lecture 18

Question 1

describe paracentric inversion heterozygote

Answer 1

doesnt include centromere
cross over in loop - problem during meiosis
as long as did not affect important gene or regulatory region = then person with inversion is fine
crossing over in paracentric inversion hetero –> dicentric chrom = causes lots of problems
leads to deletions

Question 2

describe pericentric invasion heterozygote

Answer 2

Involves centromere
leads to duplications and deletions
inverted region = no chrom breaks
normal, duplicated a arm and deletion d arm, duplicated d arm and deletion a arm, inversion product
major duplications and deletions
crossing over in peri inversion hetero = products with major deletions

Question 3

what clinical consequences might you expect in an adult individual with a chromosomal inversion

Answer 3

real pairing problems with meiosis
heterozygotes = will have problem having kids
when making eggs or sperm= conception will not survive
at best = 50% of gametes viable, problem with conception = sign that chromosomal inversion
recomb does occur but not all chromatids participate - some of daughter cells will be normal

Question 4

describe Effect on frequency of recombinant progeny

Answer 4

ex from drosophila = wild type x homozygous for 2 recessive mutants
expect 45% recomb progeny from crossing over during meiosis 1 - should be single mutant, not double
much reduced tho = indication of inversion
the larger the inversion = greater the chance crossover will happen in between inversio
50% of gametes affect so affects result

Question 5

describe chromosomal translocations - gen

Answer 5

breaks
crossing over during meiosis
balanced translocation = no gain or loss of genetic material
repaired wrong = fused to another chrom

Question 6

describe chromosomal translocations - somatic consequences

Answer 6

balanced transolcation = balanced since all genetic materal all there, just connected diff

Question 7

What phenotype would you
predict for an individual with this translocation? - balanced translocation

Answer 7

as long as break points did not disrupt important haploinsufficient gene = few symtomps if any, usually only find out if having issues with fertility

Question 8

describe balanced translocations and meiosis

Answer 8

2 segregation patterns in reciprocal translocation heterozygote
Adjacent 1
= t1 and n2 n1 and t2 = both products incomplete = not viable
or
alternate
= n1 n2 and t1 t2 = viable = both products complete

Question 9

describe consequences of balanced translocations

Answer 9

robertsonian translocation
type of balanced translocation
smallest gene product lost during subsequent cell divisions
can involve any of the acrocentric chromosomes = 13,14, 15, 21 or 22 (only where centromere close to end of chrom)
freq = 1/1000 babies
pehnotype usually normal

Question 10

name 2 conclusions that you can draw from the observation that individuals with the robertsonian translation typically exhibit no detectable somatic symptoms

Answer 10

3 chrom since 1 lost = kinda like trisomy
break points did not disrupt important genes
lost infor doesnt contain any haploinsufficient genes - doesnt contain any genes where you need 2 copies of it

Question 11

describe A balanced Robertsonian translocation resulting in inheritance of trisomy 21 (Down’s Syndrome)

Answer 11

normal progenitor –> robertsonian translocation carrier –> meiotic pairing
segregation during meiosis –> 6 possible diff gametes

Question 12

describe some grape colour genetics

Answer 12

wild type – cabernet = purple grapes
loss of function allele – chardonay green grapes, colour due to pigment gene, related to alleles of pigment gene
partially functional allele = not enough for purple so pink, ruby okuyama

Question 13

describe transposable element insertions associated with changes in grape colour

Answer 13

Vymby1A GENE required for PRODUCTion of purple pigment in cabernet grapes
initial insertion of Gret1 LTR transposon = los of function in gene = loss of colour in fruit of chardonay variety
subsequent rearrangement in gret1 results in reverent coloured grapes in varietes such as ruby okuyama
LTRs flank gret1 just upstream of Vymby1A GENE

Question 14

describe A balanced Robertsonian translocation resulting in inheritance of trisomy 21 (Down’s Syndrome) - 6 diff possibilities

Answer 14

3 x chrom 21
down syndrome arising since translocation predisposing zygote to having trisomy

translocation carrier

normal - 2 copies of each

= regenerates 2 parental genotypes or karyotypes, both viable 

lethal

lethal

3x chromosome 14 = trisomy 14 - lethal

fertility issues = mainly lethal or down syndrome