Anthro2050 1st Edition Lecture 9 Outline of Last Lecture I Mate Preference II Genetics Outline of Current Lecture I Examples of Mendelian Genetics at Work Current Lecture According to Mendel s ideas of genetics a trait is controlled by one thing one allele However this idea does not always work as there are polygenetic traits that are controlled my multiple alleles at different places on a gene The following examples in Mendelian genetics are based on the idea of the traits being controlled by one allele When Mendelian Genetics Works sickle cell anemia a homozygous recessive trait that if a person has only the recessive trait is lethal and will kill them before they reach maturity However in some ethnic populations the disease is very common and has a lot of carriers of the disease The reason for this being that sickle cell anemia is common in malaria ridden areas If a person has full blown sickle cell the mutation of their red blood cells causes them to die young If a person has full normal blood cells they are likely to catch malaria and die young However if a person is a carrier for sickle cell anemia only some of their red blood cells are affected so they will not die from the sickle cell and they are strongly resistant to malaria which cannot live in that type of blood When Mendelian Genetics Mostly Works There are several different ways a trait or genetic disease can be passed down more than just an allele on a chromosome These ways of passing information from one generation to the next can be observed in patterns in a family pedigree chart Autosomal dominant traits are dominant traits passed by either or both parent Every affected individual has at least one affected parent Most individuals are heterozygous that mate with unaffected people so there is about a fifty percent chance of passing it on to a child and These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute twenty five percent chance of having a normal child and a twenty five percent chance of having a homozygous affected child Autosomal recessive traits are passed by either parent but are only shown if a person is homozygous for the recessive trait Therefore two unaffected people who are carriers have a twenty five percent chance of having an affected child X Linked Dominant traits are passed on through the X chromosome Since males have an X and a Y chromosome and the X chromosomes only go to daughters and the Y chromosome only goes to sons an affected male will produce all affected daughters and no affected sons A heterozygous female will give the trait to half of her children both sons and daughters equally X linked Recessive traits are passed through the X chromosome and all affected males inherit the allele from their mother Affected males are called hemizygous since the trait is recessive and they only have it from one parent yet their phenotype displays the trait Daughters of affected males are heterozygous but do not show the trait phenotypically Y Linked traits are only paternally inherited and passed from father to son because only males have a Y chromosome Mitochondrial traits are passed on with Mitochondrial DNA and is passed only from the maternal line mother to her offspring through the mitochondria in her egg cells When Mendelian Genetics Gets Complicated Some traits are influenced my environmental factors such as body temperature age and hormonal problems If there is something wrong with a person s hormones then certain traits will be effected by it Androgen Insensitivity Syndrome people who are genetically XY but display a female phenotype In development when the male testes are supposed to descend they do not and stay hidden in the body This causes the body to form female genitalia that is ultimately unusable due to not having a uterus This syndrome is caused by a fault with the receptors in the body in charge of testosterone Since the body cannot detect testosterone the phenotype reverts to a female body form People with this syndrome though genetically male live their lives as females Another example of hormones affecting phenotype is a syndrome called 5 Alpha Reductase Deficiency Like AIS the male body is unreceptive to testosterone in the early phases of development However at puberty it is suddenly receptive to testosterone and the person suddenly gains masculine traits that were unapparent during childhood While extremely rare it is unusually common in the Dominican Republic and Papau New Guinnea In these areas children affected are raised with no social gender identity so that they do not get confused and have to change their identity when they reach puberty