10.1 Genetics developed from curiosity about inheritance

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10.1 Genetics developed from curiosity about
inheritance
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I. The Blending Hypothesis of Inheritance

1. A trait is a variation of a particular
   characteristic such as for red flowers or yellow
   flowers
2. In the early 1800s many biologists believed in
   the blending hypothesis, which stated that
   offspring would be a blend of their parents
   traits. A red and yellow flower would produce
   and orange flower

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II. Mendels Plant Breeding Experiments

1. Mendels work gave rise to the branch of Biology
   called genetics, the study of heredity
2. Mendel developed the particulate hypothesis which
   states that parents pass on separate and distinct
   factors, or genes

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Mendels Plant Breeding Experiments

1. To test this hypothesis, Mendel crossed
   true-breeding plants that had distinct and
   contrasting traits such as purple and white
   flowers
2. Mendel cross-fertilized all his pea plants by
   hand to control which traits he wanted to control

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Mendel methods
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10.2 Mendels Principle of Segregation
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I. Mendels Principle of Segregation

• The offspring of two different true-breeding
  varieties are called hybrids
• B. When Mendel crossed plants that differed in
  only one-trait it was called a mono-hybrid cross

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C. From these results Mendel developed the
following hypothesis

1. There are alternative forms of a gene called
   alleles.
2. For each inherited trait, an organism has two
   alleles for the gene controlling that character,
   one from each parent. If both alleles are the
   same the individual is homozygous, and if the
   alleles are different the individual is
   heterozygous.

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Mendel developed the following hypothesis

• 3. When only one of the alleles in a heterozygous
  individual appears to affect the trait, that
  allele is called the dominant trait. The allele
  that does not appear to have an affect on the
  individual is called the recessive trait

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Mendels Observation
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Mendels Observations
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Mendel developed the following hypothesis

• 4. The two alleles for a character separate
  during the formation of gametes, so each gamete
  carries only one allele for each character. This
  is known as Mendels Principle of Segregation

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II. Probability and Punnett Squares

1. The inheritance of alleles follows the laws of
   probability
2. If you were to flip two pennies the probability
   of flipping a head or a tail on one does not
   affect the probability of the other one
3. A diagram that shows all the possible outcomes of
   a genetic cross is the Punnett Square

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Probability and Punnett
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Punnett Square

• Eye color
• Homozygous
• Brown male X
• Homozygous
• Blue female

B B
b Bb Bb
b Bb Bb
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III. Genotypes and Phenotypes

1. The way an organism looks is not the same as its
   genetic make-up
2. An observable trait is called a phenotype while
   the genetic make-up of alleles is called the
   genotype

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IV. The Testcross

1. A testcross breeds individuals of unknown
   genotypes, but the dominant phenotype with a
   homozygous recessive individual
2. Depending on the ratios of the offspring, the
   genotype of the unknown can be determined

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Testcross
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V. Mendels Principle of Independent Assortment

1. Mendel also did crosses between plants that
   differed in two traits called a dihybrid cross
2. From this he developed his Law of Independent
   Assortment which states that during gamete
   formation the way in which one allele is
   inherited does not affect the way another is
   inherited if they are on separate chromosomes

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Independent Assortment
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Problem Monohybrid 1

• 1. An allele for brown eyes B is dominant over
  that for blue eyes b. A blue-eyed man, both of
  whose parents were brown-eyed, marries a woman.
  They have one child who is blue-eyed. What are
  the genotypes of all the individuals mentioned?

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Problem 1

• Mans parents Bb
• Dad bb
• Mom Bb
• Kids Bb or bb

b b
B Bb Bb
b bb bb
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Problem Monohybrid 2

• 2. The ability to taste the chemical PTC is
  determined by a single gene in humans with the
  ability to taste given by the dominant allele T
  and inability to taste by the recessive allele
  t.  Suppose two heterozygous tasters (Tt) have a
  large family. 

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Problem Monohybrid 2

1. Predict the proportion of their children who will
   be tasters and nontasters.  Use a Punnett square
   to illustrate how you make these predictions.
2. What is the likelihood that their first child
   will be a taster?  What is the likelihood that
   their fourth child will be a taster?
3. What is the likelihood that the first three
   children of this couple will be nontasters?

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Problem 2

• 31
• b. 3/4, 3/4
• c. 1/64

T t
T TT Tt
t Tt tt
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Dihybrid Cross
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Dihybrid Cross- FOIL

• First
• Outside
• Inside
• Last
• RrYy x RrYy

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Problem 3 Dihybrid

• 3. In pepper plants, green (G) fruit color is
  dominant to red (g) and round (R) fruit shape is
  dominant to square (r) fruit shape.  These two
  genes are located on different chromosomes.

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3. Dihybrid

• a.   What gamete types will be produced by a
  heterozygous green, round plant?
• b. If two such heterozygous plants are crossed,
  what genotypes and phenotypes will be seen in the
  offspring and in what proportions?

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3 Types of gametes

• FOIL
• First- GR
• Outside- Gr
• Inside- gR
• Last- gr

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Dihybrid Pepper Plants
GR Gr gR gr
GR GGRR GGRr GgRR GgRr
Gr GGRr GGrr GgRr Ggrr
gR GgRR GgRr ggRR ggRr
gr GgRr Ggrr ggRr ggrr
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Pepper Plants
1 GGRR 2 GgRR 1 ggRR
2 GGRr 4 GgRr 2 ggRr
1 GGrr 2 Ggrr 1 ggrr

• 9 Green, round
• 3 Green, square
• 3 Red, round
• 1 Red, square

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10.3 There are many variations of inheritance
patterns
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I. Intermediate Inheritance

1. When an organism has two alleles and neither is
   dominant the phenotype is intermediate between
   the two alleles
2. This pattern of inheritance is called
   intermediate inheritance

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Intermediate Example
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Problem Intermediate Inheritance

• 4. A hybrid pink CRCW snapdragon was crossed with
  a pure white one CWCW. Red flower color is
  incompletely dominant.
• Make a diagram and list the genotypic and
  phenotypic ratios of the F1 generation

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Problem 4

• 11
• CR CW CW CW
• PinkWhite

CR CW
CW CR CW CW CW
CW CR CW CW CW
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II. Multiple Alleles

1. Many genes have several alleles for each trait
   which expands the number of genotypes and
   phenotypes
2. Codominance is when a heterozygous individual
   expresses both traits equally.

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Multiple Allele Example
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Problem Multiple Alleles

• 5. Paul is blood type O. His father was blood
  type A and his mother was blood type B. What were
  the genotypes of his parents and what are the
  possible blood types and ratios expected for
  crosses involving these parental genotypes?

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Problem 5

• IAi and IBi
• 1111
• ABABO

IA i
IB IA IB IBi
i IAi ii
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III. Polygenic Inheritance

1. When multiple genes affect a character the
   variation in phenotypes can become even greater.
2. When two or more genes affect a single character,
   it is called polygenic inheritance
3. Examples of polygenic inheritance would include
   skin color, and height

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Problem Polygenic

• 6. Melanin is coded for when the gene L, M, or N
  is present. The more of these genes are present,
  then the darker the skin the individual. Number
  the following genotypes in order of the darkest
  to lightest skin color phenotypes.

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Problem 6
1 LLMMNN 5 LXMXXX
2 LLMXNN 5 XXMMXX
4 LXMMXX 3 LXMMNX

• 1 Darkest 6Lightest

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IV. The Importance of Environment

1. An individuals phenotype depends on environment
   as well as on gene
2. In humans, nutrition influences height, exercise
   affects build, and exposure to sunlight darkens
   the skin

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10.4 Meiosis Explains Mendels principles
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I. Chromosome Theory of Inheritance

• A. Biologists worked out the processes of mitosis
  and meiosis in the late 1800s and observed the
  parallels between the behavior of chromosomes and
  the behavior of Mendels heritable factors

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Chromosome Theory

• B. The chromosome theory of inheritance states
  that genes are located on chromosomes, and the
  behavior of chromosomes during meiosis and
  fertilization accounts for inheritance patterns
• C. The alleles for a gene reside at the same
  location or gene locus

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Pea Plant
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II. Genetic Linkage and Crossing Over

• Mendels principles only work when for genes that
  are located on separate chromosomes
• The tendency for the alleles on one chromosome to
  be inherited together is called genetic linkage
• C. The closer the two genes are on a chromosome,
  the greater the genetic linkage

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Linkage
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10.5 Sex-linked traits have unique inheritance
patterns
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I. Sex-linked Genes

• A. Many species have sex chromosomes, designated
  X and Y that are associated with determining an
  individuals sex XX Female, while XY Male

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Sex-linked genes

• B. Any gene located on a sex chromosome is called
  a sex-linked gene
• C. Sex-linked genes were discovered by Thomas
  Hunt Morgan while studying fruit flies

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Sex-linked eye color
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II. Sex-Linked Disorders

• A. A number of human conditions, including
  red-green color blindness and hemophilia are
  inherited as sex linked recessive traits
• B. It takes two copies of the allele to be
  present in females for them to show signs of the
  disorder while it only takes one in males

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Problem Sex-linked

• 7. A color blind father and a mother who carries
  the color blind trait (b) have a boy and a girl.
  What are the percent chances of the children
  being color blind? A carrier for color blindness?

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Color blindness Sex-linked

• 50 color blind
• children
• 25 carrier

Xb Y
XB XB Xb XBY
Xb Xb Xb XbY
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12.2 Accidents Affecting Chromosomes can Cause
Disorders
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I. Down Syndrome

• A. Trisomy 21 results in having three number 21
  chromosomes
• B. In most cases, a human embryo with an abnormal
  number of chromosomes results in a miscarriage
• C. People with trisomy 21 have Down syndrome,
  named after John Langdon Down

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II. Nonseparation of Chromosomes

• A. Nondisjunction is when homologous fail to
  separate
• B. A womans age will have an effect on the
  possibility of nondisjunction occurring
• C. This is due to the time line of egg cell
  development

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Nondisjunction
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III. Damaged Chromosomes

• A. Duplication is when part of a chromosome is
  repeated
• B. Deletion is when a fragment of a chromosome is
  lost
• C. Inversion involves reversing a fragment of the
  original chromosome
• D. Translocation occurs when a fragment of one
  chromosome attaches to a non-homologous chromosome

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Damaged Chromosomes
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Problem 8
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Problem 8 Damaged Chromosomes
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IV. Jumping Genes

• A. Single genes may move from one location to
  another in a chromosome or to a different
  chromosome
• B. This was discovered by Barbara McClintock in
  the 1940s
• C. These genes can land in the middle of other
  genes and disrupt them
• D. These genes are called transposons

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Transposons
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12.3 Mendels Principles Apply to Humans
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I. Working With Human Pedigrees

• A. Human geneticists cannot control matings, but
  must analyze the patterns of existing families
• B. A pedigree is a family tree that records and
  traces traits

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Pedigree Symbols
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II. Disorders Inherited as Recessive Traits

• A. There are over one thousand genetic disorders
  that are inherited as a dominant or recessive
  trait controlled by a single gene
• B. Most human genetic disorders are recessive
• C. A carrier is an individual who has a copy of
  the recessive disorder but does not show symptoms

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Attached Earlobes
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Pedigree 9

• Is the attached ear lobe trait a dominant or
  recessive trait? How do you know?
• Recesssive, only those ff colored.
• What two terms could be used to describe the Ff
  genotype?
• Heterozygous, or carrier

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Problem 9 Pedigree

• What are the percent chances?
• 25 FF 50 Ff
• 25 ff
• 75 Unattached
• 25 attached

F f
F FF Ff
f Ff ff
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III. Disorders inherited as Dominant Traits

• A. Dominant alleles that are lethal are more
  common than lethal recessives
• B. Usually, the person with the dominant disorder
  dies before the allele can be passed on

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Huntingtons Disease
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IV. Sex-Linked Disorders

• A. Sex-Linked alleles are usually located on the
  X Chromosome in humans
• B. A male only needs to inherit one copy of the
  allele to exhibit the trait
• C. A female must inherit two copies of the allele
  to exhibit the trait

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Colorblindness
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Deaf Pedigree

• Draw a pedigree for the punnett square. Children
  2 older boys are deaf. 2 younger girls are
  carriers.

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Deaf Pedigree
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V. Predicting and Treating Genetic Disorders

• A. A genetic counselor is trained to collect and
  analyze data about inheritance patterns
• B. This information is used by couples to
  determine the risks of passing on genetic
  disorders to their children
• C. Genetic tests are done before and after the
  baby is born