Genes Patho Exam #4

sperm and egg

only one member of each chromosome pair

all other cells
46 chromosomes (23 pairs)

one donated by father and mother to each chromosome pair

22 of 23 pairs are identical in male and female

order of display of chromosomes

uncover possible abnormalities
predict certain traits (normal and abnormal
assess risks/ benefits

leading cause of mental retardation (MR) an miscarriage

normal number of chromosomes = 46

more than diploid number = over 46
liver, bronchial, and epithelial tissues

zygote has three copies instead of two
incompatible with postnatal survival

euploidy cells have 92 chromosomes
incompatible with postnatal survival

does not contain 23 chromosomes

three copies of one chromosome

one copy of chromosome

nondisjunction
failure of chromatid separation
autosomal = down syndrome; risk increases with age
1 in 500 males; 1 in 900 females

trisomy 21 (96%)
risk increases with maternal age
risk for Alzheimer's disease

monosomy 45, X
underdeveloped sex organs
short in stature
female genitalia
thick neck -- webbed neck
ovaries are underdeveloped
wide set nipples
thickened legs

47, XXY
karyotype
small testes - underdeveloped
excessive breast tissue
limbs are very long

broken chromosomes, one chromosome is there and one is missing

two of something, less serious than deletions

piece of genetic material gets flipped around

should be on one side but flipped to otherside

second most common cause of MR

chromatin fails to condense during mitosis
affects males>females

MR
long face, large mandible, large everted ears
hyperextensible joints, high-arched palate
mitral valve prolapse
macroorchidism (difficult reproduction)

gene composition

outward appearance

observable affects

hidden effectd

has diseases gene but phenotypically normal

delayed age of onset
penetrance and expressivity

males = females in transmission
no skipped generations
transmit to 1/2 their offspring

probability of disease is subsequent offspring

males = females
disease many be seen in siblings of affected individuals but usually not in parents

mating of related individuals

1/4 normal homozygous
1/2 carriers and phenotypically normal
1/4 homozygote with disease