Lecture 10 + 11 (12) Flashcards
(48 cards)
What is the Position effect?
Due to translocations gene expression may come under the control of different regulatory sequences
Neurofibromatosis is…
How was it mapped
- genetic disease with numerous fibrous tumours of the skin and nervous system
- was mapped using translocation break points
Abnormal meiotic configurations can result from
Tranlocations
Translocations involve the movement of genetic material between…
nonhomologous chromosomes and within the same chromosome
What are the 2 types of translocations
reciprocal and nonreciprocal
how does genetic material move in Nonreciprocal translocation
genetic material moves from 1 chromosome to another without any reciprocal exchange
Translocation in meiosis __% of gametes of the segregation pattern are viable
50%
What are the 3 types of segregation patterns resulting from translocation in meiosis, and what one(s) produce viable gametes
-these are reciprocal or nonreciprocal translocations
-alternate segregation = viable gametes
-adjacent 1 (horizontal) = non viable
-adjacent 2 (vertical) RARE = non viable
are reciprocal translocations
A heterozygote with a reciprocal translocation has 1 or both normal and or translocated chromosome
1 normal and 1 translocated chromosome
What happens to the recombinants when a translocation heterozygote is testcrossed?
Why is this?
- the recombinants do NOT survive
- they carry unbalanced genomes (duplications and deletions make them nonviable)
In a translocation heterozygote testcross what are the viable progeny
progeny with parental genotypes only
Genes on translocated chromosomes (that are normally on seperate homologous chromosomes) act as though they are linked, what is this called?
Pseudolinkage
What happens in a Robertsonian translocation (x3)
-the short arm of 1 acrocentric chromosome is exchanged with the long arm of another
-Generates 2 metacentric chromosomes, 1 with 2 long arms and 1 with 2 short arms
-the short arm often fails to segregate and is lost
(see pic)
Translocation of chromosome 21 (x2) = Familial Down Syndrome
- The long arm of chromosome 21 is attached to the chromosome 14
- The carrier is phenotypically normal but is at risk of producing Down’s syndrome children
- 4% of ppl with down syndrome have this translocation familial type
Of these what ones are aborted and what one(s) result in down syndrome? Trisomy 21 Trisomy 14 monosomy 21 monosomy 12
Trisomy 21 = Down Syndrome
Trisomy 14 = aborted
monosomy 21 = aborted
monosomy 12 = aborted
Chimps, gorillas and orangutan have 48 chromosomes and humans have 46 , what casued this difference
Translocation and loss of a chromosome
What is special about Chromosome 2 (in humans) (x3)
- is a large metacentric chromosome
- G-banding patterns
- this matches the banding patterns found on 2 acrocentric chromosomes in apes
Colchicine (x2)
Inhibits spindle formation
makes polyploid plants
Meiotic paring in autotriploid results in
Trivalent OR Bivalent+Univalent
In autopolyploidy mutations can occur with/without mutations
with out
Bread =
cotton =
banana =
Bread = allopolyploid cotton = allopolyploid banana = autopolyploid
non-disjunction
failure of homologous chromosomes to separate in mitosis or meiosis
non-disjunction is the most common cause of _____ in meiosis and mitosis, but _____ is more common
Aneuploidy
meiosis is more common
Without _____ nondisjunction at meiosis 1 increases
crossing over
