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.
Trisomy 21
Abnormality shown in karyotype
Note that there are three copies of #21 chromosome.
This person has Down Syndrome.
Monosomy X
Abnormality shown in karyotype
Note this person only has 1 copy of the X chromosome.
This female has Turner’s syndrome.
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.
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.
Oocyte or Spermatocyte
This cell that can undergo meiosis originally has 6 chromosomes and has replicated to 12 chromosomes in preparation for meiosis.
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 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 cel
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.
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
Are you red-green color blind?
Yes, if you have a difficult time distinguishing a number from this picture
Let’s Review
http://www.cellsalive.com/mitosis.htm
http://www.cellsalive.com/meiosis.htm
http://www.biomanbio.com/GamesandLabs/Genegames/snurfle_meiosis_and_genetics.html
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