Human Karyotype XY Male Normal Page 319
Human Karyotype XXY Male (Klinefelter s) Sex Chromosomal aberration Sex Chromosome aneuploidy
Human Karyotype XYY Male ( Supermale ) Sex Chromosomal aberration Sex Chromosome aneuploidy
Human Karyotype XXX Female ( Superfemale ) Sex Chromosomal aberration Sex Chromosome aneuploidy
Human Karyotype XO Female (Turner s Syndrome) Sex Chromosomal aberration Sex Chromosome aneuploidy
Meiosis
Leptotene
The chromosomes are very long and thin. They most often lie in a tight knot around the nucleolus. The chromosomes at this point appear to be single, though x-ray information suggests that they are double. They have a finely beaded appearance.
Metaphase I
The chromosomes are aligned on the equatorial plane and the spindle is complete.
Telophase I
The chromosomes become vacuolated in appearance and the cell plate is more distinct.
First polar body
The two double-stranded chromosomes lying nearest the surface of the oocyte are extruded as the first polar body. This very unequal division of the cytoplasm ensures that a large supply of cytoplasm will be available to the developing embryo in the egg.
Metaphase II
During the second maturation division the two remaining chromosomes, each of which may plainly be seen to consist of two parts, line up across the spindle. The first polar body is visible just outside the oocyte near its nucleus.
2nd polar body
The second polar body, consisting of one chromatid from each of the two remaining chromosomes, is extruded. During the second maturation division of the oocyte nucleus, the sperm nucleus has increased in volume.
Mitosis
Early Prophase
The four chromosomes are becoming visible as dark threads. Replication of DNA has already taken place, so each chromosome is double-stranded.
Late Prophase
Four distinct chromosomes are visible by late prophase.
Metaphase
Chromosomes line up across the equator of the cell. Asters and spindle fibers are clearly visible. Polar bodies can be seen outside the cell.
Anaphase I
The chromosomes have separated and are moving into polar positions. The fibers of the spindle show a discontinuity in the area of the cell plate.
Late Anaphase
The two sets of single-stranded chromosomes have nearly completed their journey to opposite poles of the cell. They appear to be pulled along by the spindle fibers.
Cell Cleavage
2 cells
Each of the two daughter cells undergoes mitosis and cytokinesis.
4 cells
Mitosis has now produced an embryo of four identical cells.
8 cells
Another cleavage in each cell results in a ball of eight cells. Note that during these early cleavages the same amount of cytoplasm is progressively divided up into a greater and greater number of smaller and smaller cells.
Fertilization
Sperm entrance into oocyte
Shown here is the large primary oocyte which will mature into the female gamete, or ovum, following meiosis. The characteristically bullet-shaped sperm cell has already penetrated the oocyte. Although the sperm cell is the mature male gamete, and therefore haploid at this stage, the oocyte is immature and still diploid. Its nucleus can be seen as a diffuse dark area in the center of the cell. Notice the many large vacuoles in the oocyte.
Pronuclei before fussion
The ovum now contains two haploid interphase nuclei, one male and one female, called pronuclei. The membranes and shell surrounding the ovum are clearly visible.
Pronuclei fusing
The pronuclei fuse and the chromosomes (two in each nucleus) coil and condense, becoming visible once more as fusion proceeds.
Mitosis
Interphase
This is referred to as the resting stage. Actually, the cell is busy carrying out all of its functions except division. Note the prominent nucleolus.
Prophase
During this stage, the chromosomes condense into tight coils and appear to thicken as they become visible. The nuclear membrane breaks down.
Metaphase
A network of microtubules called the mitotic spindle has formed. Chromosomes are pulled to the equator of the cell by these fibers which have grown from the centromere of each chromatid.
Anaphase
The spindle fibers contract, pulling one chromatid from each pair to opposite ends or poles of the cell.
Telophase
When the chromatids reach the poles, they swell and disappear. The nuclear membrane forms and the cell undergoes cytokinesis and divides.
Daughter cells (interphase)
The two cells are now in interphase and the chromosomes duplicate themselves again.
Sex Linkage
Sex-linked Cross (P generation) P homogametic parent x heterogametic parent homozygous x hemizygous AA x ay or aa x AY Genotypes are contrasting F 1 homogametic sex is heterozygous: Aa F 1 heterogametic sex is hemizygous: AY or ay F 2 is produced by crossing + F 1 s. p167
Progeny at 3 months Female
Progeny at 3 months Male
Parents Male Female
Male Female Progeny at 4 days
Male Female Progeny at 21 days
Progeny at 3 months Male Female
Normal wing type Vestigial wing type
White Eye Red Eye
White eye normal wing Male Sex combs
Red eye normal wing male
Red eye normal wing female
Red eye normal wing male
Reciprocal crosses - Drosophila Sex-linked F 1 red x red 1. P red x white 2. P white x red X W Y x X w X w X w Y x X W X W F 1 white x red X w Y x X W X w X W Y x X W X w Autosomal P normal x vestigial P vestigial x normal VV x vv vv x VV F 1 normal x normal F 1 normal x normal Vv x Vv Vv x Vv If the genes are on autosomes, reciprocal crosses in the P generation will give similar results (F 1 and F 2 ). If the genes are on x chromosomes (sex-linked), reciprocal crosses in the P generation will not give similar results (F 1 and F 2 ). p168