LECTURE 22 LARGE-SCALE CHROMOSOME CHANGES II chapter 15 overview chromosome number chromosome...

LECTURE 22 LARGE-SCALE CHROMOSOME CHANGES II

chapter 15 overview chromosome number chromosome structure problems

CHANGES IN CHROMOSOME NUMBER

what are the genotypic & phenotypic probabilities in the progeny of a P cross A/A/A/a A/A/A/a? P gametes: P(A/A) = P(A/a) = ½, P(a/a) = 0 F1 genotypes: P(A/A/A/A) = (½)2 = ¼

P(A/A/A/a) = 2(½)2 = ½

P(A/A/a/a) = (½)2 = ¼

F1 phenotypes: all A A/A/a/a? A/a/a/a?

} work out these ones for next class

autopolyploids

3 classes of chromosome change

OVERVIEW

2 general questions to consider... is the genome complete?

is the genome balanced?

OVERVIEW

CHANGES IN CHROMOSOME STRUCTURE

implications chromosome structure mutations phenotypes

1. abnormal gene # segmental aneuploids 2. abnormal gene

environment position effect

3. break points disrupt gene function


things to keep in mind each chromatid is has a single DNA molecule need either...

2+ double strand breaks crossing over between repetative sequences

chromosome breakage ends highly reactive (normal telomeres not)

double strand breaks are lethal unless repaired repaired by joining broken ends


more things to keep in mind repair can restore original sequence or generate rearrangement acentric products are lost & inviable dicentric products are broken & inviable rearrangements can be

spontaneous induced by radiation... X- or -rays

mainly studied in heterozygotes


2 types of rearrangements1. unbalanced change gene dosage

deletions uncover deleterious alleles usually lethal

duplications extra material evolutionary divergence


2 types of rearrangements2. balanced change gene dosage

inversions reduced fertility reduced recombination in inverted region

translocations reorganizes linkage 50% sterility fertility novel linkage of genes on translocated

chromosomes


origins of rearrangements by 2 processes1. break / rejoining

spontaneous radiation


origins of rearrangements by 2 processes1. break / rejoining

spontaneous radiation

2. crossing over illegitimate


visualization in heterozygotes strong pairing affinity during meiotic prophase I abnormal patterns seen in rearrangement

heterozygotes (–/+)


biological importance research tools

new combinations of genes mapping recombination suppression mutant rescue

applied research medicine & agriculture evolutionary significance genome reshuffling


deletions 1 chromosome break terminal 2 chromosome break interstitial


deletions intragenic within 1 gene

do not revert ( point mutations) can be viable if gene not vital

multigenic > 1 gene do not revert usually homozygous lethal sometimes heterozygous lethal


deletions multigenic > 1 gene

uncovers recessive alleles on homologue pseudodominance deletion mapping



deletion mapping ~ linkage maps



deletion mapping ~ human disease, e.g.: cri du chat syndrome


duplications (2 chromosome breaks) adjacent, same order tandem adjacent, reverse order reverse


duplications intragenic within 1 gene

do not revert ( point mutations, see below) can be viable if genetic balance not critical

multigenic > 1 gene do not revert (see below) homozygous lethal if genetic balance critical can be heterozygous lethal if balance critical


duplications illegitimate recombination possible, e.g.: Bar


duplications important for gene evolution, e.g.: human

hemoglobin genes


inversions does not include centromere paracentric does include centromere pericentric


inversions does not include centromere paracentric

A B C D E F G H


inversions does not include centromere paracentric

A C B D E F G H


inversions does include centromere pericentric

A B C D E F G H


inversions does include centromere pericentric

A B F E D C G H


inversions no change in total genetic material breakpoints can (but not always) disrupt genes

no disruption viable homozygotes disruption heterozygotes only (majority)

do not revert recombination in inversion segm. aneuploidy

recombinant gametes lethal , fertility recombination suppression


inversions breakpoints between genes


inversions breakpoints between genes... disruption of 1

breakpoints within genes... gene fusion


inversions loops


inversions crossing over in a

paracentric inversion heterozygote



paracentric inversion heterozygote 1 normal viable 1 inversion viable 1 acentric lost 1 dicentric 2 lethal

deletion products



pericentric inversion heterozygote



pericentric inversion heterozygote 1 normal viable 1 duplication

lethal 1 deletion lethal 1 inversion viable


translocations (reciprocal or Robertsonian) no change in total genetic material do not revert meiosis segmental aneuploidy

lethality semi-sterility

rearrangement of linkage groups can restructure genomes


translocations heterozygotes

adjacent-1 4 lethal

adjacent-2 rare, 4 lethal

alternate 2 normal + 2 carrier


translocations pseudolinkage observed from test cross of

translocation heterozygote: a/; a+b+/b a/a; b/b


translocations position-effect variegation

PROBLEMS

#1-55 on pp. 512-520 consider (read & think about)

all of the questions at the very least you should do

#s 22, 23, 26, 40, 49

LECTURE 22 LARGE-SCALE CHROMOSOME CHANGES II chapter 15 overview chromosome number chromosome...

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