Gametogenesis Flashcards
diffferences
When does gametogenesis occur?
the biological process by which diploid or haploid precursor cells undergo cell division and differentiation to form mature haploid gametes
oogenesis and spermogenesis
Female differences
1 ovum + 2 polar bodies from one primary oogonium cell
no new oocytes during lifetimes, so they accumulate damage
male differences
4 sperm from one primary spermatogonium cell
new sperm generated every 60 dayss
what are the two different types of chromosome anomalies?
With phenotypic effect
- numerical - usual
- structural - abnormal structure but right number of chromosomes
without phenotypic effect
- structural
numerical errors are casued by?
non disjunction - might loose or gain a chromosome
usually results in multiple malformations
risk increases with maternal age
what is trisomy 21? how do you write it?
trisomy 21 is an extra chromosome on 21, resulting in down syndrom
its written : 47,XX,+21
what is aneuploidy?
one chromosome pair has the wrong number
trisomy?
3 or one chromosome
severe, usually lethal effects
39,XX, +2 - mummufued piglet
61,XY,+? - stillborn calf
the ? represents an unidentified extra chromosome
what is klinefelter syndrome? how is it written?
a male with an extra X chromosome resulting in sterility and in small testes
61,XXY
high female hormones
what is monosomy
1 of one chromosome
severe, usually lethal effects early in gestation
59,XX,-15
What is Turner syndrome?
a female is missing an X chromosome (can occur in humans)
63, X0(mare with one missing X)
infertile = heart defects, normal intelligence levels, lives long
What happens if a male developes turner syndome?
its lethal and it dies
63, Y0 is not viable
when do abortions occur for chromosome anomalies?
- monosomies abort earliest
- trisomies may abort later
- aneuploids of larger chromosomes abort earlier
what is Mosaicism
a type of numerical error
more than one cell type effected - moderate abnormalities
60,XX/59,XX,-?
likely a mitotic error - mixture of cell types
what is a chimera
special type of mosiac more than 1 cell type derived from more than one individual
over 10% of abnormalities lead to a problem
freemartin (60,XX/60XY)
heifer is steril and male has low sperm count do to cell and hormone sharing through placenta
how common is chimeric twins?
99% in cattle
less then 10% in goats
few sheep
rare in dogs, humans (different placenta types)
wha is polyploidy?
multiple haploid sets:
- triploidy = 3 (pig embryos die, chickens and fish live, dispermy - heavy sperm thats less mobile
tetraploidy - 4 haploid sets
chickens die, cattle mosaics live
What are structural errors?
deletion, duplication and ring - rarely reported in animals becasue they are rarely studied
structural errors without phenotypic effects
translocation and inversion
What are indications of structural errors without phenotypic effects
subfertility:
- 25% reduction in litter size
- les that 10% of cows serviced by bull
- greater then 2 abortions (or late concentions)
What is a Robertsonian translocation?
2 acrocentric chromosomes fuse and the count is off by one (2n-1)
What is a reciprocal translocation?
2 chromosomes exchange pieces
number is unchanged (2n)
what is the most common robertsonian translocation in cattle?
t(1;29) - 10% in SOME continental breeds
or t(14;20) - which is extremely rare and usually only found in simmental
what breeds are manadory in testing for translocations
charolais and simmental
what countries require translocation testing
australia, brazil, england, new zeland, sweden
and some A.I companies
what are some implications of a robertsonian translocation
cull unbalanced
screen relatives
cull carriers
implications of reciprocal translocation
carrier will have low fertility (litter size)
may observe mummified piglets
serious if a boar
