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52 Cards in this Set
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Compare & Contrast discontinuous with continuous variation within a population. |
Discontinuous variation: Phenotypes that fall into two or more distinct, nonoverlapping classes. (controlled by single gene pair; ex. height in pea plants) Continuous variation: A distribution of phenotypic characters that is distributed from one extreme to another in an overlapping, or continuous fashion. (Controlled by two or more gene pairs; ex. height in tobacco plants, height in humans) |
Think numbers of pairs... |
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Compare and contrast single gene inheritance with polygenic inheritance. |
Some traits are controlled by single genes...mendelian patterns of inheritance. Polygenic inheritance: controlled by multiple loci, phenotypes are measured in population, phenotypic traits are distributed over a range of the population. |
Dont think too abstract. |
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What assumptions must be made to explain the number of phenotypic classes related to the number of genes in simple polygenic inheritance. |
The different loci are not linked (assorted independently), dominant alleles contribute equally to phenotype. Assume same baseline phenotype, then each dominant allele adds equally to that phenotype, recessive alleles make no contribution to phenotype beyond baseline. Environment acts equally on all genotypes |
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Given certain # of phenotypic classes in simple polygenic inheritance could you determine the number of genes most likely involved...and vice versa |
2n+1... where n= # of loci. |
Equation |
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What happens to the population distribution of phenotypic classes as the number of genes responsible increases? |
Variation in the population will approach a normal "bell shaped" distribution as the number of loci increases. contolled by two or more genes...few individuals are at the extremes of phenotype, and most individuals are clustered around the average value. Ex. 3 loci = 7 phenotypic classes. 4 loci= 9 phenotypic classes. |
Bell |
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What is multifactorial inheritance? |
*Phenotype is result of multiple loci & environmental interactions *No direct relationship b/t # of loci and # phenotypic classes *Most complex human traits are multifactorial -examples are height, weight, personality, & IQ |
Open exposure |
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What is the threshold effect and how does it affect phenotypic variation in multifactorial phenotype? What are the two components of the threshold effect? |
Explains discontinuous distribution of some complex traits. Liability for a genetic disorder is distributed among individuals in a normal curve. The liability is caused by # of genes, each acting additively. Only individuals who have liability above a certain threshold are affected if exposed to certain environmental conditions. Severity of disease increases as the genetic liability moves away from the mean, and is affected by environmental factors. *genetic predisposition (liability/susceptability) *environmental trigger (nongenetic) |
Two factors |
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What are the two components of the threshold effect? |
*Genetic predispostion: individul must inherit minimum # of defective genes (genetic threshold) *Environmental trigger: at genetic threshold, exposure to proper environmental conditions raise liability of developing disorders. In other words: environmental conditions are most likely to have the greatest impact on those individuals who have the highest level of genetic predisposition |
Nature nuture |
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Compare & Contrast environmental variance with genetic variance... |
Phenotypic variation is dervied from both sources. (1) different genotypes present in population (2) different environments in which identical phenotypes are expressed. *Genetic Variance: The phenotypic variance of a trait in a population that is attributed to genotypic differences. *Environmental Variance: The phenotypic variance of a trait in the population (or individuals with the same genotype) that is attributed to differences in the environment. |
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What is Heritability? How is it interpretted and what are its limitations?? |
Heritability: Expression of how much of the observed variation in a phenotype is due to differences in genotype. *uses a single # b/t 0 and 1 to express the fraction of phenotypic variation among individuals in a pop. that is due to their genotypes. Limitations: a calculated H value is only valid for the population being studied under the particular environmental conditions present at the time. |
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H=0 |
100% of the phenotypic variation in the population is due to difference in the environment . Genetics play NO role. |
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H=1 |
100% of the phenotypic variation in population is due to the difference in genotypes of the individual in the population. GENES ARE ENTIRELY RESPONSIBLE FOR CHARATERISTICS ex. Fingerprints (H almost 1.0) |
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Concordant |
Agreement between traits exhibited by both twins. Both teins have phenotype |
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Discordant |
Only one twin has phenotype/exhibits trait |
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Monozygotic Twins (MZ) |
Twins dervived from single fertilizatio. Involving one egg amd one sperm; such twins are genetically identical |
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Dizygotic Twins (DZ) |
Twins derived from 2 seperate a d nearly simultaneous ferilizations, each involving 1 egg & 1 sperm. Such twins on average share 50% of their genes |
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What is concordance in MZ twins when phenotype is completely controlled by genetics? Why? |
100% concordance or H=1 Because MZ twins are genetically identically. Sharing one egg one sperm and same environment |
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What is concordance for DZ twins? Why? |
H=0.5 50%, Because 2 seperate ova. No more genetically related than siblings |
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Explain genetocs of obesity in both mice & man... |
Ob gene: leptin hormone fat cells secrete. Db gene: leptin receptor in hypothalamus *mutation in either ob or bd resulted in fat mice. In twin studies: H= range from 0.3-0.7 twin concordance *human ob & db genes are mutated in only 5% of obese individuals studied. Environment/activity has more of an effect on human obsesity that in mice. |
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Chromosome #'s |
Autosomes 1-22 Sex chromosome X&Y 24 chromosomes in humans |
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Chromosome arm designation |
P arm: short, smaller arm Q arm: long, bigger arm |
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Chromosome region number correlation |
# from centromere outward |
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Band # |
Treat with banding techniques Get exactly same banding patterns consistent from person to person. Unique to chromosome #. Allows geneticists to refer to a particular region on chromosome. |
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Metacentric |
Almost equal arm lengths |
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Submetacentric |
Clearly unequal arm lengths |
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Acrocentric |
P arms are very small |
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Telacentric |
Looks like no arms, but arms are present..just so small almost not visiable |
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What is a karotype? |
Picture of the 22 chromosome + sex chromosomes. Organized and numbered...mapped out neatly |
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How is a karotype done? |
Mitogens are used to stimulate cell division. Arrest cells in metaphase with colcemid. Spindle appartus is inhibited. Chromosomeds spread...cuz cells are treated to break open. *specimins that can be uses are -leukocytes -fibroblasts -amniotic cells (amniotic fluid) - chorionic cell (placenta) |
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What is chromosome banding? |
Reproducible and chromosome specific patterns of light & dark areas Produced by chemical or heat treatment of chromosomes on slides. Every chromosome has unique banding pattern. |
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G bands |
*most common used Stains with Giemsa to produce dark & light bands. Chemical digests proteins. Dark bands= G bands |
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R bands |
Same treatment as G bands, but stain with quinacrine mustard to make flourese under UV light |
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C bands |
Chemicals digest DNA, stain w/ Giemsa * only centromeres show dark bands, hence C bands |
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Chromosome Painting |
Chromosome specific probes have been designed. These probes only react with a particular chromosome. *dye to particilar chromosome. Differeny color shades **look at interphase on living cells Chrimosome territories allowed them to follow colors |
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Compare & Contrast Amniocentesis with Chorionic Villi Sampling (CVS) |
Amniocentesis: *aniotic fluid done at 16 weeks * needle into sac around baby. Risk of complications. Week to get results back. Invasive and can hurt baby if not done properly. CVS: *sample placental tissues, lots of cells * similar risks as amnio *8 weeks gestation, several days to get results Non-invasive and quicker results |
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Polyploidy |
Abnormality based on # Chromosome number is a multiple of haploid set -multiple of 23(humans) Common in plants |
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Triploidy |
Three haploid sets (Human= 3x23=69) 15-18% spontaneous aborted fetuses 75% of the extra chromosomes are paternal. Dispermy..2 sperm fertilize same ova |
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Tetraploidy |
Four haploid sets (4x23=92) 5% spontaneous aborted fetuses Due to first cleavage division failure |
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Aneuploidy |
Abnormality of chromosome number that is not polyploidy (DOES NOT INVOLVE COMPLETE HAPLOID SET) Due to nondisjunction (chromosome did not seperate as supossed to) -homologous pair in meiosis I - sister chromatids in meoisis II - sister chromatids in mitosis cleavage divisions *Chimera (some cells normal, one will be missing 21, one will have extra 21 |
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Compare/Contrast type of gametes in meiosis 1 vs meiosis 2 |
In meiosis , 2 xtra chromosome, 2 missing.(4 total gameyes) In meiosis 2 , 1 xtra, 1 missing(4 total gametes) |
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Automsomal vs. Sex chromosone monosomy |
Autosomal : 1 chromosome is missing human 45..lethal no live births Sex: can survive if have x and missing 2nd...x0 turners syndrome |
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Trisomy 13 |
Patau Syndrome. Xtra 13..cns 💖 malformations severe congenial malformations |
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Trisomy 18 |
Edwards- xtra 18 similiar malformations as 13. More females affected |
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Trisomy 21 |
Down Syndrome. Xtra 21 mental retardation. Protruding tongue, heart defects |
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Sex chromosome aneuploidy |
Turners(XO) monosomy. normal iq, slightly abnormal appearance. Klinefelter's (XXY) trisomy tall stature, 60% due to maternal nondisjunction. Additonal Xs XYY- impulse control...normal appearence. Normal fertility tall. Slightly lower iq |
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Inversion |
Part of chromosome is rearranged now inverted. |
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Translocation |
1 part of chromsome is transferred to another. |
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Reciprocal translocation |
No gain or loss of genetic material. Balanced exvhange. Gametes may be unbalanced May lead to monosomy or trisomy |
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Robertsomian translocation |
Exchange is not balanced. Some material lost. |
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Inherited form of down syndrome |
T14/21 balanced translocation. Carrier is phrnitypicall normal but unbalanced gametes, may lead to down's in offspring |
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Pericentric vs paracentric inversions |
Peri- include centromere breakpoint in each arm Para- not include centromere n both breaks occur in one arm on chromisome |
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Hardy-weinberg |
P= frequency dominant alleles Q= frequency recessive allles P2 + 2pq + q2 = 1 |
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