HOW MANY CHROMOSOMES ARE FOUND IN EACH HUMAN BODY CELL?
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Transcript of HOW MANY CHROMOSOMES ARE FOUND IN EACH HUMAN BODY CELL?
• In the body cells of animals and most plants, chromosomes occur in pairs.
• In each pair, one you inherited from your mom, the other from your dad.
Diploid Cells
From Mom
From Dad
The two chromosomes of a pair are called homologous chromosomes.
Each pair of homologous chromosomes has genes for the same traits.
Homologous Chromosomes
• Body cells (diploid) are different from sex cells.
• Each person can only pass on ONE of their homologous chromosomes to their young.
HUMANS = 46 CHROMOSOMES
IN THEIR BODY CELLS
Each parent passes 23 to their young, so that when the sperm and egg combine- it
will equal 46 Chromosomes.
• So, sex cells CANNOT be diploid.
•A cell containing only one of each kind of chromosome is called a haploid cell.
Haploid Cells
Chromosome Numbers of Common Organisms
Organism Body Cell
Fruit fly 8
Garden pea 14
Corn 20
Tomato 24
Leopard Frog 26 13
Apple 34
Human 46
Chimpanzee 48
Dog 78
Adder’s tongue fern 1260
Sex Cell
4
7
10
12
17
23
24
39
630
Diploid and Haploid Cells
In Humans, how many chromosomes would each of these cells have…..
CHEEK CELL
46
SPERM CELL
23
EGG CELL
23
NERVE CELL
46
HomologsHomologsseparateseparate
Sister Sister chromatidschromatidsseparateseparate
DiploidDiploid
MeiosisMeiosis I I
MeiosisMeiosisIIII
DiploidDiploid
HaploiHaploidd
The kind of cell division that produces sex cells (haploid) containing half the number of chromosomes as a body cell, is called meiosis.
Meiosis: cell division that makes SEX CELLS.
It starts with a DIPLOID cell 46
Chromosomes Replicate
92
46 46
23 23 23 23
It ends with FOUR HAPLOID cells (not identical)
Click here to see the animation http://www.cellsalive.com/meiosis.htm
• These haploid cells are called sex cells— gametes.
• Male gametes are called sperm.
• Female gametes are called eggs.
Meiosis
• When a sperm fertilizes an egg, the resulting zygote once again has the diploid number of chromosomes.
Meiosis
Meiosis I: Reduction DivisionMeiosis I: Reduction Division
NucleusNucleus SpindleSpindlefibersfibers NuclearNuclear
envelopeenvelope
Prophase IProphase I
Chromatin coils up.Chromatin coils up.
Spindle forms.Spindle forms.
Nuclear envelope Nuclear envelope fragments.fragments.
Tetrads Form in Tetrads Form in Prophase IProphase IHomologous Homologous
chromosomeschromosomes(each with sister chromatids) (each with sister chromatids)
Join to form aJoin to form a TETRADTETRAD
Crossing-Over in Crossing-Over in Prophase IProphase I
The tetrads pair so tightly that non-sister chromatids from homologous chromosomes can actually break and exchange genetic material in a process known as crossing over.
Crossing-OverCrossing-Over
Crossing over can occur at any location on a chromosome, and it can occur at several locations at
the same time.
• The centromere of each chromosome becomes attached to a
spindle fiber.
Metaphase IMetaphase I• In Metaphase I, the tetrads line up in the middle, or equator.
Anaphase IAnaphase I
Homologous Homologous chromosomes chromosomes separateseparate and move and move to opposite poles.to opposite poles.
Sister chromatids Sister chromatids remain remain attached attached at theirat their centromerescentromeres.
Telophase ITelophase I
Nuclear envelopes Nuclear envelopes reassemble.reassemble.
Spindle disappears.Spindle disappears.
Cytokinesis Cytokinesis divides cell divides cell into two.into two.
Meiosis II: Reducing Chromosome Meiosis II: Reducing Chromosome NumberNumber
Prophase Prophase IIII
MetaphaMetaphase IIse II
AnaphasAnaphase IIe II
TelophasTelophase IIe II 4 Identical 4 Identical
haploid haploid cellscells
The second division in meiosis is simply a mitotic division of the products of Meiosis I.
Prophase IIProphase II
Nuclear Nuclear envelope envelope fragments.fragments.
Spindle forms.Spindle forms.
Metaphase IIMetaphase II
Chromosomes align Chromosomes align along along equatorequator of cell of cell..
Anaphase IIAnaphase II
Sister Sister chromatidschromatids separate and separate and move to move to opposite polesopposite poles.
EquatorEquator
PolePole
Telophase IITelophase IINuclear envelope Nuclear envelope assembles.assembles.
Chromosomes Chromosomes decondense.decondense.
Spindle Spindle disappears.disappears.
Cytokinesis Cytokinesis divides cell into divides cell into two.two.
Results of MeiosisResults of MeiosisGametes (egg & sperm) Gametes (egg & sperm) formform
Four haploid cells with Four haploid cells with one copy of each one copy of each chromosome chromosome
One allele of each geneOne allele of each gene
Different combinations Different combinations of alleles for different of alleles for different genes along the genes along the chromosomechromosome
• The failure of homologous chromosomes to separate properly during meiosis is called nondisjunction.
•This would occur in Anaphase I, when homologous chromosomes are suppose to separate from each other.
Nondisjunction
When a gamete with an extra chromosome is fertilized by a normal gamete, the zygote will have an extra
chromosome.
• This condition is called trisomy.
•An example of this in humans is Downs Syndrome
Nondisjunction
Downs Syndrome
• Extra chromosome on 21
• 1 in every 1100 live births
• Range from mild to severe physical and mental disabilities
• Although organisms with extra chromosomes often survive, organisms lacking one or more chromosomes usually do not.
When a gamete with a missing chromosome fuses with a normal gamete during fertilization, the resulting zygote lacks a
chromosome.
• This condition is called monosomy. An example of this in humans is Turner’s Syndrome.
Nondisjunction
Turners Syndrome
• Absence of one X chromosome
• Occurs in 1 out of every 2,500 live female births.
• Physical characteristics
• No mental disability
A cell with two of each kind of chromosome is __________.
Question 1
D. polyploid
C. biploid
B. haploid
A. diploid
The answer is A. The two chromosomes of each pair in a diploid cell are called homologous chromosomes. Each has genes for the same traits.
Homologous Chromosome 4
a A
Terminal Axial
InflatedD
Constrictedd
Tall
T
Short
t
What is the importance of meiosis in sexual reproduction?
Question 2Meiosis
Meiosis
Sperm Cell
Egg Cell
Haploid gametes
(n=23)
Fertilization
Diploid zygote
(2n=46)
Mitosis and Development
Multicellular
diploid adults
(2n=46)
Meiosis is cell division that produces haploid gametes. If meiosis did not occur, each generation would have twice as many chromosomes as the preceding generation.
Meiosis
Meiosis
Sperm Cell
Egg Cell
Haploid gametes
(n=23)
Fertilization
Diploid zygote
(2n=46)
Mitosis and Development
Multicellular
diploid adults
(2n=46)