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| theory that traits observed in a mother and father blend together to form the traits observed in the offspring |
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| set of matings where the mother’s phenotype in the first cross is the father’s phenotype in the second cross, and the father’s phenotype in the first cross is the mother’s phenotype in the second cross |
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different version of same gene
• responsible for the variation in traits Mendel studied |
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o alleles that are found in a particular individual
• has a profound effect on its phenotype |
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| mating between parents that are both heterozygous at gene in question |
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| physical location of a gene |
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physical association of genes on same chromosome
• if two or more genes are linked, they are on same chromosome
• are inherited together unless crossing over occurs
• violate theory of independent assortment
• When referring to linked genes, use a slash to separate the alleles that are found on homologous chromosomes. (wy+/w+y)
• if a single gene is sex-linked, it is found a sex chromosome
• 1:1:1:1 if independent
• 100:100:1:1 if linked
• should go through anaphase together – have some exceptions b/c crossing over, generating a new type of gamete |
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• combination of alleles different from combinations of alleles in parents
• proposed that gametes with new, recombinant genotypes were generated when crossing over occurring during prophase of meiosis I
• frequency in cM = (recombinant/total offspring) x 100
• biggest frequencies are far apart
• crossing over breaks up linkage and makes it appear as if independent assortment is occurring
• when genes are 50 or more map units apart, they have as if they assort independently because 50% of the gametes are recombinant |
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| genetic map and unit of distance |
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Definition
| • unit of distance along a chromosome should simply be the percentage of offspring that have recombinant phenotypes with respect to two genes |
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| centiMorgan (cM) or map unit |
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| represent physical distance that produce 1% recombinant offspring |
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| existence of more than two alleles of the same gene |
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| existence of more than two alleles of the same gene |
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| when more than two distinct phenotypes are present in a population due to multiple allelism |
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| have only 1 copy of allele |
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| intermediate phenotype (black + white = gray) |
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| have phenotypes associated with both alleles (AB blood) |
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| why differences in dominance? |
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Definition
• codominance common in alleles associated with membrane proteins, such as MN protein
• complete and incomplete dominance common in alleles that code for enzymes
o complete
• recessive allele has defect that keeps enzyme from functioning
• example: in plant height, homozygotes are dwarfed
• dominant allele codes for an enzyme that functions normally
• in heterozygotes, one normal allele is enough to make normal plant height
o incomplete
• flower color: not enough pigment to be dark pink |
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| a gene that influences many traits, rather than just one trait |
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| “stopping” or “diminishing,” occurs when an allele of one gene masks the affect of an allele of another gene |
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| transmission of quantitative traits is said to result _______ |
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from polygenic inheritance
• polygenic inheritance: “many-genes,” each gene adds a small amount to the value of the phenotype |
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• Mendel’s theory to counter blending theory
o hereditary determinants for traits do not blend together or acquire new or modified characteristics through use
o maintain their integrity from generation to generation
o act like discrete entities |
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two alleles of same gene segregate into different gamete cells
o explains 3:1 ratio
o means each gamete has one allele of each gene
o physical separation of alleles during anaphase of meiosis I is responsible for this |
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Term
| principle of independent assortment |
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Definition
independent behavior of two genes; not being packaged in same gamete (normally means on different chromosomes)
o alleles of different genes are transmitted independently of each other
o physical basis: when genes are located on different nonhomologous chromosomes, they assort independently of one another at meiosis I
• results in four types of gametes, produces in equal proportions
o key issue: genes cannot undergo independent assortment if on same chromosome |
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Term
| chromosome theory of inheritance |
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Definition
| Mendel’s rules can be explained by the independent alignment and separation of homologous chromosomes at meiosis I |
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Definition
• a female has two copies of the gene that specifies eye color because she has two X chromosomes
• one of these chromosomes came from her mom and one came from her dad
• a male has only one copy of this gene because he has only one X chromosome, which comes from his mom |
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| the discovery of ___________ convinced most biologists that the chromosome theory of inheritance was correct |
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| Sutton & Boveri’s central insight |
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| chromosomes are composed of Mendel’s hereditary determinants, or genes |
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| if a phenotype appears about equally between males and females, _________ |
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| if a phenotypes appears more on males, _________ |
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it is likely X-linked
• because so few genes occur on Y chromosome, Y-linked inheritance is rare |
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| if a phenotype is due to an autosomal dominant allele, ________ |
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affected individuals are either homozygous dominant or heterozygous
• any affected child must have an affected parent |
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| if a phenotype is due to an autosomal recessive allele, _______ |
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Definition
affected individuals must be homozygous
• if the parents are not affected, both parents must be heterozygous (carriers) |
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| if a phenotype appears in an affected male’s daughters but none of his sons, _________ |
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Definition
it is likely X-linked dominant
• female offspring get one X from dad, sons get X from mom |
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Term
| __________ determines how often crossing over occurs between them |
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Definition
| the physical distance between genes |
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