Patterns of Inheritance

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Chapter 9 Patterns of Inheritance
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Genetic Myths

• Changes gained during a lifetime are passed on to
  offspring
• Blending of traits occurs

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Mendelian Genetics

• Gregor Mendel
• Austrian monk
• Father of Genetics
• Studied pea plants

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The Garden Pea
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• Self-Fertilization pollen is used to fertilize
  the plant that it came from
• Cross-Fertilization pollen is used to fertilize
  a different plant than the one it came from
• True breeding self fertilization results in
  offspring that are identical to the parent

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Cross Fertilization
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Pollinated carpel matured into pod
Planted seeds from pod
Offspring (F1)
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Flower color
Purple
White
Flower position
Axial
Terminal
Seed color
Yellow
Green
Seed shape
Round
Wrinkled
Pod shape
Inflated
Constricted
Pod color
Green
Yellow
Dwarf
Stem length
Tall
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Cross
Parental
Hybrid
Filial
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Mendels Four Hypotheses

• There are alternative forms of genes that account
  for variation
• alleles Alternative forms of the same gene

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Mendels Four Hypotheses (cont.)
2. For each characteristic, an organism inherits
two alleles, one from each parent Homozygous
Each allele is identical Heterozygous Each
allele is different
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Mendels Four Hypotheses (cont.)
3. If the alleles differ, only one contributes to
the organisms appearance Dominant allele
the one that contributes Recessive allele
the one that has no effect
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Mendels Four Hypotheses (cont.)
4. A sperm or egg only carries one allele for
each gene Law of Segregation the alleles
separate during gamete formation
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Dominant vs. Recessive
p
P
PP purple Pp purple pp white
PHENOTYPE
GENOTYPE
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Alleles reside on different chromosomes
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Punnett Square
Pp
Pp
X
P
p
P
p
P
p
P
PP
Pp
p
pp
Pp
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Dihybrid Cross

• Predicting the results of two traits
• R Round peas
• r Wrinkled peas
• Y Yellow peas
• y Green peas
• RRYY x rryy ?

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Dihybrid Cross (cont.)

• If alleles are transferred together
• F1 all would be round/yellow
• F2 should get ¾ round/yellow and ¼
  wrinkled/green
• Should not get any round/green or wrinkled/yellow

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Dihybrid Cross (cont.)

• If alleles are transferred separately
• F1 all would be round/yellow
• F2 should get ¾ round/yellow and ¼
  wrinkled/green
• Should not get any round/green or wrinkled/yellow

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Law of Independent Assortment
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Probability

• Independent Event not affected by previous
  event (e.g. flipping a coin)
• Compound Event combination of two independent
  events (flipping two separate coins
  simultaneously)
• Use rule of multiplication (multiply the separate
  probabilities of each event)

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Dominant vs. Wild Type
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Pedigree

• Scientists cannot control matings in humans
• So, they must gather as much information about a
  family history
• They organize it onto a family tree called a
  pedigree

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Joshua Lambert
Abigail Linnell
John Eddy
Hepzibah Daggett
Abigail Lambert
Jonathan Lambert
Elizabeth Eddy
Dd
Female
Male
Deaf
Hearing
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Cystic Fibrosis

• Autosomal recessive
• Most common, lethal genetic disorder in USA
• Affects
• 1/17,000 African-Americans
• 1/90,000 Asian-Americans
• 1/2,500 European-Americans
• Characteristics
• Excess mucus production leading to bacterial
  infections
• Lethal by age 5 if left untreated

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Genetic Testing

• Identifying carriers (e.g. sickle cell)
• Fetal testing (e.g. Down syndrome)
• Amniocentesis
• Chorionic villus sampling (CVS)
• Fetal Imaging
• Newborn Testing (e.g. PKU)
• ETHICAL CONSIDERATIONS???

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Incomplete Dominance

• Complete dominance one allele completely masks
  the other
• Incomplete dominance there is a blending of
  alleles

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Incomplete Dominance
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F1 generation
1 2
1 2
R
r
Gametes
Sperm
1 2
1 2
R
r
1 2
Pink rR
Red RR
R
F2 generation
Eggs
1 2
White rr
Pink Rr
r
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Multiple Alleles

• Most genes are controlled by more than 2 alleles
• Each individual still only gets 2, but there are
  more than 2 to chose from
• Example Blood types in humans

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Human Blood Types

• 3 alleles controlling 4 blood types A, B, AB, O
• Comes down to presence or absence of
  carbohydrates on blood cell surface
• Having carbohydrates is dominant
• Controlled by a gene I
• There are two types of carbohydrates
• A (IA) and B (IB)

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Human Blood Types
Genotype IAIA or IAi
Phenotype A Phenotype B Phenotype
AB Phenotype O
Genotype IBIB or IBi
Genotype IAIB
Genotype i i
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Blood Type Determination
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Biology at home!

• See if you can determine your blood group
  genotype from your familys phenotypes
• My family
• Dr. Melvin A
• Mom A
• Dad B

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Biology at home!

• We know dad IBi
• Possibilities for mom IAIA or IAi

IB
i
IB
i
IA
IAIB
IAi
IAIB
IAi
IA
IA
IBi
i i
i
IAIB
IAi
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Pleiotropy
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Polygenic Inheritance

• Polygenic inheritance is when more than one gene
  controls a single trait.
• Skin color
• Controlled by the separately inherited genes A,
  B, and C
• Dark alleles are A B and C
• Light alleles are a b and c
• AaBbCc would have the same skin color as AABbcc.

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Chromosomal Theory of Inheritance
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Sex Determination
XX
XY
x
X
Y
X
XX
XY
X
XY
XX
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What makes a boy a boy?

• It is complicated, but scientists think it is
  mostly controlled by one gene
• SRY
• Found on the Y chromosome
• Protein made from the SRY gene affect other genes
  on the Y chromosome
• These genes say make testis
• Testis make testosterone male