probability of each phenotype?
Lets do some crosses!
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Cross a plant with green peas with one that is
heterozygous.
What is the probability of each genotype?
What is the probability of each phenotype?
More crosses!!!!!
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Cross two heterozygous plants for pea shape where
Round is dominant to wrinkled.
What is the probability of each genotype?
What is the probability of each phenotype?
Bikini Bottom Genetics time
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Work with a partner to complete the worksheet.
Ask questions when needed.
Test cross
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Test cross: cross between an unknown genotype
and a homozygous recessive individual
#9
EXAMPLE:
 Heterozygous yellow Spongebob marries yellow
Susie and they have one blue baby and one yellow
baby. Susie says she is a purebred.
 Is she correct?
If not, what is her genotype?
#10
1.
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Heterozygous yellow Spongebob has a yellow
brother and 2 blue sisters. His Dad is yellow and
his mom is blue. Mom is pregnant with
Spongebaby #5.
What are the genotypes of Mom and Dad?
What is the probability their new baby will be
yellow like Dad or blue like Mom?
Incomplete dominance
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Phenotype of heterozygous individual is an
intermediate trait
flower color in four o’clocks
 RR
– red
 rr – white
 Rr – pink
Codominance
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Two dominant alleles
 Both
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are expressed in heterozygote
Blood type: A, AB, B, O
IA and IB are both dominant to i
IAIA, IAi = type A
IBIB, IBi = type B
IAIB = type AB
ii = type O
Dihybrid cross
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Cross in which two characteristics are tracked
Round dominant to wrinkled. Yellow dominant to
green
Cross two individuals who are heterozygous for
both traits