© 2013 Pearson Education, Inc. Extensions of Mendelian Genetics  Incomplete Dominance is when a heterozygote expresses a phenotype intermediate between both alleles.  For example, RR produces red flowers, Rr produces pink flowers and rr produces white flowers  Codominance is when two alleles are expressed at the same time.  ABO blood type is an example of this with both the dominant A and B being expressed in a type AB person.  Multiple allelism occurs when there are more than two alleles of a gene.  ABO blood types exhibit this.

© 2013 Pearson Education, Inc. Extensions of Mendelian Genetics  ABO blood group has three alleles of one gene:  I A and I B are codominant to each other; i is recessive to both other alleles.

© 2013 Pearson Education, Inc.  Another blood group is called the Rh factor.  Rh + is caused by a dominant allele.  Rh + Rh + or Rh + Rh -  Rh - is caused by 2 recessive alleles.  Rh - Rh -  Blood typing can be used to exclude potential parents.  E.g., an AB parent can never have an O child and two Rh - parents can never have a Rh + child.  See Table 8.2 for compatibilities of blood types.

© 2013 Pearson Education, Inc.  Pleiotropy is the ability of a single gene to cause multiple effects on the individual’s phenotype.  Hemophilia is an example of pleiotropy.  The inability to clot blood normally due to the absence of a clotting factor  Gene for this clotting factor is on the X chromosome

© 2013 Pearson Education, Inc. Sex Determination and Sex Linkage  Humans have 22 pairs of autosomes and one pair of sex chromosomes  Women: two X chromosomes  Men: one X and one Y chromosome

© 2013 Pearson Education, Inc. Sex Determination and Sex Linkage  Sex-linked genes: genes located on the sex chromosomes  X-linked: located on the X chromosome  Y-linked: located on the Y chromosome  SRY gene on Y chromosome leads to the development of the testes  Males always inherit their X from their mother  Males are more likely to express recessive X-linked traits than females due to carrying only 1 X.  Females are less likely to express X-linked traits since they have to have 2 copies of the bad X’s.

© 2013 Pearson Education, Inc. Sex Determination and Sex Linkage  Carriers express the normal trait but are heterozygous, so they carry the allele for the recessive trait.  Hemophilia, red-green color blindness, and Duchenne Muscular dystrophy are examples of X-linked traits.

© 2013 Pearson Education, Inc. Pedigrees  Pedigree: a family tree, showing the inheritance of traits through several generations  Symbols commonly used in pedigrees are circles and squares  Pedigrees reveal modes of inheritance

© 2013 Pearson Education, Inc. Pedigree for an autosomal dominant trait: 1.Every affected person has an affected parent 2.About half of the offspring of just one affected parent are also affected 3.The phenotype occurs equally in both sexes

© 2013 Pearson Education, Inc. Pedigree for an autosomal recessive trait: 1.Carriers: (Gg) have one allele for trait/disorder, they do not display the recessive phenotype 2.Carriers: 2 parents that show no symptoms can have affected child: Cystic Fibrosis, Sickle Cell Anemia

© 2013 Pearson Education, Inc.  Pedigree for an X-linked trait:

© 2013 Pearson Education, Inc. Practice Pedigrees: Steps 1.Identify if the trait is dominant, recessive (autosomal or x-linked), or other. 2.Write out all possible genotype as affected or unaffected. (AA, Aa, aa) 3.Fill in the easy sections first (obviously affected) Figure 7.13

© 2013 Pearson Education, Inc. What type on Inheritance is this? What are the genotypes?

© 2013 Pearson Education, Inc. What type on Inheritance is this? What are the genotypes?

© 2013 Pearson Education, Inc. DNA Fingerprinting  No two individuals are genetically identical except for identical twins.  Small differences in nucleotide sequences of their DNA  This is the basis for DNA fingerprinting  Unambiguous identification of people  When sample size is small it is necessary to copy the genetic material to increase the quantity available for testing.

© 2013 Pearson Education, Inc. 7.6 DNA Fingerprinting  Steps in DNA fingerprinting:  DNA isolated from tissue sample  DNA cut into fragments with enzymes  DNAs of different sequences produce fragments of different sizes  Fragments separated on basis of size and visualized  Each person’s set of fragments is unique

© 2013 Pearson Education, Inc. DNA Fingerprinting  Small amounts of DNA can be amplified using PCR (polymerase chain reaction)  DNA is mixed with nucleotides, specific primers, Taq polymerase, and then is heated  Heating splits the DNA molecules into two complementary strands  Taq polymerase builds a new complementary strand  DNA is heated again, splitting the DNA and starting a new cycle.

© 2013 Pearson Education, Inc.  Each cycle, the amount of DNA doubles.

© 2013 Pearson Education, Inc.  DNA is cut into fragments using restriction enzymes, which cut around DNA sequences called VNTRs (variable number tandem repeats).

© 2013 Pearson Education, Inc.  Gel electrophoresis separates DNA fragments on basis of their sizes  Electric current is applied to an agarose gel  Smaller fragments run faster through the gel  Fragments are transferred to a sheet of filter paper  Labeled probe reveals locations of fragments containing VNTRs

© 2013 Pearson Education, Inc.  Each person’s set of fragments is unique.  All of a child’s bands must be present in one or both of the parents.

© 2013 Pearson Education, Inc. Who is more likely to suffer from colorblindness, a disorder caused by a recessive allele on the X- chromosome?  Males  Females  Babies  The elderly

© 2013 Pearson Education, Inc. What type of trait does this pedigree show? A.Recessive trait B.Sex-linked trait C.Dominant trait D.Codominant trait

© 2013 Pearson Education, Inc. Gel electrophoresis separates DNA fragments based on _______.  Shape  pH  Number of strands  Size

© 2013 Pearson Education, Inc. ______ is used to amplify DNA.  PCR  Gel electrophoresis  RFLP  VNTR