Tab Topics 4

Sex Cells

The game can help...

During gameplay, students will see that each robot type is defined by one pair of alleles, and that each bot gets one allele from each parental bot put into the recycler. This process mirrors inheritance through sex cells. Each human has two pairs of each type of chromosome, and gets half of each pair from the parents. The half-set of chromosomes is passed from each parent to the offspring via sex cells—sperm and ova. When the sex cells combine, a new individual is produced with a full set of chromosomes.

Teaching Snapshot

A teacher introduces the concept that organisms, such as humans, contain two pairs of each type of chromosome (the genetic materials that hold alleles), and produce genetically unique offspring by each parent providing half their genetic material. It is randomly determined which half is passed on during the production of sex cells (sperm and ova); the sex cells from the parents combine to produce offspring with a full set of genes. The teacher then asks which part of the game reflects this process. The students reply by describing the process of using the recycler, and its role in generating offspring robots.

Heredity Slideshow

Slides 2, 3, and 4 relate to the process of reproduction. They highlight that both parents have two homologous pairs of each allele, and pass only one half of each pair to the offspring. While the slideshow does not mention sex cells, they are cells that contain half the genetic material of each parent, and are combined to produce the offspring. When sex cells are made, the genetic material is randomly divided so that each sex cell has one half of each homologous pair of each allele.

Download slideshow PPT

What the Textbooks Say

Some textbooks cover egg and sperm cells in the genetics chapter. They generally explain that dominant and recessive traits are carried by chromosomes, that chromosomes are made up of long strands of DNA, and that a gene is one section of the DNA strand. Unlike other cells, which contain two sets of chromosomes, sex cells each contain only one set. When an egg cell and a sperm cell fuse, they create a pair of chromosomes for their offspring; the offspring’s chromosomes are different from those of either parent. A single gene on a single chromosome in a sex cell is called an allele. Two alleles—one from each parent—form their offspring’s genes. Students frequently do not understand the relationships among DNA, chromosomes, and genes.

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