68 terms

Mendel and the Gene Idea

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