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Seabury 1

QuestionAnswer
Dirty Trait A trait that doesn't follow simple, Mendelian genetics
True Breeding When an organism has two copies of a given allele
Backcross Mate one generation with an earlier one
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.
Independent Assortment Alleles segregate randomly so that each gamete receives one or the other with equal likelihood
Mendel's First Three Postulates Unit Factors in Pairs Dominance and Recessiveness Segregation
Unit Factors in Pairs Genetic characters are controlled by unit factors that exist in pairs in individual organisms
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
Segregation During gamete formation, the paired alleles separate or segregate randomly so that each gamete receives one or the other with equal likelihood.
Codominance The joint expression if both alleles in the heterozygote
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
Epistasis One gene masks the expression of a different trait for a DIFFERENT GENE. (n.b. NOT the same as dominance)
Hemizygous Only have one allele
Sex-influenced inheritance The extent of phenotypic expression varies with sex/gender; NOT located on sex chromosomes
Sex-linked inheritance Genes are on sex chromosomes Generation is skipped in inheritance Males are hemizygous
Sex-limited inheritance NOT located on sex chromosome Expression of genotype is limited to one sex/gender
Penetrance The percentage of individuals that show a clearly defined phenotype that reflects the genotype
Expressivity The range of mutant phenotypic expression
Primary vs Secondary Sexual Differentiation Primary: only where gametes are produced Secondary: other places
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)
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
Lygaeus Sex Determination XX/XY Females have XX, Males have XY
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)
Heterogametic Sex The gender that produces unlike gametes In Protenor, Lygaeus, and Humans, is the male In chickens, the female(ZW)
Genic Balance Theory/Dosage Compensation When gene is transcribed, mechanisms reduce the level of X-transcription lionization in humans
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
Reptile sex The depth of egg in sand has impact on gender
Bird sex Split 80MYA Ratite birds have Z & W morphologically the same; Z & W morphologically different in Carinate
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
Monotreme sex Diverged 210MYA In males, sex chromosomes are unpaired; meiotic chain in male Females have paired sex chromosomes
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
X chromosome trivia 5% of genome 155 Mb 1100 protein-coding genes (LOW gene density) X chromosomes similar in most mammals
NR0B1 (DAX1) XY sex reversal, hypogonadism on X chromosome
AR has over 300 possible mutations with many phenotypes (infertility, intersexuality, sex reversal) on X chromosome
Rhox family make up some genes pretaining to the testes on X chromosome
MAGE-TC family 32 genes coding for testicular things on X chromosome
X chromosome genes (3 places in body) Sex/reproduction Brain Muscle
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
formula for number of barr bodies N-1 N is total # of X chromosomes
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
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
X-linked anhidrotic ectodermal dysplasia male: absence of teeth, sparse hair growth, no sweat glands female:sweat glands absent in patches
R-G color blindness X-linked; random X inactivation females are mosaic
XIC critical component of XIST gene, which smothers the chromosomes and prevents transcriptional mechanism --> genes silenced
Y-chromosome not highly conserved among diff spp all small and mostly heterochromatic difficult to sequence b/c of palindromes
Y-chromosome genes many copies of same thing (ampliconic) SRY=sex determination DAZ, TSPY, RBMY=testis specific multicopy genes
heterochromatic highly compacted
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
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
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
Aneuploidy pertains to a single chromosome
Polyploidy pertains to single chromosome set
NUMBER OF GENES OF MAMMAL ~20,000-35,000
G-banding Gimesa stain A/T stain dark (gene poor regions)
Q-banding staind heterochromatin
R-banding heated phosphate buffer + Gimesa stain C/G stain dark (gene rich regions)
Types aneuploidy monosomy, trisomy, tetrasomy, pentasomy 2n +/- x chromosomes ***caused by nondisjunction***
Types euploidy diploidy, polyploidy, autopolyploidy, allopolyploidy
autopolyploidy multiples of same genome
allopolyploidy multiples of different genome
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
Partial monosomy Cri-du-chat syndrome (segmental deletion of 5p)
Trosomy better tolerated if of small chromosomes and better tolerated than monosomy in mammals viable in plants
Trisomy 21 Caused by nondisjunction in Meiosis I or II Maternal age
Trisomy 13 Patau syndrome usually lethal at embrionic stage low life expectancy 47, 13+
Trisomy 18 Edwards syndrome fingers/toes fused together 47, 18+
Ploidy Triploidy = unbalanced gametes = not viable Tetraploidy = balanced gametes = viable; parent cell never divides
Triploidy in humans Almost ALWAYS caused by 2 sperm fertilizing 1 egg
Deletion Removed fragment is lost during cell division because has no centromere, so no spindle fiber attachment
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
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
pAracentric inversion does NOT involve the centromere
pEricentric inversion involves the centromere
Translocation because maintains bp#, well tolerated UNLESS one of genes is a strong promoter
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
Reason for familial trisomy 21 chromosome 14 has chromosome 21 attached to it AND there are 2 copies of chromosome 21 in the soma
Linkage Condition in which two or more genes tend to be inherited together
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
Crossing Over The exchange of (non-sister) chromosomal material between homologous chromosomes by breakage and reunion Occurs during meiotic prophase
Independent Assortment Genes on separate chromosomes will always assort independently
Linkage without crossing over COMPLETE linkage produces only parental or non-crossover gametes
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
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
Created by: Jessica S Jessica S on 2013-01-31



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