Download Bio.B.2- Genetics

BIO.B.2- GENETICS
CHAPTER 11
B2: Genetics
1.
Describe and/ or predict observed patterns of
inheritance i.e. dominant, recessive, co-dominant,
incomplete dominance, sex- linked, polygenic and
multiple alleles.
B2 Vocabulary
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genetics
fertilization
trait
hybrid
gene
allele
Principle of dominance
segregation
Gamete
probability
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homozygous
heterozygous
phenotype
genotype
punnett square
incomplete dominance
codominance
multiple allele
polygenic trai
Review…
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What are the four macromolecules?
 1.
Carbohydrates
 2. Proteins
 3. Lipids
 4. Nucleic Acids
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Which of the four macromolecule is
responsible for an individuals unique
characteristics?
 Nucleic
acids - DNA
Introduction
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Genetics = study of heredity
Heredity = transfer of characteristics from parent to
offspring
Gregor Mendel:
Father of Modern
Genetics
 Studied Pea Plants
 Observed recurring
patterns
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What Mendel Knew…
1.
A trait is a specific
characteristic

EX: pea color, pea shape, flower
color
What Mendel Knew…
2.
Mendel could control
fertilization
Self-pollination – one plant fertilizes
itself
 Cross-pollination – two different plants

What Mendel Knew…
3.
“true-breeding” plants always
produced offspring plants that
had the same trait as the
parent
 EX:
a true-breeding purple flower
plant produces plants that also have
purple flowers
What Mendel Knew…
4.
A “hybrid” = a cross between two
different plants
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Offspring showed the characteristic of
one parent
What Mendel
Saw
1st generation
parental trait
disappears
2nd generation
parental trait
reappears in a 3:1
ratio
What Mendel saw
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READ ONLY
P-generation
True-breeding
 When
self pollinated, always produce
offspring plants with identical traits
 Ex: a true-breeding purple plant
ALWAYS produces plants with purple
flowers
F1 generation (hybrids)
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READ ONLY
F1 Generation
Produced by crossing pure-bred P plants
 Always
saw the same results (parental trait disappears)
Mendel
F2 generation
READ ONLY
• Produced by self-pollination of F1 plants
– Always saw the same results (parental trait reappears) in
a specific ratio
Mendel’s Conclusions:
1.
Traits are determined by “factors” that get passed
from one generation to the next
 Factors
= genes
Mendel’s Conclusions:
2.
There are different “forms” of a gene that account
for variations in inherited characteristics
 Forms
= alleles
 EX: purple allele or white allele
Mendel’s Conclusions:
3.
For each trait, an organism inherits two alleles (one
from each parent)
 The
alleles may be identical or they may be different
 Homozygous = two identical alleles
 Heterozygous = two different alleles
Mendel’s Conclusions:
4.
Physical appearance (phenotype) is influenced by
the alleles inherited for the trait (genotype)
 some
“alleles” are dominant and some are recessive
 One
dominant allele will give the dominant trait
 Need two recessive alleles to have the recessive trait
 Letters used to differentiate alleles
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dominant = uppercase
recessive = lowercase
Mendel’s Conclusions:
5.
Alleles segregate during gamete formation
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Gamete = reproductive cell that contributes to the new
organism
Each parent contributes only one allele to their offspring
Gene (A) or Allele (B)
Hair color……..
Brown hair…....
Purple flowers.
Flower color….
Tall plant………
Plant height…..
Tail length…….
Long tail……….
GENE
ALLELE
ALLELE
GENE
ALLELE
GENE
GENE
ALLELE
Homozygous (A) or Heterozygous (B)
AA …….
Bb …….
BB …….
bb …….
Rr …….
dd …….
Homozygous Dom.
Heterozygous
Homozygous Dom.
Homozygous Rec.
Heterozygous
Homozygous Rec.
Genotype (A) or Phenotype (B)
AA …….
Blue eyes
heterozygous
Bb
Freckles
Visible trait
Genotype
Phenotype
Genotype
Genotype
Phenotype
Phenotype
Dominant Trait (A) or Recessive (B)
AA …….
Bb …….
BB …….
bb …….
Rr …….
dd …….
Dominant
Dominant
Dominant
Recessive
Dominant
Recessive
APPLYING MENDEL’S
PRINCIPLES
11.2
Probability
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Probability = the likelihood that a particular event will
occur
The way alleles separate during gamete formation is just
as random as a coin toss
Therefore, probability can be used to predict genetic
outcomes.
Punnett Squares: mathematical tool used to
predict genetic outcomes
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Axes of grid = possible gamete genotypes of parents
Grid boxes = possible genotypes of offspring
 Reminders
 Genotype
= genetic makeup (alleles)
 Phenotype = physical appearance
 When
constructing Punnett Squares, ALWAYS
 Define
the terms
 Define the genotypes of the parents
 Analyze the results
Punnett Squares can be used to explain
Mendel’s results…
F1 generation
Punnett Squares can be used to explain
Mendel’s results…
F1 generation
Punnett Squares can be used to explain
Mendel’s results…
F2 generation
For Simple
Dominance
Practice
Problems, Click
Here
PRACTICE WITH PUNNETT
SQUARES
11.2
Exceptions to Mendel
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Incomplete Dominance
Codominance
Multiple Alleles
Sex-linked Traits
Polygenic traits
Epistasis
Interaction of environment and genotype
Incomplete Dominance
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Neither allele is completely dominant
Heterozygote has a blended phenotype
Codominance
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Both alleles get expressed
Heterozygote has both traits
Multiple Alleles
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Trait with more than two alleles in a population
Example – Blood Types
3
different alleles (A, B, O)
 A and B alleles are codominant
 O allele is recessive
Heterozygous
for the
A allele
Homozygous
for the
A allele
Read Only
Sex-Linked Genes (X-linked)
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Carried on the sex chromosomes (female = XX; male =
XY)
More common in males
 XY
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= only need one allele for trait to be present
Females need two copies of allele for trait to be present
 Can
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be carriers of the trait (heterozygous genotype)
Passed from mother to son
Examples include colorblindness and hemophilia
Polygenic Traits
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Traits that are
determined by the
interaction of 2 or
more genes
Ex: Skin color, eye
color, height, etc
PRACTICE WITH PUNNETT
SQUARES