Chromosomal inheritance Flashcards
cytogenetics and somethings we can see within it
the study of chromosomes
-multiple malformations
-fertility problems
-phylogeny/evolution
-sexing animals
when does DNA get turned into chromosomes
after interphase it gets condensed into chromosomes in prophase I
how are chromosomes packed up
-DNA double helix
-DNA and histones
-chromatin fiber
-super coiled DNA
-chromosome
types of chromosomes
-depends on centromere placement
-telocentric (no P arm)
-acrocentric (small P arm)
-submetacentric (bigger p arm)
-metacentric (almost equal p and q arm
what are the part of the chromosome
-centromere
-p arm (short)
-q arm (long)
karyotype
-arranges by size (depending order b-s)
-numbered
-sex chromosomes last
-short arm up (p)
-autosomes
-grouped by centromere placement
-homologous chromosomes, same size, band patterns
how many chromosomes do pigs have
38
how many chromosomes to humans have
46
how many chromosomes do cows have
60
sexing birds
-now done with DNA typically
-many chromosomes
-6-9 pairs of macrochromosomes
(including sex chromosomes)
how many chromosomes do dogs have
78
how many chromosomes do horses have
64
chromosomes nonenclature
- total # of chromosomes
- sex
- special findings (e.g. + or -)
ie. 78, XX, (normal bitch)
65, XY, +15(abnormal colt fetus)
origin of chromosomal anomalies
-many chromosomal anomalies arise “de novo” during meiosis of one of the parents
-arise through mismatching of homologues during meiosis
-also can occur through an error in cell division
how do chromosomes divide
-mitosis
-meiosis
mitosis
-exact duplication of somatic cells
-DNA replicates
-chromatids separate
-results in 2 diploid cells
stages of mitosis
-interphase (DNA replicates)
-prophase (chromosomes become visible as extended double structures)
-metaphase (nucleus is replaced by the spindle, chromosomes become aligned on the equator)
-anaphase (chromosomes pairs split and move towards opposite poles
-telophase (chromosomes reach poles)
cytokinesis (nuclei reform; each daughter cells has complete set of chromosomes, one member of each pair derived from each parent
meiosis
-(reduction division-in gametes)
-meiosis I
-DNA replicates
-homologous pair (crossing over)
-chromosomes separate
-result in 2 haploid cells
-meiosis II
-chromatids separate
-result in 4 haploid gametes
meiosis I
Prophase I - chromosomes become visible
Metaphase I - bivalents align at the equator
Anaphase I - homolog pairs move to opposite poles
Telophase I - homolog pairs enter separate cells
meiosis II
Prophase II - chromosomes re-form
Metaphase II - homologs line up at equator
Anaphase II - homologs move to opposite poles
Telophase II - four gametes each have one copy of each
chromosome
when does meiosis occur
gametogenesis
gametogenesis
- a biological process by which diploid or haploid precursor cells undergo cell division and differentiation to form mature haploid gametes
- Oogenesis, spermatogenesis
▪ Timing is different depending on if female or
male
oogonum
immature egg cell
what does the oogonum turn into
-primary oocyte (2n)
-gains zona pellucida after puberty
-after meiosis I becomes secondary oocyte + polar body (1n)
-then because of fertilization meiosis II occurs and turns into zygote + second polar body (2n)
what happens to spermatogonium
-(2n) can become dormant for later division or active
-active undergoes mitosis
-16x (2n) primary spermatocytes
-meiosis I
- two (n) secondary spermatocytes
meiosis II
-four (n) spermatids
-turns into spermatozoa
what are the differences in gametogenesis
-female
-one ovum + two polar bodies form one primary oogonium cell
-male
-four sperm form one primary spermatogonium cell
-female
-no new oocytes during lifetime, so accumulate damage (initiated in fetus)
-males
-new sperm generated every 60 days
different types of chromosome anomalies
-with phenotypic effect: numerical, structural
-w/o phenotypic effect: structural
chromosome numerical errors
-called aneuploidy (loose or gain)
-cause is usually non disjunction
-usually results in multiple malformations
-risk increases with maternal age
non disjunctional
-chromosomes in egg do not separate properly during meiosis I or II
-either have too many chromosomes or too little in fertilized eggs
risks of downs and chromosomal mutations
-risk increases exponentially in humans at the age of 35 (less then 1 % before)
-cows after 9 years of age
incidence of chromosomal problems
-~30% of human conceptuses abort
-2.5-10% of “late” spontaneous abortions have chromosomal problems/causes
-assume a high proportion of early abortions have chromosomal problems
-live birth weights with major malformations
-many chromosomal
type of numerical errors
-aneuploidy
which includes:
-trisomy
-monosomy
-mosaicism
-chimera
aneuploidy
one chromosome pair has the wrong number (i.e. not 2)
trisomy
-3 of one chromosome
-severe, usually lethal effects
klinefelter syndrome
-sex chromosome aneuploidy
-61, XXY
-infertile
monosomy
-1 of one chromosome
-severe, usually lethal effects early in gestation
-59, XX, -15
turner syndrome
-sex chromosome aneuploidy
-63, X0 (mare with one X missing)
-infertile
-note if X is missing in a male, lethal (i.e 63, Y0 is not viable)
what are the deaths of the different types of numerical errors like
-monosomies abort earliest
-trisomies may abort later
-aneuploids of larger chromosomes abort earlier
-few survive to term
-usually the bigger the chromosome that is affected= abort earlier
mosaicism
-> 1 cell type
-moderate abmornalities
-60, XX/59, XX, -?
-likely a mitotic error
-some cells normal but not all
-if less then 10% of their cells have abnormal chromosome karyotype, individuals may not exhibit symptoms
chimera
-own karyotype plus other (twin)
-special type of mosaic
-> 1 cell type, derived from >1 individual
->10% of cells abnormal leads to problems
-60, XX/60, XY
-freemartin heifer is sterile and male co-twin has lower sperm count
placenta anastomosis
a cross connection between cotyledons
chimeric twins in different species
-~99% of cattle
-<10% of goats
-few sheep (who have the same kind of placenta)
-rare in dogs, humans, etc. none of who have this form of placenta
implications of a numerical error
-cull affected individual (but they aren’t viable)
-usually retain parents unless old
-recurrence risk ~1% if “young”
polyploidy
-triploidy
-tetraploidy
triploidy
-3 haploid sets
-fert egg becomes 3n
-dispermy?
tetraploidy
-4 haploid sets
-chickens die
-cattle mosaics live (also have normal cells)
types of chromosome anomalies with and with out phenotypic effects
with phenotypic effects:
-numerical
-structural
without phenotypic effects:
-structural
structural errors (with phenotypic effects)
-deletion
-duplication
-ring
(rarely reported in animals because rarely studied)
types of chromosomal structural errors (without phenotypic effect)
-translocation
-inversion
indications of structural errors with out phenotypic effect
-sub fertility
-25% reduced litter size
->10% of cows serviced by bull remain open
->2% spontaneous abortions
(or late conception in cows)
robertsonian translocation
-2 acrocentric chromosomes fuse
-count is off by one (2n-1)
reciprocal translocation
-2 chromosomes exchange pieces
-number is unchanged (2n)
what is the most common translocation in cattle
robertsonian translocation t(1;29)
-normal and balanced translocation=live calf
-trisomy 1, 29 and monosomy 1,29=aborted calf
where is translocation in cattle more commonly seen
10% in some continental breeds not common in british breeds
t(14;30)
extremely rare but seen in some simmintals
where is translocation testing mandatory in
some breeds:
-charolais
-simmental
some countries:
-australia
-brazil
-england
-newzeland
-sweden
some AI companies
implications of robertsonian translocation
-cull unbalanced bulls (usually lethal but in the case they arent)
-screen relatives if economic
-cull translocation carriers?
reciprocal translocation example
part of chromosome 7q exchanged with chromosome 11q
implications of reciprocal translocations
-translocation carrier will have low fertility (litter size)
-may observe mummified piglets
-serious if a boar
two kinds of translocations
reciprocal and robertsonian
phylogeny evolutionary relationship
-acrocentric= more primitive
-fusion of chromosomes=more recent
-results in increase metacentric chromosomes
-decrease in chromosome number
hybrid fertility
-if karyotype is different; both sexes are sterile,
(eg. horses have 64, donkey 62, mule 63)
-if karyotype is similar; only the heterogametic sex is sterile, increased embryo mortality
(eg. bison and domestic cattle, yak and domestic cattle)
dogs/wolf/coyote hybrids
-both sexes of canid hybrids are fertile
-species or subspecies
-canis lupus
-canis latrans
bos taurus and indicus hybrids
-both sexes oh hybrids are fertile
-species or sub species
-but when they are crosses with yak and bison (all have 60 chrmosomes) sterile male
