Mendel

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character

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a heritable feature that varies among individuals (flower color)

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trait

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each variant for a character (purple vs. white)

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true-breeding

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when the plants self-pollinate, all their offsrping are of the same variety.

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hybridization

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mating or crossing of two varieties

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monohybrid cross

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a cross that tracks the inheritance of a single character (i.e. flower color)

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P generation

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true breeding parents

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F1 generation

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hybrid offspring (F for first fillial). all show the dominant trait these self pollinate to create F2

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F2 Generation

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this generation led to Mendel's discovery of the law of seg. and the law of ind. assortment. ratio 3:1

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1. Alternative versions of genes (different alleles) account for variations in inherited characters

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each gene resides at a specific locus on a specific chromsome, but DNA can very somewhat in its sequence of nucleotides

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alleles

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alternative versions of genes

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

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one chromsomes, allele etc. is inherited from each parent

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3. If the two alleles differ, then the dominant allele shows above the recessive allele

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dominant-fully expressed in the organism's appearence
recessive- no noticable effect on the organism's appearence

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4. The two alleles for each character segregate during gamete production

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an ovum and a sperm each get only one of the two aleles that are present in the somatic cells of the organism

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law of segregation

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allele pairs separate during gamete formation and then randomly re-form pairs during the fusion of gametes at fertilization

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law of independent assortment

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each allele pair segregates independently during gamete formation, applies when genes for two traits are located on different pairs of homologous chromosomes

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homozygous

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having a pair of identical alleles for a character. true breeding

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heterozygous

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having two different alleles for a gene. can produce either

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phenotype

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appearence (PP and Pp are the same)

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genotype

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genetic makeup (PP and Pp are different)

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test cross

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breeding of a recessive homozygote with an organism of dominant phenotype but unknown genotype

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dihybrid cross

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mating of parental varieties differeing in two characters

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the rule of multiplication

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to compute the probability that two independent events will occur in some specific combination, multiply the individual probabilities. (.5 x .5=.25)

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the rule of addition

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the probability of an event that can occur in two or more different ways is the sum of the separate probabilities of those ways (.25+.25=.5)

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incomplete dominance

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F1 hybrids have an appearence somewhere in between the phenotypes of the two parental varieties. (written in subscript)

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complete dominance

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the phenotypes of the heterozygote and dominant homozygote are indistinguishable

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codominance

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both alleles are separately manifest in the phenotype

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important points about dominant and recessive

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1. they range from complete dominance, through various degrees of incomplete dominance, to codominance
2. they reflect the mechanisms by which specific alleles are expressed in phenotype and do not involve the ability of one allele to subdue another at the level of the DNA
3. they do not determine the relative abundance of alleles in a population

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multiple alleles

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like blood type

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pleiotyopy

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the ability of a gene to affect an organism in many ways

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epistasis

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a gene at one locus alters the phenotypic expression of a gene at a second locus

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dihybrid cross ratio

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9:3:3:1

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quantitative characters

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characters vary in a population along a continuum

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polygenic inheritance

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additive effect of two or more genes on a single phenotype character

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norm of reaction

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a range of phenotypic possibilities over which there may be variation due to environmental influence. broadest for polygenic traits

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multifactorial

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many genetic and environmental factors influence the phenotype

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pedigree

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family tree describing the interrelationships of parents and children across the generations

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carriers

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phenotypically normal people who transmit the recessive allele of a disorder to their offspring

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cystic fibrosis

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hits those of euro descent. abnormally high concentration of extracellular chloride do to lack of chloride channels, which leads to mucus/bacter.

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Tay-Sachs disease

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hits ashkenazic jews. dysfunctional enzyme cant break down brain lipids of a certain class

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sickle cell disease

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hits blacks. substitution of a single amino acid in the hemoglobin protein of red blood cells. when oxygen in the blood is low, cells are deformed. one allele of it helps ward of malaria.

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huntingtons disease

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degenerative disease of the nervous system is caused by allele that has no effect until age 35-45

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amniocentesis

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inserts a needle into the uterus, extracts amniotic fluid, tests it for chemicals and then cultures cells for karyotyping

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chorionic villus sampling

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suctions of a small amount of fetal tissue from placenta. can do in 8th week of pregnancy, and know results sooner.