Inheritance Patterns

Gregor Mendel discovered the basic principles of heredity by breeding garden peas in carefully planned experiments

Mendel’s Results

Mendel’s 3 Laws Law of Dominance Law of Segregation Law of Independent Assortment

Law of Dominance There are two alleles for each gene One is dominant over the other, which is recessive Dominant means it is always expressed, recessive is only expressed if there are two copies of the allele

Mendel’s Laws: Law of Segregation Sexual organism have two copies of a gene One from mom and one from dad The law of segregation states that the two alleles separate (segregate) during meiosis and end up in different gametes (sex cells) Thus, an egg or a sperm gets only one of the two alleles that are present in the somatic cells of an organism

Mendel’s Laws: Law of Independent Assortment The law of independent assortment states that each pair of alleles segregates independently of other pairs of alleles during gamete formation Strictly speaking, this law applies only to genes on different, non- homologous chromosomes Genes located near each other on the same chromosome tend to be inherited together

Non-Mendelian Inheritance

Incomplete dominance No dominant allele - blending The phenotype of F1 hybrids is somewhere between the phenotypes of the two parental varieties Ex: a red and white flower makes a pink flower

P Generation Red CRCR White CWCW F1 Generation CR CW Gametes Pink CRCW 2 2 Sperm F2 Generation 1 CR 1 CW 2 2 1 CR 2 CRCR CRCW Eggs 1 CW 2 CRCW CWCW

Codominance Two dominant alleles Each allele affects the phenotype in separate, distinguishable ways Ex: a red and white flower make a marbled, or speckled, flower

Multiple Alleles Most genes exist in populations in more than two allelic forms For example, the ABO Blood type system has 3 alleles: The IA allele adds the A carbohydrate, The IB allele adds the B carbohydrate; The i allele adds neither

Blood Type Punnett square

Blood Typing lab!

Skin Color How do we get skin color?

Polygenic Inheritance AaBbCc AaBbCc aabbcc Aabbcc AaBbcc AaBbCc AABbCc AABBCc AABBCC Polygenic inheritance results from an additive effect of two or more genes on a single phenotype Skin color in humans is an example of polygenic inheritance Eye color is another example: at least 8 genes code for eye color in humans 20/64 15/64 Fraction of progeny 6/64 1/64