History of Genetics:
Lots of modern genetics originate from studies done by Gregor Mendel. He studied pea plants and taught us many concepts. He is famous for his work with genetics and is considered to be the "father of genetics".
Mendel's Laws of Genetics:
Mendel developed three basic laws that are still used today. The Law of Dominance, the Law of Independent Assortment and the Law of Segregation. Dominance states that some traits are dominant and some traits are recessive. The dominant traits are traits that will always be expressed when present in the phenotype, while the recessive traits are passed on, but only expressed when they are the only alleles present in the genotype (homozygous). The Law of Independent Assortment states that the way traits are expressed does not depend on one another. All traits are independent, and all trait's phenotype are independent from one another. Mendel's last law, the Law of Segregation states that you receive one part of a gene from each of your parents. These laws are the basis of genetics that Mendel was able to create, but he also learned many other concepts from his studies. What he learned was the very basis to all modern genetics. (Wikipedia-GregorMendel)
Mendel's Laws of Genetics:
Mendel developed three basic laws that are still used today. The Law of Dominance, the Law of Independent Assortment and the Law of Segregation. Dominance states that some traits are dominant and some traits are recessive. The dominant traits are traits that will always be expressed when present in the phenotype, while the recessive traits are passed on, but only expressed when they are the only alleles present in the genotype (homozygous). The Law of Independent Assortment states that the way traits are expressed does not depend on one another. All traits are independent, and all trait's phenotype are independent from one another. Mendel's last law, the Law of Segregation states that you receive one part of a gene from each of your parents. These laws are the basis of genetics that Mendel was able to create, but he also learned many other concepts from his studies. What he learned was the very basis to all modern genetics. (Wikipedia-GregorMendel)
BASICS OF GENETICS:
Genes:
Genes are what determine the traits that an organism has. They are the genetic code found within chromosomes that make us who we are. In order to determine what someones genes might be, and where they got them from, Mendel performed many studies. The concepts that we use today require knowledge about everything from alleles, to genotype and phenotype.
Traits:
There are two types of traits, dominant traits, and recessive traits. Dominant traits are the trait that we see most common. When they are present in someones genes they are always expressed because they are the "stronger" of the two types of genes. Dominant genes are always being expressed before dominant genes. The only way for a recessive gene to be expressed is that it must be the only type of gene present.
Alleles:
Alleles and traits are linked. Dominant vs. recessive trait expression is dependent on the alleles that are present. Alleles are the letters that code for an organisms traits. Dominant alleles are written with capital letters (A, B, C) while recessive alleles are expressed with lowercase letters (a, b, c). These letters are always found in pairs, and these pairs determine whether the dominant or recessive trait will be expressed. If a dominant allele is present within the pair (AA, or Aa), then the resulting trait will be dominant. If no dominant allele is present within the pair (aa), then the resulting trait will be recessive.
Homozygous, Heterozygous, and the use of Punnett Squares:
When alleles are paired together they are in either homozygous or heterozygous pairs. A homozygous pair has two of the same type of alleles (both dominant or both recessive). While heterozygous pairs have a dominant and a recessive allele (one dominant and one recessive, Aa) These two types of pairs can help us identify what type of traits future generations may receive. The method used for calculating future traits is known as a Punnett Square. A Punnett Square takes a pair of alleles from each parent and crosses the two to calculate possible traits for the offspring. There are two types of Punnett Squares, monohybrid and dihybrid crosses. A monohybrid cross mixes one pair of alleles from each parent and compares only one trait, while a dihybrid cross mixes two pairs of alleles from each parent and compares two trait. A monohybrid cross can actually be used when one parent's genes (or genotype) are unknown. By crossing the unknown parent with a homozygous parent (with a known genotype) you can figure out the genes (genotype) of the unknown parent based on the resulting offspring. (MakGene.com)
Genes are what determine the traits that an organism has. They are the genetic code found within chromosomes that make us who we are. In order to determine what someones genes might be, and where they got them from, Mendel performed many studies. The concepts that we use today require knowledge about everything from alleles, to genotype and phenotype.
Traits:
There are two types of traits, dominant traits, and recessive traits. Dominant traits are the trait that we see most common. When they are present in someones genes they are always expressed because they are the "stronger" of the two types of genes. Dominant genes are always being expressed before dominant genes. The only way for a recessive gene to be expressed is that it must be the only type of gene present.
Alleles:
Alleles and traits are linked. Dominant vs. recessive trait expression is dependent on the alleles that are present. Alleles are the letters that code for an organisms traits. Dominant alleles are written with capital letters (A, B, C) while recessive alleles are expressed with lowercase letters (a, b, c). These letters are always found in pairs, and these pairs determine whether the dominant or recessive trait will be expressed. If a dominant allele is present within the pair (AA, or Aa), then the resulting trait will be dominant. If no dominant allele is present within the pair (aa), then the resulting trait will be recessive.
Homozygous, Heterozygous, and the use of Punnett Squares:
When alleles are paired together they are in either homozygous or heterozygous pairs. A homozygous pair has two of the same type of alleles (both dominant or both recessive). While heterozygous pairs have a dominant and a recessive allele (one dominant and one recessive, Aa) These two types of pairs can help us identify what type of traits future generations may receive. The method used for calculating future traits is known as a Punnett Square. A Punnett Square takes a pair of alleles from each parent and crosses the two to calculate possible traits for the offspring. There are two types of Punnett Squares, monohybrid and dihybrid crosses. A monohybrid cross mixes one pair of alleles from each parent and compares only one trait, while a dihybrid cross mixes two pairs of alleles from each parent and compares two trait. A monohybrid cross can actually be used when one parent's genes (or genotype) are unknown. By crossing the unknown parent with a homozygous parent (with a known genotype) you can figure out the genes (genotype) of the unknown parent based on the resulting offspring. (MakGene.com)
Genotype and Phenotype:
The punnett square allows you to calculate possible genotypes for an organism. A genotype is the genetic code (expressed as lowercase and uppercase letters in the punnett square) that determines your traits. Your genotype codes for your phenotype. An organisms phenotype is the traits that it expresses.
The punnett square allows you to calculate possible genotypes for an organism. A genotype is the genetic code (expressed as lowercase and uppercase letters in the punnett square) that determines your traits. Your genotype codes for your phenotype. An organisms phenotype is the traits that it expresses.
Possible Punnett Square Crosses:
Monohybrid
Cross
Cross
Using a monohybrid cross like this you could generate an idea of what the parent's genotype might be based on the offspring that they have.
Dihybrid Cross
This dihybrid cross compares two pairs of alleles from each parent (AABB and AaBb). Dihybrid crosses allow you to compare two types of traits at the same time.
Digging Deeper:
Multiple Alleles, Codominance, and Incomplete Dominance:
As genetics begin to become more complex we introduce some new concepts such as multiple alleles, codominance, and incomplete dominance. Multiple alleles refers to when a single trait has more than two options for possible alleles. In the case of blood type there are three types of alleles: Type A (IA), Type B (IB) and Type O (i). Because there is a third allele the possible outcomes changes. With blood type there are three possibilities, Type A (IAIA or IAi) Type B (IBIB, or IBi) Type AB (IAIB) and Type O (ii). In this case there are two types of dominant alleles IA, and IB, and one recessive allele i. Because there are two dominant genes there is a possibility for codominance in this situation. Codominance is where both dominant alleles are passed on to the offspring. The result of codominance is equally shared expression of both genes. When two dominant genes are passed on it's also possible to have incomplete dominance. With incomplete dominance a middle ground is achieved between the two dominant traits. If you had two dominant alleles for color (one red and one blue), then an incomplete dominance would likely result in a purple flower. The difference between these two types of dominance is that codominance would result in a flower that contained both red and blue, while incomplete dominance would combine the two to make purple. As you can see basic genetics can quickly become complex. (Wikipedia-Alleles)
As genetics begin to become more complex we introduce some new concepts such as multiple alleles, codominance, and incomplete dominance. Multiple alleles refers to when a single trait has more than two options for possible alleles. In the case of blood type there are three types of alleles: Type A (IA), Type B (IB) and Type O (i). Because there is a third allele the possible outcomes changes. With blood type there are three possibilities, Type A (IAIA or IAi) Type B (IBIB, or IBi) Type AB (IAIB) and Type O (ii). In this case there are two types of dominant alleles IA, and IB, and one recessive allele i. Because there are two dominant genes there is a possibility for codominance in this situation. Codominance is where both dominant alleles are passed on to the offspring. The result of codominance is equally shared expression of both genes. When two dominant genes are passed on it's also possible to have incomplete dominance. With incomplete dominance a middle ground is achieved between the two dominant traits. If you had two dominant alleles for color (one red and one blue), then an incomplete dominance would likely result in a purple flower. The difference between these two types of dominance is that codominance would result in a flower that contained both red and blue, while incomplete dominance would combine the two to make purple. As you can see basic genetics can quickly become complex. (Wikipedia-Alleles)
Codominance
Incomplete Dominance
Sex-Linked Traits:
Sex linked traits are simply traits that are affected by gender. Because of the fact that males have the XY chromosome and females have the XX chromosome the way certain traits are expressed can depend slightly on our gender. (SexLinkedGenes)
As shown in the picture above, the factor that can determine whether you are affected by one of your parents genes can be dependent partially on your gender. Because the male has a Y chromosome that is shorter than the extra X chromosome that a female has, the male may not have coding to cancel out (via a dominant overriding gene) a possible gene passed down from a parent. This sounds complex and confusing, but basically because males have a different chromosome, they can receive traits differently than a female may have received the gene.
Citations:
Wikipedia-GregorMendel:
"Gregor Mendel." Wikipedia. Wikimedia Foundation, 03 July 2014. Web. 10 Mar. 2014. <http://en.wikipedia.org/wiki/Gregor_Mendel>
MakGene.com:
"What Is the Difference between Homozygous and Heterozygous?" What Is the Difference between Homozygous and Heterozygous? MakGene.com, 2008. Web. 13 Mar. 2014. <http://www.makgene.com/index.cfm?fa=content.display&content_id=39>
Wikipedia-Alleles:
"Allele." Wikipedia. Wikimedia Foundation, 03 Oct. 2014. Web. 10 Mar. 2014. <http://en.wikipedia.org/wiki/Allele>
SexLinkedGenes:
O'Neil, Dennis. "Biological Basis of Heredity: Sex Linked Genes." Biological Basis of Heredity: Sex Linked Genes. N.p., 2012. Web. 10 Mar. 2014. <http://anthro.palomar.edu/biobasis/bio_4.htm>.
Wikipedia-GregorMendel:
"Gregor Mendel." Wikipedia. Wikimedia Foundation, 03 July 2014. Web. 10 Mar. 2014. <http://en.wikipedia.org/wiki/Gregor_Mendel>
MakGene.com:
"What Is the Difference between Homozygous and Heterozygous?" What Is the Difference between Homozygous and Heterozygous? MakGene.com, 2008. Web. 13 Mar. 2014. <http://www.makgene.com/index.cfm?fa=content.display&content_id=39>
Wikipedia-Alleles:
"Allele." Wikipedia. Wikimedia Foundation, 03 Oct. 2014. Web. 10 Mar. 2014. <http://en.wikipedia.org/wiki/Allele>
SexLinkedGenes:
O'Neil, Dennis. "Biological Basis of Heredity: Sex Linked Genes." Biological Basis of Heredity: Sex Linked Genes. N.p., 2012. Web. 10 Mar. 2014. <http://anthro.palomar.edu/biobasis/bio_4.htm>.