Variations on Mendels Laws NonMendelian Traits 1 Incomplete

Variations on Mendel’s Laws (Non-Mendelian Traits) 1. Incomplete dominance 2. Codominance 3. Polygenic traits 4. Pleiotropy 5. Genomic imprinting 6. Linked traits 7. Sex linked traits

Incomplete dominance, in which the heterozygote appears to be intermediate between the two homozygotes.

Hypercholesterolemia (mild disease: Incomplete dominance Hh) HH hh

Codominance, in which the heterozygote displays characteristics of both homozygotes. blood type AB is an example With incomplete dominance, the phenotype of a heterozygote appears to be an intermediate blend of the phenotypes of the two homozygotes. With codominance, a heterozygote has a phenotype that exhibits characteristics of both homozygotes

Multiple Allelism (a single gene has more than two alleles) q A, B, and O alleles q The A and B alleles are both completely dominant to O. q The A and B alleles are codominant to each other. q Individuals can be one of four different blood types: A, B, AB, and O.

Multiple alleles-there are 3 alleles for blood type. Genotype Phenotype A type blood AA, AO B type blood BB, BO AB type blood AB O type blood OO A and B are called “_____" alleles O is “_____. "

Who is your daddy? Can this child belong to this couple? A. Yes B. No

A B B AB AB A A AB AB A B o AB Ao o A B AB Bo B B AB Bo o AB Ao A AB Ao o Bo oo

Polygenic Trait: A trait that is influenced by several different genes Eg: skin color, eye color, height. We do not know all the genes for height; there at least 20! Polygenic inheritance Multiple genes Single trait (e. g. , height, skin color) The term “additive effects” describes what happens when the effects of alleles from multiple genes all contribute to the ultimate phenotype

PLEIOTROPY : SICKLE CELL DISEASE q. In pleiotropy, one gene influences multiple unrelated traits. q. Most, if not all, genes may be pleiotropic.

What is the benefit of “almost” having sickle cell disease?

Pleiotropy a single gene has multiple traits Example: SRY gene Sex-determining Region on the Y-chromosome” SRY gene 1. 2. 3. 4. Causes testes development Internal and external male reproductive structures Following the gonads secretion of testosterone, other developmental changes also occur Behavioral traits SRY protein

Genomic Imprinting Gene is expressed depending on which parent it is inherited from

Genomic imprinting in humans • Angelman syndrome Learning difficulties, speech problems, seizures, jerky movements, and an unusually happy disposition (Individuals are missing gene activity that normally comes from mom) • Prader-Willi syndrome Symptoms include learning difficulties, short stature, and compulsive eating. Individuals are missing gene activity that normally comes from dad.

Linked Genes Freckles and red hair are examples of linked genes Genes on the same chromosome are sometimes inherited together.

What of the following traits are most likely to be unlinked due to crossing over? Scale size Scale shape Scale sharpness Scale color Scale shininess A. Scale size and scale shape B. Scale color and scale sharpness C. Scale shape and scale sharpness D. Scale size and scale shininess

What law does linked traits violate? A. Law of segregation B. Law of independent assortment C. Both the laws D. None of the laws

Sex-linked traits • genes are USUALLY on ____ • more frequent in ____ • why? • X-linked genes: – Hemophilia – Baldness – Duchenne muscular dystrophy

The gene for baldness is… • Known: recessive & found on X chromosome • alleles: – – • genotypes: – normal – bald – carriers female?

Sex linked trait- Calico cats Can a male cat ever be a calico?

White eyes in fruit flies is a X- linked recessive trait Alleles X R – red eyes (normal) Genotype? ? Red eyed Female: ? ? White eyed Female: ? ? Red eyed Male: ? ? White eyed Male: ? ? ? X r – white eyes

In a cross between a pure bred, red-eyed female fruit fly and a white-eyed male what percent of the male offspring will have white eyes? (White eye is an X-linked recessive trait) A. 100% B. 75% C. 25% D. 0%

Cross a heterozygous red eyed (normal) female fruit fly with a white eyed male. White eye is an X-linked recessive trait. What are the possibilites? A. All normal eye colored fruit flies B. White eyed female, Red eyed female, White eyed male and Red eyed male are all possibilities C. Red eyed female, Red eyed male and White eyed male

Survey: Your phenotype is 100% determined by your genotype. A. True B. False

Environment can affect phenotype

Identical twins!! Epigenetics: Lifw experiences can change the gene expression and that is heritable !!!

To what extent is your IQ heritable? Is intelligence about inheritance of traits? or Is it a function of the environmental conditions one is raised in? The average correlation between IQs of parents & their children is 42% Alcoholism – Is it Genetic? Studies done using 1. Identical Twins from families in which alcoholism runs 2. Twins Adopted by Non-Alcoholic Parents Estimated: 50% Environmental Factors 50% Genetic