Human Genetic Traits

1. Human Genetic Traits

2. Sex Chromosomes • In most animal species, chromosomes can be categorized • as two types: • Autosomes – non sex chromosomes • Sex chromosomes – determine if the individual is male • or female. • Sex chromosomes in the human female are XX, male XY. • Males produce X- containing and Y-containing gametes; • therefore males determine the sex of the offspring. • Besides genes that determine sex, sex chromosomes carry • many genes for traits unrelated to sex. • X- linked gene is any gene located on X chromosome.

3. Autosomes and Sex Chromosomes

4. Disorders Down’s Syndrome (chrom 21) Alzheimer’s (chrom 1, 10, 14, 19, 21) Huntington’s (chrom 4)

5. X- Linked Alleles Work with fruit flies by Thomas Hunt Morgan confirmed that Genes were on chromosomes. X- linked alleles are designated as superscripts to X Chromosome. Heterozygous females are carriers but do not show the trait But can pass it on. Males are never carriers but express the one allele on the X Chromosome. One form of colour blindness is X- linked recessive.

6. Importance of genetics • Understanding hereditary diseases and to develop new treatments • Donor matches • Paternity • Forensics • Evolution

7. Genetic Testing • Would you want to know? • Ethical concerns • Cost • Insurance companies • see GATTACA

8. Genes- genetic material on a chromosome that codes for a specific trait Genotype- the genetic makeup of the organism Phenotype- the expressed trait Allele- an alternative form of a gene

9. Dominance Mechanism • Two alleles are carried for each trait • In true-breeding individuals, both alleles are the same (homozygous). • Hybrids, on the other hand, have one of each kind of allele (heterozygous). • One trait is dominant, the other trait is recessive

10. Allele Example • Gene = “eye color” • Alleles • brown • blue • green • lavender

11. Allele Examples appearance eye color:homozygous

12. Allele Examples appearance eye color:heterozygous, brown dominant over blue

13. Genotype vs Phenotype genotype phenotype homozygous(dominant) heterozygous homozygous (recessive) appearance

14. Punnett Square If male & female are heterozygous for eye color male female X brown: 3/4 offspring blue: 1/4 offspring

15. Red-Green Color Blindness Sex-linked trait XC Y XC Y XC XC XC Normal male XC Y X XC Xc XC Xc Xc Xc Y Normal female recessive gene Possible outcomes: XCXC XCXc XCY XcY Normal female Normal Female (carrier) Normal male Color-blind male

16. Dominance Most traits show complete dominance Blending unexpected

17. allele gene E unconnected earlobe e connected earlobe unconnected P EE x ee connected E e gametes F1 Ee

18. F1 Ee x Ee 1/2 E 1/2 e1/2 E 1/2 e gametes E e E EE Ee PunnettSquare e Ee ee F2 1 EE 2 Ee 1 ee

19. generation genotypes unconnected E:e P EE, ee 50% 1:1 F1 Ee 100% 1:1 F2 EE, 2 Ee, ee 75% 1:1 phenotypes ratio of alleles in the population Basis of the Castle-Hardy-Weinberg Law

20. Human Genetic Traits

21. Tongue Roller R = Tongue Rollerr = Unable to Roll Tongue

22. Widow’s Peak W = Widows Peakw = Lack of Widow’s Peak

23. Free Ear Lobe Attached Ear Lobe E = Free Ear Lobee = Attached Ear Lobe

24. Hitchhiker’s Thumb Hi = Straight Thumbhi = Hitchhiker’s Thumb

25. Bent Little Finger Bf = Bent Little Fingerbf = Straight Little Finger

26. Mid-digital Hair M = Mid-Digital Hairm = Absence of Mid-Digital Hair

27. Dimples D = Dimplesd = Absence of Dimples

28. Short Hallux Ha = Short Halluxha = Long Hallux

29. Now complete Human Traits Assignment

30. Predicting Offspring Genetic disorders are medical conditions caused by alleles inherited from parents. These disorders are mapped on a Pedigree. A carrier is a heterozygous individual who has no apparent abnormality but can pass on an allele for a recessive inherited genetic disorder.

31. Autosomal Dominant and Autosomal Recessive Characteristics of autosomal dominant disorders: 1. Affected children usually have an affected parent. 2. Heterozygotes are affected. Two affected parents can produce unaffected child; two unaffected parents will not have affected children. Characteristics of autosomal recessive disorders: 1. Most affected children will have normal parents since heterozygotes have a normal phenotype. 2. Two affected parents always produce an affected child. 3. Close relatives who reproduce together are more likely to have affected children.

32. Chance has no memory! Each child born to heterozygous parents has a 25% chance of having a disorder regardless of prior sibling’s conditions.

33. Tracking Human Traits A pedigree is a diagram of family relationships that symbols to represent people and lines to represent genetic relationships. These diagrams make it easier to visualize relationships within families, particularly large extended families. Pedigrees are often used to determine the mode of inheritance (dominant, recessive, etc.) of genetic diseases. .

34. In a pedigree, squares represent males and circles represent females. Horizontal lines connecting a male and female represent mating. Vertical lines extending downward from a couple represent their children. Subsequent generations are therefore written underneath the parental generations and the oldest individuals are found at the top of the pedigree. If the purpose of a pedigree is to analyze the pattern of inheritance of a particular trait, it is customary to shade in the symbol of all individuals that possess this trait. In the pedigree , the grandparents had two children, a son and a daughter. The son had the trait in question. One of his four children also had the trait.

35. Autosomal Dominant Disorders Achondroplasia - Achondroplasia is inherited as an autosomal dominant disorder. It is diagnosed in the first years of life and affects 1 in 26,000 births; the majority of cases are sporadic. This is the classic circus dwarf with disproportionate shortness of the limbs and large head, but apparently normal trunk. Huntington's disease - Huntington's disease is a disorder passed down through families in which nerve cells in certain parts of the brain waste away, or degenerate. Marfan's syndrome - Marfan syndrome is a genetic disorder that affects the body's connective tissue - the tissue that makes up our tendons, ligaments, joints, and muscles, including the heart, blood vessels, and eyes. People with this condition are generally very tall and slim with long arms and fingers. It's quite rare - roughly 1 in 5,000 people have it. Neurofibromatosis - is a disorder characterized by the growth of noncancerous tumors called neurofibromas. They usually form on or just underneath the skin, as well as in the brain and peripheral nervous system. But they can also develop in other parts of the body, such as the eye.

36. Autosomal Recessive Disorders Cystic fibrosis (CF) Cystic fibrosis is one of the most common inherited single gene disorders in Caucasians. About one in 2500 Caucasian babies is born with CF and about one in 25 Caucasians of northern European descent carries the gene for CF. People with CF secrete abnormal body fluids, including unusual sweat and a thick mucus which prevents the body from properly cleansing the lungs. The mucus interrupts the function of vital organs and leads to chronic infections. Classic CF also involves the pancreas and causes decreased absorption of essential nutrients. Life expectancy has improved, but, ultimately, death most often occurs from respiratory failure. Other people with variants of CF may have only lung involvement, sinusitis, or infertility. Tay Sachs Disease Tay Sachs disease is a fatal disorder in children (usually by age 5) that causes a progressive degeneration of the central nervous system. It is caused by the absence of an enzyme called hexosaminidase A (or hex A). Without hex A, a fatty substance builds up on the nerve cells in the body, particularly the brain. The process begins early in pregnancy when the baby is developing, but is not apparent until several months after the birth. To date, there is no cure for Tay Sachs. Dr. Tay and Dr. Sachs, who originally described this condition, noted that most Tay Sachs babies were usually of eastern European Jewish origin. About one in 30 persons of Ashkenazi Jewish ancestry carries the Tay Sachs gene.

37. Sickle cell anemia (SC) Sickle cell anemia is one of the most common, inherited single gene disorders in African-Americans. About one in 600 African-American babies is born with SC, and about one in 12 African-American people carries the gene for SC. SC involves the red blood cells, or hemoglobin, and their ability to carry oxygen. Normal hemoglobin cells are smooth, round, and flexible, like the letter "O", so they can move through the vessels in our bodies easily. Sickle cell hemoglobin cells are stiff and sticky, and form into the shape of a sickle, or the letter "C" when they lose their oxygen. These sickle cells tend to cluster together and cannot easily move through the blood vessels. The cluster causes a blockage and stops the movement of healthy, normal oxygen carrying blood. This blockage is what causes the painful and damaging complications of sickle cell disease.

38. phenylketonuria (PKU) Phenylketonuria (commonly known as PKU) is an inherited disorder that increases the levels of a substance called phenylalanine in the blood. Phenylalanine is a building block of proteins (an amino acid) that is obtained through the diet. It is found in all proteins and in some artificial sweeteners. If PKU is not treated, phenylalanine can build up to harmful levels in the body, causing intellectual disability and other serious health problems.

39. Complexities • Multiple genes for one trait • Example: eye color • Blended traits (“incomplete dominance”) • Influence of the environment

40. Many human traits are controlled by single genes. True for disorders, too. Cystic fibrosis, deafness, Tay Sachs. Hitchhiker thumb. Pedigrees used to predict potential disorders in children, help make a reproductive strategy. Some people may chose to not have children but adopt instead.

41. Family pedigrees are used to determine patterns of inheritance and individual genotypes Dd Joshua Lambert Dd Abigail Linnell D_ JohnEddy ? D_ HepzibahDaggett ? D_ Abigail Lambert ? dd JonathanLambert Dd Elizabeth Eddy Dd Dd dd Dd Dd Dd dd Female Male Deaf Hearing Figure 9.8B

42. Inherited Genetic Disorders: • Most mutations usually involve recessive alleles • Phenylketonuria, PKU • Tay-Sachs disease • Cystic fibrosis • A few are caused by dominant alleles: Achondroplasia, Huntington’s disease

43. Sex-linked disorders affect mostly males • Most sex-linked human disorders are due to recessive alleles • Ex: hemophilia, red-green color blindness These traits appear mostly in males. Why? • If a male receives a single X-linked recessive allele from his mother, he will have the disorder; while a female has to receive the allele from both parents to be affected Figure 9.23A

44. Pedigree Chart: Inheritance Pattern for an X-linked Recessive Disease Figure 19.12

45. A high incidence of hemophilia has plagued the royal families of Europe QueenVictoria Albert Alice Louis CzarNicholas IIof Russia Alexandra Alexis inherited hemophilia from his mother Alexandra, a condition that could be traced back to her maternal grandmother Queen Victoria. Alexis Figure 9.23B

46. Hemophilia in European royalty • Hemophilia figured prominently in the history of European royalty in the 19th and 20th centuries. Britain's Queen Victoria, through two of her five daughters including Princess Alice and Princess Beatrice, passed the mutation to various royal houses across the continent, including the royal families of Spain, Germany and Russia.

47. General Pedigree

48. Autosomal Dominant Pedigree

49. Look for: • Trait in every generation • Once leaves the pedigree does not return • Every person with the trait must have a parent with the trait • Males and females equally affected

50. Autosomal Recessive Pedigree