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Genetics
• Conception: ovum and sperm fuse to create
zygote
• Chromosomes: contain all biologically
inherited information (DNA)
• Ovum: 23 chromosomes (mom’s
contribution)
• Sperm: 23 chromosomes (dad’s
contribution)
Zygote
• 46 chromosomes (23 pairs: 23 from mom
and 23 from dad)
• 22 pairs are called autosomes
• 23rd pair contain the sex chromosomes
Karotype
Mitosis
• Cell division resulting in new diploid cells
(46 chromosomes)
• Chromosomes replicate, then split into two
diploid cells
Mitosis
Body Cell
46
Chromosomes
Daughter Cell
46
Chromosomes
Daughter Cell
46
Chromosomes
Meiosis
• Cell division resulting in haploid (23
chromosomes) cells
• Creation of gametes (sex cells: ovum and
sperm)
Meiosis
Germ Cell
46
Chromosomes
Gamete
23
Chromosomes
Gamete
23
Chromosomes
Polygenic Inheritance
• Affected by many genes rather than by a
single pair.
Sex-linked Chromosomal
Abnormalities
•
•
•
•
•
Kleinfelter’s syndrome: XXY
XYY syndrome
Fragile X
XXX
Turner’s syndrome
Non Sex-linked Chromosomal
Abnormalities
• Down Syndrome (Trisomy 21)
– Translocation trisomy
– Mosaicism
– Nondisjunction during meiosis
Down
Syndrome
Simian Crease
Maternal Age – Chromosomal
Abnormalities
•
•
•
•
•
•
•
Age
20
25
30
35
40
45
Trisomy 21 rate
1/1667
1/1250
1/952
1/378
1/106
1/30
Other chromosomal rate
1/526
1/476
1/385
1/192
1/66
1/21
Genetic Disorders
•
•
•
•
TaySachs (autosomal recessive)
Cystic Fibrosis (autosomal recessive)
Phenylketonuria (PKU) (recessive)
Muscular Dystrophy (dominant)