Origins of Genetic Variation Flashcards
Three origins of genetic variation?
Independent Assortment
Crossing Over
Random Fertilization
How tetrads land on the metaphase I plate =
Independent Assortment
Exchange of genetic material between non-sister chromatids
Crossing Over
One in 8 million chance?
Random Fertilization
Number over permeations possible in humans? Independent Assortment.
2 to the 23
Over 8 million permeations
This happens in Prophase I and includes recombination of DNA & exchange of DNA between non-sister chromatids.
Crossing Over!
Crossing over happens in…
Prophase I
First step of crossing over?
2 Homologous chromosomes align & synapsis
During synapsis…
All genes lined up & every gene perfectly aligned
This is thought to be the point where two homologous non-sister chromatids exchange genetic material during chromosomal crossover
Chiasma
Where the chormatids cross exists an ______/_____ ________ which will ___ each chromatid and _______ __.
Enzyme/Protein Complex
Cut
Reattach It
Typically there are this many crossover events on each homologous pair.
4-5
Once exchange happens ________ belong to the other & vice-versa.
Alleles
Random fertilization ratio?
1:64 trillion
Is random fertilization true in other species?
No - in species with promiscuous females there is a competition between soldier sperm!
Problems with Meiosis arise in what phase?
ANAPHASE - MI or MII
Seperation in Meiosis is called…
Disjunction
Abnormal seperation?
Non-disjunction
In non-disjunction the daughter cells can be:
N+1 or
N-1
When N+1 egg fertilizes with an N sperm we get a zygote with:
Trisomy! 3 Copies of 1 chromosome
T/F In humans, Trisomy conditions exist for every chromosome.
TRUE
Trisomy 21 =
Down Syndrome
T/F Trisomy can’t exist in sex chromosomes.
FALSE - Can
If we have a fertilization with an N-1 egg?
Monosomy
