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Chapter 11 &14
Human Genetics
and Meiosis
The study of
inheritance patterns
in humans
Oculocutaneous albinism
What each of the human
chromosomes look like
Karyotype: A photomicrograph of
chromosomes arranged according to
a standard classification
In other words…
• Chromosomes are digitally arranged so
that they are matched with their
homologue or “partner” chromosome.
• Homologue chromosomes are the same
size, shape, and carry the same genes,
and one is inherited from each parent.
• They are numbered according to size.
Sex determination with karyotype
• This karyotype has 23
exact pairs, which
means the person is
female.
• Note that #23
chromosomes are
both X.
Normal human male
• Note that #23
chromosomes
are X and Y.
Is this person female or male?
Trisomy 21
• Abnormality
shown in
karyotype
• Note that there
are three copies
of #21
chromosome.
• This person has
Down
Syndrome.
Photos of Down Syndrome patients from
the National Down Syndrome Society
Correlation between mother’s age
and Trisomy 21 incidence
Monosomy X
• Abnormality
shown in
karyotype
• Note this
person only has
1 copy of the X
chromosome.
• This female has
Turner’s
syndrome.
XXY Male (Extra X)
How are DNA samples obtained for
karyotypes?
Amniocentesis: obtaining amniotic
fluid which has cells from the fetus
Chorionic villi sampling: removing
cells from the chorion with fetal tissue
If there are chromosomal number
abnormalities, how do they form?
• Meiosis: the process of creating sperm or
egg from a diploid cell
• If there is a mistake when chromosomes
are separating, then the resulting sperm or
egg will have too many or too few
chromosomes.
Click on image to play video.
Meiosis 1
Meiosis II
Prophase II
Metaphase II
Anaphase II
Meiosis I results in two
The chromosomes line up in a The sister chromatids
haploid (N) daughter cells,
similar way to the metaphase separate and move toward
each with half the number of stage of mitosis.
opposite ends of the cell.
chromosomes as the original.
Telophase II
Meiosis II results in four
haploid (N) daughter cells.
Oocyte or Spermatocyte
• This cell that can
undergo meiosis
originally has 6
chromosomes and
has replicated to 12
chromosomes in
preparation for
meiosis.
Prophase I: homologous
chromosomes pairing into tetrads
Metaphase I: tetrads align, along
the metaphase plate
Anaphase I: homologous chromosomes
separate from the metaphase plate
• If chromosomes
do not properly
separate, this is
called
nondisjunction.
• Nondisjunction
leads to trisomy
and monosomy
disorders.
Telophase I: membranes form
around the separated homologues
Prophase II: spindle fibers bind to the
sister chromatids of each chromosome
Metaphase II: chromosomes align
along the metaphase plate
Anaphase II: sister chromatids
separate to opposite poles
Telophase II: nuclear membrane forms
around newly separated chromatids
• Note that each new nucleus formed has ½
the amount of DNA as the original cell.
• These cells are haploid cells.
Nondisjunction
How can siblings look alike but not
exactly the same if they come from the
same parents?
Crossing over
• The chromosomes during prophase I
undergo crossing over, where parts of the
homologues randomly switch places.
Importance of crossing over
• The gene
combinations that a
person gets from his
or her parents will be
different, to varying
degrees, than the
combination a sibling
may get.
More sibling similarities
What other
chromosomal
disorders can arise?
•
•
•
•
Deletion
Inversion
Translocation*
Duplication
*Don’t worry about this one.
Chromosomal mutations
Deletion
Duplication
Inversion
Translocation
Problems with chromosomes
• Duplication: copied parts of chromosome
A
A
B
B
C
B
D
B
C
D
Problems with chromosomes
• Deletion: missing parts of chromosome
A
A
B
D
C
D
Problems with chromosomes
• Inversion: parts of chromosome tched
A
A
B
C
C
B
D
D
Human genetic disorders from
deleterious genes
•
Sometimes the alleles inherited contribute to
disorders and not from the number or shape of
the chromosomes.
1. Sex-linked: genes found on X or Y
chromosome
2. Recessive: requires 2 allele copies to express
disorder
3. Dominant: requires only 1 allele copy to
express disorder
Recessive disorders
Dominant disorder
Sex-linked disorder
Are you red-green color blind?
• Yes, if you
have a difficult
time
distinguishing
a number from
this picture
Pedigrees: a chart which can show trait
inheritance through several generations
Albinism
Symbols
marriage
Male
Female
More symbols
She gave birth!
Pain! Suffering!
Even more symbols
… and they have a litter of 4!
Still more symbols
Affected. AA
or aa
Normal
heterozygous
Albinism – recessive disorder
aa
Aa
Aa
aa
Aa
Aa
Deafness – dominant disorder
aa
Aa or AA?
Mother must be AA.
Aa
Aa
Aa
Aa
Colored blindness – Sex linked
XcY
XcY
XCXc
XCXc
XCY
XcXc
Pedigree of Hsu family
Me!
Review Videos
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