1. Sex Determination & Nondisjunction Disorders
April 24, 2017

2. Karyotype Human Karyotype:
46 chromosomes organized in 23 pairs in order of decreasing size
Pairs # 1-22:
autosomes
somatic (body) chromosomes
all 22 pairs are homologous
Pair # 23:
sex chromosomes
contain genes that code for sexual characteristics
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3. Female Karyotype XX homologous pair 2 sets of genes for every trait
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4. Sex Chromosomes XY not homologous (no pair)
each one contains different genes
males only have 1 copy of genes on X & Y chromosome
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5. Sex Determination X X X Y
meiosis X Y X X
eggs
sperm X X X Y
Who determines the gender of offspring in humans?
all eggs carry one X chromosome
½ of sperm carry one X chromosomes
½ of sperm carry one Y chromosomes
Therefore:
male determines the gender
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6. Nondisjunction Disorders
anaphase I
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7. Nondisjunction Disorders
one pair of homologous chromosome doesn’t separate during anaphase I
Result:
½ gametes have one chromosome too few
other ½ gametes have one chromosome too many
in females, nondisjunction occurs more often if
>35 years old
missing one chromosome
one extra chromosome
April 24, 2017

8. Nondisjunction Disorders
amniocentesis :
recommended for all women over 35 years old
fetal cells removed with a needle from amniotic fluid
karyotype of fetal cells examined for nondisjunction disorders
April 24, 2017

9. Chromosomal Abnormalities
occur when a normal gamete (n = ___)joins with a gamete that has:
n + 1:
individual will have ______________________
n - 1:
in either case the resulting individual will suffer from some disabilities depending on which chromosomes are involved 23
(24) 47
(1 chromosome too many)
(22) 45
(1 chromosome less)
April 24, 2017

10. Nondisjunction Disorders
Common Examples:
Down Syndrome trisomy 21
Klinefelter’s syndrome XXY
Turner’s syndrome X0 monosomy
Trisomic female (super female) XXX
Jacob’s syndrome (super male) XYY
(47)
male
(47)
female
(45)
(47)
(47)
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11. Chromosomal Abnormalities
Down Syndrome
trisomy 21
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12. Chromosomal Abnormalities
Down Syndrome
developmental delays
physical abnormalities
short
folds around eyes
stubby fingers & toes
large protruding tongue
weak muscles
heart defects
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13. Chromosomal Abnormalities
Klinefelter’s syndrome
XXY
male
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14. Chromosomal Abnormalities
Klinefelter’s syndrome
tall
small testicles
after puberty develop some feminine traits (ex. breasts)
sterile
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15. Chromosomal Abnormalities
Trisomic Female
XXX
super female
have very few problems
most are fertile
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16. Chromosomal Abnormalities
Turner’s syndrome XO
female
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17. Chromosomal Abnormalities
Turner’s syndrome
short
thick neck
never goes through puberty
sterile
15 year old
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18. Chromosomal Abnormalities
Jacob’s syndrome
XYY
super male
very tall
low mental ability
often aggressive
April 24, 2017

19. FUN QUIZ Fill out the Atypical Meiosis Sheet 7 min
Switch with the person behind you
1 mark for every fill in the blank correct
Total in top right hand corner
Hand in to me!
April 24, 2017

20. Homework
Karyotype Assignment
April 24, 2017