Gametogenesis

Question 1

When does gametogenesis occur?

Answer 1

the biological process by which diploid or haploid precursor cells undergo cell division and differentiation to form mature haploid gametes
oogenesis and spermogenesis

Question 2

Female differences

Answer 2

1 ovum + 2 polar bodies from one primary oogonium cell
no new oocytes during lifetimes, so they accumulate damage

Question 3

male differences

Answer 3

4 sperm from one primary spermatogonium cell
new sperm generated every 60 dayss

Question 4

what are the two different types of chromosome anomalies?

Answer 4

With phenotypic effect
- numerical - usual
- structural - abnormal structure but right number of chromosomes
without phenotypic effect
- structural

Question 5

numerical errors are casued by?

Answer 5

non disjunction - might loose or gain a chromosome
usually results in multiple malformations
risk increases with maternal age

Question 6

what is trisomy 21? how do you write it?

Answer 6

trisomy 21 is an extra chromosome on 21, resulting in down syndrom
its written : 47,XX,+21

Question 7

what is aneuploidy?

Answer 7

one chromosome pair has the wrong number

Question 8

trisomy?

Answer 8

3 or one chromosome
severe, usually lethal effects
39,XX, +2 - mummufued piglet
61,XY,+? - stillborn calf
the ? represents an unidentified extra chromosome

Question 9

what is klinefelter syndrome? how is it written?

Answer 9

a male with an extra X chromosome resulting in sterility and in small testes
61,XXY
high female hormones

Question 10

what is monosomy

Answer 10

1 of one chromosome
severe, usually lethal effects early in gestation
59,XX,-15

Question 11

What is Turner syndrome?

Answer 11

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

Question 12

What happens if a male developes turner syndome?

Answer 12

its lethal and it dies
63, Y0 is not viable

Question 13

when do abortions occur for chromosome anomalies?

Answer 13

• monosomies abort earliest
• trisomies may abort later
• aneuploids of larger chromosomes abort earlier

Question 14

what is Mosaicism

Answer 14

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

Question 15

what is a chimera

Answer 15

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

Question 16

how common is chimeric twins?

Answer 16

99% in cattle
less then 10% in goats
few sheep
rare in dogs, humans (different placenta types)

Question 17

wha is polyploidy?

Answer 17

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

Question 18

What are structural errors?

Answer 18

deletion, duplication and ring - rarely reported in animals becasue they are rarely studied

Question 19

structural errors without phenotypic effects

Answer 19

translocation and inversion

Question 20

What are indications of structural errors without phenotypic effects

Answer 20

subfertility:
- 25% reduction in litter size
- les that 10% of cows serviced by bull
- greater then 2 abortions (or late concentions)

Question 21

What is a Robertsonian translocation?

Answer 21

2 acrocentric chromosomes fuse and the count is off by one (2n-1)

Question 22

What is a reciprocal translocation?

Answer 22

2 chromosomes exchange pieces
number is unchanged (2n)

Question 23

what is the most common robertsonian translocation in cattle?

Answer 23

t(1;29) - 10% in SOME continental breeds
or t(14;20) - which is extremely rare and usually only found in simmental

Question 24

what breeds are manadory in testing for translocations

Answer 24

charolais and simmental

Question 25

what countries require translocation testing

Answer 25

australia, brazil, england, new zeland, sweden
and some A.I companies

Question 26

what are some implications of a robertsonian translocation

Answer 26

cull unbalanced
screen relatives
cull carriers

Question 27

implications of reciprocal translocation

Answer 27

carrier will have low fertility (litter size)
may observe mummified piglets
serious if a boar