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Heredity: The passing of characteristics from parents to offspring
Genetics:The science of heredity and the
process by which traits are passed from parents to offspring
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)
Mendel’s Hypotheses
1.) For each inherited character ( red, freckles, etc.), an individual has 2 copies of the gene – 1 from each parent
2.) There are alternative versions of the gene known as alleles
BrownHair
Blonde Hair
Black Hair
Red Hair
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
The expressed form a characteristic as: Dominant
R = dominant allele For example R = red hair Rr or RR
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?
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**)
Heterozygous
• If the alleles of a gene in an individual are different, the individual is: heterozygous
Genotype: set of alleles an individual has for a characteristic
Example: Rr is the genotype for red hair
Phenotype: the physical appearance of a characteristic
So … if the genotype is Rr then the phenotype is ____________________.
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? ____________
Law of Segregation - states that the two alleles for a characteristic
are segregate or SEPARATE when gametes are formed
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
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
Punnett Square: --predicts the outcome of a genetic cross
-- the basic 4 chambered Punnett Square can predict the outcome of a monohybrid cross
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
If half of the offspring express the dominant trait and half express the recessive trait, then the unknown individual’s genotype is?
______________________________________
IF all of the offspring express the dominant phenotype which genotype is the unknown individual?
_____________________________________
Section 4: Complex Patterns and Heredity
Polygenic Inheritance: when several genes influence a character
Incomplete dominance: an individual that displays a phenotype that is intermediate between the two parents
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
Roan Fur in CattleRR = all red hairsWW = all white hairs
RW = red & white hairs together
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
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
Dihybrid Crosses
- A genetic cross that consists of two different traits instead of one
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
Parent 2
Parent 1
RRYY x rryy
RRYY RRYy RrYy
RrYy
RrYY RrYy
RrYy
Parent 2
Parent 1
Parent 2
Parent 1
Pedigree
--- A family history that shows how a trait is inherited over several generations
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
Determining Information From a Pedigree
2. ) Dominant or Recessive
Autosomal Dominant: EVERY individual with the condition will have a parent with that condition
If the condition is recessive:
-- an individual that expresses the condition can have one, two or neither parent express the condition
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
Individual is homozygous recessive,
their phenotype will show the recessive allele
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
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
Human Genetic Disorders
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
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*
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 )
- 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
Hemophilia - Recessive genetic disorder that impairs the blood’s ability to clot
- Sex- linked Trait
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
- HD causes loss of muscle control, uncontrollable physical spasms, severe mental illness, and eventually death
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