Genetics Exam 2

2 genes on 2 different homologous pairs of chromosomes

2 genes on a single pair of homologs

• only parental gametes
• very rare

crossing over occurs only in females

• 1) Find and map the smallest distance.
• 2) continue this process until the map is complete and all distance add up to observed recombination frequencies

% of SCO x % of SCO = DCO %

• 1) individual must be heterozygous at all 3 loci
• 2) must be able to determine genotype by examing phenotypes of offspring
• 3) must have large # of offspring

reduction in the number of DCO events relative to what is expected based on the map distance

• a single hybrid cell with 2 nuclei
• only 2 cells (mouse and human) can be induced to form heterokaryon

nuclei in heterokaryon will fuse to form synkaryon

• reproductive cells
• similar to our haploids

take a single gene and map according to the centromere

(1/2 2nd division segregant asci)/(total asci scored)

• must know order
• destinguishes 1st and 2nd division segregants which is necessary to map gene in relation to the centromere

• determine if 2 genes are linked (occur on the same chromosome)
• map distance between the two loci

22, XY

22, XX

• 47, XXY
• genetalia/internal ducts male
• underdeveloped testes - cant produce sperm (sterile)
• some masculine development
• slight breast enlargement
• 2/1000 male births
• occur from nondisjunction of x-chromosome

• 45, X
• female external genetaliea/internal ducts
• underdeveloped ovaries
• short
• webbed neck
• broad chest
• 1/3000 female births
• occur from nondisjunction of X-chromosome

• 1/1200 female births
• highly variable:
• - normal to underdeveloped secondary sexual characters
• - sterility
• - mental retardation

spontaneously aborted

spontaneously aborted

• 47, XYY
• 9/315 males in Scottish Maximum Security proson
• taller
• criminal acts
• 7/9 subnormal intelligence
• all 9 personality disorder
• known as the "criminal" phenotype
• actually found that these individuals dont have antisocial behaviors and live normal lives

• every embryo goes through period when is hermaphrodite
• 5th week --> gonadal tissue arise associated with kidney
• primordial germ cells migrate to these ridges -- outer cortex and inner medulla form
• 2 sets of undifferentiated male and female ducts exist
• if cells have XY development into testes takes place - 7th week
• testicular tissue secretes 2 hormones for continued male development
• absences of Y - ovarian tissue forms
• absence of male development oogonia begin meiosis and oocytes can be detected - 12th week
• 25th week - all oocytes remain dormant untill puberty
• males - spermatocytes are not produced until puberty

• 2% of live birth
• 2 eggs are fertilized in womb - one XX and one XY
• eggs merge to become one zygote

• shares homology with X-chromosome
• synapses and recombines

• 20 genes in this region
• 12 groups into 2 different groups
• 5 of 12 have homologs on X-chromosome
• other 7 lack X -homologs - expressed only in testes

encodes TDF (testis determining factor)

• the actual proprtion of male to female offspring
• 1:1

the proportion of males to females conceived in the population

the proportion of males to females born in a population

Dosage Compensation

• inactivation is random
• occurs early in embroyonic development
• all progeny cells have the same X chromosoem inactivated

• hemizygous males are fully color-blind
• heterozygous females display mosaic retinas - patches of defective color perception and surrounding areas of normal color

• Hemizygous males - absence of teeth, sparse hair growth, lack of sweat glands
• heterozygous females - patches of tissues without sweat glands

• a threshold for maleness is reached with X:A is 1:2
• presence of additional X alters this balance and results in femaleness

• master switch for activation of at least 4 separate regulatory genes
• activated when X:A = 1 --> results in female development
• if X:A = .5 --> results in male development
• mutations of Sxl kill females but have no effects on males

• no X-chromosome inactivation
• male X-linked genes transcribed at 2 times the level compared to females
• dosage compensation is regulated by at least 4 autosomal male specific lethal genes
• these genes are under the control of Sxl
• mutations in these genes reduces the increased expression of X-linked genes in males --> causing lethality

• complete haploid sets of chromosomes are present
• we are euploids

• organisim gains or losses one or more chromosomes but not a complete haploid set
• monosomy - loss of a single chromosome (2n-1) - they die
• trisomy - addition of a chromosome to a diploid complement

• 3 or more complete haploid sets of chromosomes
• triploid = 3n
• tetraploid = 4n
• pentaploid = 5n
• 2 types: autopolyploid & allopolyploid

• partial monosomy in humans
• segmental deletion
• chromosomal designation = 46, -5p
• - have all 46, but missing part of chromosome 5
• cardiac and gastrointestinal malfunctions
• mentally retarted
• abnormal development of glottis and larynx --> meowing cat sound
• 1/50,000 live births
• some can learn to develop self care skills and communication

only a part of a chromosome is lost

• trisomy 21 = 47, 21+
• mom age 20 = < 1/1000
• mom age 30 = 1/1000
• mom age 40 = 1/100
• mom age 45 = 1/50 to 1/12
• almond shape eyes
• short
• flat round heads
• protruding tongue
• characteristic palm and fingerprint
• retardation
• shortened life expectancy
• prone to respiratory disease, heart malformation, leukemia, alzheimers disease

• trisomy 13 = 47, 13+
• harelip
• cleft palate
• pplydactyly - extra finger
• congenital malformations of most organs
• abnormal development early in gestation
• survive around 3 months
• 1/19,000 live births
• average mom age = 32

• tisomy 18 = 47, 18+
• small newborn
• elongated skulls
• webbed neck
• congenital disloaction of hips
• receding chin
• average survival time: 4 months
• death usually caused by pneumonia or heart failure
• 1/8000 live births
• more common in female offspring

• each additional set of chromosome is identical to parent species
• autotriploid: AAA
• autotetraploid: AAAA
• produce by heat/cold shock during meiosis or apply colchicine to somatic cells undergoing mitosis

potatoes, winesap apples, commerical bananas, seedless watermelons

alfalfa, coffee, peanuts, mcintosh apples

• AAAAAAAA
• commerical strawberries

• polyploids that result from hybridization of two closely related species
• may be sterile

cells in normal diploid organism becomes polyploid through the process of Endomitosis

• Deleting part of a chromosome
• - Terminal Deletion: deleting at the end of the chromosome
• - Intercalary Deletion: deleting in the middle of the chromosome

• duplication in a single allele on a chromosome
• -Terminal Duplication: duplicating on the end of the chromosome
• -Intercalary Duplication: duplicating in the middle of the chromosome

• taking a chunk of DNA and flipping it 180 degrees, then putting it back
• -Paracentric inversion: does not include the centromere
• -Pericentric Inversion: centromere is involved in inversion

• 2 centromeres in chromosomes
• doesnt produce viable cells

• no centromere in the chromosome
• doesnt produce viable offspring