11-3 Heredity Following Different Rules Mulitple Alleles, Sex-linked traits, and Polygenic Inheritance

Multiple Alleles Presence of more than 1 allele for a genetic trait Mice fur Pigeon feathers

Multiple Alleles in Humans Blood Types 4 types A, B, and O Rh Different blood types determined by the presence of a protein on blood’s surface

Blood Groups Human blood comes in a variety of genetically determined blood groups Using the wrong blood during a blood transfusion can be fatal A number of genes help determine blood type but we will focus on two: ABO blood groups Rh blood groups

Blood Groups—the easy one first The Rh blood group is determined by a single gene with 2 alleles—positive and negative The positive allele is dominant You need two Rh- alleles (Rh-/Rh-) to be Rh negative

ABO Blood Groups This is a case of multiple alleles There are 3 alleles for this gene—A, B, and O. AND…A and B are codominant! O is recessive to A and B Alleles A and B produce antigens (which are carbohydrates) on the surface of red blood cells O produces NO antigens

ABO Blood Groups—the wrong blood can be FATAL Antigens are recognized by the immune system and induce an immune response If the wrong blood is transfused, the body will respond to these antigens by producing antibodies Antibodies are named for what they attack Antibodies bind to the foreign molecule (the antigen) and blood clumping will occur, which leads to blood clotting, which leads to death

ABO Blood Groups If you have blood type A, then you have: The “A” antigen on the surface or your RBCs You have anti-B antibodies You can receive type A blood and type O blood Remember: Your antibodies are named for what they attack—so if you received type AB or type B blood then clumping would occur.

ABO Blood Groups Try this cross Cross a person who’s genotype is IAIA with a person who is IAIB. Give the possible genotypes and phenotypes

Cross a person who’s genotype is IAIA with a person who is IAIB Gametes= IA ,IA and IA, IB Cross: IA IA IA IAIA IAIA IAIB IB IAIB

Genotypes= ½ IAIA, ½ IAIB Phenotypes = ½Type A, ½ Type AB

Sex Linked Genes Many sex-linked genes are found on the X-chromosome What are linked genes? They can be separated during meiosis through CROSSING OVER Genes carried on the X or Y chromosome are sex linked because they are on the sex chromosomes Many sex-linked genes are found on the X-chromosome

Sex Linked Genes The X chromosome has many genes that are important for growth and development The Y-chromosome only contains a few genes All X-linked traits are expressed in males WHY??????? Males only have 1 copy of the X chromosome, while females need 2 copies of the defective gene

Carrier: An individual possessing an unexpressed recessive trait

Sex-Linked Gene Disorders Colorblindness 3 human genes associated with color vision are located on the X-chromosome In males, a defective version of any one of these produces colorblindness Females must receive 2 copies of the allele to be colorblind XCXc XCXC XCY XcY

Sex-Linked Gene Disorders cont. Hemophilia 2 important genes on the X-chromosome that code for proteins control blood clotting A recessive allele in either of these 2 genes may lead to hemophilia “bleeders disease” Injections of normal clotting proteins prevent death

Sex-Influenced Genes A person’s phenotype is affected by their sex Ex: Pattern Baldness WOMEN: MEN: BB: not bald BB: not bald   Bb: not bald Bb: bald  bb: bald bb: bald

X-Chromosome Inactivation Females have 2 X-chromosomes… if 1 is enough for males, how does the cell “adjust” to the extra x-chromosome in females? One X-chromosome is randomly switched off Condenses and is called a Barr body

Polygenic Inheritance Remember, poly = many, genic = genes So…polygenic inheritance means A trait that is controlled by 2 or more genes Examples: Skin color Cob length

Upper case and lower case represent alleles BUT Upper case does not mean that it is dominant All heterozygous alleles have intermediate phenotypes Examples: aabbcc: very little melanin in skin AABBCC: a lot of melanin in skin

Other Influences on Gene Expression External Environment Temperature Nutrition Light Chemicals Infectious agent

Phenotype is influenced by your environment (ex: nutrition & exercise) Average height is 10cm more than it was in the 1800’s in the US & Europe due to nutritional improvements Genes that are denied a proper environment in which to reach full expression in 1 generation, can achieve full potential in a later generation (genes are inherited, the environment is not)

Internal Environment Males and females have different structures and hormones therefore genes are expressed differently Peacock feathers Human bald patterns Age