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Chapter 16 Blog: Simple Patterns of Inheritance (Suma)

Page history last edited by Suma Gondi 13 years, 3 months ago

Gregor Mendel, an Austrian monk, is credited as the father of modern genetics from his experiments doing monohybrid crosses with pea plants.  Since peas have seven known traits that are either dominant or recessive, they are easy to use to see how inheritance occurs.  We also did Punnett squares and pedigrees, which can be used to trace the inheritance of a gene across many generations. 


Genes often have dominant or recessive alleles.  A locus is the physical location of a gene on a chromosome.  The genotype is the genetic composition of an individual, while the phenotype is the physical expression of these genes.  During meiosis, the two copies of the genes segregate from each other, which is called Mendel’s Law of Segregation.   


The Chromosome Theory of Inheritance is the idea that chromosomes contain DNA and genes, are replicated and passed on from parent to offspring or cell to cell in an organism, the nucleus of a diploid cell contains two sets of chromosomes (homologous pairs) that each carry a full complement of genes, one member of each pair segregates into different daughter cells and these segregations occur independently, and gametes are haploid cells that combine to form diploid cells with each gamete transmitting one set of chromosomes.  The law of independent assortment states that the chromosomes align randomly in meiosis I, leading to alleles on different chromosomes being assorted independently.


Mendelian inheritance is the inheritance pattern of genes that segregate and assort independently.  There are many types of this kind of inheritance.  Simple Mendelian inheritance is when one trait is dominant over the other, like height in pea plants.  X- linked inheritance is when dominant and recessive alleles are found on the X chromosome.  Since males have only one, they always express the allele, whether it is dominant or recessive.  Incomplete dominance is when the phenotype expressed is a cross between the parents.  Codominance is when both alleles are expressed at the same time, like blood types in humans.  Sex-influenced inheritance is when the allele is dominant in one sex and recessive in the other, like male-pattern baldness, which is dominant in males and recessive in females.  The environment can also play a role in phenotypes- genetically identical plants grow to different heights in different temperatures.  


1)Inherited Resistance to HIV-1 conferred by an inactivating mutation in CC chemokine receptor 5: studies in populations with contrasting clinical phenotypes, defined racial background, and quantified risk (submitted 2/20/11):  This article references what we talked about in class, with how some people have a mutation on a gene that codes for receptors on T-cells, and therefore those people are not affected by the HIV virus.  This study did testing to determine which populations have those genes, and found that Caucasians are the most likely to have the mutation out of any racial group.  I never knew that there was a small percentage of people who were immune to HIV, and I found that really interesting.


2) This chart (submitted 2/20/11) show the different blood types, as well as the antigens on the surface and antibodies in the blood.  Blood types show codominance, which means both alleles are dominant and are expressed to form a new phenotype.  Blood types are controlled by three different alleles, not just two like in simple inheritance.


3)  Probability and Punnett Squares: (submitted 2/20/11)  This website has a nice overview about Punnett squares and how to figure out the expression of different alleles through probability.  It is a good review if you don't remember how to do a Punnett square or are struggling with probability.



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