Mendelian Genetics - PDF

**Mendelian**\ Definition of Terms\ **Allele**- One of 2 or more forms a gene may exist in.\ **Dominant**- Allele that overshadow the other one allele. (Usually express in capital letter. Ex. T for tallness in pea plant)\ **Recessive**- Allele that is being covered by the dominant allele. (Usually e...

**Mendelian**\ Definition of Terms\ **Allele**- One of 2 or more forms a gene may exist in.\ **Dominant**- Allele that overshadow the other one allele. (Usually express in capital letter. Ex. T for tallness in pea plant)\ **Recessive**- Allele that is being covered by the dominant allele. (Usually express in small letter. Ex. t for shortness in pea plant)\ **Homozygous** - Same alleles are present in a gene. It can be homozygous dominant (TT) or homozygous recessive (tt).\ **Heterozygous**- Different alleles are present in a gene (Tt).\ **Pure line**- Group of individuals possessing similar genetic background.\ **Hybrid**- Group of individuals with different genetic background.\ **Phenotype**- Referring to the physical trait.\ **Genotype**- Referring to the genetic made-up.\ **Gametes**- Sex cells carrying genes\ **Progeny**- Another term for offspring.\ \ **Punnett Square\ **-Punnett square is a square diagram that is used to predict the genotypes of a particular cross or breeding experiment.\ -It is named after Reginald C. Punnett, who devised the approach in 1905.\ -Allows the prediction of the percentages of phenotypes in the offspring of a cross from known genotypes.\ -A Punnett square can be used to determine a missing genotype based on the other genotypes involved in a cross.\ **Non-Mendelian Genetics**\ -Inheritance of characteristics is not always as simple as it is for the characteristics that Mendel studied in pea plants. -In Mendelian inheritance 2 phenotypes are only observe. But geneticists now know that inheritance is often more complex than this\ **Non-Mendelian Genetics - Incomplete dominance\ **-Phenotype of a heterozygote offspring is somewhere in between the phenotypes of both homozygous parents.\ -This occurs when the dominant allele is not completely dominant. In this case, an intermediate phenotype results in heterozygotes who inherit both alleles.\ -The genotype of an organism with incomplete dominance can be determined from its phenotype.\ **Non-Mendelian Genetics - Codominance\ **-Both alleles are expressed equally in the phenotype of the heterozygote.\ -Occurs when two alleles for a gene are expressed equally in the phenotype of heterozygotes.\ -The red and white flower in the figure has codominant alleles for red petals and white petals.\ **Non-Mendelian Genetics - Multiple Alleles\ **-Many genes, have multiple (more than two) alleles.\ An example is ABO blood type in humans. -The majority of human genes are thought to have more than two normal versions, or alleles. Traits controlled by a single gene with more than two alleles are called multiple allele traits.\ **Non-Mendelian Genetics - Multiple Alleles\ **-Complete dominance and codominance may occur in this pattern of inheritance.\ -A is dominant over O, B is dominant over O and A is codominant with B hence, both alleles are express.\ **Non-Mendelian Genetics - Polygenic traits\ **-Controlled by more than one gene, and each gene may have two or more alleles. The genes may be on the same chromosome or on non-homologous chromosomes. -The inheritance of polygenic characteristics is very complicated. Such characteristics may have many possible phenotypes. -Human physical traits such as hair color, height, skin color, blood pressure, intelligence, autism, and longevity are some of the examples of polygenic inheritance.