Packaged Instructions for Life. Chromosomes are packages of DNA wrapped with help of proteins called...

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