sex linkage.txt

based on cytological appearance

chromosomes that look like any other (not cytologically different), but differ in major sex determination of genes

one of the homologues carrying the major sex determination gene ecomes degenerate or cytologically different

• x/y system: humans, mammals, dogs, cats, some plants (ie cannabis, female is xx, male is xy)
• Z/W system: birds and butterflies, and wild strawberries (ie zz is male, zw is female)

• in x/y: humans xx is female
• in z/w: birds zz is male
• (homozygous)

• x/y: human xy is male
• z/w: bird zw is female
• (hemizygous)

• expressed in ONE sex or the other, but gene can be combined anywhere in the genome
• ie milk production gene

• heterozygotes express one phenotype in one sex and another in the other sex
• ie baldness (male pattern)
• BB - baldness in female and male
• Bb - baldness in MALE, NOT females
• bb - no baldness

• Red-Green colorblindness: in 4-8% males
• Hemophilia: bleeding
• Lesch-Nyham syndrome: movement problems, self mutilation
• Duchenne muscular dystrophy: muscular degeneration

testicular feminization: recessive on X insensitive to testosterone - XY ind develop as FEMALES (gene on x does NOT produce testosterone)

• Has to come from males
• ie: hairy ears

• X-linked DOMINANCE
• X-linked RECESSIVE
• Y-linked Inheritance

• XA Xa
• Affected males pass on trait to ALL daughters, but NO sons (sons get Y)
• Affected females pass on traits to HALF of sons and HALF of daughters

• Many more MALES vs females show the trait
• OFFspring of affected males will NOT be affected (all DAUGHTERS will be carriers and ALL sons will be affected)
• Sons of affected males do NOT inherit X from father so NOT affected OR NOT a carrier

ONLY affected in males, NOT females

• Addition or Subtraction of chromosome relative to their normal number
• Ie downsyndrome: chrom 21 ADDED

• Normal # of chromosomes characteristic of a species or exact multiples of that #
• ie fruit: if increase in Ploidy level, fruit Increases in size

• Aneuploids caused by NON-disjunction (failure of separation of chromosomes or chromatids
• (2n-1)
• one member OF a pair of homologues is missing (ie 22 on one pair, and 23 on another pair, so total chrom for human of monosomic 18 (chrom 18 missing) is 45 (as opposed to 46))

• Aneuploids caused by NON-disjunction (failure of separation of chromosomes or chromatids
• (2n +1)
• EXTRA copy of a chromosome is present

DRAW it

• characterized by mental retardation, eye folds, shorter lifespan
• Maternal age: as females increase in age, increase chances of Downs (as eggs stay in body longer, increase in mutation)

• 1/180 live births have some aneuploid condition
• 15% of pregnancies spontaneously abort - many aneuploidy

• XO
• survivable condition

• XXY
• Males: mostly detected if have problems conceiving children (reduced fertility)

• XYY
• Taller than average
• CAN produce normal offspring

Withdraw fluid, centrifuged & cell culture for biochem & chromosomal studies

• Holocentric: entire chromosome acts as centromere
• Metacentric: Centromere is in the center (how we normally draw chromosomes…looks like this - X)
• Telocentric: centromere is at the END (on the bottom), NOT in humans
• Aerocentric: centromere is at the beginning (on the top)

genes residing in the SAME chromosome pair

• if both RECESSIVE mutations on the same member of chromosome pair, they are COUPLING (CIS)
• A----B / a----b
• If recessive mutations on DIFFERENT chrom pairs, they are TRANS
• A----b / a----B
• CLOSER Genes are, the LESS recombination occurs

• Freq. of recombinants b/w 2 genes is a fxn of physical distribution b/w them (ie - closer genes, LESS recombination occurs)
• Recombination as measured by markers is RECIPROCAL (ie - both products of exchanging occur w/equal freq)
• Recombination occurs @ PROPHASE I of meiosis, when homologues are synapsed together & may continue into metaphase
• Any one recomb. occurs b/w 2 of the 4 chromatids, ONE from each homologue, but NEVER b/w sister chromatids (always occurs b/w two different X's)
• ie X X, these 4 chromosomes can recombine, but not the first two with each other, only the first with one of the last two)
• 2 of the 4 chromatids will be recombinant and 2 will be parental
• occurs at different places in different meiocytes

• OBSERVED crossover / EXPECTED crossover =
• ie - observed crossover is the addition of both amount of crossovers
• expected crossover is the multiplication of crossover occurrences b/w both regions and these percentages multiplied by the total (ie .16 x .48 x 879[total offspring])

• 1 - COC = .6 ie
• so 60% interference