Degrees of Dominance Complete dominance occurs when phenotypes

Degrees of Dominance • Complete dominance occurs when phenotypes of the heterozygote and dominant homozygote are identical Copyright © 2008 Pearson Education Inc. , publishing as Pearson Benjamin Cummings

Extending Mendelian Genetics for a Single Gene • Inheritance of characters by a single gene may deviate from simple Mendelian patterns in the following situations: – Sex Linked Traits -When alleles are on the sex chromosomes. (color blindness) – Incomplete Dominance -When alleles are not completely dominant or recessive (pink flowers from red and white phenotype) – Multiple Alleles - When a gene has more than two alleles. (Blood Type) Copyright © 2008 Pearson Education Inc. , publishing as Pearson Benjamin Cummings

Sex linked traits *Hemophilia *Muscular dystrophy *Red/green colorblindness *Rickets

Discovery of Sex Linkage Thomas Hunt Morgan • First to associate a specific gene on a specific chromosome (early 1900’s) • Mated flies

Sex linked genes • Genes located on sex chromosomes • Most are usually genes on X chromosomes • Have unique patterns of inheritance – Mothers pass sex-linked alleles to daughters and sons – Fathers pass sex-linked alleles to daughters, NOT sons

Muscular Dystrophy • • Absence of a key protein called dystrophin Symptoms: weakening of muscles 1 out of 3500 males in US Rarely live past 20’s

Hemophilia • Sex linked recessive • Absence of proteins required for blood clotting • Sons born to women with a family history of hemophilia • Queen Victoria of England – Introduced to royal family thru a mutation in one of sex cells: carrier of allele – The royal families of Prusia, Russia, Spain had Hemophilia genes that spread thru their families

• In Codominance, phenotypes of both alleles are exhibited in the heterozygote Example: Pink/white flower, Roan horse both colors are being expressed.

How can I make lots of money? • If I was a horse breeder and I wanted to sell Roan horses what horse color do I want for my breeding stock? RR (red), rr (white), Rr (Roan)? Draw Punnent Square.

Incomplete Dominance • Offspring has a phenotype that is intermediate between the traits of its two parents. • Ex. Red flowering Snapdragon is crossed with a white flowering Snapdragon the offspring is pink flowers. Neither the red or the white Allele is dominant. There is just less pigment.

Fig. 14 -10 -1 P Generation Red CRCR Gametes White CW CW CR CW

Fig. 14 -10 -2 P Generation Red CRCR Gametes White CW CW CR CW Pink CRCW F 1 Generation In incomplete dominance, the phenotype of F 1 hybrids is somewhere between the phenotypes of the two parental varieties Gametes 1/2 CR 1/ 2 CW

Fig. 14 -10 -3 P Generation Red CRCR White CW CW CR Gametes CW Pink CRCW F 1 Generation Gametes 1/2 CR 1/ CW 2 Sperm 1/ 2 CR 1/ 2 CW F 2 Generation 1/ 2 CR Eggs 1/ 2 CRCR CRCW CW

Incomplete Dominance

What would happen? • Could a plant breeder produce only pink flowering snapdragons by crossing pinkflowering snapdragons and white – flowering snapdragons? • Why?

Multiple Alleles • Most genes exist in populations in more than two allelic forms • For example, the four phenotypes of the ABO blood group in humans are determined by three alleles for the enzyme (I) that attaches A or B carbohydrates to red blood cells: IA, IB, and i. • Multiple alleles control the ABO blood groups. Different combinations of three alleles result in four blood phenotypes (A, AB, B, and O) Copyright © 2008 Pearson Education Inc. , publishing as Pearson Benjamin Cummings

Fig. 14 -11 Allele IA IB Carbohydrate A B i none (a) The three alleles for the ABO blood groups and their associated carbohydrates Genotype Red blood cell appearance Phenotype (blood group) IAIA or IA i A IBIB or IB i B IA IB AB ii O (b) Blood group genotypes and phenotypes

• Antigens – Located in Plasma. “Bad Guy” • Antibodies – located on surface of red blood cells. “Anti-A antibodies” Blood Group Antigens Antibodies Can give blood to… Can receive blood from… AB A, B NONE AB AB, A, B, O Universal Receiver A A B A, AB A, O B B A B, AB B, O O NONE A&B A, B, AB, O Universal Donor O

What Blood Types will be… • An Universal Donor? O. Does not contain any A or B antigens (bad guys) at all. • An Universal Recipient? AB. Can receive blood from all other blood groups.

Did you know? • Another inheritance pattern demonstrated by the ABO blood group is CODOMINANCE. • Explain why?

Oh No! We need to go the ER! • You need blood now what?

ABO Blood System

Rh Factor • Rh is a protein that is attached to a red blood cell. • Rh- is the absence of the Rh factor on the red blood cell. (Just like the O blood cell. ) • You can give Rh- blood to a patient with Rh+ blood but not vice versa. • Mother has 1 st child…the child is Rh+ (from the father)…baby’s and mother’s blood mix at time of delivery. Once exposed to Rh+ mother makes Rh antibodies. • Mother is pregnant with 2 nd child (Rh+, same dad) The mother has Rh antibodies so her body attacks the babies blood cells and she miscarries.

Rh factor • Treatment: Rh Immune Globulin- It destroys baby cells in mom’s blood and suppresses mom’s Rh antibody production.

Fig. 14 -15 b 1 st generation (grandparents) 2 nd generation (parents, aunts, and uncles) Ww ww ww Ww Ww Ww ww 3 rd generation (two sisters) WW or Ww Widow’s peak ww No widow’s peak (a) Is a widow’s peak a dominant or recessive trait?

Fig. 14 -15 c 1 st generation (grandparents) Ff 2 nd generation (parents, aunts, and uncles) FF or Ff ff ff Ff Ff Ff ff ff FF or Ff 3 rd generation (two sisters) Attached earlobe Free earlobe (b) Is an attached earlobe a dominant or recessive trait?