Chapter 11 &14 Human Genetics and Meiosis
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Transcript of Chapter 11 &14 Human Genetics and Meiosis
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Chapter 11 &14
Human Geneticsand Meiosis
The study of inheritance patterns in humans
Oculocutaneous albinism
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What each of the human chromosomes look like
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Karyotype: A photomicrograph of chromosomes arranged according to a standard classification
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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.
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Sex determination with karyotype
• This karyotype has 23 exact pairs, which means the person is female.
• Note that #23 chromosomes are both X.
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Normal human male
• Note that #23 chromosomes are X and Y.
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Is this person female or male?
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Trisomy 21
• Abnormality shown in karyotype
• Note that there are three copies of #21 chromosome.
• This person has Down Syndrome.
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Photos of Down Syndrome patients from the National Down Syndrome Society
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Correlation between mother’s age and Trisomy 21 incidence
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Monosomy X
• Abnormality shown in karyotype
• Note this person only has 1 copy of the X chromosome.
• This female has Turner’s syndrome.
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XXY Male (Extra X)
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How are DNA samples obtained for karyotypes?
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Amniocentesis: obtaining amniotic fluid which has cells from the fetus
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Chorionic villi sampling: removing cells from the chorion with fetal tissue
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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.
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Click on image to play video.
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Meiosis 1
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Meiosis II
Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.
Prophase II Metaphase II Anaphase II Telophase IIThe chromosomes line up in a similar way to the metaphase stage of mitosis.
The sister chromatids separate and move toward opposite ends of the cell.
Meiosis II results in four haploid (N) daughter cells.
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Oocyte or Spermatocyte
• This cell that can undergo meiosis originally has 6 chromosomes and has replicated to 12 chromosomes in preparation for meiosis.
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Prophase I: homologous chromosomes pairing into tetrads
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Metaphase I: tetrads align, along the metaphase plate
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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.
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Telophase I: membranes form around the separated homologues
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Prophase II: spindle fibers bind to the sister chromatids of each chromosome
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Metaphase II: chromosomes align along the metaphase plate
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Anaphase II: sister chromatids separate to opposite poles
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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.
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Nondisjunction
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How can siblings look alike but not exactly the same if they come from the same parents?
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Crossing over
• The chromosomes during prophase I undergo crossing over, where parts of the homologues randomly switch places.
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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.
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More sibling similarities
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What other chromosomal disorders can arise?
• Deletion• Inversion• Translocation*• Duplication
*Don’t worry about this one.
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Chromosomal mutations
Deletion
Duplication
Inversion
Translocation
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Problems with chromosomes
• Duplication: copied parts of chromosome
A
B
C
D
A
B
B
B
C
D
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Problems with chromosomes
• Deletion: missing parts of chromosome
A
B
C
D
A
D
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Problems with chromosomes
• Inversion: parts of chromosome tched
A
B
C
D
A
C
B
D
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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
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Recessive disorders
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Dominant disorder
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Sex-linked disorder
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Are you red-green color blind?
• Yes, if you have a difficult time distinguishing a number from this picture
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Pedigrees: a chart which can show trait inheritance through several generations
Albinism
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Symbols
Male Female
marriage
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More symbols
She gave birth!
Pain! Suffering!
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Even more symbols
… and they have a litter of 4!
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Still more symbols
Affected. AA or aa
Normal heterozygous
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Albinism – recessive disorder
aa Aa
Aa aa Aa Aa
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Deafness – dominant disorder
Aa or AA?
Aa Aa Aa Aa
aa
Mother must be AA.
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Colored blindness – Sex linked
XCXc
XcY XCXc XCY XcXc
XcY
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Pedigree of Hsu family
Me!
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Review Videos
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