Mendelian Inheritance of Human traits  A pedigree is a graphic representation of genetic inheritance.  Looks very similar to a family tree.  If III-2 marries a person with the same genotype as individual I-1, what is the chance that one of their children will be afflicted with hemophilia?  0% Homozygous dominant Homozygous recessive  What type of inheritance pattern does the trait represented by the shaded symbols illustrate?  Sex linked  What would these be classified as?  Carriers  What is the relationship between I-1 and III-2?  Grandmother-grandson I II III

Pedigrees cont. I II III IV  What is the probable mode of inheritance?  Sex linkage  What do you know about III-1’s mother?  She was a carrier  How many offspring in the III generation show the normal trait? 44

 A child is diagnosed with a rare genetic disease. Neither parent has the disease. How might the child have inherited the disorder?  The disorder is recessive and carried by both parents  Most genetic disorders are caused by recessive alleles.  Cystic fibrosis and Tay-Sachs disease are typical of recessive disorders concentrated in ethnic groups.  PKU is the failure to metabolize phenylalanine.  A homozygous PKU newborn appears healthy at first because its mother’s normal enzyme level prevented phenylalanine accumulation during development.  Following the detection of PKU, dietary adjustments are made in order to prevent mental retardation.

Simple Dominant Heredity  In Mendelian inheritance, a single dominant allele is inherited from one parent is all that is needed for a person to show the dominant trait.  Phenotypic traits that result in single dominant allele:  Polydactyly  Tongue rolling  Hitchhiker’s thumb  Thick lips  Hair in the middle section of the fingers  Huntington’s disease  Huntington’s disease is the progressive deterioration of the nervous system.  Every child of an affected individual has a 50% chance of being affected and then a 50% chance of passing the defective allele to his or her own child.

When Heredity Follows Different Rules  Incomplete dominance is when the phenotype of the heterozygous is intermediate between those of the two homozygous.  For example, if a homozygous red-flowered snapdragon plant is crossed with a homozygous white-flowered snapdragon plant, all of the offspring will have pink flowers. (Figure 12.7 pg 322)  A cross a white rooster and a black hen results in 100% blue Andalusian offspring. When 2 of these blue offspring are mated the probable phenotypic ratio seen in their offspring would be?  WW(white) X ww(black)=blue (all would be Ww)  Then you would do a cross between those offspring: W w W w WWWw ww 25% would be white 50% would be blue 25% black

 Codominant alleles cause the phenotypes of both homozygotes to be produced in heterozygous individuals  Both alleles are equally expressed  Examples:  Figure 12.8 all of the offspring would be checkered; some feathers are black and other feathers are white  Roan cattle-coat consists of red and white hairs  Traits controlled by more than two alleles have multiple alleles.  A trait controlled by 4 alleles

 There are 22 pairs of matching homologous chromosomes call autosomes.  The 23 rd pair of chromosomes that differ in males and females are called sex chromosomes.  *A male is said to be hemizygous for genes on the X chromosome. Explain why you think this term was chosen.  The prefix hemi- means half. Because only one of the male’s 2 sex chromosomes is an X chromosome, only half of his sex chromosomes can carry the genes.

 Traits controlled by genes located on sex chromosomes (X or Y chromosomes) are called sex-linked traits.  Fig pg 325  Polygenic inheritance is the inheritance pattern of a trait that is controlled by two or more genes.  More than two phenotypes result from both multiple and polygenic inheritance.  Human traits skin color and height would show similar inheritance pattern and frequency of distribution. Fig pg 326  *How does polygenic inheritance differ from Mendelian inheritance?  In Mendelian inheritance, traits are determined by dominant and recessive paired alleles of single genes. In polygenic inheritance, a trait is controlled by two or more genes.

 *Discuss how the external environment of an organism can affect gene function.  Pg 327  Temperature, nutrition, light, chemicals, and infectious agents all can influence gene expression.  *Discuss how the internal environment of an organism can affect gene function/  Pg 327  Age  Gender  Sex hormones

Complex Inheritance of Human Traits  Individuals afflicted with sickle-cell anemia suffer tissue damage resulting from oxygen deprivation.  The blood types A, B, AB, and O are the results of multiple allelic inheritance.  A man heterozygous for blood type A marries a woman heterozygous for blood type B. The chance that their first child will have type O blood is ? I A i I B i IA IBIB i IA i ii IA IB=AB IB i=B IA i=A ii=O Answer: 25%

 Which baby belongs to each couple?  Mrs. Page—BMr. Page—AB  Mrs. Baker—BMr. Baker—A  Baby #1—A  Baby #2—O  Page’s  Baker’s IAIB i IA IBIB IA iIB i IA IB=Blood type AB IB IB=Blood type B IA i=Blood type A IB i=Blood type B IB i IA i IA IBIA i IB iii IA IB=Blood type AB IA i=Blood type A IB i=Blood type B ii=Blood type O  Page’s  Only baby 1 could be theirs.  Bakers  Either baby could be theirs

 Examples of sex-linked traits:  Hemophilia(Royal hemophilia)  Red-Green color blindness  Red-Green color blindness is caused by a recessive allele.  Because the gene for red-green color blindness is located on the X-chromosome, it is normally not possible for a color blind father to pass the gene to his son. (Fig pg 332)  A karyotype can be valuable in pinpointing cases of aneuploidy.  Aneuploidy—having lower or higher than the normal diploid number of chromosomes.  Down Syndrome and Turner Syndrome can be detected by karyotyping