1. Chapter 14 The Human Genome Biology I

2. Humans are difficult to study -produce few offspring -mature slowly with long reproductive cycle -controlled breeding is unethical -scientists have studied human genes directly or by looking for patterns in population studies

3. Human Chromosomes To analyze chromosomes, biologists photograph cells in mitosis (chromosomes are condensed) To analyze chromosomes, biologists photograph cells in mitosis (chromosomes are condensed) Biologists then cut out the chromosomes from the photograph and group them together in pairs Biologists then cut out the chromosomes from the photograph and group them together in pairs Karyotype- picture of chromosomes arranged in pairs Karyotype- picture of chromosomes arranged in pairs

4. Human Chromosomes Human body cells have 46 chromosomes Human body cells have 46 chromosomes 2 of the 46 are sex chromosomes which determine an individual’s sex 2 of the 46 are sex chromosomes which determine an individual’s sex Females have two large X chromosomes Females have two large X chromosomes Males have 1 X and 1 small Y Males have 1 X and 1 small Y 44 of the 46 chromosomes are autosomal chromosomes or autosomes 44 of the 46 chromosomes are autosomal chromosomes or autosomes

6. -All human egg cells carry a single X chromosome -Half of the sperm cells carry an X and half carry a Y -Thus, half the zygotes will be XX and half XY XX XY X Y X X -Males and females are born in a roughly 50:50 ratio because of segregation in meiosis

7. -Human genes are inherited according to the principles of Gregor Mendel and his work with garden peas -Biologists study how traits are passed from one generation to the next using a Pedigree chart Pedigrees -show relationships within a family -genetic counselors analyze pedigrees to infer genotypes of family members

8. Pedigrees Many traits can’t be traced easily because they are polygenic and influenced by the environment Many traits can’t be traced easily because they are polygenic and influenced by the environment For those that can, pedigrees can predict how a trait and the genes that control it are inherited For those that can, pedigrees can predict how a trait and the genes that control it are inherited

9. Square-maleCircle-female Full color- trait expressed Half color- carrier of the trait Roman Numerals- generation Numbers- individuals ?- unknown genotype Horizontal line between parents- marriage Vertical line- children

10. A circle represents a female. A square represents a male. A horizontal line connecting a male and female represents a marriage. A vertical line and a bracket connect the parents to their children. A half-shaded circle or square indicates that a person is a carrier of the trait. A completely shaded circle or square indicates that a person expresses the trait. A circle or square that is not shaded indicates that a person neither expresses the trait nor is a carrier of the trait. Figure 14-3 A Pedigree

11. What do you know about person II-2? What do you know about person II-2? Is the trait for hitchhiker’s thumb dominant or recessive? How do you know? Is the trait for hitchhiker’s thumb dominant or recessive? How do you know? Which individuals are carriers? Which individuals are carriers?

13. Tt tt T_ Tt

14. -1 st genes to be identified were those that control blood type -Blood Types are A, B, AB, and O -There are also Rh blood groups -Single gene with two alleles -Positive or Negative -Rh is from the Rhesus monkey, the animal in which this factor was discovered

15. -Many human genes have become known through the study of genetic disorders -Recessive genetic disorders are not expressed in the phenotype of the heterozygote -Heterozygous individuals are carriers -Existence of carriers allows the defective gene to remain in the gene pool, whereas many dominant alleles are reduced in numbers since homozygous individuals often do not survive - Being a carrier usually does not affect health of individual

16. - Children can’t break down phenylaline found in milk (lack the enzyme) - Buildup damages nerve cells and causes severe retardation -May be controlled by diet -Testing at birth is now required -Caused by an autosomal recessive allele on chromosome 12

17. -Fatal genetic disorders among Jewish community from central Europe -Inability to breakdown a lipid, causing accumulation of a substance in the brain -Blindness, seizures, and short life -There is no treatment, but there is a test for the allele, so parents can learn if they are at risk

18. -Found predominately in Caucasians -Recessive allele found on chromosome number 7 -Caused by a small genetic change- deletion of 3 bases in the middle of protein sequence -Excessive secretion of thick mucus which accumulates in the pancreas, lungs and other organs -The deletion removes 1 amino acid causing the protein to fold incorrectly

19. Chromosome # 7 CFTR gene The most common allele that causes cystic fibrosis is missing 3 DNA bases. As a result, the amino acid phenylalanine is missing from the CFTR protein. Normal CFTR is a chloride ion channel in cell membranes. Abnormal CFTR cannot be transported to the cell membrane. The cells in the person’s airways are unable to transport chloride ions. As a result, the airways become clogged with a thick mucus. The Cause of Cystic Fibrosis

20. - Always expressed -Individuals may die before they pass the trait -Less common than recessive traits -Dwarfism- achondroplasia Huntington’s Disease - Huntington’s Disease - fatal- deterioration of nervous system -symptoms begin in early 40’s- because symptoms appear later in life, alleles may be passed to offspring

21. Huntington’s Disease

22. -both alleles express themselves in the heterozygous -heterozygous may show milder or fewer symptoms Examples: Sickle Cells Anemia

23. -Abnormal hemoglobin causes a sickle shape of red blood cell -Red blood cells with sickle cell anemia have a bent and twisted shape, they are more rigid and easily get stuck in capillaries -Heterozygous- mix of normal and sickle cells- they are carriers and have some attacks -Homozygous- all red blood cells sickle shaped and they have painful attacks and blood clots -Caused by a change in one base for making hemoglobin -Heterozygous can be beneficial because they are resistant to malaria

24. caused by include Concept Map Autosomol Disorders Recessive alleles Dominant alleles Codominant alleles Albinism Galactosemia Tay-Sachs disease Huntington’s disease Sickle cell disease Cystic fibrosis PhenylketonuriaAchondroplasia Hypercholes- terolemia

25. -Chromosomes 21 and 22 are the smallest autosomes -22 has 43 million base pairs & 21 has 32 million base pairs Chromosome 22 -As many as 545 different genes -Disorders -Form of leukemia -Neurofibromatasis- tumor causing nervous system disease -Long stretches of repetitive DNA that does not code for proteins -Area is unstable and rearrangement occurs

26. Chromosome 21 - 225 genes - Disorders -ALS- amyotrophic lateral sclerosis (Lou Gehrig’s disease) -Many regions with no genes

27. As we discover what the larger chromosomes contain, we can learn more about how the arrangement of genes on a chromosome affect gene expression and development As we learned in Chapter 11, some genes are linked-they are located on the same chromosome This is true for human genes -Genes located on the sex chromosomes -Most are found on the X -The Y chromosome is smaller and has only a few genes -There are more than 100 sex-linked genetic disorders

30. -There are 3 genes associated with color vision and they are found on the X chromosome -Colorblindness is the inability to distinguish between certain colors -The most common is red-green colorblindness, found in 1 in 100 males -X-linked recessive allele -Females must be homozygous recessive to be colorblind (X c X c ) -Males only need 1 allele for the condition (X c Y)

31. Father (normal vision) Colorblind Normal vision Mother (carrier) Daughter (normal vision) Son (normal vision) Daughter (carrier) Son (colorblind) Male Female Colorblindness

32. Father (normal vision) Colorblind Normal vision Mother (carrier) Daughter (normal vision) Son (normal vision) Daughter (carrier) Son (colorblind) Male Female Colorblindness

33. -2 genes control blood clotting -Found in 1 in 10,000 males - Individuals can bleed to death from minor cut or suffer internal bleeding from bruises -Females are usually carriers -It is believed to have begun in the Royal family of Europe in the 19 th century -It can be treated by giving normal clotting protein

35. -Progressive weakening and loss of muscle tissue -Almost all cases are male -Death by age 20 -Genes consists of about 3,000,000 nucleotides (longest known human gene) -First symptoms appear in childhood when child has difficulty standing up -It is caused by a defective muscle protein

36. -Females have two X chromosomes -If males only need 1, why not females? Mary Lyon, a British genetists, discovered in female cells, one X chromosome will randomly be switched off -The turned off chromosome becomes a dense region in the nucleus called a Barr body

37. Cats -The gene for coat color is found on the X chromosome -One chromosome may the allele for orange spots and another for black spots -Cells in some parts of the body will inactivate one X and in other parts the other X -As a result a female cat may be a mix of orange and black spots

38. -Mistakes made in meiosis -Most common mistake Nondisjunction- failure of homologous chromosomes to separate

39. -Occurs when 2 copies fail to separate -As a result, an individual has three copies of a chromosome - trisomy “3 bodies” -Trisomy 21- individual has 3 copies of chromosome 21 -1 in 800 babies -Mild to severe retardation, an increase in the susceptibility to disease and birth defects

40. Down syndrome is correlated with the age of the mother; older mothers have an increased risk of giving birth to a child with Down syndrome Down syndrome is correlated with the age of the mother; older mothers have an increased risk of giving birth to a child with Down syndrome

41. Turner’s Syndrome -Female has only 1 X chromosome -Sterile- unable to reproduce -Short -Sex organs do not develop at puberty Klinefelter’s Syndrome - Male with XXY -Extra X interferes with meiosis and usually prevents individuals from reproducing -Individuals have been found with XXXY and XXXXY There have been no cases of babies born with just a Y which indicates that the X chromosome contains genes necessary for survival and development

43. Human DNA Analysis 6 billion base pairs exist in the human genome 6 billion base pairs exist in the human genome Can’t read them like a book, there are too many Can’t read them like a book, there are too many Genetists “look up” gene sequences to find disorders and traits Genetists “look up” gene sequences to find disorders and traits To test for disorders, genetists look for changes in the normal sequence To test for disorders, genetists look for changes in the normal sequence DNA fingerprinting- used to identify people DNA fingerprinting- used to identify people Look at DNA with little or no function, but varies from person to person Look at DNA with little or no function, but varies from person to person

44. Human Genome Project Project to analyze the human DNA sequence Project to analyze the human DNA sequence Scientists have found there are very few genes despite all of the base pairs that exist Scientists have found there are very few genes despite all of the base pairs that exist Scientists when searching for genes look for promoters- binding sites for transcription Scientists when searching for genes look for promoters- binding sites for transcription PromoterStart signal GeneStop signal

45. Normal hemoglobin gene Bone marrow cell Chromosomes Genetically engineered virus Nucleus Bone marrow Gene Therapy Cure for genetic disorders Absent or faulty gene replaced by a normal working gene