(REP) Reproduction Lesson

Reproduction Lesson

An ultrasound uses sound waves to create images of internal organs and structures within the human body.  Ultrasounds are also used quite often to see an image of a fetus. The 32-week-old fetus in the video below can be seen yawning thanks to a 4D ultrasound image. Most humans, infants and adults, have 46 chromosomes. Humans and most multicellular organisms reproduce sexually. In sexual reproduction, the offspring receives a set of chromosomes from both parents. The chromosomes are located in specialized cells called gametes. The male and female gametes are haploid which means they have only one set of chromosomes. When the female gamete combines with the male gamete; a zygote forms with two sets of chromosomes. This new organism or zygote is now diploid. It has the genetic information from both parents.

 

Watch the video below of a baby yawning in the womb.

 

 

 

The parent cell gets ready for meiosis by copying its chromosomes. In Meiosis I, all of the chromosomes have copies of themselves. This doubles the number of chromosomes within the cell. The phases of meiosis are very similar to the stages of mitosis. During Prophase I, homologous chromosomes from each parent pair up to form two attached sets of chromatids called a tetrad. The homologous pair of chromosomes can exchange genetic information. This exchange of genetic information is known as crossing-over, and it provides important genetic variation among offspring. The image below depicts how crossing-over occurs when segments of DNA are swapped between two homologous chromosomes. In Metaphase I, each tetrad lines up along the center of the cell and attaches to a single spindle fiber; crossing over may occur to provide additional genetic variation among offspring. In Anaphase I, tetrads are separated and go to different new cells; the sister chromatids remain attached. In Telophase I, cells may finish cytokenesis, or may stay only partially divided. The two cells are haploid because they now contain one of each pair of chromosomes.

Meiosis II begins with the two cells just created at the end of meiosis I. During prophase II, the nuclear membrane breaks down as the cell gets ready to divide. In Metaphase II, sister chromatids line up on individual spindle fibers.

Metaphase II looks like metaphase as seen in mitosis, the chromosomes are aligned in the center of the cell. During anaphase II, sister chromatids move to the opposite sides of the cells.

This separation ensures that each new cell will have only half as many chromosomes as the original cell in prophase I. In telophase II, the nuclear membrane reforms around the nuclei in each of the four cells. Cytokenesis separates the four new haploid cells.

The following humorous, but informative, video focuses on the process of meiosis as it occurs in the testes of Drosophila melanogaster, the fruit fly, commonly used in genetic research. A cartoon fly named Dros flies into a lab scene humming the tune to the meiosis square dance song. What follows is a musical and memorable explanation of meiosis.

 

Watch the video on The Meiosis Square Dance. Complete the Meiosis Square Dance Note-guide while watching. 

Meiosis Square Dance Note-guide Links to an external site.

 

 

 

See description of diagram Links to an external site.

 

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