Exploring Human Genetics and Chromosomes

1. Chapter 14The Human Genome Group 1: Julia Banas, Griffin Cason, Olivia Katulka, Brianna Shinko, Julianna Stella

2. Section 14-1 Human HeredityBy Olivia Katulka & Julia Banas Homo sapiens have always been interesting to research and they have always made scientists wonder. Scientists are now beginning to understand human genetics more than ever before.

3. Human Chromosomes In order for biologists to analyze human chromosomes, they photograph cells in mitosis when the chromosomes are condensed and easier to see. Then, the biologists cut the individual chromosomes from their photographs and pair them up with their homologous chromosome. This picture of chromosomes grouped in order in pairs is known as a karyotype.

4. Human Chromosomes A human body cell contains 46 chromosomes. A human begins life when a haploid sperm with 23 chromosomes fertilizes a haploid egg with 23 chromosomes. The result is a diploid zygote, or fertilized egg, with 46 chromosomes total.

5. Human Chromosomes Two of the 46 chromosomes are the sex chromosomes because they determine a person’s sex. Females have two large X chromosomes. Males have one X and one small Y chromosome. The other 44 chromosomes that are not the sex chromosome are autosomes. Both autosome and sex chromosomes are written together: Males- 46XY Females- 46XX

6. Human Chromosomes Autosomes (numbers 1- 22) Sex Chromosomes Based on the Karyotype above, is the zygote a male or a female?

7. Human Chromosomes The way in which sex chromosomes segregate during meiosis allows males and females to be born in a 50:50 chance. ***All egg cells carry a single X chromosome (23X). Although, half of all sperm cells carry an X chromosome (23X) and half carry a Y chromosome (23Y). This makes the ratio half and half, ensuring that half of the zygotes will be 46XX and half will be 46XY.*** Human chromosomes are just like the chromosomes of other eukaryotes and human genes are coded directly into the nucleotide sequence in DNA.

8. Human Chromosomes • Egg cells will always have a single X chromosome, while half male sperm cells have an X and half have a Y. • In every cross between a male and a female, the ratio will always be half XX : half XY.

9. Human Traits To apply Mendelian genetics to humans, biologists need to identify an inherited trait controlled by a single gene. They need to first establish that the trait is inherited and not influenced by the environment. Biologists then must study how the trait is passed from one generation to the next. Pedigree charts, that show relationships within a family, help biologists to do that job.

10. Human Traits: Pedigree Charts

11. Pedigree Chart A circle represents a female. A square represents a male . A vertical line and a bracket connect the parents to their children. A horizontal line connecting a male and a female represents a marriage. A half shaded circle or square indicates that a person is a carrier of the trait. A circle or square that is not shaded indicates that the person neither expresses the trait nor is a carrier of the trait. A completely shaded circle or square indicates that a person expresses the trait.

12. Human Traits • ***Females who have one allele for the trait are only carriers, while males who have one allele express the trait.*** • In this pedigree chart, a male that expresses red-green color blindness marries a woman with normal vision. • They have five children: A male with normal vision, a female who carries the color blindness trait, a male with normal vision, a female who carries the color blindness trait, and a male with normal vision. • The second female child (of the couple in the first generation) that carries the color blindness trait marries a man with normal vision. Their children are a female who carries the color blindness trait, a female with normal vision, and a male who expresses the color blindness trait.

13. Human Traits Some of the most obvious of human traits are impossible to associate with single genes! Why? 1.) Things that we think are single traits, such as the shape of your eyes or ears, are actually polygenic because they are controlled by many genes. 2.) Many of our personal traits are only partly controlled by genes because the phenotype is only partially determined by the genotype. Many genes are even influenced by environmental, nongenetic, factors such as exercise or nutrition.

14. Human Traits An example of this is human height. Genes may control the maximum height of a person, but nutritional improvements in the United States and Europe in the 1800s have increased the average height of these countries’ populations about 10 centimeters over their usual average height. However, environmental effects on gene expression are not inherited as genes are. If genes are denied a proper environment to reach their full potential in one generation, they can reach their full potential in a later generation.

15. Human Genes Our complete set of genetic information is often called the human genome. The human genome includes tens of thousands of genes. The DNA sequences of these genes determines certain characteristics, such as eye color and structure of proteins in cells. By 2000, the DNA sequence of the human genome was nearly complete. Studying human genes are not easy, which is why until recently the identification of a human gene took years of research. Why? Humans have a complex life cycle and produce very few offspring, compared to pea plants or fruit flies.

16. Human Genes Some of the very first genes that were discovered that could directly control a single human trait were those of blood type.

17. Human Genes:Blood Group Genes Human blood comes in a variety of different blood groups. Knowing a person’s blood type is very important because using the wrong type of blood for a transfusion during a medical procedure can be fatal or harmful to that person. ABO blood groups and Rh blood groups are the best known blood groups.

18. Human Genes:Blood Group Genes Rh blood group is determined by a single gene with two alleles- one is positive and the other is negative. Rh stands for “rhesus monkey” because that was the animal that the Rh factor was discovered in. The positive allele (Rh+) is dominant, meaning people who are Rh+/Rh+ or Rh+/Rh- are Rh-positive. People with two Rh- alleles are Rh- negative.

19. Human Genes: Blood Group Genes • In humans, the Rh factor is not usually a threat until a woman is pregnant. • If the mother of a child is Rh-negative and the father is Rh-positive it may result in a child with Rh-positive blood. • Although the child’s blood system is separated from the mother’s, the baby’s blood may enter the mother’s system at different times. When the baby’s blood enters the mother’s system,it will act as an intruder because of the difference in the Rh factor.

20. Human Genes:Blood Group Genes Source http://pregnancy.about.com/od/rhfactor/a/Rh-Factor-in-Pregnancy.htm If this happens, the mother will become sensitized and her body will make antibodies against the Rh-positive baby . The antibodies will break down the baby’s red blood cells. This is also called a hemolytic disease and it can cause brain damage, anemia, and severe illness in the child. Rh immunoglobulin (RhIg) can prevent this hemolytic disease in pregnant women

21. Human Genes:Blood Group Genes ABO Blood Groups- Four Blood Types: A B AB O *There are three alleles for this gene, IA, IB,and i. Alleles IA and IBare codominant. These alleles produce antigens on the surface of red blood cells that can be recognized by the immune system. The i allele is recessive.*

22. Human Genes:Blood Group Genes People with alleles IA and IBproduce both antigens, giving them blood type AB. People with alleles IA IA or IA i produce only the A antigen, giving them the blood type A. Those with alleles IB IB or IB i alleles produce only the B antigen, giving them the blood type B. People homozygous for the i allele (ii) do not produce any antigens, and are said to have blood type O. This is why blood type O is the universal donor.

23. Human Genes:Blood Group Genes

24. Human Genes: Blood Group Genes Both Rh and ABO groups are said together when referring to a person’s blood type. For example if a patient has AB-negative blood, it means they have IA and IB alleles from the ABO gene and the Rh- allele from the Rh gene.

25. Recessive Alleles • Through the study of genetic disorders, many genes have become known. • Usually, the presence of a normal, functioning gene is revealed only when an abnormal or nonfunctioning allele affects the phenotype. • One of the first genetic disorders that was understood this way was phenylketonuria (PKU), which is when someone doesn’t have the enzyme that breaks down phenylalanine. PKU is caused by a recessive allele on chromosome 12. • Another disorder, caused by autosomal recessive alleles, is Tay-Sachs disease. This results in nervous system breakdown and death in the first few years of life. Chromosome with Tay-Sachs disease

26. Dominant Alleles Some genetic disorders are caused by dominant alleles. Remember, dominant alleles are always expressed, even if there is a recessive allele present. One example of a disorder caused by autosomal dominant alleles is achondroplasia, a form of dwarfism. Another example is Huntington’s disease, a progressive loss of muscle control and mental function until death occurs. Usually no symptoms are shown until middle age.

27. Codominant Alleles Sickle cell disease is found in 1 in 500 African Americans. It is a serious disease that is caused by a codominant allele.

28. From Gene to Molecule Though scientists are still trying to figure out the link between alleles for genetic disorders and the genetic disorder, in cystic fibrosis and sickle cell disease, they learned that there is a small change in the DNA of a single gene that affects the structure of a protein. This causes a serious genetic disorder.

29. Cystic fibrosis (CF) is caused by a recessive allele on chromosome 7. • People with CF have serious digestive problems along with producing heavy mucus that clogs their lungs and breathing passageways. • CF involves a small genetic change, caused by the deletion of 3 bases in the middle of a sequence for a protein. • This protein normally allows chloride ions to pass across biological membranes. • The deletion of these bases removes an amino acid from the protein, making it fold improperly. • Cells therefore do not transport the protein to the cell membrane and the misfolded protein is destroyed. • Because the chloride ions can’t be transported, tissues throughout the body malfunction.

30. Sickle Cell Disease Sickle cell disease is a genetic disorder found in African Americans. It’s characterized by a bent and twisted shape of red blood cells, more rigid than normal cells. They tend to get stuck in capillaries, stopping blood from moving through vessels, damaging cells and tissues beyond the blockage. This produces physical weakness and damage in the brain, heart, and spleen.

31. Sickle Cell Disease Hemoglobin is the protein that carries oxygen through the blood. The cause of sickle cell disease is one base in DNA—valine is placed where glutamic acid should be. Because of this, abnormal hemoglobin is somewhat less soluble than normal hemoglobin. A decrease of blood oxygen levels causes hemoglobin molecules to come out of the solution and stick together, making the shape of the sickle cells.

32. Sickle Cell Disease Many African Americans carry the gene because malaria is common in Africa. The sickle cell allele makes someone resistant to malaria. This happens because when the body destroys the sickled cells, it gets rid of the parasite at the same time. Sickle cell disease region Malaria region

33. Dominant or Recessive? What makes an allele dominant, recessive, or codominant? • The answer is the nature of a gene’s protein product and its role in the cell. • In CF, one copy of the normal allele can supply cells with enough chloride channel proteins to function. • Therefore, the normal allele is considered dominant over the CF allele that is considered recessive. • The sickle cell allele was once considered recessive, too, but biologists have discovered that a person with both normal and sickle cell alleles have a different phenotype from someone with only normal alleles. • Because of this, sickle cell alleles are codominant, because both alleles contribute to the phenotype.

35. 14-2 Human Chromosomes By Brianna Shinko

36. Human Genes and Chromosomes • Chromosomes 21 and 22 are the smallest human autosomes. • Chromosome 22 contains approximently 43 million DNA bases. • Chomosome 21 contains roughly 32 million bases. • Chromosome 22 contains as many as 545 different genes, some of which are very important for health. • Genetic disorders on chromosome 22 include an allele that causes a form of leukemia and another associated with neurofibromatosis, a tumor causing disease of the nervous system.

37. Chromosome 22 also contains long stretches of repetitive DNA that don’t code for proteins. • The structure chromosome 21 is similar. It contains about 225 genes, including one associated with ALS or amyotrophic lateral disease, also know as Lou Gehrig’s disease. Lou Gehrig

38. Sex-Linked Cells • Is there a special pattern of inheritance for genes located on the X chromosome or the Y chromosome? The answer is Yes. Because these chromosome determine sex, genes located on them are said to be sex-linked genes. • More than 100 sex-linked genetic disorders have now been mapped to the X chromosome. • The human Y chromosome is much smaller than the X chromosome and appears to contain only a few genes.

39. Colorblindness • 3 human chromosomes associated with color vision are located on the X chromosome. • In males, a defective version of any one of these genes produces colorblindness, an inability to distinguish certain colors. • The most common form of this disorder, red-green colorblindess, is found in 1 and 10 males in the U.S. • Among females, however, colorblindness is rare. Only 1 female in 100 has colorblindness.

40. Hemophilia • Hemophilia is another example of a sex-linked disorder. • 2 important genes carried on the X chromosome help control blood clotting. • A recessive allele in either of these 2 genes may produce this disorder. • In hemophilia, a protein necessary for normal blood clotting is missing. About 1 in 10,000 males are born with a form of this disease. People with hemophilia can bleed from bumps or bruises. • Hemophilia can be treated by injections of normal clotting proteins.

41. Duchenne Muscular Dystrophy • This disease is a sex-linked disorder that results in the progressive weakening and loss of skeletal muscle. • People with this disease nearly live past adulthood. • In the U.S., 1 out of every 3,000 males are born with Duchenne Muscular Dystrophy. • Duchenne Muscualar Dystrophy is cause by a defective version of the gene that codes for a muscle protein.

42. X-Chromosome Inactivation • Females have two X chromosomes, but males have only one. • If just one X chromosome is enough for cells in males, how does the cell “adjust” to the extra X chromosome in female cells? The answer was discovered by the British geneticist Mary Lyon. • In female cells, one X chromosome is randomly switched off. That’s turned-off chromosome forms a dense region in the nucleus known as a Barr body. Barr bodies are generally not found in males because their single X chromosome is still alive.

43. Chromosomal Disorders • The most common error in meiosis occurs when homologous chromosomes fail to separate. • This is known as nondisjunction, which means “not coming apart.” • If nondisjunction occurs, abnormal numbers of chromosomes may find their way into gametes, and a disorder of chromosomes numbers may result.

44. Down Syndrome • If 2 copies of an autosomal chromosome fail to separate during meiosis, an individual may be born with 3 copies of a chromosome. This is known as trisomy, meaning “three bodies”. • The most common form of this involves 3 copies of chromome 21 and is called Down Syndrome. • In the U.S., 1 baby in 800 is born with Down Syndrome.

45. Sex Chromosome Disorders • Disorders also occue amoung the sex chromosomes. two of these abnormalities are Turner’s syndrome and Klinefelter’s syndrome. • In females, nondisjunction can lead to Turner’s syndrome. A female with Turner’s syndrome inherits only one X chromosome (genotype XO). Women with Turner’s syndrome are sterile because their sex organs don’t develop at puberty. • In males, nondisjunction causes Klinefelter’s syndrome (genotype XXY). The extra X chromosome interferes with meiosis and usually prevents these individuals from reproducing. Cases of this syndrome have been found in which individuals were XXXY or XXXXY. There have been no reported instances of babies being born without an X chromosome, indicating that the X chromosome contains genes that are vital for normal development.

46. These sex chromosome abnormalities point out the role of the Y chromosome in sex determination. The Y chromosome contains a sex-determining region that is necessary to produce male sexual development, even in combination with several X chromosome. However, in this region if the Y chromosome is absent, the embryo develops as a female.

47. Chapter 14 Section 3 Human Molecular Genetics By: Julianna Stella & Griffin Cason

48. Human DNA analysis • There are roughly 6 billion base pairs you carry in your DNA that are like an encyclopedia with thousands of volumes • Biologists search through volumes of human genomes using DNA sequencing • A variety of genetic tests have been develop to spot different alleles & genetic disorders • This makes it possible for parents to determine the risk for passing on alleles to their children

49. The great complexity of human genome assures that no two individuals are exactly alike

50. DNA fingerprinting is one way to identify individuals • It has been used in the U.S. since 1980 • DNA fingerprinting does not analyze the cells most important genes • Instead, DNA fingerprinting analyzes the sections of DNA that have little or no function but vary widely from one individual to another