Mendel’s Peas were ideal for learning about inheritance, but they do not represent the norm… Traits in pea plants are determined by just two alleles In peas, one allele is clearly dominant & the other is clearly recessive However, things aren’t always this clear- cut and simple in the world of genetics.

What if Mendel looked at mice?  If a female black mouse and a male white mouse were crossed, what will the offspring look like? GREY - 100% are GREY  If the F1 offspring were crossed, what will there offspring look like? - 25% black - 50% grey - 25% white

Incomplete Dominance A cross between two organisms with different traits results in an offspring with a third phenotype that is a blending of the parental traits. It’s like mixing paints: –Red + White = Pink –Red does not totally block (dominate) white, we end up with something in-between.

Inheritance in Snapdragons

Codominance Similar to incomplete dominance in that there is a 3 rd phenotype In COdominance, the “recessive” and “dominant” alleles appear together in the phenotype of hybrid organisms. Red x White = red & white

Let’s look at cattle…. This cow resulted from a cross between a cow with red fur (RR) and a cow with white fur (WW) This is called ‘roan’ fur; red & white fur together (RW)

Sickle Cell Anemia: Codominance & Incomplete Dominance Normally, a person inherits two copies of the gene that produces beta- globin, a protein needed to produce normal hemoglobin (hemoglobin A, genotype AA). A person with sickle cell trait inherits one normal gene and one abnormal gene encoding hemoglobin S (hemoglobin genotype AS).genebeta- globinproteinhemoglobin A Hb A Hb A - normal Hb S Hb A – carriers or sickle cell trait Red blood cells “sickle” and break apart when there is a low [O 2 ](incomplete dominance of A allele; A is not completely expressed all the time); Overall lower concentration of hemoglobin all the time (codominance = both normal and mutant alleles expressed) Hb S Hb S – sickle cell anemia All red blood cells sickle shaped; very painful; anemia ; Requires transfusion

Sickle Cell Anemia and Natural Selection Carriers for sickle cell have an advantage in tropical locations where malaria is prevalent. Carriers have protection from malaria. Malaria is a blood-borne disease transmitted by mosquitoes.

Polygenic (Multifactorial) Traits Phenotype is determine by more than one gene Often results in gradations, where each gene has an additive effect Ex) If 10 gene loci are turned on plant will be 20cm tall, if only 5 loci are turned on plant will be 10cm tall Results in a bell-shaped curve –Skin color & Height are examples in humans

Phenotype Distribution:Polygenic Traits

Full color: CC, Cc ch, Cc h, or Cc Chinchilla: c ch c h, c ch c ch, or c ch cHimalayan: c h c, or c h c h AIbino: cc KEY C = full color; dominant to all other alleles c ch = chinchilla; partial defect in pigmentation; dominant to c h and c alleles c h = Himalayan; color in certain parts of the body; dominant to c allele c = albino; no color; recessive to all other alleles Multiple Alleles More than 2 alleles for a particular trait

ABO Blood Types In addition to having multiple alleles, ABO blood type also exhibits codominance ‘I A’ & ‘I B’ are codominant (A and B = codominant) ‘i’ is recessive (O is recessive to A and B)

ABO Blood Typing GenotypeBlood Type I A I A or I A I (AA or AO) A I B I B or I B I (BB or BO) B I A I B AB ii OO O

What does your ABO blood type mean?  Remember the ‘flags’ on our cell membranes? They help cells to recognize each other.  Some of those flags ‘announce’ your blood type. We call these flags antigens Blood Type Antigen AA BB ABA and B Onone

ABO Blood Transfusions Blood Type Can receive: AA or O BB or O AB*All (Universal recipient) O*O (Universal donor)

Summary of ABO Blood Types

ABO Blood Type Summary

Rh Factor Blood can also be categorized as + or – This refers to the presence (dominant) or absence (recessive) of the Rh antigen PhenotypeGenotype(s)Antigen Rh + Rh + /Rh + or Rh + /Rh - present Rh - Rh - /Rh - Not present

Rh Factor Compatability Mom is Rh- and baby is Rh+ If baby’s blood mixes with mom’s, mother will make Rh antibodies. If the next pregnancy is a Rh+ baby, antibodies will cross the placenta and attack baby’s red blood cells (hemolytic disease) Rh factors must also be taken into account in blood transfusions. Rh- cannot get Rh+ blood

Chromosomal Theory of Inheritance This theory states that genes occupy specific loci on chromosomes and it is the chromosomes that undergo segregation and independent assortment during meiosis.

Gene Linkage & Mapping Chromosomes recombination-and-gene-496 Genes that are farther apart are more likely to cross over. Use frequency of crossover events (recombinant chromosomes to map gene locations. May be separated (Not inherited together) Get inherited together (linked)

Gene Linkage & Mapping Chromosomes According to the chromosomal theory of inheritance, genes on the same chromosome are more likely to be inherited together Crossing over helps to increased variation, but the closer two genes are on a chromosome the more likely they are to be “linked” The frequency of crossing over between two genes can be used to estimate the relative positions of genes on chromosomes linkage1.htmhttp:// linkage1.htm morgan-genetic-recombination-and-gene-496http:// morgan-genetic-recombination-and-gene-496

Sex Chromosomes & Autosomes Recall that two of the 46 human chromosomes are known as sex chromosomes, because they determine the individual’s sex. –Females have two copies of an X chromosome. –Males have one X chromosome and one Y chromosome. The remaining 44 chromosomes are known as autosomal chromosomes or autosomes.

Sex-Linked Genes Located on one of the sex chromosomes (X or Y) Since the X chromosome is longer, it has many genes not found on the Y chromosome. Most sex-linked genes are X-linked genes.

Sex-Linked Genes

X-Linked Inheritance Examples: –Hemophilia The protein necessary for normal blood clotting is missing –Colorblindness Defective version of one or all of the 3 genes responsible for color vision –Male Pattern Baldness Hair loss –Duchenne Muscular Dystrophy Weakening and loss of skeletal muscle These traits are recessive & more common in males. Why?

Possible Inheritance of Colorblindness Allele

Complete the following sex-linked crosses: Eva and Paul just had a son, Michael. Paul has normal color vision, but Eva’s father was colorblind. What is the likelihood that Michael is colorblind? Laura and Steve are expecting their first child. They are concerned about the chances their child might be hemophiliac because Steve is hemophiliac and Laura’s father is hemophiliac. What is the probability of Laura and Steve having a hemophiliac child?

Complete the following pedigrees. Which is for a sex-linked trait? How do you know?

Pleiotropy One gene  one polypeptide but… One gene can affect MULTIPLE traits/conditions (Pleiotropy)