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w/different traits alleles
What are the combinations of Alleles??
- Random Fertilization
- Crossing over
- Independent assortment
What are the Forms of Genes??
- -DNA copying mistakes
Allelic variation and allele shuffling is the basis of _____,_____, and ____
evolution, disease, and genetics
transmission of traits from one generation to next
scientific study of heredity
What did Josef Kolreuter cross??
he crossed tobacco strains to produce hybrids that differed from both parents
What did T.A. Knight cross?
- he crossed 2 varieties of garden pea, Pisum sativa
- -crossed 2 true-breeding strains
- -1st generation resebled only 1% strain
- -2nd generation resebled both (grandparents)
following one character
heritable feature that varies among individuals
variant of a character
repeated generations have consistent traits, (self-fertilization)
offsprng of two different true-breeding varieties (cross-fertilization)
True-breeding parents ='s
Hybrid offspring ='s
Mating of F1 plants (self fertilization) ='s
Mating of F2 plants (self-fertilization) ='s
Monohybrid crosses consists of ....
only 2 variations (traits) of a single character
Medel produced true-breeding of what...??
- of pea strains for 7 different character
- -each character had 2 variants
- -First filial generation
- -offspring produced by crossing 2 true-breeding strains
- -for every trait mendel studied, all F1 plants resembled only 1 parent
- *referred to trait as dominant
- *Alternative trait was recessive
- -No plants with characteristics intermediate btw the 2 parents were produced
- -Second filial generation
- -Offspring resulting from self-fertilization of F1
- -Although hidden in F1, recessive trait had reappeared among some F2
- -Counted proportions of traits
- *always found about 3:1 ratio of dominant: recessive
3:1 of dominant to recessive in _____?
- -3/4 plants w/ dominant form
- -1/4 plants w/ recessive form
- - dominant to recessive ratio was 3:1
Mendel Discovered that the ratio is actually _____??
- -1true-breeding dominant plant
- -2 not-true-breeding dominant plants
- -1 true breeding recessive plant
What did Mendel Conclude??
His plants did not show intermediate traits (each trait is intact, dicrete, not blended)
For each character, one trait was dominant, other recessive
Pairs of alternative traits examined were segregated among progeny of a particular cross
Alternative traits were expressed in F2 generation in raio of 3/4 dominant to 1/4 recessive
2 of the same allele
both alleles for a gene are identical (TT, tt)
gene has 2 differnt alleles (ex Tt)
Recessive (trait or allele)
phenotype observed only when two copies of allele (homozygous) (tt)
Dominant (trait or allele)
phenotype observed when homozygous or heterozygous (TT, Tt)
physical, biochemical, physiological traits of an individual based on genotype
Two versions of each chromosome
- -genes for characters at specific loci on chromosome
- -forms of genes = alleles
Principle of Segregation
Two alleles for a gene segregate during gamete formation and are rejoined at random, one from each parent, during fertilization
physical basis for allele segregation is the behavior of chromosomes during meiosis
what does Chromosome theory of inheritance state??
States that ..
- -genes are located at specific positions on chromsomes
- -behavior of chromosomes during meiosis and fertilization account for inheritance patterns
What do chromsomes undergo...??
Chromosome undergo segregation andindependent assortment during meiosis to account for mendel's observations, conclusions and 5-element model
mating of parental varieties differing in two characters
1. do the traits of two characters remain together: dependent Assortment
2. Do the traits of two characters separate: independent Assortment
In Characters studied, inheritance of one character has no effect on the inheritance of another Why??
each pair of alleles for a given character segregates independently of the other pair during meiosis
='s Law of Independent Assortment
a Dihybrid cross ratio of 9:3:3:1 if genes are on ______???
Probability scale ranges from ___ to ___
0 to 1
- -Event certain to occur: probability of 1
- -Event that is certain not to occur: probability of 0
- -The probabilities of all possible outcomes for an event must ass up to 1
SsYyAa * SsYyAa
what is the probability that an offspring will be homozygous recessive for all three genes???
Ss *Ss: probability of ss offspring = 1/4
Yy *Yy: probability of yy offspring = 1/4
Aa *Aa: probability of aa offspring = 1/4
Apply rule of multiplication to calculate the probability offspring will be ssyyaa???
1/4 ss * 1/4 yy * 1/4 aa = 1/64
to determine genotype of individual w/ dominant phenotype
-Cross individual w/ unknown genotype (ex B_) w/ a homozygous recessive (bb)
-phenotype ratios among offspring are different, depending on genotype of unknown parent
Dominant heterozygote (Aa) displays what??
displays the dominant phenotype
Recessive phenotype expressed when _____ copies (aa) are present
2 copies aa are present
Dominant doe not imply _____ or more common than a recessive
Dominant does not imply normal or more common than a recessive
Wild-type traits (those prevailing in nature) are _______??
not necessarily specifies by dominant alleles
Many inherited disorders in humans are controlled y one gene
Monogenic inherited human disorders ='s
Recessive inheritance need what??
- -2 recessive alleles are needed to show disease
- -Heterozygous parents
- -probability of inheritance increases w/ inbreeding, mating btw close relatives
Dominant inheritance requires what???
- -One dominant allele is needed to show disease
- -Dominant lethal alleles are usually eliminated from the population
What is controlled by a single gene locus??
Over 10,000 monogenic human genetic disorders, dominat or recessive traits
What is the majority trait in inherited human disorders??
Majority are recessive
What is the Range in severity in inherited human disorders??
relatively harmless conditions (free/attached earlobe) to severe (HD, CF, hemophillia etc)
Most people w. recessive disorders are born to ______ heterozygous parents (carriers)
are born to normal heterozygous parents
What kind of disorder is Cystic Fibrosis??
- -A Recessive Disorder
- -Most common lethal genetic disease in US
What is Cystic Fibosis characterized by??
an excessive secretion of very thick mucus from lungs, pancreas, and other organs
What is the risk of CF in caucasion population when allele carred by 1 in 25 caucasions w/ a chance that 2 caucasian carriers marry??
1/25* 1/25 = 1/625
What is the risk of CF in caucasion population when allele carred by 1 in 25 caucasions w/ a chance that 2 carriers will be homozygous recessive???
Cc * Cc ='s 1/4
What kind of disorder is Achondroplasia??
a form of dwarfism and Dominant Disorder
-only heterozygotes display phenotype
-homozygous dominant genotype is embryonic lethal
Why are Dominant lethal alleles rarer than recessive lethal alleles??
- -Recessive alleles have normal heterozygote carriers
- -Dominant alleles cannot be carried by heterozygotes w/o affecting them
- -Many lethal dominant alleles result from mutations in a sperm or egg that kill embryo
Mendel's model of inheritance assumes that ....??
- -each character is controlled by a single gene
- -each gene has only 2 alleles
- -there is a clear dominant-recessive relationship btw the alleles
Most genes do not meet these criteria
heterozygous phenotype is intermediate to homozygous phenotypes
incomplete dominance in humans
- -dangerously high levels of blood cholesterol
- -heterozygotes have blood cholesterol levels about twice normal
- -homozygotes have blood cholesterol levels about five times normal
neither allele is dominant to the other, both are expressed if present
heterozygote shows some aspect of phenotypes of both homozygotes
heterozygote is intermediate in phenotype btw 2 homozygotes
may br more than 2 alleles for a gene in a population (ABO blood types)
Each individual can only have 2 alleles
For any given gene, usually more than two alleles exist
When genes and enviornment interact
- Continuous variation
variation due to both genetic and environmental difference
- Large range of phenotypes
- Ex. height, weight, intelligence, cancer susceptibility
proportion of the variation w/in a population due to genetic differnce among individuals
average: sum of all phenotypic values divided by number of individuals
occurs when multiple genes are responsible for controlling phenotype
Phenotype is accumulation of contributions by multiple genes
Characters show continuous variation (quantitative)
multiple genes turn into a single character (skin color)
impact of a single gene on more than one character, symptoms
Sickle cell disease exhibits pleiotrophy
What are the characterisrics to get Sickle cell disease
Heterozygotes are normal carriers (recessive traits)
Causes disk-shaped rbcs to deform into a sickle shape w/ jagged edges
Who are carriers of the sickle cell trait??
heterozygotes (Ss): usually healthy, can experience pleiotropic effects in low O2
what is the difference btw Pletotrophy and Polygenic inheritance??
Pleiotrophy uses a Single gene to produce multiple characters
Polygenic inheritance uses multiple genes to produce a single character (skin color)
Pleiotrophy refers to an allele which has ...??
more than one effect on the phenotype
Pleiotrophic effects are difficult to predict b/c???
because a gene that affects one trait often performs other, unknown function
- This can be seen in human diseases such as CF or sickle cell anemia
- -multiple symptoms can be traced back to one defective allele
interaction btw genes at two or more loci (phenotype differs from expected if the loci were expressed independently)
- -R.A. Emerson crossed 2 white varieties of corn
- -F1 was all purple
- -F2 was 9 purple : 7 white
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