1. Chromosomes
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2. Why Cell Division? 2 trillion new cells each day, 25 million a second!
Why is it needed?
Growth, repair, asexual reproduction, and making gametes
New cells come from old cells dividing
All of the information stored in DNA must be present in each of the new cells
When a cell divides, DNA is copied and distributed
Each cell ends up with a complete set
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3. Prokaryotic Cellular Division
Bacterial cellular division is not as complex as eukaryotic cellular division.
Due to the fact that bacteria have one circular DNA chromosome.
Bacterial divide using a process called Binary Fission.
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5. Binary Fission Bacterial cell division happens in 2 stages:
1. Circular DNA is copied
-starting at one point of the circular DNA, the molecule is copied
-two copies of the DNA are attached to the interior surface of the cell
2. Bacterial cell splits into 2 separate cells
-a new membrane and cell wall form between the DNA
copies
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7. Eukaryotic Cellular Division
When eukaryotic cells prepare to divide, their DNA is packaged into tightly wound structures called Chromosomes.
Why? Chromosomes are easily split into two.
Chromosomes contain Genes.
A Gene is a segment of DNA that codes for a protein or RNA molecule.
Genes play an important role in determining how a person’s body develops and functions.
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8. Chromosome Structure
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9. DNA Coiling
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10. Chromosome Structure
Prior to cellular division, each chromosome is composed of two genetically identical parts called chromatids, held together at a region called the centromere.
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12. Eukaryotic Cells Continued
Each organism has a characteristic number of chromosomes.
A typical human cell contains 46 chromosomes.
Chromosomes are housed inside the nucleus.
Each chromosome must be copied exactly before cellular division can take place.
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13. Types of Chromosomes Humans have 23 pairs of chromosomes.
The first 22 pairs of chromosomes are called Autosomes.
Autosomes are chromosomes that are not directly involved in determining the gender of an individual.
The 23rd pair of chromosomes are called Sex Chromosomes.
Sex chromosomes contain genes that determine the gender of the individual.
XX in females & XY in males.
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14. The elusive “Y Chromosome”
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15. Homologous Chromosomes
The first 22 pairs of chromosomes consists of homologous chromosomes or homologues.
Homologous Chromosomes are chromosomes that are similar in size, shape, and genetic content.
Each homologue in a homologous pair comes from one of your two parents
The 23rd pair isn’t homologous -- sex chromosomes!
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16. Homologous Chromosomes
both chromosomes of a pair carry “matching” genes
control same inherited characters
homologous = same information
diploid 2n
2n = 4
eye color
(brown?)
eye color
(blue?)
homologous chromosomes
double stranded homologous chromosomes
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17. Chromosome Number
All of the cells in the body, other than Gametes (sex cells), are Somatic Cells (body cells).
Somatic cells contain two sets of chromosomes.
Diploid 2n=46
Gametes have one set of chromosomes.
Haploid n=23
The fusion of two haploid gametes during fertilization produces a zygote.
Zygote = fertilized egg
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18. Fertilization
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19. Karyotypes
Each organism has a characteristic number of chromosomes that can be identified by a Karyotype.
A karyotype is an arrangement of all chromosomes within a cell by pairs in a fixed order.
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20. Chromosomes of Human Female
23 pairs
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21. Chromosomes of Human Male
23 pairs
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22. Chromosomal abnormalities
Incorrect number or amount of chromosomes
nondisjunction
chromosomes don’t separate properly during meiosis
breakage of chromosomes
deletion
duplication
inversion
translocation
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23. Nondisjunction
Problems with meiotic spindle cause errors in daughter cells
tetrad chromosomes do not separate properly during Meiosis 1
sister chromatids fail to separate during Meiosis 2
too many or too few chromosomes 2n
n-1
n+1 n
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24. Alteration of chromosome number
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25. Nondisjunction Baby has wrong chromosome number trisomy monosomy
cells have 3 copies of a chromosome
monosomy
cells have only 1 copy of a chromosome
monosomy
2n-1
trisomy
2n+1
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26. Down syndrome Trisomy 21 Effects 3 copies of chromosome 21
1 in 700 children born in U.S.
Effects
Mental handicap
Heart defects
Short stature
Shorter lifespan
Sexually underdeveloped, often
sterile
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27. Trisomy 21
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28. Sex chromosomes
Human development more tolerant of wrong numbers in sex chromosome
But produces a variety of distinct conditions in humans
XXY = Klinefelter’s syndrome male
XXX = Trisomy X female
XYY = Jacob’s syndrome male
XO = Turner syndrome female
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29. Klinefelter’s syndrome
XXY male
one in every 2000 live births
have male sex organs, but are sterile
feminine characteristics
tall
normal intelligence
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30. Jacob’s syndrome male XYY Males 1 in 1000 live male births
extra Y chromosome
somewhat taller than average
Often learning disabilities
normal sexual development
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31. Trisomy X XXX 1 in every 1000 live births produces healthy females
Why?
How many Barr bodies would you expect?
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32. Turner syndrome Monosomy X or X0 1 in every 5000 births
Only viable monosomy in humans
varied degree of effects
webbed neck
short stature
Normal intelligence
Sterile
How many Barr bodies would you expect?
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33. Changes in chromosome structure
During what process would his happen?
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34. Changes in chromosome structure
deletion
loss of a chromosomal segment
duplication
repeat a segment
inversion
reverses a segment
translocation
move segment from one chromosome to another
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35. Cri du Chat (Cry of the Cat)
Part of Chromosome 5 has been deleted
Severe mental handicap
Small head with unusual facial features
Cry that sounds like a distressed cat
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36. Fragile X Syndrome Part of X chromosome is hanging
Most common form of mental handicap
1:1500 males, 1:2500 females
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