Chromosomal mutations Flashcards
Chromosomal mutations
Entire chromosomes extra/ missing(aneuploidy)
Pieces of chromosome missing or moved onto a different chromosome.
how are chromosomal mutations identified
Identified by Karyotypes
nondisjunction
how chromosomes go missing. It is the failure to undo the joining of either homologous chromosomes or sister chromatids
non disjunction in homologous chromosomes
happens in meiosis 1
in meiosis 2 one cell has 3 separated homologous chromosomes and the other has one. ends up making 2 gametes with n+1 and 2 gametes with n-1
nondisjunction in sister chromatids
happens in meiosis 2
sister chromatids don’t split in one cell, so forms 1 gamete with n+1, 1 gamete with n-1, and 2 normal n gametes
nondisjunction is the leading cause of
pregnancy loss and birth defects.
90% of chromosome 21 nondisjunction are due to
to maternal meiotic errors
homologous chromosomes are arrested in prophase I for
10 to 50 years
what age are moms at the highest risk for chromosomal mutations
40 and older. The older the mom is the higher the risk
autosomal non disjunction
too many or too few autosomes
nearly always fatal (miscarriages)
what are the three exceptions to autosomal non disjunction
1) Trisomy 18 – Edwards syndrome
2) Trisomy 13 - Patau syndrome
3) Trisomy 21 – Down syndrome
Trisomy 18
Edwards syndrome
3 copies of chromosome 18
Half of infants with this condition do not survive beyond the first week of life.
Small head (microcephaly)
Can children survive with trisomy 18/ Edwards syndrome
Some children have survived to the teenage years, but with serious medical and developmental problems.
trisomy 13
Patau syndrome
most children with trisomy 13 die in the first year
small head(microcephaly)
trisomy 21
down syndrome most common cause of human birth defects Down syndrome varies from mild to severe Most are cognitively impaired Adults may live semi-independently
Sex Chromosome Non-disjuction
At least one X chromosome is needed to live!!
Females who are XXX are fine
Males who are Xyy are fine
y alone
will not survive
x alone
gives turner syndrome
XXy gives
kleinfelters syndrome
Turner syndrome
monosomy- only X
girls with: short stature, poorly developed ovaries
Turner syndrome treated with
growth hormones, female hormones like estrogen
Kleinfelter’s syndrome
XXy
men with low testosterone levels and infertility
treated with hormone replacement therapy
why can we survive with an extra x or y
Dosage Compensation Theory: both females and males receive the same dosage of X. one X is inactivated, turns into Barr body
Mechanism of X inactivation
In each embryonic cell the 2 X C pair up
Then one of them activates its XIST gene
XIST gene products (RNA) wrap up & inactivate that X C
Which X is inactivated is random in each cell
Occurs in morula stage of
Embryo (ball of 2-16 cells)
Mosaic tissues
somatic tissues are mosaic
patches of cells have different X chromosomes activated. Ex: calico cats and sweat glands
how boys become boys
SRY regulatory proteins activate genes that cause baby to develop into a boy
Absence of these …baby develops into girl
2 month old embryos=
generic gonads
SRY gene activation
make regulatory proteins
Sex determining Region of the Y chromosome
Deletion
1) Deletion: lost section of C
Inversion
2) Inversion: section of C flipped end for end
Translocation
3) Translocation: section of C moved to new C
Duplication
4) wDuplication: section of C moves to sister C…one chromatid has 2 copies the other none
Inversion
2) Inversion: section of C flipped end for end
Translocation
3) Translocation: section of C moved to new C
Duplication
4) wDuplication: section of C moves to sister C…one chromatid has 2 copies the other none
