1140 Genetics Blood Types & Sex-linked Inheritance PDF

BIOL 1140: Inheritance of Blood Types & Sex-linked Traits Prof. Susan Cordova (Tappen)  Review: Codominance Both alleles are dominant, so both phenotypes are expressed equally instead of showing a ‘blend’ of the two of them. No small letters...

BIOL 1140: Inheritance of Blood Types & Sex-linked Traits Prof. Susan Cordova (Tappen)  Review: Codominance Both alleles are dominant, so both phenotypes are expressed equally instead of showing a ‘blend’ of the two of them. No small letters since there is no recessive allele – must use superscripts instead. Cannot use my * notation here! Example: Roan cattle – CBCB = Brown – CWCW = White – CBCW = Roan pattern ABO Blood Types – General Info RBCs vs plasma – RBCs have the antigens on their surfaces (A, B, both A & B, or none) – Plasma contains the antibodies (anti-A, anti-B, both, or none) Most blood donations are of ONLY the RBCs  ABO Blood Types – General Info If donated RBCs’ antigens cross-react with patient’s plasma antibodies, agglutination can occur – pain/death Type ____ blood is the “universal donor” (dOnOr) – RBCs have no antigens, so can’t react with any antibodies Type ____ blood is the “universal recipient” – No antibodies in plasma, so can’t react with anyone’s RBCs ABO Blood Types - Genetics Phenotyp Genotype e Type O ii ABO Blood Groups show more than 1 type of inheritance: Type A IAIA or IAi Multiple alleles: Type B IBIB or IBi – 3 alleles possible: IA, IB, i Type IAIB – 6 possible genotypes: IAIA, IAi, IBIB, IBi, IAIB, ii AB – 4 phenotypes: Type A, B, AB, or O blood Codominance: – both A and B antigens express on heterozygote Recessive/Dominant inheritance: – IA and IB alleles are dominant – i allele is recessive  Blood Type & Multiple Allele Practice Both Hermione & Ron are heterozygous for Type A blood. Do a cross between them and give the genotypic and phenotypic ratios: Genotypic Ratios: I A i IA IAIA IAi i Phenotypic Ratios: IAi ii  Blood Type & Multiple Allele Practice – Your Turn Patience is heterozygous for Type A blood, while Justice is heterozygous for Type B blood. What are the chances that their child will have Type O blood?  What about Rh+ and *The B+ blood type is actually Rh-? Rh is another RBC antigen way more common in Asian- (Rh for Rhesus monkeys) Americans, and – Rh+ allele is dominant over is the most Rh- common blood – ~84% in US are Rh+ type in India. ~37% ~35% ~8% ~3% ~7%Commonality ~6%of blood types in the US ~2% ~1% You could do a dihybrid cross with ABO & Rh antigens!  How is Biological Sex Determined? Males are Xy Females are XX Egg is X or X Sperm is X or Y – So biological sex is determined by sperm (male parent)  How is Biological Sex Determined? Punnett Square with XX & Xy 50% chance of male or female with every birth Biological sex is different from gender! “Gender is a social construct and generally based on the norms, behaviors, and societal roles expected of individuals based primarily on their sex. Gender identity describes a person’s self-perceived gender, which could be male, female, or otherwise.”  Sex-Linked Inheritance Sex-linked traits = genes on either the X or Y sex chromosome X-linked traits = genes only on the X chromosome – Much more common since larger chromosome – Can be recessive or dominant We will focus only on recessive traits here X and y are not homologous chromosomes – y chromosome has ~78 genes – X chromosome has ~2,000 genes Blood clotting proteins Muscle proteins Vision proteins and more....  X-Linked Recessive Inheritance in Females Notation: Must use X and y letters for the base letters – Can use specific letters in superscript to represent trait, capital for dominant & lowercase for recessive – OR, can use Susan’s simpler notation of X* for the disease/disordered allele Females can be heterozygous or homozygous because XX is homologous – Homozygous Dominant = XHXH (or XX) – Heterozygous = XHXh (or XX*)  Females are carriers here – Homozygous Recessive = XhXh (or X*X*) Female Expression of Trait: – If heterozygous for X-linked recessive disease, other X serves as ‘backup’ and can prevent expression of disease – Will only express if both alleles are affected (this is much more rare in females)  X-Linked Recessive Inheritance in Males Males can only be hemizygous for X-linked traits because only 1 X – NOT homozygous or heterozygous – Example: Xhy or XHy (or X*y or Xy) Male Expression of Trait: – Will express whatever allele is on the X, regardless of dominant/recessive – Males have no ‘backup’ like females do – Why X-linked recessive traits are more common in males Examples of X-linked Recessive Disorders/Diseases Duchenne Muscular Dystrophy (DMD) – Mutation in DMD gene that codes for dystrophin muscle protein needed to anchor, protect, & strengthen muscle filaments – Severe, progressive, muscle- wasting disease beginning in lower limbs – Death is due to effect on muscles for breathing Examples of X-linked Recessive Disorders/Diseases Red-Green colorblindness – Affects one of 3 types of cone receptors  Examples of X-linked Recessive Disorders/Diseases Hemophilia A – Mutation in gene for “Factor VIII” blood clotting protein – Spontaneous internal bleeding, can’t stop bleeding once it starts, etc. – Can bleed out (fatal) if not injected with replacement proteins in time  X-Linked Practice Susan is homozygous for normal color vision. Juan is colorblind. They have 1 daughter and 1 son. Do a cross and give the genotypic and phenotypic ratios. Then answer the questions. What are the chances that their daughter is colorblind like her dad? What are the chances that their daughter is a carrier of the colorblind gene? What are the chances that their son is colorblind?  X-Linked Practice Continuing from the previous example.... What if the daughter, who is a carrier of the color-blind gene, goes on to marry and have a son with someone who is not colorblind - what are the chances that the son (Susan’s grandson) will be colorblind? What if they have a daughter instead?  Pedigrees Can be used to visually track inheritance through generations Useful to back-track inheritance from children to grandparents.... Can help determine the type of inheritance involved – autosomal, sex-linked, dominant/recessive, etc.  X-Linked Practice with Pedigree John has hemophilia. Neither parent has symptoms. From whom did he inherit this disease - his mother or father?  X-Linked Practice with Pedigree There are 3 children – the son has DMD, while the other two daughters do not. What are the genotypes and phenotypes of the parents?