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46 Cards in this Set
- Front
- Back
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Incomplete dominance |
Phenotype of the heterozygote falls between the phenotypes of both homozygotes Each genotype has a specific phenotype 1:2:1 Genotypic ratio 1:2:1 Phenotypic ratio Ex: Four O'Clock Plants (Red, Pink, White) |
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Codominance |
Phenotype of the heterozygote expresses the phenotypes of both homozygotes simultaneously 1:2:1 Genotypic ratio 1:2:1 Phenotypic ratio Ex: Tay-Sachs at protein level; AB blood type |
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Multiple alleles |
There are multiple alleles for one gene Each human gamete would still only have 2 copies Ex: Fur color in mice; IA, IB, i blood types |
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Complementation |
2 mutants cross to make a wild type Mutations are on different genes and are not allelic |
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Complementation Test |
Used to determine if two mutations are on the same gene or not Cross 2 individuals with different recessive mutations
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Recessive Lethal Alleles |
If there are two copies of this allele, the result is lethality Genotypic ratio: 1:2:1 Phenotypic ratio: 2:1 in live births (1 is lethal) |
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Pleiotropy |
Single mutation causes multiple phenotypes Ex: AY allele is dominant for coat color, but recessive for lethality |
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Dominant Lethal Alleles |
If one of these alleles is present, it results in lethality Kept in population by: -late onset -incomplete penetrance
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Incomplete Penetrance |
Failure to express the phenotype that is normally expressed with a genotype
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Variable Expressivity |
Has a wider range of expression of a phenotype Ex: Eyes in flies: red, dark, all shades between; Rickets (Vitamin D deficiency-intolerance) |
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Complementary Gene Action |
A dominant allele for 2 different genes must be present to make a specific phenotype 9:7 ratio |
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Duplicate Gene Action |
2 genes are involved in producing a phenotype with both genes appearing equivalent Needs a dominant allele at either A or B 15:1 ratio
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Epistasis |
Phenotype of one gene masks the phenotype of another gene Recessive Epistasis: 9:3:4 ratio [albino masking color] Dominant Epistasis: 12:3:1 ratio [A- -- = white, aaB- = yellow, aabb = green] |
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Suppression |
A gene that pushes the mutant phenotype toward the wild-type phenotype Suppressor can be dominant or recessive Can suppress dominant or recessive MUTANT genes |
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Epigenetics |
Heritable modification of gene function without a change in the DNA sequence Ex: X chromosome inactivation |
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Complete Linkage |
Genes are so close together on a chromosome that they can not have a crossover between them because of: -Not enough space between them -Characteristics in the DNA in space between them don't allow recombination |
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No Linkage |
Genes that are: -On different chromosomes OR -More than 50 m.u. apart on the same chromosome
These genes segregate independently |
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Linkage |
Linear relationship of genes on a chromosome
Doesn't follow Law of Independent Assortment |
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Nonrecombinants |
Parental type- There were not any cross overs occur 2 largest categories |
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Recombinants |
There was one crossover between the three points 4 middle categories |
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Importance of Creighton and McClintock's Maize Experiment |
Cytogeneticists visually saw the chromosomes crossing over Also, it demonstrated that crossovers could happen anywhere on the chromosome, not just between two genes |
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Map Units How do you calculate? |
Relative distance between genes on a chromosome
=cMorgans=% recombination
You find the percent recombination |
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Three-Point Testcrosses How to calculate a linkage map |
1. Determine gene order -Compare largest to smallest, see which one changes 2. Find distances between the genes |
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Measured Map Distances Actual Map Distances |
Measured= value obtained by finding % recombination between 2 genes that are far apart
Actual= value obtained by adding up smaller map distances |
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Restriction Fragment Length Polymorphism |
Nucleotide change that results in the elimination or creation of a restriction enzyme site
Advantage: There are A LOT of these, so its more precise to find small, accurate recombination distance between genes and a RFLP |
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Heteroduplex DNA |
Double-stranded DNA where 2 of the strands are not completely complementary Forms a bulge, which is recognized and one of these strands is fixed |
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Linkage Pedigree Analysis |
Seeing if organisms have the same combination of traits consistently |
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Types of Chromosome Breaks How they repair or not Potential Problems with Repair |
Single Break in a Chromosome Two Breaks in one Chromosome Two Breaks in Nonhomologous Chromosomes |
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Single Breaks |
Can go through restitution and be repaired Can stay broken: 1 centric, 1 acentric; 2 centric chromosomes combine to make a dicentric chromosome, which pulls apart to make a deletion or duplication usually
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Two Breaks in the Chromosome |
Can go through restitution and be repaired Can go through inversion- no bad problems Can end in a chromosome with a deletion with an acentric fragment |
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Two Breaks in Nonhomologous Chromosomes |
Can be reciprocal translocation- 2 nonhomologous chromosomes exchange pieces Can be nonreciprocal translocation- 2 nonhom. chromosomes lose a piece, 1 gets the others, 1 acentric fragment is lost |
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Basic Notation for Chromosome Complement |
46,XX - normal human girl 47,XXY - Klinefelter's 45,X - Turner's 47,XX,+21 - Down syndrome 46,XX,21q22ter+ - long arm of chrom. 22 moved to terminus of 21 |
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Deletions Associated Problems |
Loss of chromosomal material Forms a deletion loop at Prophase I Can lead to pseudodominance Results in genetic imbalance |
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Pseudodominance |
Only one allele determines the phenotype of an organism, even if the allele is normally recessive |
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Genetic Imbalance |
Unnatural ratio of gene expression from an extra or missing gene |
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Cri Du Chat Syndrome What is the chromosomal problem? |
Large scale deletion in Chromosome 5 (5p-) Monosomy is lethal in humans except for in sex chromosomes |
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Inversions Associated Problems
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2 breaks in 1 chromosome; segment flips and reattaches
Pericentric- inversion includes centromere Paracentric- inversion doesnt include centromere
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Suppression of Recombination and Gamete Formation |
Suppression of Recombination: 1. Real suppression- corners are not close enough to synapse and cross over 2. Apparent suppression- recombination occurs but occurs in nonviable gametes |
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Properties of Inversions |
Inversions can inactivate an allele by placing it in a heterochromatin region Both para- and peri- result in 1 normal nonrecombinant chromosome, 1 viable recombinant chromosome, and 2 nonviable chromosomes
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Evolutionary Consequences of Inversions |
Can change linkage groups |
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Translocations Associated Problems
Gamete Formation |
Alternate segregation- normal/reciprocal translocation- each gamete has all genes Adjacent segregation- results in nonviable gametes
Robertsonian chromosome- centromeres fuse together OR acentric chromosome fuses with a centromere |
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Duplications Associated Problems
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Can be caused by an unequal crossover Genes with similar codes can get mixed up and cross over where its not lined up point-by-point Ex: Fragile X syndrome; Red-green colorblindness; Bar eye |
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Dynamic Mutations
Fragile X Syndrome |
There is a change in the chance of an organism inheriting a trait from generation to generation [due to repetition] Fragile X syndrome Tend to be neurodegenerativve |
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Variations in Chromosome Number Terminology |
Aneuploids-Have varied number of a single chromosome (nullisomic, monosomic, trisomic, tetrasomic)
Euploids-Have varied number of sets of chromosomes (haploid, diploid, triploid, tetraploid) |
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1 Trisomy 21 2 Familial Down Syndrome 3 Edwards Syndrome 4 Patau Syndrome 5 Turner Syndrome 6 XYY 7 Klinefelter Syndrome 8 XXX |
1 3 copies of Chromosome 21 2 Translocation of part of Chrom. 21 to 14 3 3 copies of Chromosome 18 4 3 copies of Chromosome 13 5 X0 6 Extra Y- age 35, extra Y degenerates 7 XXY 8 Extra X inactivation |
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Autopolyploidy
Allopolyploidy |
Auto- all chromosomes come from the same species
Allo- chromosomes are result of hybridization of 2 separate species |
