Chapter 8. Chromosomal structure

Bands 1.Heterochromatin 2.EuChromatin

-dna dyed; 1.condensed and dark; takes more stain 2.loose and light

Problems in chromosome structure: 4. translocations — balanced —unbalanced

-large pieces of dan move from one chromo to another 1. balanced: 2 chrom swap same portions of arm 2. unbalanced: uneven trade of portions of chromo;happen around centromere and end up with extra long chromosome ( 2 q arms) and fragment of chromosome(p arms)

Cytological analysis

-test for down syndrome (see if baby is going to be healthy)

Turner syndrome

1. (45,X):missign X chrom 2. clinical findings -short stature -ovarian dysfunction -broad chest -low posterior hairline -webbed neck -elbow anomalies -some cognitive delays -preterm loss: 95%

Problems in chromosome number: 1.Chromosome rearrangement DUPLICATION

1. (duplication): 2n=6 2.mutations that change the structures of individual chromosomes.

Chromosome staining: Banding 1. 2.

1. G-banding:areas of DNA that are rich in adenine-thymine (A-T) base parties 2.C-staining:centromere stain

Chromosomal aberrations vs phenotype:

1. aberrations change relative ratios of gene products; Example: can receive too much of one gene effecting phenotype:fish receiving too much b and developing spots instead of strips

Problems in chromosome structure: 1.Duplications — tandem duplication — displaced duplication

1. extra copies of genes 2. a mutation in which part of the chromosome has been doubled. 3.duplicated region is immediately adjacent to the original segment 4. the duplicated segment is located some distance from the original:either on same or different chromosome.

Trisomy 21 3. clinical findings

1. hypotonia: poor muscle tone -protruding tongue 2.congenital heart malformations( shorter lives) 65% loss 3. mental retardation 4. 47,XX,+21(number of chromosomes, sex, particular adnormation)=karyotype 5. down syndrome

Trisomy 18

1. major organ and musculoskeletal issues -<1 year of life expected (80%) -

Trisomy 21 1. spontaneous 2. familiar

1. nondisjunction, 3 copies at chrom 21 2. an indidvidual had a translocation, part of a chromosome is fused with another...phenotypical normal but off spring will have issues:one chromosome 21 the other somewhere else

Arms 1. P 2. q

1. petit/short on top 2. long on bottom

Problems in chromosome structure: 3. Inversions

1. two breaks in chromosome, broke section 180 flip and repairs resulting and genes going in opposite direction 2. these are less problematic unless break happens in middle of gene and then we have lose of function

Human Karyotype

1.46XX or 46XY 2. natural picture of all the chromosomes of a particular individual 3. organized from longest chrom(1) to shortest (22) then sex chromo

Triploidy

1.69,XXY -3 copies of every chromosome -not compatible with life, aborted in first semester (99+)

Centromere:constriction 1. 2. 3.

1.metacentric: P and Q arms same length:Centro mere is approximately in the middle. 2.sub-metacentric: P arm short and long Q arms 3.acrocentric: constricted area located at tips:long arm and a knob 4.telocentric:centromere is at the telomere

Statistics

1.pregancies:40-50% lost to chromosome aberations;don't even realize they were lost 2.newborns: -1/118 visible chrom.abs. -1/650 chrom translocation -1/700 down's syndrome 3.Gen. pop -3% is mentally retarded

Problems in chromosome number: 2. Aneuploidy

2. (trisomy): 2n+1=7 1. The gain of a single chromosome: a human trisomy would then have 47 chromosomes: the gain of a chromosome means there are 3 homologous copies of one chromosome 3.most cases of down syndrome result from this at chromo 21

Problems in chromosome structure: 2.Deletion

2. fewer copies 1.Segment of a chromo is deleted:chromo is noticeably shorter —Heterozygous for deletions chromo must loop out during pairing of chromosomes in prophase 1 of meiosis in order to allow everything to match up.

Problems in chromosome number: 3. polyploidy

3. autotriploid: 3n=9 1.presence of more than two two chromosomes

Intro: Building a better banana

Bananas are often polyploidy, with 3n,4n and higher. Many are tripled, AAA, AAB, ABB, BBB and some are even tetraploid(four sets of chromosomes)...AAAA etc. Bananas are cultivated, thus are identical genetically, this make sit hard for them to fight disease. In order to save the bananas and build a better one, they sequenced the DNA. The genome consists of over 500 million base pairs of DNA and encodes 36,500 protein encoding genes.

Aneuploidy and gametogenesis: 1. non-disjunction at M1 -reproductive issues

Chromosomes don't split during M1, end up with trisomic(down syndrome) and monosomic zygote(no compatible with life)

Aneuploidy and gametogenesis: 2. non-disjunction at M2 -reproductive issues

Chromosomes dont split during M2>end up with trisomic, monosomic(dead), 2 normal

Karyotype

Complete set of chromosomes possessed by an organism:is usually presented as a picture of metaphase chromosome lined up in descending order of their size.

Bar chromosome

in fruit fly -the more copies of a gene that you duplicate the more prominent the aberrated phenotype will be. -important for eye development -one extra chromo =bar eye -more than one copy ultra bar eye

Inversion loop

in prophase 1 of meiosis, the chromosomes form an inversion loop, which allows the homologous sequences to align

Chromosomal aberrations and cell division

normal chromosomes (N1&N2) line up with transverse (balanced) chromo (T1&T2)>try to line up>variety of things could happen:viable verses nonviable

Robertsonian translocation:

the long arms of two afrocentric chromo become joined to a common centromere: generating a metacentric chromo with 2 long arms and another with 2 very short arms