BIO 105 1st Edition Lecture 3 Outline of Last Lecture I. How does inheritance work?II. How and why do people get genetic diseases?III. How do people inherit their blood type?IV. How do genes interact with each other and with the environment?Outline of Current Lecture I. How do people become male or female?II. Why are certain genetic traits more common in men/boys than in women/girls?III. How can you tell how human traits are inherited?IV. What happens if a person inherits the wrong number of chromosomes?Current LectureBiology 105 Chromosomal Basis of Inheritance Essential Questions 1. How do people become male or female?2. Why are certain genetic traits more common in men/boys than in women/girls? 3. How can you tell how human traits are inherited?4. What happens if a person inherits the wrong number of chromosomes? Interactive Class Notes How do people become male or female? I. Chromosomes A. Chromosomes consist of a single long DNA molecule and some proteins. Humans have 23 types of chromosomes. Each type of chromosome carries a unique set of genes. Genes that are found together on the same chromosome are called linked genes or a linkage group. 1. Chromosomes 1-22 are the autosomes. There are two copies of each autosome in most human cells. (Definition: An autosome is any chromosome that is not a sex chromosome.) 2. The 23rd type consists of the sex chromosomes, X and Y. Males are XY; females are XX. a. The X is much larger than the Y and has many more genes on it. (It doesn’t have to be that way: in birds males have two of the same chromosome and females have the different one.) b. So all eggs contribute an X chromosome to a human baby, and the father determines its 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.gender by providing either an X or a Y chromosome. i. This was not understood by King Henry VIII of England, who divorced his wife Catherineof Aragon for failing to provide a living male heir. B. A karyotype is a picture of a person's chromosomes, taken from a dividing cell. Each chromosome is cut out of the photo and placed with its partner on a chart. 1. A karyotype from placental cells tells the sex of a fetus and whether it has a correct set of chromosomes before it is born. There are two ways to get a prenatal karyotype: a. amniocentesis: amniotic fluid is removed from the uterus and fetal cells in the fluid are grown. Done during the 4th month, it requires another month for results. b. Chorionic villus sampling: placental tissue is removed and examined. Done in the 10th week, results require about 2 weeks, and so are available much earlier in the pregnancy. However there are greater risks of fetal problems with cvs than with amniocentesis C. Human gender determination 1. About 1/20,000 people's karyotypes do not match their gender (XX males or XY females). These "mistakes" help us see how chromosomes are related to gender. 2. A gene called SRY (sex-determining region of Y) on the Y chromosome is largely responsible for making a person male. SRY causes expression of the gene TDF, or testis-determining factor. Without TDF, testosterone cannot be made and no male organs can develop. a. If SRY is transferred to an X chromosome, the person getting that X will be male, while a person getting the mutant Y without its sry gene will be female. 3. Besides needing a functional sry protein to be male, a person must also have testosterone receptor protein. If the body makes testosterone but cells can't respond to it, the person will be female, so some XY females make testosterone, but their cells don't recognize it. a. in some cases, there is a partial response to testosterone, which can lead to the development of "intersex" people.Why are certain genetic traits more common in men/boys than in women/girls?I. Y-linked and X-linked (or sex-linked) Traits A. The Y chromosome only carries a few genes, mainly necessary for maleness. 1. The identifying characteristic of Y linkage is that genes would be passed only from fathers to sons B. The much larger X carries genes affecting all parts of the body. 1. Since males only have one X, the concepts of dominance and recessiveness do not apply to genes on their X chromosomes, called x-linked (or sometimes sex-linked) genes. 2. Every trait on the X chromosome is expressed in males, which is why men are more likely than women to have certain genetic conditions. 3. X-linked traits include colorblindness, Duchenne's muscular dystrophy, Norrie syndrome, and hemophilia. A man whose X chromosome has one of these traits will express the condition; a woman who has an X chromosome with one of these traits will be a carrier. Note: Women can express these recessive conditions if both of their X chromosomes carry the same allele. However, this is often unlikely or impossible, if the condition reduces male fertility or kills boys before they grow up to become fathers. a. Hemophilia is a disease in which the gene for a clotting factor in the blood is lacking. Thisdisease has had a huge impact on European history because it ran in the British royal family. It first appeared in Queen Victoria, who had a hemophiliac son and through carrier daughtersspread hemophilia to the Russian and Spanish royal houses. The single heir to the Russian throne, Alexis, was a hemophiliac. Due to his condition the mystic Rasputin was able to dominate the royal family, and may have helped create the conditions leading to the Bolshevik revolution and overthrow of the tsar. How can you tell how human traits are inherited?I. Pedigree analysis A. To determine whether a trait is inherited as an autosomal dominant, autosomal recessive, X-linked dominant or X-linked recessive in humans, a pedigree can be used. 1. A pedigree is a diagram of a family. Men are squares and women are circles. From each couple, their children are suspended underneath, in order of oldest on the left to youngest on the right. People with a genetic condition are marked by coloring in their symbol, and a deceased person can be indicated by a slash. B. Because female humans have 2 X chromosomes and males only have 1, you might think thatfemales' cells have more X chromosome products than males' cell do. However,