Nondisjunction Alterations of Chromosomes Chapter 15 Section 4 Pgs Objective: I can predict how the number of chromosomes will change based off of errors that occur during meiosis.

Normal Meiosis Meiosis with Nondis- junction Normal Zygote: Fertilization: Abnormal Zygotes: Metaphase I Diploid 2n = 4 Anaphase I Disjunction (normal) Haploid Gametes n = 2 2n = 4 2n+1 2n -1

Types of Nondisjunctions “Standard” Meiosis I: Homologs fail to separate “Standard” Meiosis I: Homologs fail to separate Meiosis II: “Sister” chromatids fail to separate Meiosis II: “Sister” chromatids fail to separate *Note: sometimes, so much nondisjunction, it happens for EVERY homologous pair (vocab in 2 slides)

Mitosis “Nondisjuction” Both cells will die (if somatic) … Is this a problem? No! No further cells carry wrong # of chrms But, meiosis  gametes  zygotes…

Nondisjunction Vocabulary Aneuploidy (cell = aneuploid) Aneuploidy (cell = aneuploid) An abnormal number of chromosomes An abnormal number of chromosomes Trisomy (cell = trisomic) Trisomy (cell = trisomic) There are 3 chromosomes of ONE type (should be 2 of each type  diploid) There are 3 chromosomes of ONE type (should be 2 of each type  diploid) Monosomy (cell = monosomic) Monosomy (cell = monosomic) There is 1 chromosome of ONE type (should be 2 of each type  diploid) There is 1 chromosome of ONE type (should be 2 of each type  diploid) Polyploidy (cell = polyploid) (so much nondisjunction) Polyploidy (cell = polyploid) (so much nondisjunction) More than 2 of EACH and EVERY type More than 2 of EACH and EVERY type 3 of each type = triploid (3n); 4 of each type = tetraploid (4n) 3 of each type = triploid (3n); 4 of each type = tetraploid (4n)

karyotype

Autosomes Sex Chromosomes Female = XXMale = XY Fertilization!!! AFTER meiosis

Female = XXMale = XY Oogenesis (only 1 egg)Spermatogenesis (all) Size Difference

Female = XXMale = XY Doubled Chromosomes seen after S phase

Missing just 1 autosome (even though have homologue) is FATAL in humans This karyotype belongs to is an aneuploid (has aneuploidy) : 2n-1 (46-1) = 45 chrms. Monosomy #9 (monosomic) Always NEED to have two (2) chromosomes (one from each parent) for each type of chromosome (except for…) sex chromosomes

Turner’s Syndrome = XO a.k.a. Monosomy X 1/5000 births Develops externally as a sterile female Short stature, webbed neck, abnormal puberty Lower math, but most normal intelli. Only viable monosomy in humans

Monosomy Y = YO Zygote is not viable (will not survive) X chromosome is TOO important (has some “regular” traits on it, besides sex traits Can survive with one X chrmsm (normal males do it), but cannot survive without any X

Trisomy X = XXX 1/1000 births Develops externally as a female Taller than average, symptoms vary Tend to be mentally handicapped or retarded, but overall healthy

Klinefelter syndrome = XXY 1/2000 births Develops externally as a sterile male Even though extra X is inactivated… Testes abnormally smaller, breast enlarge a little, other female characters, and sometimes has diminished mental capacity

Down’s syndrome (Trisomy 21) 1/700 births Mentally handicapped Distinctive facial features Age-Dependent…

Polyploidy If Nondisjunction affects ALL chromosomes (not just one pair…) – ALL fail to separate… If Nondisjunction affects ALL chromosomes (not just one pair…) – ALL fail to separate… Offspring has more than 2 sets of chrm. Offspring has more than 2 sets of chrm. Could be a triploid (3n): 3 of each type Could be a triploid (3n): 3 of each type Could be a tetraploid (4n): 4 sets Could be a tetraploid (4n): 4 sets Remember: Diploid = 2n; Haploid = n Remember: Diploid = 2n; Haploid = n Occurs often in plants (end up larger) Occurs often in plants (end up larger) In humans, always fatal… In humans, always fatal… But found a tetraploid mammal recently But found a tetraploid mammal recently Changing ploidy (chrmsm #)  evolution (most species have different # of chrms.) Changing ploidy (chrmsm #)  evolution (most species have different # of chrms.)

Summarizing Nondisjunction Nondisjunction – failure of chromsomes to separate correctly If gamete resulting from nondisjunction fertilizes/gets fertilized to form zygote… Can be monosomic: lost a chromsm. (always fatal in humans except for sex chrms: but must have at least 1 X) Can be trisomic: gain a chromsm. – NOT fatal depending on which (small) chrms, but moderate to severe defects Nondisjunction can happen in mitosis, too! 13, 15, 18, 21, 22

Chromosomal Mutations Normally, may have crossing over (random) Normally, may have crossing over (random) Exchange of equal amounts of DNA Exchange of equal amounts of DNA But, if amount broken off does not equal (reciprocate) amount received, chromosome is altered (also if exchange with non-homolog) But, if amount broken off does not equal (reciprocate) amount received, chromosome is altered (also if exchange with non-homolog) Normal Crossing Over Chromosomal Mutation due to Abnormal Crossing Over

Types of Chromosomal Mutations Deletion and Duplication go hand in hand with sister chromatids crossing over… Deletion and Duplication go hand in hand with sister chromatids crossing over… Crossing over SUPPOSED to be with non- sister chromatids (between homologs)… Crossing over SUPPOSED to be with non- sister chromatids (between homologs)… Deletions often lethal (missing gene) Deletions often lethal (missing gene) Duplications can be harmful (i.e. trisomy) Duplications can be harmful (i.e. trisomy)

Types of Chromosomal Mutations Inversion is a flip: Inversion is a flip: Attempt at crossing over, fail, then try to reattach to same chrmsm but in wrong way Attempt at crossing over, fail, then try to reattach to same chrmsm but in wrong way Translocation is a jump: Translocation is a jump: Crossing over with non-homologous chr. Crossing over with non-homologous chr. Don’t seem bad, but… (neighbors affect…) Don’t seem bad, but… (neighbors affect…)

Human Chromosomal Mutations (examples) Cri du chat Syndrome (“cry of the cat”) Cri du chat Syndrome (“cry of the cat”) Specific deletion on Chrms. #5 Specific deletion on Chrms. #5 Mentally retarded, small head, unusual face, cry sounds like mew, usually dies in childhood Mentally retarded, small head, unusual face, cry sounds like mew, usually dies in childhood Chronic Myelogenous Leukemia (CML) Chronic Myelogenous Leukemia (CML) Reciprocal translocation Reciprocal translocation Take large portion of Chrms. #22 and replace with tip of Chrms. #9 Take large portion of Chrms. #22 and replace with tip of Chrms. #9 Chrms. #22 shortened  called a Philadelphia chromosome  cancer Chrms. #22 shortened  called a Philadelphia chromosome  cancer

Cri du chat Syndrome (“cry of the cat”) Chronic Myelogenous Leukemia (CML) Chronic Myelogenous Leukemia (CML)