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ChromosomesandKaryotypes

Review of Chromosomes Super coiledDNA Structure: Itmay be– A single coiledDNA molecule

Chromosomes Or after replication, it may betwo coiled DNA moleculesheld together at the center.– The area it is held together iscalled the “centromere.”– Chromatid: Each DNAmolecule in a double strandedchromosome (therefore, eachreplicated chromosome has 2chromatids).

Chromosomes Humans have 46 chromosomes– 23 chromosomes from Mom– 23 chromosomes from DadTwo Types of Chromosomes:1. AutosomesALL chromosomes except the sexchromosomes 22 pairs (Chromosomes #1-22)

Two Types of Chromosomes:2. Sex Chromosomes:1 pair (human chromosome #23) Determine the sex of an organism – In mammals & fruit flies XX is female, XY is maleFemaleMale– In birds ZZ is male, ZW female *FIX IN NOTE TEMPLATE

Two Types of Cells1.Somatic Cells: 2.All cells of the bodySex Cells: Egg and Sperm

1. Somatic Cells:Chromosomes are Homologues:“Homo” means same.– Homologous chromosomes are the same sizeand shape, and carry genes for the same traits.– Called a “homologous pair”

Homologous Chromosomes Humans have 23 homologous pairs in allcells except sex cells– Cells with 23 homologous pairs care called“DIPLOID” or 2N N stands for number of unique chromosomesCells with 23 homologous pairs are called “somaticcells”In humans, all cells except sperm and egg are somaticcells

2. Sex cells (sperm and egg)–only have one of each chromosome– No homologous pairs– Called “HAPLOID” or N (think “half”)– Sex Cells are called “GAMETES.”

Karyotypes A picture of thechromosomes inwhich thechromosomesarranged inmatching(homologous)pairs

Karyotypes– Arranged in sizeorder from largestpair to smallestpair– The sexchromosomes (Xand Y) are usuallythe last pair,though they arenot the smallest.

Karyotypes How are they used?– They are used for diagnosis of geneticabnormality based on the number ofchromosomes.– They are used to determine the sex of anunborn child.

Karyotypes How are theyprepared?– Cells are collectedfrom a variety ofsources: Amniotic fluid via apre-natal“amniocentesis”Blood Sample

Karyotypes How are theyprepared?– Sample of cells areallowed to continuedividing– Cells are stoppedwhen inMETAPHASE ofMITOSIS.

Karyotypes A photograph of thechromosomes is takenand enlarged.A trained technicianmatches thechromosomes into thehomologous pairsbased on threecharacteristics:– Size– Banding– Centromere position

Chromosomal Disorders Normal:– Have 2 matching chromosomes for eachof the 23 pairs Aneuploidy:– Having one more or one less of one ofthe chromosomes of the 23 pairs.

Chromosomal DisordersMonosomy:Missing onechromosome ofone of the pairs –Turner’ssyndrome;Monosomy 23 Missing one of theX chromosomesFemale who is X0instead of XX

Chromosomal DisordersSymptoms: –––––––Short statureWebbed neckLack of secondary sexcharacteristicsA hollow appearance to thechestLack of menstruationLow hairline"Droopy" eyelids

Chromosomal DisordersTrisomy: An extra chromosome of one ofthe pairs –Down syndrome; Trisomy 21 Extra chromosome #21 (so, there are 3chromosome #21)

Chromosomal DisordersIncidence ––One of the most commonchromosomal abnormalitiesFrequency varies a lotaccording to the age of themother. The rate is only 1 in 2,000 forwomen 20 years oldIn those 40 or older, it is 1 birthin 100.

Genetic DisordersSymptoms: Small head, flattened in thebackBroad, flat faceRelatively small eyes,turned up at the outercornersOversize tongue in a smallmouthSingle horizontal line acrossthe palm, instead of theusual "head" and "heart"linesShort stature, with shortlimbs and stubby fingers

Genetic DisordersKleinfelter’sSyndrome; Trisomy23 –––Extra sexchromosomeMale who is XXYinstead of XYThe most commonsex chromosomeabnormality in males

Genetic DisordersSymptoms: –––––––Arm span exceeds height by more that aninch.No or very little body hair and no facial hair.High voiceMinimal muscle growth in arms/legsSmall testiclesBreast Tissue (not just fat, but actually firmbreasts)Low Testosterone Level

22 pairs (Chromosomes #1-22) Two Types of Chromosomes: 2. Sex Chromosomes: . A picture of the chromosomes in which the chromosomes arranged in matching (homologous) pairs . Karyotypes –Arranged in size order from largest pair to smallest pair –The sex chromosomes (X and Y) are usually

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Human Chromosomes. Karyotypes. Scientists then cut out the chromosomes from the photographs and arrange them in a picture known as a . karyotype. It shows the complete diploid set of chromosomes grouped together in pairs, arranged in order of decreasing size. A karyotype from a typical human cell, which contains 46 chromosomes, is arranged in .

" The picture of the chromosomes are then cut up so that each chromosome is removed. The chromosomes are matched up and attached to a paper according to size, banding patterns, & centromere position. " The chromosomes pairs are numbered from largest to smallest. " There are 22 pairs of chromosomes that are aligned first

In their body cells, humans have 46 chromosomes, made up of 23 pairs. There are 44 chromosomes numbered 1-22 (called autosomes) according to size from the smallest to the largest and two sex chromosomes: X and Y Women’s chromosomes are described as 46,XX; men’s as 46,XY A mother passes 23 chromosomes to her child through her egg .

This "dropping your chromosomes" will determine which one of the pair of chromosomes will enter the successful germ cell. Each parent, mom and dad, donate one and only one of each of their 23 pairs of chromosomes. Therefore, they each donate 23 chromosomes. Since genes ride in the DNA of the chromosomes, each child will end up with a pair of

Biologists can analyze human chromosomes by looking at a karyotype. A karyotype is a picture of the chromosomes from a cell arranged in homologous pairs. Humans have 46 chromosomes. Two of these chromosomes, X and Y, are the sex chromosomes. Females have two X chromosomes (XX). Males have one X and one Y chromosome (XY). The other

Picture 2: 23 pairs of chromosomes arranged according to size; chromosome 1 is the largest. The last two chromosomes are sex chromosomes. The chromosomes (see Picture 2) numbered 1 to 22 look the same in males and females. These are called the autosomes. Pair number 23 is different in males and females and they are called the sex chromosomes.

DNA condenses into duplicated chromosomes Each chromosome contains two copies of the same DNA (the copies were made in interphase) Note about diagram: Red chromosomes from mom; blue chromosomes from dad Each pair of chromosomes with the same shape and length contains the same gene locations: they are a homologous pair of chromosomes.

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