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Packaged Instructions for Life
Chromosomes
Chromosomes are packages of DNA wrapped with help of proteins called histonesComposed of two identical sister
chromatids attached at centromere
A.Structure
Each sister chromatid contains thousands of identical genes in the same locations on eachGene: segment of DNA that codes for
specific proteinsEx: hair color, eye color, lip shape, etc
Gene AGene BGene C
Gene DGene E
Each human somatic or body cell contains two copies of each chromosome23 sets of chromosomes x 2 = 46 total
(other species differ in numbers)Combination of all 23 is TOTAL DNA genome (3 billion base pairs)
One set (23rd) contains sex chromosomes X and/or YFemales have XX
Males have XY (Y is just shorter)
Females: XX
Males: XY
Two sets of chromosomes = diploid (somatic cells)
One set of chromosomes = haploid (gametes)Necessary since combination of
chromosomes from egg & sperm must be diploid to produce viable (able to live) offspringFertilized egg = zygote
= =
Diploids have same gene (eye color) but may have different variations (brown vs. blue eyes)called homologous chromatids (similar info)
One from mother, one from father
gene for eye color (mom’s brown eyes)
dad’s blue eyes
Map of all 23 sets of chromosomes from a body/somatic cell is called a karyotypeNumbered from 1 – 23 based on length,
location of centromere, and banding pattern
Typical Karyotype w/ 23 Chromosome Pairs
female
male
Karyotypes are usually only completed for cases where there might be a chromosomal abnormality Monosomy (missing homolog)Trisomy (Extra homolog)Incorrect sex chromosome numbers
Result of mistakes in gamete production (meiosis)Each gamete (sperm & egg) is
haploidDuplication of gamete can result in accidents causing 2 or more sets of specific chromosome (rather than necessary 1 set)
B. Chromosomal abnormalities
Down Syndrome Trisomy 21 (3 #21
chromosomes) resulting in mental retardation
1 in 1,300 at age 25 1 in 1,000 at age
30 1 in 400 at age
35 1 in 100 at age
40 1 in 35 at age 45
He was born with an extra #21
Edward SyndromeTrisomy 18 (3 #18
chromosomes) resulting in medical complications that usually result in 50% stillbirths & high mortality rate in general
1 in 5,000 births
Patau SyndromeTrisomy 13 (3
#13 chromosomes) resulting in cleft lip or palate, close-set eyes, severe mental retardation
1 in 16,000 births
Turner SyndromeFemales with monosomy
(missing) X (also shown as XO)
1 in 2,500 girls
Triple-X Syndrome Females with XXX (or XXXX or
XXXXX) No physical defects, some have
learning disabilities, tall stature 1 in 1,000 girls
Klinefelter SyndromeMales with XXY or XXXY
1 in 1,000 boysLow levels of testosterone, female-like features, infertile
Jacobs or Super Male Syndrome Males with XYY1 in 2000Mostly average, but excess acne,
very tall, slightly increased aggression
Breakage of entire chromosome, and sometimes reattachment can lead to four types of drastic mutations that may involve MANY genes:1. Deletion2. Duplication3. Inversion4. Translocation
Effects depend on number of genes involved and on which chromosome
C. Chromosomal mutations
ABC
FGH
ABCDE
FGH
DE
Segment of chromosome gets deleted (missing genes)
1. Deletion ABCDE
FGH
ABE
FGH
before
after
Cri-du-chat (cat cry) syndrome deletion on
chromosome 5children have a cat-
like, high-pitched cry during infancy
mental retardation and physical abnormalities
About 1 in 20,000 to 50,000 babies is born with this disorder
Deletion disorders
Allie Wallace, left, who is 5, and Katie Castillo, who is 20, both have "cri du chat" or cat cry syndrome, a rare genetic disorder that causes an array of mental and physical impairments.
Prader-Willi syndrome deletion on
chromosome 15mental retardation
or learning disabilities, behavioral problems and short stature
may develop extreme obesity
About 1 in 10,000 to 25,000 babies is affected.
22q11 deletion syndromeSpecific deletions on chromosome 22About 1 in 4,000 babies borndeletions cause a variety of problems
that can include heart defects, cleft lip/palate, immune system abnormalities, characteristic facial features and learning disabilities
Certain combinations of these features are sometimes called DiGeorge or velocardiofacial syndrome.
Individuals with this disorder have a 50-percent chance of passing the chromosomal abnormality on to their offspring with each pregnancy.
deletion on chromosome 4
characterized by mental retardation, heart defects, poor muscle tone, seizures and other problems
affects about 1 in 50,000 babies
Wolf-Hirschhorn syndrome
Segment of chromosome gets attached to normal chromosome, duplicating certain genes
2.Duplication ABCDE
FGH
before after
FGH
ABCDCDE
Charcot-Marie-Tooth disease Duplication on
chromosome 17destroys muscle tissue and
hinders the sense of touchbreaks down strong tissue
and cripples the hands & feet
one of the most common inherited neurological disorders, with 36 in 100,000 affected
Duplication disorders
The lack of muscle, high arch, and hammer toes are signs of the genetic disease.
Segment of chromosome gets broken off, then reattached upside down
3.Inversion ABCDE
FGH
before
ABDCE
FGH
after
Norrie DiseaseCauses blindness
and oftentimes hearing loss
Some mental retardation
On X chromosomeAll males affectedFemales affected only if occurs on both X (otherwise are carriers)
Inversion disorders
Segments of gene from one chromosome get broken off and reattached to a different chromosome
4. TranslocationABCDE
FGH
before
ABCDXYE
after
FGH
Many common disordersInfertility (13 to14)Schizophrenia (1
to 11)Certain leukemias
(1 to 12; 17 to 15)Certain sarcomas
(11 to 22)Certain
lymphomas (11 to 14; 5 to 1; 8 to 14)
Translocation disorders