Seabury 1
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| Dirty Trait | A trait that doesn't follow simple, Mendelian genetics
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| True Breeding | When an organism has two copies of a given allele
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| Backcross | Mate one generation with an earlier one
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| Mendel's Model | 1. Genes do NOT blend together.
2. Peas have two versions (alleles) of each gene.
3. Each gamete contains one allele of each gene.
4. Males and females contribute equally to the offspring genotype.
5. Some alleles are dominant to others.
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| Independent Assortment | Alleles segregate randomly so that each gamete receives one or the other with equal likelihood
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| Mendel's First Three Postulates | Unit Factors in Pairs
Dominance and Recessiveness
Segregation
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| Unit Factors in Pairs | Genetic characters are controlled by unit factors that exist in pairs in individual organisms
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| Dominance and Recessiveness | When 2 unlike alleles responsible for a single character are present in a single individual, one is dominant to the other, which is said to be recessive
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| Segregation | During gamete formation, the paired alleles separate or segregate randomly so that each gamete receives one or the other with equal likelihood.
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| Codominance | The joint expression if both alleles in the heterozygote
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| Bombay Phenotype | A mutation in the FUT1 gene causes the H substance (an A and B antigen precursor molecule) to incompletely form, thus preventing the antigen from attaching. Affected individuals have O-type phenotype
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| Epistasis | One gene masks the expression of a different trait for a DIFFERENT GENE. (n.b. NOT the same as dominance)
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| Hemizygous | Only have one allele
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| Sex-influenced inheritance | The extent of phenotypic expression varies with sex/gender; NOT located on sex chromosomes
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| Sex-linked inheritance | Genes are on sex chromosomes
Generation is skipped in inheritance
Males are hemizygous
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| Sex-limited inheritance | NOT located on sex chromosome
Expression of genotype is limited to one sex/gender
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| Penetrance | The percentage of individuals that show a clearly defined phenotype that reflects the genotype
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| Expressivity | The range of mutant phenotypic expression
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| Primary vs Secondary Sexual Differentiation | Primary: only where gametes are produced
Secondary: other places
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| Nematode Sex Determination | -hermaphrodites have XX
-males have only X
-ratio of number of X chromosomes determines the sex (1.0=hermaphrodite, 0.5=male)
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| Protenor Sex Determination | XX/XO mode
Females have XX, Males have XO
All females have eggs with 1X; all males have sperm with either 1X or no X chromosome
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| Lygaeus Sex Determination | XX/XY
Females have XX, Males have XY
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| Homogametic Sex | The gender that produces uniform gametes (in humans, females b/c male gamete determines sex)
In Protenor and Lygaeus, the females
In chickens, the male(ZZ)
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| Heterogametic Sex | The gender that produces unlike gametes
In Protenor, Lygaeus, and Humans, is the male
In chickens, the female(ZW)
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| Genic Balance Theory/Dosage Compensation | When gene is transcribed, mechanisms reduce the level of X-transcription lionization in humans
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| Drosophila Sex Determination | XXX/2A-inviable
XXX/3A-fertile female
XX/2A-fertile female
X/4A-inviable
XX/3A-inviable
X/2A-sterile
XY/2A-fertile
XY/3A-inviable
essentially, F: X/A ratio>1; M:X/A ratio <0.5
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| Reptile sex | The depth of egg in sand has impact on gender
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| Bird sex | Split 80MYA
Ratite birds have Z & W morphologically the same; Z & W morphologically different in Carinate
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| Marsupial sex | SRY controls testis formation
XXY - has testis, pouch, mammary glands but no scrotum
XO - no testis, no pouch, no mammary glands but has scrotum
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| Monotreme sex | Diverged 210MYA
In males, sex chromosomes are unpaired; meiotic chain in male
Females have paired sex chromosomes
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| Mammalian Sex Chromosome Exceptions | -Ryukyu:ZFY gene important in sex-determination
-Microtidae: Female germ cells XX, somatic cells XO; Male germ cells YO, somatic cells XY
-Primates and Deer: translocation of X or Y chromosome
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| X chromosome trivia | 5% of genome
155 Mb
1100 protein-coding genes (LOW gene density)
X chromosomes similar in most mammals
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| NR0B1 (DAX1) | XY sex reversal, hypogonadism
on X chromosome
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| AR | has over 300 possible mutations with many phenotypes (infertility, intersexuality, sex reversal)
on X chromosome
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| Rhox family | make up some genes pretaining to the testes
on X chromosome
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| MAGE-TC family | 32 genes coding for testicular things
on X chromosome
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| X chromosome genes (3 places in body) | Sex/reproduction
Brain
Muscle
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| Bar Bodies | Discovered by Barr and Bertram, these are the genetic mechanism to compensate X chromosome dosage disparities; can be seen during interphase; is an INACTIVE X chromosome
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| formula for number of barr bodies | N-1
N is total # of X chromosomes
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| Time/Extent of X inactivation | Time-occurs once initial sex determination has occured
Extent-some genes are escapees:PAR(allow for faithful dissemination of sex chromosomes during meiosis; many genes of X short arm
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| Lyon Hypothesis | Once X is inactivated, all progenetor cells have same one inactivated --> all mammalian females are mosaics for heterozygous X-linked alleles
e.g. tortiseshell and calico cats, X-linked anhidrotic ectodermal dysplasia, X-linked red-green color blindness
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| X-linked anhidrotic ectodermal dysplasia | male: absence of teeth, sparse hair growth, no sweat glands
female:sweat glands absent in patches
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| R-G color blindness | X-linked; random X inactivation
females are mosaic
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| XIC | critical component of XIST gene, which smothers the chromosomes and prevents transcriptional mechanism --> genes silenced
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| Y-chromosome | not highly conserved among diff spp
all small and mostly heterochromatic
difficult to sequence b/c of palindromes
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| Y-chromosome genes | many copies of same thing (ampliconic)
SRY=sex determination
DAZ, TSPY, RBMY=testis specific multicopy genes
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| heterochromatic | highly compacted
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| SEX CHROMOSOME ABNORMALITES (4) | 1. 47, XXY - Kleinfelter syndrome
2. 45, X0 - Turner syndrome
3. 47 XXY - normal or sterile female
4. 47, XYY - 'super' male
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| SRY | -protein contains HMG (high mobility group) box domain
-SRY encodes transcription factor that can bind and bend DNA --> causes DNA to be either discouraged or encouraged to transcription around bend
-member of SOX gene family, which all contain HMG
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| Sex Chromosome evolution | 1. Ancestral homologous chr. pair
2. Mutation in one homolog; blocks recombination
3. More mutation, spreading of suppressed recombination
4. loss of X-Y homology
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| Aneuploidy | pertains to a single chromosome
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| Polyploidy | pertains to single chromosome set
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| NUMBER OF GENES OF MAMMAL | ~20,000-35,000
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| G-banding | Gimesa stain
A/T stain dark (gene poor regions)
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| Q-banding | staind heterochromatin
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| R-banding | heated phosphate buffer + Gimesa stain
C/G stain dark (gene rich regions)
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| Types aneuploidy | monosomy, trisomy, tetrasomy, pentasomy
2n +/- x chromosomes
***caused by nondisjunction***
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| Types euploidy | diploidy, polyploidy, autopolyploidy, allopolyploidy
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| autopolyploidy | multiples of same genome
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| allopolyploidy | multiples of different genome
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| Monosomy | rare b/c unmasks lethal gene
Monosomy X in mammals = Turner syndrome (45, XO)
Monosomy 4 in fly = reduced viability
Better tolerated in plants
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| Partial monosomy | Cri-du-chat syndrome (segmental deletion of 5p)
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| Trosomy | better tolerated if of small chromosomes and better tolerated than monosomy in mammals
viable in plants
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| Trisomy 21 | Caused by nondisjunction in Meiosis I or II
Maternal age
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| Trisomy 13 | Patau syndrome
usually lethal at embrionic stage
low life expectancy
47, 13+
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| Trisomy 18 | Edwards syndrome
fingers/toes fused together
47, 18+
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| Ploidy | Triploidy = unbalanced gametes = not viable
Tetraploidy = balanced gametes = viable; parent cell never divides
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| Triploidy in humans | Almost ALWAYS caused by 2 sperm fertilizing 1 egg
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| Deletion | Removed fragment is lost during cell division because has no centromere, so no spindle fiber attachment
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| Duplication | eduring meiosis
Part of one chromosome goes with other chromosome and so there is a duplication of one or more genes within one chromosome
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| Inversion | Needs 2 breaks, then DNA flips
more common ~100-n thousand bp
If a promoter is moved, can have a stromg affect on local gene expression
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| pAracentric inversion | does NOT involve the centromere
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| pEricentric inversion | involves the centromere
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| Translocation | because maintains bp#, well tolerated UNLESS one of genes is a strong promoter
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| Robertson translocation | break occurs at centromere, then swap
ones that contain centromere fuse together
ones w/o centromere are lost
2 types: balanced and unbalanced
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| Reason for familial trisomy 21 | chromosome 14 has chromosome 21 attached to it AND there are 2 copies of chromosome 21 in the soma
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| Linkage | Condition in which two or more genes tend to be inherited together
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| Linked genes | -have loci along same chromosome
-do NOT free to undergo independent assortment b/c on same chromosome
-the closer together, more likely to be linked
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| Crossing Over | The exchange of (non-sister) chromosomal material between homologous chromosomes by breakage and reunion
Occurs during meiotic prophase
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| Independent Assortment | Genes on separate chromosomes will always assort independently
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| Linkage without crossing over | COMPLETE linkage
produces only parental or non-crossover gametes
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| Linkage with crossing over | Result in 2 new allele combinations -- recombination or crossover gametes
The frequency with which crossing over occurs between 2 loci is proportional to the distance separating them
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| Linkage Ratio | If complete linkage exists between 2 loci AND organisms heterozygous at both loci are mated, then a unique F2 phenotypic ratio will be produced
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