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Chapter 16 Blog: Genetics (Maria W)

Page history last edited by Maria Waterhouse 13 years, 3 months ago

In the first section of this page, you will write a daily summary of that day's class.  For example in  your chapter 2 blog, your first entry should be titled9/3/10.  You should then write a one or two paragraph summary of that day's lecture, outlining the major points.  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 16.1 The beginning of chapter 16 starts off with an explanation of Mendel and how his experiments changed the world. He used peas to trace dominant and recessive genes throughout breeding, including color, height, pea shape, and pod shape. Peas were useful because they were fast, self fertilized, and had a variety of traits that could be one or the other. Mendel bred pea plants of the same phenotypes, and was able to come up with many useful explanations, such as genes, alleles, and genotypes. He did this through noticing patterns between each generation, and used Punnett squares to organize the different traits. He was able to determine that offspring get one allele from each parent when they are produced, and the dominant gene will mask the recessive gene. He also did experiments with dihybrid crosses, or plants with more than one different trait. With these different amount of traits, the different alleles that the child would be given could vary, depending on probability. Mendel also created a law stating that the alleles of different genes assort independently from one another during gamete production.

 

16.2 Chromosome theory of inheritance has many different principles, including that chromosomes contain DNA, children inherit the DNA from their parents, and how meiosis relates to how the separation of chromosomes occur. Each parent gives one set of chromosomes to the child, which each of them received from their own parents. Each chromosome contains different genes, and each of those genes is segregated in meiosis, and randomly given to the child. Separation of the homologous pairs of chromosomes allows for the child to only receive one set of genes. Mendel theorized this by called it independent assortment. Scientists used his findings and made up a set of principles that explain the chromosome theory of inheritance. These are best described in the book's words, so I will be copying and pasting. 


  • Chromosomes contain DNA, which is the genetic material. Genes are found in the chromosomes.

  • Chromosomes are replicated and passed from parent to offspring. They are also passed from cell to cell during the development of a multicellular organism.

  • The nucleus of a diploid cell contains two sets of chromosomes, which are found in homologous pairs. The maternal and paternal sets of homologous chromosomes are functionally equivalent; each set carries a full complement of genes.

  • At meiosis, one member of each chromosome pair segregates into one daughter nucleus, and its homologue segregates into the other daughter nucleus. During the formation of haploid cells, the members of different chromosome pairs segregate independently of each other.

  • Gametes are haploid cells that combine to form a diploid cell during fertilization, with each gamete transmitting one set of chromosomes to the offspring.

 

 

16.3 Pedigrees are used to analyze an inherited trait over generations in one family. Females are represented by a circle, males by a square. Homozygous for the trait is indicated by a black circle (or colored in), while completely unaffected persons are shown as a blank shape. Those who are heterozygous are shown as a half colored in, half blank shape. Pedigrees are useful for determining if parents exhibit the gene, and whether the trait is dominant or recessive, according to patterns it shows. It also predicts the possibility of an individual to receive that trait.

 

16.4 Although in mammals, sex is determined by the chromosome given by the father, not all animals follow this way of sex determination. Mammals exhibit the X-Y system, in which the presence of a Y chromosome indicates a male mammal. In insects, an X-O system is used to determine the sex. Females have two X chromosomes, while males have only one. The sex is determined by the ratio between the X chromosome and its set of autosomes. In birds, the males have two of the same chromosome, ZZ, while females have two different chromosomes, ZW. In bees, the sex of the bee is determined by the haplodiploid mechanism. Males stem from an unfertilized haploid cell, whereas females come from a fertilized diploid cell. Environmental factors can play a role in determining the sex in species of reptiles and fish. Some traits can be linked to sex, such as in the experiment run by Thomas Hunt Morgan on fruit flies. The females all exhibited red eyes, whereas males exhibited white and red eyes in different generations. Due to the fact that sons and daughters can exhibit different traits regardless of parental genotypes, genes are indicated to be found on chromosomes and passed on through sexual reproduction.

 

16.5 Mendel only considered that genes could be dominant or recessive, and are passed on so that dominant genes mask over the recessive genes. He never considered that there would be different ways for genes to be expressed in offspring. X-linked inheritance is one way that traits can be passed down. Since male humans only have one X chromosome from their mothers, they are more likely to receive a recessive trait, rather than have it masked over by the X their father gave them in the case of a female. Incomplete dominance is when the two traits are blended together in a heterzygote, meaning a red flower and a white flower would make a pink flower. Blood types follow codominance, in which the heterozygote expresses both genes together. There is also a sex-influenced inheritance, in which the trait is recessive in one gender, but dominant in the other, which affects the phenotypes. This changes scientists views on the dominant and recessive genes, and changes the ratios Mendel originally came up with.

 

16.6 the type of allele each parent holds is important in figuring out the probability of what the offspring would receive. When each parent is heterozygous, they each have a 1/2 chance of giving the child the recessive gene. Multiplying those two halves together makes the child have a 1/4 chance of being homozygous recessive. However, when each event is mutually exclusive, or which the question includes an either/or statement, the probabilities of the two parents would be added together. This is how scientists conclude the probability of a child having a trait.

 

 

 

B.  Useful Materials

 

This video shows how to interpret pedigrees for humans. The woman on the screen describes why she made her decisions and how the children would be affected.

 

http://www.sciencecourseware.org/vcise/drosophila/Drosophila.php?guestaccess=1

This is a virtual experiment of the Thomas Hunt Morgan experiment. It shows the way the experiment is run and lets you run it hands on to understand it more.

 

http://www.ncbi.nlm.nih.gov/pubmed/19938636

This PubMed article describes the differences between genotype and phenotype of those with Huntington's disease in their family.

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