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Genes located on chromosomes =
gene locus
Y chromosome determines
sex
SRY gene is expressed
-> testes develop
-> testosterone
-> male
If no SRY
female default pathway → ovaries
One X inactivated during embryonic
development →
Barr body (see nuclear
envelope)
how many Barr body in males
0
How many Barr body in female
1
Females are ____ for X-linked traits
mosaics
Chromosomal abnormalities
Can occur due to sperm or egg in meiosis
Non-disjunction
Meiotic spindle error
Sister chromatids do not disjoin in anaphase I or II
abnormal number of chromosomes
Aneuploidy
Monosomy
Turner syndrome
Only viable monosomy in humans
Trisomy 21
Down syndrome
Deletion
fragment lost
Duplication
repeated fragment
Translocation
fragment attaches to other chromosome
Inversion
fragment break → inverts
Non disjunction in meiosis can lead to
aneuploidy in offspring
Note 
Flashcard (33)