 We discussed earlier in this unit, the usage of karyotype charts  Humans have 23 pairs of chromosomes ◦ 1 sex chromosome pair ◦ 22 autosome pairs  Recall that males have one X and one Y, while females have two X’s  These split during meiosis, and we can use a Punnett square to determine the possible outcomes for sex of offspring

 From this, we can see that the mother can only supply an X chromosome  The sex of the child is solely due to the father  Sperm cells should be produced in equal numbers for X and Y

 Recall human blood type has multiple alleles  The traditional convention for expressing dominance and recessiveness no longer works  Alleles are often expressed as superscripts  Both A and B types are codominant, and O is recessive  A is I A, B is I B, and O is i  The following chart summarizes the genotypes and phenotypes

 Because A and B are codominant, they both show up, but do not blend  The individual will be AB  A lack of either results in O

 A male heterozygous for blood type A plans to have children with a female who is heterozygous for B. What possible blood types could their offspring have?

IAiIAi IBiIBi IAIA i IBIB i IAIBIAIB IAiIAi IBiIBiii

 The possible blood types for the offspring would be AB, A, B or O  Additionally, the Rh + factor is a dominant allele

 After identifying the nature of a trait, geneticists often look at family history  By understanding the phenotypes of certain members of a family, they can gather more info about others  This is organized in a pedigree chart

A circle represents a female. A horizontal line connecting a male and a female represents a marriage. A shaded circle or square indicates that a person expresses the trait. A square represents a male. A vertical line and a bracket connect the parents to their children. A circle or square that is not shaded indicates that a person does not express the trait.

 These only work for traits that are thought to be controlled by genetics alone  Also works best on traits the are due to one gene

 Many conditions are due to recessive alleles  These will only manifest themselves if a dominant allele is present  An example is cystic fibrosis (CF)

 Caused by a recessive allele  Sufferers of cystic fibrosis produce a thick, heavy mucus that clogs their lungs and breathing passageways

 The most common allele that causes cystic fibrosis is missing 3 DNA bases.  As a result, the amino acid phenylalanine is missing from the CFTR protein.

 Normal CFTR is a chloride ion channel in cell membranes  Abnormal CFTR cannot be transported to the cell membrane  If it does, it will not transport Cl - as easily  Part 1 Part 1  Part 2 Part 2

 Many other conditions are caused by recessive alleles

 Other conditions arise from codominant alleles  In these cases, the heterozygotes have a different phenotype  You saw this with thalassemia in question 12  Sickle cell disease is another example  Individuals that are heterozygous for this usually have normal blood cells, but are resistant to malaria

 Finally, some conditions are caused by dominant alleles, although it is uncommon Disorders Caused by Dominant Alleles DisorderSymptoms AchondroplasiaA type of dwarfism Huntington’s DiseaseLoss of neurons, resulting in mental deterioration and loss of muscle control. HypercholesterolemiaExcess cholesterol in blood