Heredity: The passing of characteristics from parents to offspring

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