Beyond Mendelian Genetics: Understanding Complexity in Heredity
In this brief overview, we explore the intricacies of genetics beyond Mendelian principles. While Mendel focused on simple traits determined by one gene with two alleles, modern genetics reveals a much more complicated landscape. We delve into concepts such as incomplete dominance, where alleles blend in heterozygotes, and codominance, where both alleles manifest in the phenotype. Additionally, we discuss multiple alleles in traits like human blood groups and polygenic traits, influenced by several genes. Gain insight into the complexities shaping heritable characteristics.
Beyond Mendelian Genetics: Understanding Complexity in Heredity
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Presentation Transcript
Beyond Mendelian GeneticsQuick Notes We now know a LOT more than Mendel did!
Remember Mendelian Genetics • In Mendel’s Genetics we talk about a trait that has • 1 gene and that gene has • 2 alleles and one of those alleles has • Complete Dominance
Beyond Mendel • Most genes ARE NOT Mendelian, especially in humans. We now know that most genes are more complicated than that.
Incomplete Dominance • In Incomplete Dominance one allele is not completely dominant over the other resulting in a blending of the characteristics in the heterozygote (a.k.a. an intermediate). • For eample, in one species of plant its flowers can be Red, Pink or White:
The Letters we use: R = Red W = White Incomplete Dominance Genotype Phenotype RR = Red Flowers The Pink is from blending the red allele and the white allele. RW = Pink Flowers WW = White Flowers
Codominance • In Codominance both alleles contribute to the phenotype and BOTH are seen in the phenotype. • For instance, in one breed of chickens we see black chickens, white chickens and black & white speckled chickens.
The Letters we use: B = Black W = White Codominance Genotype Phenotype BB = Black Chicken In the Speckled chicken we SEE both alleles in the phenotype BW = Black & Whitespeckled chicken WW = White Chicken
Multiple Alleles • Multiple alleles is when a trait has only one gene but there are more than 2 alleles. • Example: Human Blood Group has 3 alleles. O B A recessive Codominant We will look at human blood types in more detail later. This is why human blood groups are sometimes referred to as the ABO blood groups.
Polygenic Traits • Polygenic traits or characteristics are ones that are controlled by many genes (3 or more). • Examples are: • Human skin color (up to 8 genes) • Human Eye color • Human hair color (at least 3 genes) • Human height
