HEREDITY The passing of characteristics (also knows as traits) from parents to offspring.
Heredity: The passing of characteristics from parents to offspring.
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Transcript of Heredity: The passing of characteristics from parents to offspring.
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Heredity: The passing of characteristics from parents to offspring
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Genetics:The science of heredity and the
process by which traits are passed from parents to offspring
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P generation: The 1st two individuals that are crossed (parental generation)
F1 generation : The offspring of the P generation (offspring of the parents)
F2 generation: The offspring of the F1 generation(offspring of the F1 generation)
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Mendel’s Hypotheses
1.) For each inherited character ( red, freckles, etc.), an individual has 2 copies of the gene – 1 from each parent
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2.) There are alternative versions of the gene known as alleles
BrownHair
Blonde Hair
Black Hair
Red Hair
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2.) Two different alleles occur together, one of them may be completely expressed while the other shows no observable appearance
Mother:Brown Hair
Father:Blonde Hair
Child:Brown Hair
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The expressed form a characteristic as: Dominant
R = dominant allele For example R = red hair Rr or RR
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Trait NOT expressed while the dominant form is present is known as the: recessive allele
r = recessive trait = brown hair
Rr
If the allele combination is rr is the recessive trait expressed? _____________ Why or why not?
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Homozygous
- IF 2 alleles of a certain gene are the same, the individual is said to be: homozygous
(** true regardless of if the two are dominant OR recessive**)
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Heterozygous
• If the alleles of a gene in an individual are different, the individual is: heterozygous
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Genotype: set of alleles an individual has for a characteristic
Example: Rr is the genotype for red hair
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Phenotype: the physical appearance of a characteristic
So … if the genotype is Rr then the phenotype is ____________________.
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Questions:
T = tan colored featherst = white color feathers
Is t the dominant allele or the recessive allele?_________________
An owl has white colored feathers ( tt ) , this physical appearance of having white feathers is known as the owl’s ________________ ?
If an owl’s genotype is Tt, what color feathers will it have? ____________
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Law of Segregation - states that the two alleles for a characteristic
are segregate or SEPARATE when gametes are formed
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Law of Independent Assortment:
--Alleles of different genes separate independently of one another during gamete formation
-- The inheritance of one characteristic did not influence the inheritance of any other characteristic
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Law of Independent Assortment/Segregation Lab
B – brown hairb – blonde hair F – freckles f– no frecklesC – curly hairc – straight hairG – gap in between front teethg – no gap in between front teeth
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Punnett Square: --predicts the outcome of a genetic cross
-- the basic 4 chambered Punnett Square can predict the outcome of a monohybrid cross
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How could you find the genotype of an
individual if it was not known?
Test Cross- Is performed when an individual shows a dominant
phenotype but we are not sure whether they are heterozygous or homozygous.
- These individuals are crossed with a homozygous recessive individual
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If half of the offspring express the dominant trait and half express the recessive trait, then the unknown individual’s genotype is?
______________________________________
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IF all of the offspring express the dominant phenotype which genotype is the unknown individual?
_____________________________________
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Section 4: Complex Patterns and Heredity
Polygenic Inheritance: when several genes influence a character
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Incomplete dominance: an individual that displays a phenotype that is intermediate between the two parents
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Codominance:
With codominance, a cross between organisms with two different phenotypes produces offspring with a third phenotype in which both of the parental traits appear together.
red x white ---> red & white spotted
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Roan Fur in CattleRR = all red hairsWW = all white hairs
RW = red & white hairs together
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Sex-linked gene’s allele is located ONLY on the X or Y chromosome
Carried on the X chromosomeand are recessive
Males: only have one X chromosome (XY)
Male who carries a recessive allele on the X chromosome will express the sex-linked condition
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Female: if she is a carrier
of the recessive allele on
one X chromosome,
she will NOT exhibit
the allele if her
other X chromosome
exhibits the dominant allele
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Dihybrid Crosses
- A genetic cross that consists of two different traits instead of one
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Dihybrid Crosses
Instead of Rr x rr R= round, r = wrinkled
You are now including another trait into the cross: Y= yellow, y = green
RRYY x rryy
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Parent 2
Parent 1
RRYY x rryy
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RRYY RRYy RrYy
RrYy
RrYY RrYy
RrYy
Parent 2
Parent 1
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Parent 2
Parent 1
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Pedigree
--- A family history that shows how a trait is inherited over several generations
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Determining Information From a Pedigree
1.) Autosomal or sex-linked?
Autosomal: the gene will appear in both sexes equally
- Autosomes are all the other chromosomes other than the X or Y sex chromosome
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Determining Information From a Pedigree
2. ) Dominant or Recessive
Autosomal Dominant: EVERY individual with the condition will have a parent with that condition
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If the condition is recessive:
-- an individual that expresses the condition can have one, two or neither parent express the condition
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Determining Information From a Pedigree
3.) Homozygous or Heterozygous
- if individuals with autosomal traits are homozygous dominant or heterozygous,
- their phenotype will show the dominant allele
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Individual is homozygous recessive,
their phenotype will show the recessive allele
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Two people who are heterozygous carriers of a recessive mutation
Will not show the mutation, but can produce children who are homozygous for the recessive allele
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Characters Influenced by Environment
An individual’s phenotype often depends on the
condition of the environment
Identical twins are used in these types of studies
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Human Genetic Disorders
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Sickle Cell Anemia - Recessive Genetic Disorder
-Cause: Mutated allele that produces a defective form of the protein hemoglobin
1 in 500 African Americans have sickle cell anemia
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Heterozygous Superiority
- Individuals that are heterozygous for sickle cell have what is considered “heterozygous superiority”
-The recessive allele that causes the sickle cell shape protects the individual from malaria * Also do not have sickle cell anemia because they are heterozygous*
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Cystic Fibrosis (CF) - Airways of the lungs become clogged with thick mucus, and the ducts of the liver and pancreas become blocked
- Most common, fatal, hereditary recessive disorders among Caucasians ( 1 in 25 have at least one copy of the defective gene )
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- Caused by a mutated protein that does not allow chloride to be moved into or out of cells
- Then…causes mucus to dehydrate and become thick and sticky in the lungs
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Hemophilia - Recessive genetic disorder that impairs the blood’s ability to clot
- Sex- linked Trait
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Huntington’s Disease (HD)
- Caused by a dominant allele located on an autosome
- Symptoms: Mild forgetfulness and irritability appear in people in their thirties and forties
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- HD causes loss of muscle control, uncontrollable physical spasms, severe mental illness, and eventually death