AOS 1 Overview
HUMAN VARIATION
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People vary in their appearance.
Members within a family are more alike than those from different families.
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A complete instruction manual for human development is found within the
nucleus of every cell.
This information is coded for in DNA.
DNA (deoxyribonucleic acid) is a long molecule similar in shape to a
twisted rope ladder (double helix). The sides of the ladder are composed of
alternating sugar and phosphate units. The rungs are made of paired bases.
Adenine pairs with thymine and cytosine pairs with guanine. The
instructions for development are coded in the order of the bases.
A section of DNA that codes for one particular characteristic is called a
gene.
Genes are linked together to form chromosomes.
determined by
DNA STRUCTURE
organised into
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KARYOTYPE
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Inherited through
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MEIOSIS
FERTILISATION
MITOSIS
Determines
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The number of chromosomes in cells of organisms of the same species is
usually the same.
Eg human cells all have 46 chromosomes. (Except gametes)
In human cells the chromosomes are paired. Paired chromosomes
(homologous) carry the same genes but the alleles for these genes may be
different.
An allele is an alternative form of a gene. For example the gene for the
CFTR protein is found on the 7th pair of chromosomes. It has 2 possible
alleles, one coding for normal CFTR protein and one coding for an
abnormal protein which leads to cystic fibrosis.
Because human chromosomes are paired, each cell has 2 pieces of
information for every gene.
Cells that contained paired chromosomes are diploid and cells that only
have one of each type of chromosome are haploid.
The last “pair” of human chromosomes are called sex chromosomes. In
females cells these chromosomes are matching and are called X
chromosomes. In males they are not matching. Males have one X
chromosome “paired” with a smaller Y chromosome.
Meiosis is a nuclear division that results in the production of ova and sperm
that contain only one of each pair of homologous chromosomes.
Ova and sperm are haploid. (They contain only one allele for each gene)
When a sperm fertilises an ovum the new cell is diploid. In this way each
child inherits one allele for each gene from her mother and one from her
father.
http://gslc.genetics.utah.edu/units/basics/b
uilddna/
http://gslc.genetics.utah.edu/units/basics/to
ur/
http://www.sumanasinc.com/webcontent/a
nisamples/molecularbiology/lifecyclemrna
_fla.html
http://gslc.genetics.utah.edu/units/basics/tr
anscribe/
http://207.207.4.198/pub/flash/26/transme
nu_s.swf
http://www.ultranet.com/%7Ejkimball/Bio
logyPages/M/Mutations.html#point
http://www.biology.arizona.edu/human_bi
o/activities/karyotyping/patient_c/13c13.html
http://www.biology.arizona.edu/cell_bio/t
utorials/cell_cycle/cells3.html
http://www.biology.arizona.edu/cell_bio/t
utorials/meiosis/page3.html
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INDIVIDUAL’S
GENOTYPE
expression depends on
1. PATTERN OF
INHERITANCE
-complete dominance
-incomplete dominance
-co-dominance
-multiple alleles
-X linkage and
determination
-linked genes
-polygenes
2. GENE
INTERACTION IN
ENVIRONMENT
= PHENOTYPE
Tracked by
PEDIGREES
The new cell is the first cell of the new child. It divides by mitosis to
produce cells that are identical to the first cell.
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Cell growth occurs by mitosis.
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The alleles that a child inherits from her parents are called her genotype.
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If both alleles for a particular characteristic are the same she is homozygous,
if they are different she is heterozygous.
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How the alleles are expressed is the child's phenotype.
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Expression depends on the gene’s pattern of inheritance, how it interacts
with other genes and its interaction with the environment.
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Early experiments were carried out by Gregor Mendel.
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In complete dominance heterozygous individuals have the same phenotype
as one of the homozygous forms.
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In incomplete dominance the heterozygous phenotype is between both
homozygous forms.
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In co-dominance both phenotypes are expressed in the heterozygous
individual.
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It is the male that determines the sex of a child.
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½ the sperm produced by males contain an X chromosome and ½ contain a
Y chromosome.
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The Y chromosome is smaller than the X chromosome and so carries fewer
genes.
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A characteristic that is X linked does not have an allele on the Y
chromosome.
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There is a greater chance of a male showing an X linked recessive disorder
as only one allele for the disorder is required for the disorder to be
expressed.
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A female can have an X linked recessive disorder but it is less likely as she
must have 2 copies of the recessive allele.
Used to follow the inheritance of characteristics over many generations
http://www.biology.arizona.edu/mendelian
_genetics/problem_sets/monohybrid_cross
/monohybrid_cross.html
http://www.biology.arizona.edu/mendelian
_genetics/problem_sets/dihybrid_cross/dih
ybrid_cross.html
http://www.sonic.net/~nbs/projects/anthro
201/exper/
http://www.biology.arizona.edu/mendelian
_genetics/problem_sets/sex_linked_inherit
ance/sex_linked_inheritance.html