Sex Determination

• 46 Chromosomes per cell
• 44 (22 pairs) Autosomes è don’t directly effect gender
• 2 (1 pair) Sex Chromosomes

Gametes

• 23 Chromosomes per cell
• 22 Automsomes
• 1 Sex Chromosome

X= Female Chromosome Y= Male Chromosome

Female = XX Male= XY

The male chromosome determines sex of offspring in humans because the mother donates the X chromosome.

X X If the male donates: y= male; x= female.

X XX XX

Y XY XY

Birth ratio: 106X :100C

• Y chromosome is somewhat smaller and lighter in weight than the X chromosome.
• Y sperm is lighter and faster than the X sperm.
• More Y sperm will reach the egg than X sperm.
• There is a somewhat greater chance (106:100) that the Y sperm will fertilize the egg.

1. Fraternal twins- 2 eggs present, each of which is fertilized by its own sperm.
2. Identical twins- 1 egg fertilized by 1 sperm. The zygote (fertilized egg) divides.

1. Siamese twins- identical twins born from a zygote that did not separate completely

Variations in Sex Chromosomes

1. XO- X - Turner’s Syndrome- 45 chromosomes per somatic cell (44 autosomes, 1 sex chromosome), "O" stands for absence of 1 sex chromosome, sexually immature, falps run down from the ear areas to the upper shoulders.
2. XXY- C - Kleinfelter’s Syndrome- 47 chromosomes per somatic cell (44 autosomes, 3 sex chromosomes), sterile- don’t develop at puberty, sexually immature.
3. XXX- C - Superfemale- 47 chromosomes per somatic cell (44 autosomes, 3 sex chromosomes).
4. XYY- X - Supermale- 47 chromosomes per somatic cell (44 autosomes, 3 sex chromosomes), tall, more aggressive.

Gamete Formation (normal) THIS GOT ALL SCREWED UP JUST LEAVE IT

Replication (46 XX) (23 X)~~~~Y sperm

Primitive Sex Cell- can’t (46 YY) (23 Y)~~~~Y sperm

take part in fertilization; (23 Y)~~~~Y sperm

takes part in a series of changes.

Gamete Formation (abnormal) THIS GOT ALL SCREWED UP JUST LEAVE IT

Replication (46 XX) (22)~~~~Sperm

(46 XY) (92 XXYY) (24 XX)~~~~Sperm

Primitive sex cell (46 YY) (22)~~~~Sperm

(24 YY)~~~~Sperm

Non-Disjunction- failure of chromosomes to separate during gamete formation. (Not restricted to sex chromosomes; can happen in autosomes as well).

Turner’s Syndrome: (24)~~~~ + (23 X)= 45 XO

Supermale: (24 XY)~~~~ + (23 X)= 47 XYY

Kleinfelter’s Syndrome: (23 Y)~~~~ + (24 XX)= 47 XXY

Autosomal Non-Disjunction

Trisomy 21 / Down’s Syndrome (Mongolism)- 47 Chromosomes per somatic cell (45 Autosomes- extra 21^st autosome, 2 sex chromosomes), frequency of the disease is directly tied in with maternal age, mental retardation, birth defects, simian crease, overweight, short, tongue protrudes, shortened life span, poor coordination, "Oriental" appearance.

Amniocentesis- a technique in which a sample of amniotic fluid (and embryonic cells) are extracted and analyzed for defects. The embryonic cells are cultured (grown) in a laboratory and are examined under a microscope with the aim of seeing cell division. Only visible during cell division. Cells are photographed during cell division.

"Water break"- leakage of the amniotic fluid out of the amniotic sac.

Karyotype- a photograph of the chromosomes arranged in pairs.

Sex Linkage- traits whose genes are located on the X chromosome only. There are no alleles for these traits on the Y.

Somatic Cell- 44 autosomes è homologous

2 sex cells è non homologous

Color Blindness

C= normal color vision

c= color blindness

C : CC- normal X : CY

Cc- normal (carrier) cY

cc- colorblind in any sex-linked trait males get recessive more.

CY (normal) x Cc (carrier)

C c

C CC Cc {C

Y CY cY {X

25% Colorblind

50% sons – colorblind

cY x CC

C X

c Y

C Cc CY

C Cc CY

100% Carriers

• The inability of blood to clot.

C : HH- normal X :Hy

Hh- normal (carrier) hy

hh- hemophilia

• Very rare; mostly in males
• h- can’t produce Factor VII (a chemical that causes blood clotting).
• Known as the "royal disease" in England.

Environment and Heredity

1. Green color in plants

• Light is needed to activate the dominant gene.

1. Baldness in humans

• Testosterone is needed to activate the dominant gene.

1. Intelligence in humans