Non-Mendelian Genetics

Beyond Dominant and Recessive Alleles

More Complex Patterns of Heredity Incomplete Dominance Codominance Multiple Alleles Polygenic Traits Sex-Linked Traits

Incomplete Dominance – Blending of traits; heterozygous phenotype is somewhere between the two homozygous phenotypes. Ex: Pink flower offspring of white and red flower

Codominance: two dominant alleles are expressed at the same time CRCR CWCW CRCW

NSNA NSNA NANA NANA Codominance NA NA NS NA Sickle-Cell Anemia is another codominant trait. NA NA NSNA NSNA NS NA=Normal RBC NANA NANA NA NS=Sickle Cell RBC

Codominance – Both genes expressed simultaneously; heterozygous individuals exhibit both phenotypes. ~ erminette ~

Multiple Alleles – Some genes have more than two alleles – not more than two alleles in an individual but more than two alleles in a population. Full color: CC, Ccch, Cch, or Cc Himalayan: chch or chc Chinchilla: cchcch, cchch, or cchc Albino: cc

Blood Type Four Blood Types: A, B, AB, O Blood types refer to different carbohydrates on the surface of red blood cells Type A Type B Type AB Type O

Blood Types Blood type is inherited One blood gene is from your mom, one is from your dad Three different alleles: IA -- Type A carbohydrate molecules IB -- Type B carbohydrate molecules i -- neither type of carbohydrate molecule.

Blood Type Blood types are an example of multiple alleles AND codominance A and B are codominant over O O is recessive

Phenotypes and genotypes Can Receive From Can Donate To A IAIA, IAi A, O A, AB B IBIB, IBi B, O B, AB AB IAIB A, B, AB,O O ii A, B, AB, O Awesome Blood Typing Game

Polygenic Traits – Many traits are the result of many genes acting together. ? ? ?

Chromosomes Chromosomes Pairing   Body cells contain 46 chromosomes These 46 cells are arranged in 23 pairs Each of these pairs is called a homologous pair   with one exception, each pair contains chromosomes that are exactly alike in size

Sex Chromosomes Only one pair differs (23rd pair): in females this pair is alike XX in males this pair is different XY

We can use a Punnett square to predict the chances of having a baby boy vs a baby girl 50% chance boy; 50% chance girl X X X Y XX XX XY XY

What are Sex-Linked Traits? Traits that are located on one of the sex chromosomes (X or Y) Hemophilia: Failure of blood to clot Alix and Nicholas II Muscular Dystrophy: wasting away of muscles

Sex-linked traits usually refer to X-linked traits The human X chromosome is much larger than Y So, there are more X-linked traits than Y

Can I inherit a sex-linked disease? Fathers (XY) can only pass disorders to daughters (XX) Mothers (XX) can pass disorders to both sons (XY) and daughters (XX) In humans, the term sex-linked traits usually refers to X-linked traits. The human X-chromosome is much larger than the Y. Thus, there are more X-linked than Y-linked traits. Most X-linked genes have no homologous loci on the Y chromosome. Most genes on the Y chromosome not only have no X counterparts, but they encode traits found only in males (e.g. testis- determining factor). Examples of sex-linked traits in humans are color blindness and hemophilia. Fathers pass X-linked alleles to only and all of their daughters. Males receive their X chromosome only from their mothers. Fathers cannot, therefore, pass sex-linked traits to their sons. Mothers can pass sex-linked alleles to both sons and daughters. Females receive two X-chromosomes, one from each parent. Mothers pass on one X-chromosome (either the maternal or paternal homologue) to every daughter and son. Most disorders are carried on the X chromosome, so males are more likely to inherit them.