• If you are citizen of an European Union member nation, you may not use this service unless you are at least 16 years old.

  • You already know Dokkio is an AI-powered assistant to organize & manage your digital files & messages. Very soon, Dokkio will support Outlook as well as One Drive. Check it out today!


Chapter 16: Simple Patterns of Inheritance (Robert)

Page history last edited by Robert Canuel Jr. 12 years, 9 months ago

In the first section of this page, you will write a daily summary of that day's class.  For example your first entry should be titled 9/3/10.  You should then write a one or two paragraph summary of that day's topic.  In the second section, you are required to add two items (link to a website, video, animation, student-created slide show, student-created PowerPoint presentation) and one journal article pertaining to a topic in this chapter.  A one-paragraph summary must accompany each item describing the main idea and how it applies to the lecture topic.  Please see the PBWorks help guide for assistance embedding video and other items directly in the page.  I will also produce a how-to video on using tables to wrap text around items and other useful tips.  Please see the syllabus for organization and grading details.


A.  Daily Blog


     Chapter 16 is about simple patterns of inheritance. Sadly writing the wall of text that summarizes this chapter isn't. It all started with the father of genetics, Gregor Johann Mendel. He was a monk who had too much time on his hands. So instead of teaching he decided to grow peas. Yes, peas. Those little spherical vegetables that kids don't like to eat. Whilst he was growing these he noticed that when he mated two pea plants that exhibited different traits, the offspring would take on a characteristic of one of the parents. Then when he crossed the offspring some of the traits that disappeared in the previous generation reappeared. He became so fascinated by this that he did this for 8 years, and it's not even a job. Mendel's experiment was true genius at the time, because it came with so many advantages. Such advantages include: the lack of the degenerate effects of inbreeding, the short time it takes for the plants to mature, the relative ease of mating the plants, and the many characteristics that pea plants had that could be expressed in 2 ways. Because it does not take a long time for the plants to mature (unlike humans which take about 21 years and 9 months) the expressed phenotypes can be measured quickly. Also since the pea plants have many traits that have only 2 variations, that eliminates other factors that could mess up Mendel's experiment. Mendel only looked at 7 of these traits: height, seed color, flower position, flower color, seed shape, pod shape, pod color. First he would breed the plants so that he could establish a set of plants whose offspring (via self-fertilization) generations later would yield the same trait as its ancestor. Once established he would then cross these pure bred plants with another pure bred plant that exhibited the other variation for that trait, e. g. a pure bred tall plant with a pure bred short plant. This specific cross would yield plants that are all hybrids for that trait, i. e. they have the tall gene and the short gene. The thing though with these plants is that they exhibit the tall phenotype. Mendel let these plants self-fertilize and found out that the short phenotype popped up again. He then concluded that the plants have 2 alleles for each trait, each trait has a dominant and a recessive form, that each allele is inherited from the parent plants, and that the gametes receive only have one allele each during its formation. This is easier shown in a table (this is known as a Punnett Square, which was named after a guy named Punnett):


First Cross    Parent Genotype: TT Phenotype: Tall
  Parent's Gametes
Parent Genotype: tt Phenotype: Short Tt Tall Tt Tall
Tt Tall Tt Tall
Second Cross   Parent Genotype Tt Phenotype: Tall
  F1's Gametes 
Parent Genotype: Tt Phenotype: Tall  TT Tall Tt Tall
Tt Tall tt Short


Here the genotypes (The alleles they have for that trait) and the phenotypes (The trait expressed) are shown for both parents and offspring. Notice how each gamete only has one of the parents alleles for that trait. The upper case letter signifies an allele for the dominant trait and a lower case letter stands for an allele for the recessive trait. The dominant trait masks the recessive trait when it comes to expression. In order for the recessive trait to be expressed, the plant has to have two alleles for the recessive trait. When an organism has two alleles that are the same then the organism is said to be homozygous (dominant or recessive). If it has an allele for the dominant trait and an allele for the recessive trait then it is said to be heterozygous. Then Mendel decided to do something wicked. He wanted to track two traits at the same time. So he crossed two pure bred plants, one that was dominant for seed color and shape and the other being recessive to those same traits. The first generation yielded the expected hybrids exhibiting the dominant phenotypes (Yellow and Round). But when he let that generation self-fertilize, he found some thing amazing. The second generation yielded plants whose phenotypic ratio was 9 Yellow and Round: 3 Yellow and wrinkled: 3 green and Round: 1 green and wrinkled. Here's is the Square for this dihybrid cross:

F1 cross    Parent Genotype: YyRr Phenotype: Yellow, Round    
  F1's gametes  YR  Yr  yR  yr 
Parent Genotype: YyRr Phenotype: Yellow, Round     YR  YYRR Yellow, Round YYRr Yellow, Round YyRR Yellow, Round YyRr Yellow, Round
Yr  YYRr Yellow, Round YYrr Yellow, wrinkled YyRrYellow, Round Yyrr Yellow, wrinkled
yR  YyRR Yellow, Round YyRr Yellow, Round yyRR green, Round yyRr green, Round
yr  YyRr Yellow, Round Yyrr Yellow, wrinkled yyRr green, Round yyrr green, wrinkled

This led to Mendel believing that alleles are not linked together and sort themselves out independently during the formation of gametes.

     The 2nd section of chapter 16 basically puts chapter 15 and 16.1 together. Alleles are carried on chromosomes as genes. A diploid cell has two sets of DNA, one from the mother and one from the father, that are homologous. During meiosis, the process that produces gametes, the chromosomes independently sort themselves and thus the alleles on the chromosomes. The haploid gametes then combine to form a diploid cell which contains genetic information from each gamete.

     The 3rd section is all about human pedigrees. These are charts that track a specific phenotype. Those individuals who exhibit the trait are marked and those who do not are not marked. For recessive traits, those who are heterozygous are marked halfway for and autosomal trait or with a dot for a sex-linked trait. Pedigrees are useful for tracking diseases that run through families.

     Part 4 talks about determining sex and X-linked inheritance. There are many different ways of determining which sex an organism is. Humans for example use the XY system. A person with XX would be a female and a person with XY would be male. Birds use the ZW system. It basically works the same way but the male has the 2 similar chromosomes i.e. ZZ for male and ZW for female. Bees use a haploid-diploid system, with males hatching from haploid unfertilized eggs and females from fertilized eggs. Some insects use the XO system where the male lacks an X chromosome. The American Alligator uses temperature to determine sex. That having been said let's go back to humans. Since the X chromosome is bigger than the Y chromosome then that means the Y chromosome does not have a gene to match a few of the genes on the X chromosome. That means that if the X chromosome had a gene for a disease that does not have a counterpart in the Y chromosome then the male will express that disease. The best and well-known example of this is Haemophilia.

     Section 6 just talks about probabilities and how to calculate them.


B.  Useful Materials





A website that focuses on Mendel's law of segregation. Because the book only supplies a paragraph for this topic, I looked up a website for it. Mendel's law of segregation is very important because it provides the basis for the Punnett square. That and it ties meiosis with this chapter.




Current Options and New Developments in the Treatment of Haemophilia

     This article is about the current ways to treat Haemophilia, an X-linked disorder that causes extended bleeding time. Normal people form a blood clot with thrombocytes and then held together afterwards by a protein called fibrin. Haemophiliacs are deficient in a protein that aids in fibrin formation, thus effectively extending the period for which the person bleeds. The scientists are thinking about using gene therapy and some other ways to treat haemophilia.


Comments (0)