1. Pedigrees

2. Studying Pedigrees: How are traits inherited???
Pedigree= a family history that shows how a trait is inherited over several generations

3. Why are pedigrees helpful/useful?
Common Genetic Disorders:
Angelman Syndrome
Canavan Disease
Charcot-Marie-Tooth Disease
Cri du Chat Syndrome
Duchenne Muscular Dystrophy
Fragile X Syndrome
Gilbert's Syndrome
Joubert Syndrome
Klinefelter Syndrome
Krabbe Disease
Lesch–Nyhan Syndrome
Myotonic Dystrophy
Neurofibromatosis
Noonan Syndrome
Pelizaeus-Merzbacher Disease
Phenylketonuria
Porphyria
Prader-Willi Syndrome
Retinoblastoma
Rubinstein-Taybi Syndrome
Spina bifidia
Smith-Magenis Syndrome
Stickler Syndrome
Turner Syndrome
Variegate Porphyria
Von Hippel-Lindau Syndrome
Wilson's Disease
Wolf-Hirschhorn Syndrome
XXXX Syndrome
YY Syndrome
Pedigrees are helpful if couples are concerned that they might be carriers of genetic disorders

4. Pedigree Symbols

5. Pedigree Numbers
Roman numerals (I, II, III, IV) represent = Generations
Regular numbers (1,2,3,4) represent = Individuals in each generation

6. Pedigree Symbols – Male and Female
= Normal Male
= Normal Female
= Male with trait
= Female with trait
Horizontal line between a male and female indicates MATING/MARRIAGE
Branching vertical lines point to OFFSPRING

7. Autosomal vs. Sex-linked Traits
Autosomal Trait = appears in both sexes equally, alleles appear on the autosomal chromosomes
Sex-linked Trait = a trait whose allele is located on the X chromosome
Appears mostly in males
Mostly recessive
Female only exhibits the condition if she inherits two recessive alleles

8. Human Chromosomes Humans have 46 chromosomes:
1 pair of sex chromosomes (X and Y)
22 pairs of autosomes
Females have 2 X chromsomes (XX).
Males have an X chromsome and a Y chromosome (XY)

9. Karyotypes
A Karyotype is a test to identify and evaluate the size, shape, and number of chromosomes in a sample of body cells.

10. Dominant vs. Recessive Trait
Autosomal Dominant Traits = each individual with the trait will have a parent with the trait
Autosomal Recessive Traits = an individual with the trait can have one, two, or neither parent who exhibit the trait

11. Recessive Disorder: Albinism
Albinism = a genetic disorder in which the body is unable to produce an enzyme necessary for the production of melanin (dark color to hair, skin, scales, eyes, and feathers)

12. Genetic Disorders = Carriers
Carriers = individuals who are heterozygous for a recessive inherited disorder, but do not show symptoms of the disorder
Can pass the recessive allele for the disorder to their offspring

13. Red-Green Color Blindness: A Sex-Linked Recessive Disorder
Among Caucasian individuals:
8% of males
0.5% of females
Difficulty distinguishing between shades of green and red

14. Red-Green Color Blindness: A Sex-Linked Recessive Disorder
Males have the disorder more often than females because they only have one X chromosome.
Unaffected female = XRXR
Affected female = XrXr
Carrier female = XRXr
Unaffected male = XRY
Affected male = XrY

15. Red-Green Color Blindness: A Sex-Linked Disorder

16. Heterozygous vs. Homozygous
Homozygous Dominant or Heterozygous individuals = phenotype will show the dominant characteristic
Homozygous Recessive individuals = phenotype will show the recessive characteristic
***Heterozygous carriers of a recessive mutation will not show the mutation, can produce children who are homozygous for the recessive allele

17. Let’s look at a pedigree for polydactyly: a dominant trait

18. Let’s look at a pedigree for phenylketonuria (PKU): a recessive disorder
The trait skips a generation!!

19. Human Genetics

20. Traits Controlled by a Single Gene: Autosomal Dominant Disorders
Huntington’s Disease
Marfan Syndrome
Lynch Syndrome (familial
colorectal cancer)
Neurofibromatosis Type 1

21. Traits Controlled by a Single Gene: Autosomal Dominant Traits
Widow’s Peak
Tongue Rolling
Free Earlobes
Vulcan Hand Sign
Cheek Dimples

22. Traits Controlled by a Single Gene: Autosomal Recessive Disorders
Cystic Fibrosis
Tay-Sachs Disease
Sickle Cell Anemia
Robert’s Syndrome

23. Traits Controlled by a Single Gene: Autosomal Recessive Traits
Attached Earlobes
Hitchhiker’s Thumb
Cleft Chin
Thumb Crossing (R/L)

24. Traits Influenced by Several Genes
Polygenic Trait = when several genes influence a trait
Genes can be:
Scattered along the same chromosome
Located on different chromosomes
Independent Assortment = many different combinations in offspring
Polygenic traits =
Eye color, height, weight, hair and skin color

25. Intermediate Traits
Incomplete Dominance = an individual displays a trait that is intermediate between the two parents
Examples:
Red snapdragon + White snapdragon = Pink snapdragon offspring
Curly hair + Straight hair = Wavy haired offspring
Neither allele is dominant to the other

26. Traits With Two Forms Displayed At The Same Time
Codominance = when two dominant alleles are expressed at the same time, both forms of the trait are displayed
Example:
Red Horse + White Horse = Roan Horse

27. Traits Controlled By Genes With Three or More Alleles
Multiple Alleles = Genes with three or more alleles
Example: ABO blood groups in humans
IA and IB = Dominant to i;
A & B are two carbohydrates on the surface of red blood cells
i = Recessive
When IA and IB are present together = Codominant

28. Traits Controlled By Genes With Three or More Alleles
An individual can only have two of the possible alleles for the gene

29. Genotypes of Each Blood Type

30. Traits Influenced By The Environment
Phenotype is affected by environmental conditions
Hydrangeas (flowers) range from blue to pink based upon the pH of the soil
Acidic soil = blue flowers
Basic soil = pink flowers

31. Traits Influenced By The Environment
Siamese Cat
Fur on ears, nose, paws, and tail is darker than the rest of the body
Dark fur at locations which are cooler than normal body temperature

32. Traits Influenced by the Environment: Identical Twins

33. Human Examples: Traits Influenced By The Environment
Height
What can influence height besides genes?
Skin Color
Human Personality

34. Traits Caused By Mutation
Damaged genes/genes which are copied incorrectly – result in faulty proteins
Mutations are RARE
Inherited Mutations cause Genetic Disorders
Many mutations are carried in recessive alleles
Carrier = heterozygous individual
Carry the recessive allele but do not exhibit the disorder

35. Sickle Cell Anemia Recessive Defective hemoglobin Sickle-Cell Shape
Red Blood Cells
Binds and transports oxygen
Sickle-Cell Shape
Rupture-prone
Clotting in blood vessels
Heterozygote Advantage = protection from malaria

36. Hemophilia Recessive Sex-linked Impairs blood clotting
X chromosome
More males afflicted than females
Impairs blood clotting
English royal family

37. Hemophilia: The Royal Family

38. Huntington’s Disease Dominant
First symptoms appear in thirties or forties:
Mild forgetfulness
Irritability
Long-term symptoms:
Loss of muscle control
Chorea (physical spasms)
Severe Mental Illness
Death

39. Detecting and Treating Genetic Disorders
Genetic Counseling = a form of medical guidance that informs people about genetic problems that could affect them or their offspring
Phenylketonuria (PKU)
Lacks enzyme to convert phenylalanine into tyrosine
Can cause mental retardation
Early intervention involves low-phenylalanine diet
Gene Therapy = replacing defective genes with healthy ones