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Blending model

Idea of inheritance before Mendel
People thought that genetic material was contributed to offspring by parents blending their traits together
Didn't explain how some traits would disappear and return in later generations


Haritable feature that varries among individuals
Has multiple variations called traits


The variations of a character
EX: character is a flower but the trait is whether it is purple or white

True Breed

A plant that produces same variety as its parent
EX: is true breeding for purple flowers if seeds produced in future generations all have purple flowers as well


crossing of 2 true-breeding varieties

P generation

parental generation
2 things initially crossed
Give rise to the f1 generation

f1 generation

first filial generation
Made by parental generation cross

f2 genertion

secong filalial genertion
Made by self polynation of f1 organisms


Trait that is expressed
Can mask the recessive
DD or Dd - homo or hetero


Is the trait masked by recessibe
dd - hetero

Mendel's First Model Element

Alternative versions of genes account fo variations in inherited characters

Mendel's Second Model Element

For each character, an organism inherits 2 alleles - one from each parent

Mendel's Third Model Element

If 2 alleles at a locus differ, then one (the dominant) determines the organism's appearance and the othr (recessive) has no noticible effect on the organisms appearance

Law of Segregation

Mendel's Fourth Model Element
2 alleles for a heritable character segregate during gamete formation and end up in different gametes


Alternate versions of a gene
At a specific locus they can be homo D homo R or hetero
True breeding = all offspring have same allele as parent
Not true = not all offspring have same allele as parent

Punnet Square

Diagramic device used to predict possible allele combinations of offspring when crossing known parents
Capital letter shows dominance and lowercase shows recessiveness


Pair of identical alleles
Can be dd or DD
Are true breeding


2 different alleles for a gene
Are not true breeding because they produce gametes with different allles


Organisms appearance or observable traits
Is dependent on genotype
Mendel flowers - purple:white = 3:1


Organisms gentic makeup - combination of alleles
Mendel flowers - PP : Pp : pp = 1:2:1

Test Cross

Cross an unknown with a homo recessive to tell what the other parent is by looking at phenotypic results
3:1 means that other parent was DD
1:1 mean other was Dd


Crossing of a single trait in terms of one dominant and one recessive home - yeilds a hybrid for 1 trait
Cross these and you see a 3:1 ratio of phenotype


Crossing 2 true breeding that are either dominat homo for 2 traits or recessive homo for 2 traits - result is Hetero for 2 traits
Cross the hetero and get 9:3:3:1 phenotypic ratio
Was studied by mendel to test insependent assortment - if independent he expected 9:3:3:1 ratio but if not then he expected the same 3:1 ratio he had been getting

Law of Independent Assortment

Is still 3:1 ratio of characters if you consider them independently but it multiply 2 traits probabilities it resutls in 9:3:3:1 --> alleles still segregated as if they were in mono cross

Each pair of alleles segregates independently of each other pair of alleles during gamete formation

Complete Dominance

One allele can completely cover the other
F1 offspring always look like either parent
Hetero looks like homo dominant and homo recessive is the only way the recessive trait is shown

Incomplete Dominance

Offspring can show a trait between the two parents when it has heterozygous alleles
One allele seems to blend - is not really blending becasue if a self cross then get back the parent traits
Both alleles are somewhat present


Both alleles affect the heterozygote equally - both are dominant when together
Standard example is type AB blood

Tay-Sachs Disease

Brain cells cannot metabolize certain lipids in child
Accumulate = seizure / poor motor ... death
Homo recessive
Biochemical level the heterozygote makes half good and half bad levels (codominant) so it is incomplete dominance --> half is good enough to be heathy tho so it has normal phenotype


Describes a gene that has multiple phenotypic effects
Cause multiple symptoms in a disease --> one defect leads to bunches of symptoms
EX: sickle cell - cascade of symptoms
EX: gene for flower color also affects color of coating on outside of seed in pea plants


A gene at one locus affects the phenotypic expression of a gene at a second locus
Don't worry about this ??????/

Polygenic Inheritance

Additive effect of 2 or more genes on a single phenotypic character
Opposite of pleiotropy
More genes affecting a trait the more possible combinations and the more grades within a pop
Bell distribution - some are a lot more common than others
Are still inherited separately
Accounts for things like skin color and height - why there is so much variation

Quantitative Characters

Traits that vary in degree within a population (in grades)
height / skin color
Indicates polygenic inheritance


Effects of genes on the traits of an organism


Effects of environment on an organism

Nature v Nurture

Org is given phenotype by genes but the enviroment still can effect
EX: can be given leaf pattern but environment still affects varying greenes / size
EX: can be given skin color but suntan can affect

Norm of Reaction

Genotype is not assiciated rigidly to phenotype in most cases - has a range of phenotypic possibilities due to environment
EX: blood type has no range but levels of white clood cells can be afected by altitude / exercise


Phenotypes that are due to many factors - both genetic and environmental
Environment contribuses to the quantifying of a character


Family tree showing history for a certian trait
By looking at passing you can tell if dominant or recessive and from here can deduce most genotypes
Dominant never skip generation
Both recessive parents must have all recessive kids
Square = male / circle = female / shaded has trait
Children aranged in birth order from L to R


Heterozygous individuals who, while they do not have a recessive trait themselves, can pass it to their offspring
Offspring can wither be herterozygous too or it can be homo recessive
Mating of 2 carriers = 25% chance of producing a person with the recessive trait

Cystic Fibrosis

Most common lethal genetic disease in US - mostly affects ppl of euro descent
Gene codes for membrane protein that controls flow of chloride
Defective protein = high conc outside of cell = mucus coats build on liver / pencreas / lungd ...pleiotropic
Mucus predisposes to bacterial infection
Can only help the symptoms b/c little known of cause = dislodge mucus and give antiobiotics

Sickle Cell

Caused by substitution of amino acid which changes shape - low O2 = hemo makes rods = cause clumping --> other pleiotropic effects
One allele affects phenotype but can still survive (malaria resitent too) = codominant alleles in heterozygotes
Two alleles = lethal - no good blood cells

Lethal Dominat Allele

Have to show effects late in life for it to continue to exist
Otherwise the infected would die before passing it on and the gene would not be passed on
Or be a result of a spontaneous mutation that triggers disease

Huntington's Disease

Degernatative disease of the nervous system that comes from a dominant gene
Late onset lets it be passed to offspring
There is now a test that can be done to test if a person has it

Multifactoial Dissorders

Genetic component plus environmental makes some people more succeptible to this kind of dissorder
Gene predisposes but does not gurarantee onset - depends on how a person takes care of themselves
EX: heart disease / kidney disease / diabetes / alcoholism / bipolar


Extraction of amniotic fluid from uterus
Tests determine certain chemicals in fluid - some are assocaited with certain genetic dissorders
Tests on cells found in fluid too - karyotype to tell chromosomal dissorders

Chorionic Villus Sampling (CVS)

Suction a bit of tissue (villus)from placenta - transmitts waste and nutrients between baby and mom
Cells from the taken area are derived from fetus - same genotype
Karyotype - use if suspect chromosomal abnormality or genetic abnormal
Can be done really early in preg
Still need amniotic fluid for other tests tho


sound waves used to produce image of fetus


Tube with viewing scope and piberoptics inserted into uterus


Recessive in which individuals cannot metabolize amino acid phenylalanine
Byproduct phenylpyruvate accumulates in blood
Passes brain barrier and causes mental retardation
If detected early a normal life is possible thru low levels of phenylalanine

Gene Expression

Segment of DNA that is allowed to be transcribed
Is controlled by gene regulation

Gene Regulation

Determines which segments are accessible for transcription
Is what enables differentiation

Little People Model

Before Mendel people believed that there were little people in us


What mendel called a gene
Said they were responsible for heredity


Scientist to first apply mendel's ideas of genes to meiosis

Physical Basis of Heredity

Alleles on chromosomes are units of heredity

Number of possible gametes that a cell could turn into

(8.3 x 10^6 possible )
This doesn't even include variability from crossover


Only have one allele for a gene
Describes males for sex traits - is why they get sex-linked recessive genes more


Can convert phenylanenine to tyrosine but cannot convert tyrosine to melanin = no skin pigment

Heterozygote Advantage

Have resistance to malaria but don't have all bad blood cells so it won't kill

Muscular Distrophy

X linked = affects primarily males
Issue with distrophin gene = lack protein for muscle maintenance
Normal birth and slow downhill from there


Amyloid precursor protein = protein in the brain that is hydrolysed to beta amyloid that forms plaques in the brain
Most cases = not genetic - just to say how many diseases have a genetic componenet


n cell fuses with n+1 cell = has higher dosage of DNA


n cell fuses with n-1 cell = has too low a gene dosage

Trisomy 21

Down Syndrom
Extra #21 sister - due to non-disjunction

Chromosomes 13, 18, 21, 22

Chromosomes are small = if there is a mutation organism still isn't aborted

Autosomal Chromosome Problems

Problems with dosage - too much or little
50% of misscarrages are to do with this


Baby right after birth
Check for abnormalities right away to try to deal with them

Prenatal Biochemical Disorders

Test congenital disorders using amniotic fluid immediately

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