Where are genes found?
You may recall that genes are found on structures made up of condensed DNA called chromosomes. Watch the video below to see how genes, chromosomes and DNA are related.
Early Beliefs
The fact that certain biological traits are inherited is a concept that has existed long before the time of the pioneer of genetics, Gregor Mendel.
In the past, humans participated in selective mating in order to ensure that desirable traits would be produced in their offspring. Moreover past records have shown that farmers utilized selective cross breeding of rice plants to improve rice varieties.
In the past, humans participated in selective mating in order to ensure that desirable traits would be produced in their offspring. Moreover past records have shown that farmers utilized selective cross breeding of rice plants to improve rice varieties.
Gregor Mendel
During the mid-19th century, Austrian monk Gregor Mendel conducted several experiments with green peas to explore the basis of genetic inheritance and heredity in plants.
He observed two distinct traits amongst his pea plants. He noticed that some plants produced yellow peas whereas others produced green, some were tall, some were short and both the position and colour of the flower on the stem varied.
There were two reasons that Mendel chose to conduct his experiments with garden peas:
Mendel ensured that he utilized only pure breeding plants (plants that produced offspring that were identical to their parents) and that he cross-pollinated the plants so that they did not self-fertilize. He did this by removing the anthers of a plant to prevent self-fertilization and then combining the male and female sex cells of different plants. (Figure 4)
He observed two distinct traits amongst his pea plants. He noticed that some plants produced yellow peas whereas others produced green, some were tall, some were short and both the position and colour of the flower on the stem varied.
There were two reasons that Mendel chose to conduct his experiments with garden peas:
- There were only two ways that traits could be expressed making it easier to observe inheritance from generation to generation
- Garden peas have the ability to both self and cross fertilize
Mendel ensured that he utilized only pure breeding plants (plants that produced offspring that were identical to their parents) and that he cross-pollinated the plants so that they did not self-fertilize. He did this by removing the anthers of a plant to prevent self-fertilization and then combining the male and female sex cells of different plants. (Figure 4)
Mendel found that certain traits such as a round seeds always dominated regardless of whether the trait came from the male or female plant. He noticed this to occur with several traits such as yellow peas and tall plants. He concluded that specific factors controlled for the traits inherited and expressed within a plant. These factors were later named genes. He also concluded that there are alternate forms of these genes (eg. genes that account for tall or short plants), later called alleles.
Traits that were expressed the most often in pea plants were considered dominant traits whereas those that were expressed less often were considered recessive. Mendel illustrated dominant traits with a capital letter and recessive traits with a lower case letter
Yellow seeds=dominant trait (Y)
Green seeds=recessive trait (y)
Traits that were expressed the most often in pea plants were considered dominant traits whereas those that were expressed less often were considered recessive. Mendel illustrated dominant traits with a capital letter and recessive traits with a lower case letter
Yellow seeds=dominant trait (Y)
Green seeds=recessive trait (y)
Mendel continued on to cross plants that were a hybrid of a specific trait (plant contains both dominant and recessive allele eg. Yy) and labelled this generation the filial or F1 generation. He labelled the offspring of the F1 generation the F2 generation.
He found that 75% of the F2 generation displayed the dominant trait whereas 25% of the offspring displayed the recessive trait as shown in the figure below (Figure 5). This could be explained through the law of segregation the occurs during meiosis. He concluded that each gamete or sex cell in meiosis contains a single allele during their formation. These cells later combine to display the frequency mentioned above.
He found that 75% of the F2 generation displayed the dominant trait whereas 25% of the offspring displayed the recessive trait as shown in the figure below (Figure 5). This could be explained through the law of segregation the occurs during meiosis. He concluded that each gamete or sex cell in meiosis contains a single allele during their formation. These cells later combine to display the frequency mentioned above.
Creating a Personal Profile
Single Trait Inheritance
When discussing heredity it is important to differentiate between the genetic make up of an allelic trait and the physical appearance of a trait. The specific alleles contained in an organism are called the genotype, the phenotype on the other hand is observable genetic trait that is expressed due to interactions of genes with the environment.
It is possible to have two distinct genotypes that display the same phenotype, for example a tall plant could have the genotype YY or Yy. A pure breeding organism contains two identical alleles for a specific trait such as YY or yy, this is a homozygous genotype. A heterozygous genotype however contains both variations of an allele such as Yy.
A monohybrid cross occurs when a single allele pair is crossed (eg. YY x yy). Geneticists use a chart called a Punnett square to organize and conduct genetic crosses in order to demonstrate the possible genetic combinations in the offspring of parental generation.
A test cross is used to determine the genotype of a dominant phenotype. This is done by crossing the unknown genotype and homozygous recessive genotype. As is shown in the figure below, if any offspring express the recessive trait the unknown genotype of the parent will be heterozygous. If all of the traits expressed are dominant then the parental genotype must be homozygous.
It is possible to have two distinct genotypes that display the same phenotype, for example a tall plant could have the genotype YY or Yy. A pure breeding organism contains two identical alleles for a specific trait such as YY or yy, this is a homozygous genotype. A heterozygous genotype however contains both variations of an allele such as Yy.
A monohybrid cross occurs when a single allele pair is crossed (eg. YY x yy). Geneticists use a chart called a Punnett square to organize and conduct genetic crosses in order to demonstrate the possible genetic combinations in the offspring of parental generation.
A test cross is used to determine the genotype of a dominant phenotype. This is done by crossing the unknown genotype and homozygous recessive genotype. As is shown in the figure below, if any offspring express the recessive trait the unknown genotype of the parent will be heterozygous. If all of the traits expressed are dominant then the parental genotype must be homozygous.
Two Trait Inheritance
For the most part, the laws that apply to single trait inheritance also apply to two trait inheritance (dihybrid cross). Mendel conducted dihybrid crosses using the yellow/green and round/wrinkled traits in peas.
He found that when genes are located on separate chromosomes they assort independently of one another, in other words the genes that control for pea shape are inherited independently of the genes that control for pea colour, this is called the law of independent assortment.
Dihybrid Punnett Square Cross
Punnett Square Review Activities
Modelling Activity
Complete the activity in pairs to:
- Observe genetic diversity within your classroom
- Model specific traits
- Conduct genetic crosses
- Explore new types of genetic interactions such as codominance, incomplete dominance and sex-linked traits
azim_maha_genetics_concept_workshop.docx | |
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mendelian_genetics.docx | |
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Chicken Genetics Gizmo
- Click on the image of the dancing chicken to get to a gizmo activity where you will explore how co-dominant traits are inherited in chicken
- The worksheet is attached here
Multiple AllelesUp until now we have only observed traits with two possible alleles. There are however several genes that are controlled by multiple alleles. Drosophila melanogaster, also known as the fruit fly is an organism that has multiple alleles that code for eye colour.
A red eye colour is considered the wild type as it is the most common. Fruit flies can also have apricot, honey or white coloured eyes. In cases like these where multiple alleles exist at a gene locus, upper and lowercase letters are no longer used. Instead, scientists use capital letters with subscript letters or numbers to show different alleles and their combinations. Eg. Blood type A=(IAIA) The genotypes for this trait uses E for the eye colour gene and superscript numbers to demonstrate the dominance hierarchy for the allele. The dominance hierarchy for eye colour in the fruit fly is shown below (Table 1). |
Sample Problem
Attempt the problem below and then click on it to verify your answer.
Genetic Screening
Genetic screening involves the assessment of an individuals' susceptibility to a genetic disorder prior to birth. Prenatal diagnosis can be done through amniocentesis and chrionic villi sampling (CVS).
An example of a disease that can be detected through genetic screening is Huntington's chorea, a neurological disorder that is caused by a dominant allele.
An example of a disease that can be detected through genetic screening is Huntington's chorea, a neurological disorder that is caused by a dominant allele.
Genetic Screening Debate
For the purpose of this assignment, you and your classmates will be divided into several roles for a town hall debating activity. There will be two major viewpoints: supporting or against genetic screening.
You are to look at the social, ethical, moral and economic factors that are influencing the viewpoint of your character. Keep in mind that you are trying to impress your judge (the teacher) with knowledgeable, well-researched and insightful arguments.The breakdown of the assignment, the evaluation rubric and web links to get you started on your research are located below.
You are to look at the social, ethical, moral and economic factors that are influencing the viewpoint of your character. Keep in mind that you are trying to impress your judge (the teacher) with knowledgeable, well-researched and insightful arguments.The breakdown of the assignment, the evaluation rubric and web links to get you started on your research are located below.
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Web links
Debate Rubric
Reproductive Technologies Expert Groups
Reproductive technology involves the use of technology to aid human or animal reproduction.
For this project you will be placed in groups of 4 and individually assigned to a specific type of reproductive technology. Each member of your group will be assigned a different technology and you will be conducting your research and presenting it in an expert group format.
You will be expected to research and create a presentation about this technology using PowerPoint, Glogster or Prezi. You will have 2 weeks to prepare a presentation with your expert groups and will be presenting to your research to your home group members on Week 3. You will be required to create a hand-out summarizing your key ideas for your group members. Questions from your presentations will be on your Unit Test and Final Exam. The presentation requirements are located below.
For this project you will be placed in groups of 4 and individually assigned to a specific type of reproductive technology. Each member of your group will be assigned a different technology and you will be conducting your research and presenting it in an expert group format.
You will be expected to research and create a presentation about this technology using PowerPoint, Glogster or Prezi. You will have 2 weeks to prepare a presentation with your expert groups and will be presenting to your research to your home group members on Week 3. You will be required to create a hand-out summarizing your key ideas for your group members. Questions from your presentations will be on your Unit Test and Final Exam. The presentation requirements are located below.
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Content:
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