Genetics

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Genetics
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• Heredity is the passing of traits from parent to
  offspring.
• Every organism is a collection of traits, all
  from its parents
• Trait are physical or genetic characteristics of
  an individual organism

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• Genes control the traits by producing proteins.
• A Gene is a small section of DNA that codes for
  certain proteins.
• An alternative form of genes are called alleles
• Organisms have at least two genes for every
  trait.
• They receive at least one from each parent.
• The study of how traits are inherited through
  action of genes is the science of GENETICS.

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Gregor Mendel

• Gregor Mendel is often referred to as the father
  of genetics.
• He was a monk that was born in Austria in 1822.
• He was experimenting in garden with peas.

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Through his experiments he discovered that some
genes were either dominant or recessive.

• Dominant because it dominated or is always shows
  itself (D, a capital letter)
• Recessive because it was hidden when the dominant
  gene was present (d, lowercase)

Freckles
No Freckles
Dimples
No dimples
Tongue roller
Non-roller
From Dad
From Mom
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Genotype

• Genotype is the actual genes for a particular
  trait expressed with letters
• Homozygous dominant (Purebred)
• TT - two capital letters
• Heterozygous (hybrid)
• Tt - one of each letter (big and small)
• Homozygous recessive (Purebred)
• tt - two lower case letters

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Phenotype

• Phenotype is physical expression of the genotype
• Genotype Phenotype
• TT tall plant
• Tt tall plant
• tt short plant
• dominant allele always is expressed over the
  recessive allele
• recessive trait is expressed only if there is
  no dominant gene

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If R red, and r white

• What is the genotype of homozygous dominant?
• RR
• What is the heterozygous genotype?
• Rr
• What is the homozygous recessive genotype?
• rr

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If Rred and r white

• What is the phenotype of of RR?
• Red
• What is the phenotype of Rr?
• Red
• What is the phenotype of rr?
• White

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Mendels Experiments led him to 3 Laws of
Inheritance

• The Law of Dominance
• The Law of Segregation
• The Law of Independent Assortment

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Law of Segregation

• Segregation is the separation of alleles during
  gamete formation.
• Since only one egg or one sperm will contribute
  to the new offspring, only one allele for a trait
  is passed on
• The chance that any allele will be passed on is
  50

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Segregation
- Mendels Work
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Law of Independent Assortment

• the inheritance of alleles for one trait doesnt
  affect the inheritance of alleles for another
  trait
• accounts for the many genetic variation observed
  in plants, animals and other organism.

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Predicting Traits

• A tool used to predict and compare the genetic
  variations that will result from a cross is a
  Punnett Square.

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If two parents are crossed (TT X tt), what are
the resulting offspring?
You can determine phenotypes using a Punnet
square.
T
T
parent
Tt
Tt
t
Genotypes
4 Tt
Tt
Tt
Phenotypes
4 Tall
t
This is the first or parent generation
parent
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Now try on your paper a cross of two of the
offspring from the parent generation. This is
called the first generation or the F1.
T
t
Tt
T
TT
Tt
tt
t
Genotypes
1TT 2Tt 1tt
Phenotypes
3 Tall 1 Short.
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Dihybrid Crosses

• A two-factor cross follows two different genes
  as they pass from one generation to the next.
• Explains the Law of Independent Assortment

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Lets Solve Together

• In guinea pigs, the allele for short hair (S) is
  dominant to long hair (s), and the allele for
  black hair (B) is dominant over the allele for
  brown hair (b). What is the probable offspring
  phenotype ratio for a cross involving two parents
  that are heterozygotes for both traits?

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Example 1 Dihybrid

• Short hair dominant SS or Ss
• Long Hair recessive ss
• Black coat dominant BB or Bb
• Brown coat recessive bb
• SsBb x SsBb (gametes done by the FOIL method)
• SB, Sb, sB, sb and SB, Sb, sB, sb

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Example 1 Punnett SquareParents SsBb x SsBb
sb
SB
Sb
sB




SB
SSBb
SSBB
SsBB
SsBb
SSBb
Sb
SSbb
SsBb
Ssbb
sB
SsBB
ssBB
SsBb
ssBb
sb
SsBb
Ssbb
ssBb
ssbb
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Example 1 Answer the Question

• What is the probable offspring phenotype ratio
  for a cross involving two parents that are
  heterozygotes for both traits?
• 9/16 Black, short coats
• 3/16 Black, long coats
• 3/16 Brown, short coats
• 1/16 Brown, long coats

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• Incomplete Dominance in which one allele is not
  completely dominant over another a blending in
  the heterozygous

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Incomplete Dominance
RR red RW pink WW white
RR x WW
R
R


W
RW
RW
RW
RW
W
What are the phenotypes of the offspring?
All the offspring will be Pink
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• Codominance can see both alleles at the same
  time.

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Codominance
Feathers in chickens FWFW White Feather FBFB
Black Feather FWFB Half Black Half White
FWFW x FBFB
FW
FW


FB
FWFB
FWFB
FWFB
FWFB
FB
What are the phenotypes of the offspring?
All of the offspring will be half black and half
white
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Sex-linked traits

• Are traits that are controlled by the X or Y
  chromosomes.
• Sex-linked disorders, which are disorders caused
  by abnormal sex chromosomes.
• Occurs more often in men than women.
• Most are recessive
• Two common disorders
• Colorblindness and hemophilia

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Colorblindness Test
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Hemophilia

• A persons blood clots very slowly or not at all.
• Danger from small bumps and cuts
• A recessive gene on the X-chromosome
• Occurs more in males than females

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Multiple Alleles three or more alleles of the
same gene.

• Blood Types in Humans
• Single gene, but four phenotypes
• Type A ? can be IAIA or IAi
• Type B ? can be IBIB or IBi
• Type AB ? only IAIB (codominant pattern here)
• Type O ? only ii (both recessive)
• All 3 blood types are dominant to O

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Practice Problem

• Cross a person with AB blood with a person with B
  blood. (2 crosses). What are the possible blood
  types of the children?

IA
IB
I A
IB




IB
IAIB
IB
IBIB
IBIB
IAIB
IBIB
IBi
IB
IAIB
i
IAi
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Blood tranfusions
Universal Donor
Universal Acceptor
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Polygenic Traits

• Traits controlled by two or more genes
• Examples
• Eye color
• Skin color
• Hair color

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A Pedigree
- Human Genetic Disorders

• A pedigree is a chart or family tree that
  tracks which members of a family have a
  particular trait.

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Pedigree analysis

• Pedigree analysis reveals Mendelian patterns in
  human inheritance tracks certain traits through
  a family
• data mapped on a family tree

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Simple pedigree analysis
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Genetic counseling

• Pedigree can help us understand the past
  predict the future

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The importance of the environment

• An individual phenotype depends on environment as
  well as on genes.
• Temperature
• Nutrition
• The product of a genotype is generally not
  single, rigidly defined phenotype but a range of
  possibility influenced by the environment.

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Human Genetic Diseases
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Human Genetics Disorders

• Genetic Disorder is an abnormal condition that a
  person inherits through genes or chromosome.
• Caused by mutations in the DNA of genes, or the
  overall structure and number of chromosomes

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Recessive disorders

• Your genotype is homozygous recessive (aa)
• Heterozygotes (Aa) have a normal phenotype
  because one normal allele produces enough of
  the required protein
• A carrier is a person who doesnt have the
  disease but carry the gene for the disease

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Heterozygote crosses

• Heterozygotes as carriers of recessive alleles

Aa x Aa


AA
Aa
carrier
Aa
aa
carrier
disease
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Cystic Fibrosis

• The body produces abnormally thick mucus in the
  lungs and intestines.
• This mucus makes it hard to breathe
• Caused by a removal of 3 bases from DNA

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Tay-Sachs

• Primarily Jews of eastern European (Ashkenazi)
  descent Cajuns (Louisiana)
• non-functional enzyme fails to breakdown lipids
  in brain cells
• fats collect in cells destroying their function
• symptoms begin few months after birth
• seizures, blindness degeneration of muscle
  mental performance
• child usually dies before 5yo

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Sickle-Cell Disease

• Affects hemoglobin, a protein in red blood cells
  that carries oxygen
• Cells have an unusual sickle-shape
• They clog blood vessels, make it difficult for
  blood flow

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Huntingtons disease

• Dominant inheritance
• repeated mutation on end of chromosome 4
• build up of huntingtin protein in brain causing
  cell death
• memory loss
• muscle tremors, jerky movements
• starts at age 30-50
• early death
• 10-20 years after start

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