Tonight we will look at how living things develop the way they do: through their genetic code. One way to get into this very complex mechanism is to begin with the 20 amino acids. All living things (that we know of) are composed of these simple chemical structures that only contain carbon, hydrogen, oxygen, nitrogen, phosphorus and sulfur (CHONPS). From these 20 simple chemicals (made up of only 6 elements) spring forth every possible living expression known on Earth. Your dog’s hair, the flowers on a tree, the scales on a fish — all of these are composed of amino acids, nothing more or less.
How these various amino acids are arranged to make an eye or arm is determined by the genetic code stored in each and every cell of our bodies. In the nucleus of our cells is stored our karyotype, 23 pairs of chromosomes, each one composed of hundreds of genes, or alleles, the genes built from the genetic bases codes: adenine-thymine, guanine-cytosine.
Each of our cells receives this information when it splits itself into two daughter cells, a reproductive process called mitosis. A special type of cell reproduction, meiosis, occurs when a female egg is fertilized with male sperm. This is the genetic mechanism which allows for the diversity of life, called “crossing over,” which occurs at a chiasma of a chromosome..
Please answer these following questions on the blank worksheets provided in this week’s class.
In pea plants, yellow peas are dominant over green peas.
Use a Punnett square to predict the genetic outcome (offspring) of a cross between two plants for yellow peas that yield a small amount of green peas.
The long hair of persian cats is recessive to the short hair of siamese cats. Complete a Punnett Square when a a purebred persian is mated with a purebred siamese cat.
The black coat of persian cat is dominant to the brown and tan coat of siamese. Complete a Punnett Square when a a purebred black persian is mated with a purebred brown siamese cat.
In four o’clock flowers, red plants are purebred for the dominant allele (R) of the gene for flower color. Plants with white flowers are purebred for the recessive (r) allele of the same gene. Plants with pink flowers have one of each of the two alleles. Complete a Punnett square that is expected when plants with pink flowers are intercrossed.
In humans, brown eyes (B) are dominant over blue (b). A brown-eyed man marries a blue-eyed woman and they have three children, two of whom are brown-eyed and one of whom is blue-eyed. Draw the Punnett square that illustrates this marriage.
Suppose one of the brown-eyed children marries someone with blue eyes. Use the second Punnett square to predict their offspring.
Here are some good Punnett practice problem sites. In fact, the problems above (and likely the questions on the midterm) come from these sites.
The Association for Biology Laboratory Education has a really good .pdf handout on the step by step procedure to solving Punnett square problems.Here is my own list:
If you’re daring, try the challenging Berkeley University problems (the answers are here)
So practice, practice, practice… Bring any problems you have difficulty with to class, and we’ll work them out together.
Additionally, complete one genetic disorder worksheet, using the Genetics Home Reference website, the OMIM reference number and GeneCards to complete the worksheet.