lecture 17

Question 1

describe cri du chat syndrome

Answer 1

cry sound like chat
chromosome 5 - part missing
17 genes in deletion - one or more of the 17 genes required for normal development
one or more of the genes in the deleted region are haploinsufficient

Question 2

describe chromosomal deletions and their possible causes

Answer 2

letter = landmark along chromosome - shows scale maybe a gene or not
can be large or small
all involve. breaking and rejoining - repaired but wrong way, joins 1-4 together and 2-3 are lost - 2 broken ends that do not go together
crossing over between repetitive dna, happens when chrom paired in meiosis 1 =.crossing over, repetitive sequences paire so pairs withs wrong end

Question 3

describe chromosome deletions - williams syndrome

Answer 3

possible origin of williams syndrome
pms flanks 17 genes
during meiosis = unequal crossover = misalignment of repeated sequences
results in deletion on one chrom and duplication on other

Question 4

describe williams syndrome

Answer 4

found in 1 in 10000 ppl
individuals often have musical or singing ability and hypersociality
almost always caused by a 1.5mb deletion on one homolog of chrom 7 - specifically at band 7q11.23

Question 5

how to detect chromosomal deletions

Answer 5

direct = by observing length or pairing
karyotype
in situations where 2 homologous chroms must pair (meiosis, special tissue in drosophila salivary gland)
deletion loop observed, causes looping since cant pair
by doing complementation test
through dna analysis using genomic techniques

Question 6

describe concept of complementation test

Answer 6

see if strain 1 and strain 2 have mutations in same gene
if all comes out mutant = strain 1 and 2 have mutations in same gene (could be on diff places but same gene)
if complements = comes out wild type, strain 1 and 2 have mutations in diff genes - each parent could complement = provide wild type of that mutation so get unmutated phenotype
wild type x tester = tests for deletion or gene defect in parent
if chrom is mutated = get mutant gene for certain letters

Question 7

what can known deletions be used for

Answer 7

to map deletion
map a recessive mutant allele
= what gene causing duplication of flower petals - mutant, cross deletion = ask which of the deletions uncovers mutant pheno, helps understand where genome mutation located

Question 8

describe chromosomal rearrangements = duplications

Answer 8

Breakage and rejoining = loss (deletion), chrom break and misreapaired (deletion and duplication)
crossing over between repetitive dna = loss of misalignment and crossing over
large duplications called segmental duplications

Question 9

describe chromosomal duplications- map

Answer 9

map of segmental duplications in human genome
maps out duplicated regions - Williams syndrome = specific spot

Question 10

considering the profile of duplications in the genome and the mechanism for generating them what can you conclude

Answer 10

Misalignment of repetitive sequences find many duplicated sequences
homologous sequences can misalign and give duplications
the more duplicate sequences you have the more likely you are to have misalignment and the more likely to have misalignment = the more like to generate more duplications and deletions
can be a problem - lethal for individuals sometimes but also can give genetic diversity - evolution

Question 11

describe chromosomal rearrangements = inversions

Answer 11

1-3 and 2-4 repaired after broken randomly or by meiosis
then with the repair its flipped = paracentric and pericentric

Question 12

paracentric vs pericentric

Answer 12

para = does not include centromere
peri = includes centromere

Question 13

describe generating of chromosomal inversions

Answer 13

if b and c flipped = alignment inverted since still has directionality

Question 14

describe consequences of chromosomal inversions - somatic

Answer 14

breakpoints between genes = if not affecting regulatory regions = really no effect, wild type phenotype
one breakpoint between genes = inversion, loss of function gene, where breakpoint located = gene c disrupted
breakpoints in genes a and d = a d gene fusion of both genes =both could be mutant, could create new phenotype = oncogenic = tumours

Question 15

describe consequences of chromosomal inversions - germline

Answer 15

recomb occurs during meiosis 1 = pairing of homologous chroms and crossing over = influences what happens to inversion chromosomes during meiosis

Question 16

describe effects of chromosomal behaviour during meiosis

Answer 16

when lines up = makes inversion loop, to have it align properly
to line up with homologue
always happen when heterozygous inversion chrom

Question 17

describe paracentric inversion heterozygote

Answer 17

not included centromere
but consequence depends on what part inverted
crossover in loop = v bad when chromosome try to separate

Question 18

describe dicentric chromosome

Answer 18

crossing over in paracentric inversion heterozygote leads to dicentric chrom
2 chroms - parts connected that are not supposed to be

Question 19

what do paracentric inversions lead to and explain

Answer 19

leads to deletions
crossing over in paracentric inversion heterozygote –> dicentric chromosome –> breakage –> loss of acentric fragment and products with major deletions

centromere being pulled in 2 diff directions = where as normally woudlnt be
just breaks segment - gradually lost
leads to 1 normal, 2 deletion and 1 inversion product - size depends n where break occurs