Chromosomes Chromosomes andand

KaryotypesKaryotypes

Review of Review of ChromosomesChromosomes

Super Super coiled DNAcoiled DNA

Structure: Structure: It may beIt may be– A single A single

coiled DNA coiled DNA moleculemolecule

ChromosomesChromosomes

– Or after replication, it Or after replication, it may be two coiled may be two coiled DNA molecules held DNA molecules held together at the center.together at the center.

The area it is held The area it is held together is called the together is called the “centromere.”“centromere.”

Chromatid: Each DNA Chromatid: Each DNA molecule in a double molecule in a double stranded chromosome stranded chromosome (therefore, each (therefore, each replicated chromosome replicated chromosome has 2 chromatids).has 2 chromatids).

ChromosomesChromosomes

Humans have 46 chromosomesHumans have 46 chromosomes– 23 chromosomes from Mom23 chromosomes from Mom– 23 chromosomes from Dad23 chromosomes from Dad

Two Types of Two Types of Chromosomes:Chromosomes:

1. Autosomes1. Autosomes ALL chromosomes except the sex ALL chromosomes except the sex

chromosomeschromosomes 22 pairs (Chromosomes #1-22)22 pairs (Chromosomes #1-22)

Two Types of Two Types of Chromosomes:Chromosomes:

2. Sex Chromosomes:2. Sex Chromosomes: 1 pair (human chromosome #23)1 pair (human chromosome #23) Determine the sex of an organismDetermine the sex of an organism

– In mammals & fruit flies XX is female, XY is maleIn mammals & fruit flies XX is female, XY is male

– In birds In birds ZZ ZZ is male, is male, ZWZW female female *FIX IN NOTE TEMPLATE*FIX IN NOTE TEMPLATE

Female Male

Two Types of CellsTwo Types of Cells

1.1. Somatic Cells: Somatic Cells: • All cells of the body All cells of the body

2.2. Sex Cells:Sex Cells:• Egg and SpermEgg and Sperm

1. Somatic Cells: 1. Somatic Cells:

Chromosomes are Homologues:Chromosomes are Homologues:

““Homo” means same.Homo” means same.– Homologous chromosomes are the same size and Homologous chromosomes are the same size and

shape, and carry genes for the same traits.shape, and carry genes for the same traits.– Called a “homologous pair”Called a “homologous pair”

Homologous Homologous ChromosomesChromosomes

Humans have 23 homologous pairs in Humans have 23 homologous pairs in all cells except sex cellsall cells except sex cells– Cells with 23 homologous pairs care called Cells with 23 homologous pairs care called

““DIDIPLOID” or PLOID” or 2N2N N stands for number of unique chromosomesN stands for number of unique chromosomes Cells with 23 homologous pairs are called Cells with 23 homologous pairs are called

“somatic cells”“somatic cells” In humans, all cells except sperm and egg are In humans, all cells except sperm and egg are

somatic cellssomatic cells

2. Sex cells (sperm 2. Sex cells (sperm and egg)and egg)– only have one of each chromosomeonly have one of each chromosome

– No homologous pairsNo homologous pairs

– Called “Called “HAPLOIDHAPLOID” or ” or NN (think “half”) (think “half”)

– Sex Cells are called “Sex Cells are called “GAMETESGAMETES.” .”

KaryotypesKaryotypes

A picture of the A picture of the chromosomes chromosomes in which the in which the chromosomes chromosomes arranged in arranged in matching matching (homologous) (homologous) pairspairs

KaryotypesKaryotypes

– Arranged in Arranged in size order from size order from largest pair to largest pair to smallest pairsmallest pair

– The sex The sex chromosomes chromosomes (X and Y) are (X and Y) are usually the last usually the last pair, though pair, though they are not they are not the smallest.the smallest.

KaryotypesKaryotypes

How are they used?How are they used?

– They are used for diagnosis of They are used for diagnosis of genetic abnormality based on the genetic abnormality based on the number of chromosomes.number of chromosomes.

– They are used to determine the sex They are used to determine the sex of an unborn child.of an unborn child.

Karyotypes Karyotypes

How are they How are they prepared?prepared?– Cells are Cells are

collected from a collected from a variety of variety of sources:sources:

Amniotic fluid via Amniotic fluid via a pre-natal a pre-natal “amniocentesis”“amniocentesis”

Blood SampleBlood Sample

Karyotypes Karyotypes

How are they How are they prepared?prepared?– Sample of cells Sample of cells

are allowed to are allowed to continue dividingcontinue dividing

– Cells are stopped Cells are stopped when in when in METAPHASE of METAPHASE of MITOSIS.MITOSIS.

Karyotypes Karyotypes

A photograph of the A photograph of the chromosomes is chromosomes is taken and enlarged.taken and enlarged.

A trained technician A trained technician matches the matches the chromosomes into chromosomes into the homologous the homologous pairs based on three pairs based on three characteristics:characteristics:– SizeSize– BandingBanding– Centromere positionCentromere position

Chromosomal Chromosomal DisordersDisorders Normal: Normal:

– Have 2 matching chromosomes for Have 2 matching chromosomes for each of the 23 pairseach of the 23 pairs

Aneuploidy: Aneuploidy: – Having one more or one less of one Having one more or one less of one

of the chromosomes of the 23 pairs.of the chromosomes of the 23 pairs.

Chromosomal Chromosomal DisordersDisorders MonosomyMonosomy: :

Missing one Missing one chromosome of chromosome of one of the pairsone of the pairs

– Turner’s Turner’s syndrome; syndrome; Monosomy 23Monosomy 23

Missing one of Missing one of the X the X chromosomes chromosomes

Female who is Female who is X0 instead of XXX0 instead of XX

Chromosomal Chromosomal DisordersDisorders

Symptoms:Symptoms: – Short statureShort stature– Webbed neckWebbed neck– Lack of secondary sex Lack of secondary sex

characteristicscharacteristics– A hollow appearance to A hollow appearance to

the chestthe chest– Lack of menstruationLack of menstruation– Low hairlineLow hairline– "Droopy" eyelids"Droopy" eyelids

Chromosomal Chromosomal DisordersDisorders TrisomyTrisomy: An extra chromosome of : An extra chromosome of

one of the pairsone of the pairs– Down syndrome; Trisomy 21Down syndrome; Trisomy 21

Extra chromosome #21 (so, there are 3 Extra chromosome #21 (so, there are 3 chromosome #21)chromosome #21)

Chromosomal Chromosomal DisordersDisorders IncidenceIncidence

– One of the most common One of the most common chromosomal chromosomal abnormalitiesabnormalities

– Frequency varies a lot Frequency varies a lot according to the age of according to the age of the mother.the mother.

The rate is only 1 in 2,000 The rate is only 1 in 2,000 for women 20 years oldfor women 20 years old

In those 40 or older, it is 1 In those 40 or older, it is 1 birth in 100.birth in 100.

Genetic DisordersGenetic Disorders

Symptoms:Symptoms: Small head, flattened in Small head, flattened in

the backthe back Broad, flat face Broad, flat face Relatively small eyes, Relatively small eyes,

turned up at the outer turned up at the outer corners corners

Oversize tongue in a Oversize tongue in a small mouthsmall mouth

Single horizontal line Single horizontal line across the palm, instead across the palm, instead of the usual "head" and of the usual "head" and "heart" lines"heart" lines

Short stature, with short Short stature, with short limbs and stubby fingerslimbs and stubby fingers

Genetic DisordersGenetic Disorders

Kleinfelter’s Kleinfelter’s Syndrome; Syndrome; Trisomy 23Trisomy 23

– Extra sex Extra sex chromosome chromosome

– Male who is XXY Male who is XXY instead of XYinstead of XY

– The most common The most common sex chromosome sex chromosome abnormality in abnormality in males males

Genetic DisordersGenetic Disorders

Symptoms:Symptoms:– Arm span exceeds height by more that an Arm span exceeds height by more that an

inch.inch.– No or very little body hair and no facial No or very little body hair and no facial

hair.hair.– High voiceHigh voice– Minimal muscle growth in arms/legsMinimal muscle growth in arms/legs– Small testiclesSmall testicles– Breast Tissue (not just fat, but actually Breast Tissue (not just fat, but actually

firm breasts)firm breasts)– Low Testosterone LevelLow Testosterone Level