Where does the variation Darwin observed in populations come from?? GENES!!

Mendelian Genetics Augustinian Monk Gregor Mendel In the1850s he developed LAWS of inheritance based upon his work with pea plants

mate 2 purebred peas mate 2 hybrid peas

Law of Segregation Traits exist in two forms called alleles (we now call them genes) Alleles segregate (separate) during gamete formation and re-join during fertilization

Mendelian Vocabulary Phenotype = physical characteristic Genotype = genetic compostion, AA, Aa Homozygous = two genes are the same Heterozygous = two genes are different

Punnett Square

The Test Cross

Traits controlled by a dominant allele So only one dominant allele is needed to express the trait. Example: Huntington’s disease inherited disease that causes the progressive breakdown of nerve cells in the brain. It impacts the persons functional abilities and usually results in movement, thinking and psychiatric disorders.

Self Pollination

Germinate

Sex Linked or X Linked Carried on X chromosome of the sex chromosomes. Females XX Male XY More common in Males because Males only have one copy of the X. If he has a mutated gene he has no healthy gene to override it.

Examples of sex linked Color blindness Hemophilia Muscular dystrophy

Color blind problem: Cross a man that is color blind with a homozygous female that is not color blind. What are the probability of having a child that is color blind?

Cross a heterozygous female with a male that is not color blind. What is the probability of having a son that is color blind? What is the probailitiy of having a girl that is color blind?

A Carrier Is a person that carries the gene but does not exhibit the phenotype

Being a carrier Disadvantage - can pass on some genetic disorders if both parents are carriers Tay Sachs If sex- linked mom can be a carrier and not know it and pass it on to her sons. muscular dystrophy Advantage- those in Africa that are carriers of the sickle cell trait are immune to Malaria

Modern Inheritance Patterns Incomplete Dominance Ex. Snapdragons Having 2 Red alleles produce more color than those with only one allele

Co-Dominance Another example: Roan color

Multiple Alleles 3 possible alleles, A, B, and i

Dihybrid Cross

Look at One Trait at a Time

Pleiotrophy One gene has multiple effects…

Epistasis More than one gene needed to produce a single trait. Ex. In mice… B = black coat b = brown coat C = melanin deposted c = no melanin deposited

Polygenic Inheritance Many genes effect a genotype ex. If human skin color was controlled by 3 genes… A, B, C – dark a, b, c - light

Environmental Effects