Lecture 17 Flashcards
what occurs in Cri-du-Chat syndrome?
part of chromosome 5 is deleted and missing genes required for normal development
what do we know about the genes lost in Cri-du-Chat syndrome?
none are haplosufficient –> all are haploinsufficient
2 possible causes of chromosomal deletions
- breakage + rejoining at incorrect place
- crossing over btwn repetitive DNA
what occurs in williams syndrome?
always caused by 1.5 Mb deletion on one homolog of chromosome 7
how does the deletion of Williams Syndrome occur?
region of 17 genes is flanked by PMS sequences
when the repeats pair in the wrong place during crossover, creates 2 unequal products: 1 with deletion, 1 with duplication
3 ways to detect chromosome deletions
- observe length/pairing
- DNA analysis with genomic technique
- complementation test
how can we use chromosome pairing to detect deletions?
sequences line up and will form deletion loop
what does the complementation test show if you cross a tester chr with recessive mutations and a WT chr?
will see WT phenotype –> WT genes complement for the recessive mutations
what does the complementation test show if you cross a tester chr with recessive mutations and a chr with WT alleles but some deleted?
will mutants of deleted genes
how can we use known deletions to map a recessive mutant allele?
cross tester with diff chr with deletions –> can map where certain recessive alleles are
what are large duplications known as?
segmental duplications
what does the size of the duplicated part depend on?
depends on how far apart the repeated sequences are
since we can see a lot of segmental duplications in the human genome, what does this indicate?
since duplications are caused by misalignment of repetitive sequences during crossover, having more duplicated sequences indicates that there is more misalignment
how do duplications impact an individual vs evolution?
duplication may be bad for individual but good for evolution
2 types of chromosome inversions
- paracentric –> does NOT include centromere
- pericentric –> includes centromere
describe what happens to a PARACENTRIC-inversion heterozygote during meiosis
- crossover occurs in loop
- upon segregation in anaphase, forms dicentric chromosome and an acentric fragment that is lost
- breaks randomly btwn the 2 centromeres
- forms a normal product, 2 deletion products, and an inversion product
describe what happens to a PERICENTRIC-inversion heterozygote during meiosis
- crossover occurs in loop
- no dicentric chromosome bc pericentric, so no breaks involved
- forms 2 normal products (1 of each chr), 1 product with “a” duplication and “d” deletion, and 1 product with “d” duplication and “a” deletion
