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what did gregor mendel experiment with
garden peas
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2 hypotheses as to how traits were passed through generations
Blending inheritance and Inheritance of acquired characteristics
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blending inheritance
children are a blend of their parents traits
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Inheritance of acquired characteristics
traits are modified in the parents and passed to the children in modified form
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trait
characteristic of an individual
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heredity
transmission of traits from parents to offspring
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genetics
inheritance of traits passed through generations
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can peas self pollinate
yes
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phenotype
visible characteristics
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how many phenotypes does each trait have
2
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hybrid
a mix of 2 different pure lines
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why did mendel choose a common pea
- easy to grow
- produces lots of offspring
- short reproductive cycle
- he could control matings
- easily recognizable traits
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how could mendel prevent self fertilization
by removing the male reproductive organs from the flower to allow cross fertilization using pollen from a different plant
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Mendel chose 7 easily recognizable traits
1. Seed shape
2. Seed color
3. Pod shape
4. Pod color
5. Flower color
6. Flower and pod position
7. Stem length
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adults
parental generation
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offspring
F1 (first fillial)
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genetic determinant for wrinkled seeds
recessive
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genetic determinant for round seeds
dominant
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particulate hypothesis
hereditary determinants maintain their integrity from generation to generation
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what does the particular hypothesis contradict
blending inheritance and inherently acquired characteristics
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does it matter which parent has the recessive trait
no
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in a cross between round seeds and wrinkled seeds
the F1 generation was round seeds
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what happened when mendel allowed the seeds to self pollinate
the wrinkled seed trait reappeared in the F2 generation in ¼ of the plants
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ratio of dominant vs recessive in F2 generation
3:1
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gene
hereditary determinants
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allele
different versions of a gene
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genotype
alleles in an individual
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uppercase A
dominant trait
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lowercase a
recessive trait
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homozygous
2 copies of the same allele (AA or aa)
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heterozygous
2 different copies of different alleles (Aa)
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monohybrid cross
mating between parents that are both heterozygous
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punnet square
predicts the genotype and phenotype of the offspring from a cross
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Mendel's genetic model
hypotheses explaining how a trait is inherited. Explains the results if a cross between 2 pure lines
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dihybrid cross
matings between parents that are both heterozygous for 2 traits
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why did mendel use dihybrid crosses
to see if the principle of segregation is true if parents differ in more than 1 trait
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Principle of independent assortment
alleles of different genes are transmitted independently of each other
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does mendels results support the principle of independent assortment
yes with phenotypes of f2 offspring from dihybrid cross
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Pleiotropic
a single gene that influences many traits rather than just one
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Phenotypic affects of marfan syndrome
1. Increased height
2. Disproportionately long limbs and fingers
3. Abnormally shaped chest
4. Heart problems
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why did mendel control the physical environment of his plants
to be sure that it did not affect phenotype when he studied plant height
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what are phenotypes influenced by
physical environment
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Phenylketonuria (PKU)
phenylalanine accumulates in the body and results in poor development of the nervous system and mental retardation. should be on a low phenylalanine diet
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Epistasis
one gene affects the action of another gene by masking or reducing the affects of alleles
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how are mitochondrial and chloroplast genomes typically transmitted to offspring
by the mother
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Polygenic inheritance
each gene adds a small amount to the value of the phenotype
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Quantitative traits
Traits that are not discrete but fall into a continuum
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what type of traits did mendel work with
discrete traits
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are there intermediate phenotypes in garden peas
no. only yellow and green
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what do the frequencies of different values for a quantitative trait form
a bell curve
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what are quantitative traits produced by
the actions of many genes
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pedigree
family trees used to analyze the human crosses that already exist
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To analyze the inheritance of a trait that shows discrete variation, biologists assume the simplest case
1. That a simple autosomal gene is involved
2. The alleles present in the population have a simple dominant recessive relationship
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If a phenotype results from an autosomal recessive allele...
the individuals with the trait must be homozygous and the parents are heterozygous carriers
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If a trait is autosomal dominant...
individuals who are homozygous or heterozygous for the trait will display the dominant phenotype
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huntingtons disease
dominant defect, people whos parents have it will definitely get it
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Autosomal trait
appears equally often in males and females
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x linked dominant traits
- rarely skip generations
- affected male has affected daughters and unaffected sons
- Hypophosphatemia (vitamin d-resistant rickets)
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X linked recessive diseases
- skip generations
- more in males than females
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another example of an x linked trait resulting from a recessive allele
hemophilia
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theory of inheritance
mendels rules can be explained by independent alignment and separation of homologous chromosomes at meiosis 1
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Who founded the chromosome theory of inheritance
sutton and boveri
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Principle of segregation
alleles encoding a specific trait segregate randomly into different daughter cells during meiosis
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Why do genes for different traits assort independently
they are located on different nonhomologous chromosomes
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model organism for genetic research
fruit flies
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why are fruit flies the model organism
- short generation time (2 weeks)
- many of their genes have more than 1 version
- easily identifiable phenotypes
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wild type
individuals with most common phenotypes
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mutations
some gene has changed and become different from the wild type
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what color eyes does the wild type fruit fly have
red
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what color does the mutant type fruit fly have
white
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What was the association of fruit flies
sex of the fly and eye color
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What does the small y chromosome pair with
large X
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female beetles
diploid cells contain 20 large chromosomes (xx)
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male beetles
diploid cells have 19 large chromosomes and 1 small one (xy)
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female
xx
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male
xy
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Hypothesis of x linked inheritance
the gene for white eyes resides on the x chromosome, and the y chromosome does not carry an allele for this gene
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Sex linked inheritance
various inheritance patterns occur when genes are carried on the sex chromosomes (females and males have different numbers of alleles of that gene)
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autosomes
non sex chromosomes
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What do the genes on autosomes show
autosomal inheritance
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linkage
the physical association of genes on the same chromosome
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if chromsomes are sex linked
it makes up part of a sex chromosome
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recombination
when the combination of alleles of the chromosome of progeny is different from the combinations of alleles present in the parental generation
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Can the location of genes be mapped
yes
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independent genes
genes that are 50+ map units apart on the same chromosome, can assort independently
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multiple allelism
genes with more than 2 alleles
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beta globin
component of hemoglobin that contains 500+ alleles
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incomplete dominance
heterozygotes have an intermediate phenotype
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codominance
heterozygous organism that has the phenotype of both alleles of a single gene. Neither allele is dominant or recessive to the other
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fitness
the ability to produce offspring in a particular environment
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Do dominance relationships have anything to do with fitness
no
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what violates the principle of assortment?
linked genes
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result of incomplete dominance
polymorphism
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polymorphism
heterozygotes have unique phenotype. more than 2 phenotypes associated with a single gene are present
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codominance
heterozygotes have phenotype of both alleles
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gene by gene interaction
phenotype associated with an allele depends on which alleles are present at another gene
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gene by environment interaction
phenotype influenced by environment experienced by an individual
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example of autosomal recessive trait
sickle cell diseases
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Hypothesis of the 20th century
genes were made of proteins
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