1. Essential Questions
What are the differences between various complex inheritance patterns?
How can sex-linked inheritance patterns be analyzed?
How can genetic patterns be analyzed to determine dominant or recessive inheritance patterns?
What are examples of dominant and recessive disorders?
How can human pedigrees be constructed from genetic information?
How do you determine blood types?
Copyright © McGraw-Hill Education
Complex Patterns of Inheritance

2. Recessive Genetic Disorders
A recessive trait is expressed when the individual is homozygous recessive for the trait. ( r r or t t )
Those with at least one dominant allele will not express the recessive disorder. (Rr or Tt)
An individual who is heterozygous for a recessive disorder is called a carrier.
Copyright © McGraw-Hill Education
Basic Patterns of Human Inheritance

4. Recessive Genetic Disorders Cystic fibrosis (1 in 3500)
A disorder that affects the mucous-producing glands, digestive enzymes, and sweat glands.
Gene that codes for a membrane protein is missing
Cystic fibrosis causes mucus excretion that clogs ducts in the pancreas, interrupts digestion, and blocks respiratory pathways in the lungs.
No cure – daily lung treatments – mucus thinning drugs – pancreatic enzyme supplements
Copyright © McGraw-Hill Education
Basic Patterns of Human Inheritance

5. Cystic Fibrosis

6. Recessive Genetic Disorders Albinism 1 in 17,000
Albinism is caused by altered genes, resulting in the absence of the skin pigment melanin in hair and eyes.
Individuals with albinism have very pale skin, white hair, and pink irises.
No cure
Copyright © McGraw-Hill Education
Basic Patterns of Human Inheritance

7. Albinism

8. Albinism

9. Albinism

10. Recessive Genetic Disorders Tay-Sachs disease 1 in 2500
Gene is found on chromosome 15
Cherry spot on back of the eye
Caused by the absence of the enzymes responsible for breaking down fatty acids called gangliosides
Gangliosides accumulate in the brain, inflating brain nerve cells and causing mental deterioration.
Copyright © McGraw-Hill Education
Basic Patterns of Human Inheritance

13. Recessive Genetic Disorders Galactosemia 1 in 50,000
Recessive genetic disorder characterized by the inability of the body to digest galactose.
Inability to digest milk products
Mental disabilities
No cure – restrict galactose/lactose
OTHERS
PKU
Autism
Muscular Dystrophy
Copyright © McGraw-Hill Education
Basic Patterns of Human Inheritance

14. PKU-Phenylketonuria

15. Autism

16. Muscular Dystrophy

17. Those that have the disease are homozygous recessive.
Dominant Genetic Disorders
Those that have
the disease are
homozygous
recessive.
r r or b b
Copyright © McGraw-Hill Education
Basic Patterns of Human Inheritance

18. Dominant Genetic Disorders Huntington’s disease 1 in 10,000
Affects the nervous system, causing gradual loss of brain function
Progressive break down of nerve cells in the brain.
Ability to move deteriorates over time
No cure or treatment
Copyright © McGraw-Hill Education
Basic Patterns of Human Inheritance

19. Huntington's Disease

20. Dominant Genetic Disorders
Achondroplasia
Causes small body size and limbs that are comparatively short
Caused by an abnormal gene that affects bone growth

22. Achondroplasia

23. Achondroplasia

24. The other 22 pairs of chromosomes are called autosomes.
Sex Determination
One pair of chromosomes, sex chromosomes, determine an individual’s gender.
XX: female
XY: male
The other 22 pairs of chromosomes are called autosomes.
Copyright © McGraw-Hill Education
Complex Patterns of Inheritance

25. Dosage Compensation Chromosome inactivation
Copyright © McGraw-Hill Education
Complex Patterns of Inheritance

26. In female, one X chromosome is inactivated in each cell.
Dosage Compensation
The X chromosome carries a variety of genes that are necessary for the development of both females and males.
The Y chromosome mainly has genes that relate to the development of male characteristics.
In female, one X chromosome is inactivated in each cell.
Called dosage compensation or x-inactivation
Which X stops working in each cell is random.
Copyright © McGraw-Hill Education
Complex Patterns of Inheritance

27. The inactivated X chromosome can be observed in cells.
Dosage Compensation
Barr bodies
The inactivated X chromosome can be observed in cells.
Darkly stained, inactivated X chromosomes are called Barr bodies.
Copyright © McGraw-Hill Education
Complex Patterns of Inheritance

28. Sex-Linked Traits
Traits controlled by genes located on the X chromosome are sex-linked traits.
Because males have only one copy of the X chromosome, they are more affected by recessive X- linked traits.
Copyright © McGraw-Hill Education
Complex Patterns of Inheritance

29. Red-green color blindness Recessive, X-linked trait
Sex-Linked Traits
Red-green color blindness
Recessive, X-linked trait
Mothers are carriers.
Copyright © McGraw-Hill Education
Complex Patterns of Inheritance

30. Color Blindness

33. Color Blindness Video

34. Recessive, X-linked trait that causes delayed clotting of blood
Sex-Linked Traits
Hemophilia
Recessive, X-linked trait that causes delayed clotting of blood
BLEEDER’s DISEASE
Normal blood clots in 2-8 minutes
Hemophilia take up to 30 minutes
Copyright © McGraw-Hill Education
Complex Patterns of Inheritance

35. Hemophilia

36. Hemophilia

38. Pedigrees
A pedigree is a diagram that traces the inheritance of a particular trait through several generations.
Copyright © McGraw-Hill Education
Basic Patterns of Human Inheritance

40. Analyzing Pedigrees Inferring Genotypes
Knowing physical traits can determine what genes an individual is most likely to have.
Predicting Disorders
Record keeping helps scientists use pedigree analysis to study inheritance patterns, determine phenotypes, and ascertain genotypes.
Copyright © McGraw-Hill Education
Basic Patterns of Human Inheritance

41. Incomplete Dominance
In some organisms, heterozygous individuals will display the dominant phenotype.
With incomplete dominance, the heterozygous phenotype is an intermediate phenotype between the two homozygous phenotypes.
Copyright © McGraw-Hill Education
Complex Patterns of Inheritance

42. Codominance
In codominance, both the dominant and recessive alleles are expressed in heterozygous individuals.
Copyright © McGraw-Hill Education
Complex Patterns of Inheritance

43. Changes in hemoglobin cause red blood cells to become sickle shaped.
Codominance
Sickle-cell disease
Changes in hemoglobin cause red blood cells to become sickle shaped.
People who are heterozygous for the trait have both normal and sickle-shaped cells.
Sickle-cell disease and malaria
Those who are heterozygous for the sickle cell trait also have a higher resistance to malaria.
The death rate due to malaria is lower where sickle-cell trait is higher, meaning more people live to pass it on to their offspring.
Copyright © McGraw-Hill Education
Complex Patterns of Inheritance

44. Sickle Cell Anemia

45. Multiple alleles can demonstrate a hierarchy of dominance.
Coat color of rabbits
Multiple alleles can demonstrate a hierarchy of dominance.
In rabbits, four alleles code for coat color: C, cch, ch, and c.
The hierarchy of dominance is C > cch > ch >c.
The presence of multiple alleles increases the possible number of genotypes and phenotypes.
Copyright © McGraw-Hill Education
Complex Patterns of Inheritance

47. Seen in the coat color of Labrador retrievers
Epistasis
Epistasis is an interaction where one allele hides the effects of another allele.
Seen in the coat color of Labrador retrievers
Dominant allele E determines whether the coat will have dark pigment.
Allele B determines how dark the coat will be.
When a dog has recessive ee alleles, the coat will be yellow, because the e allele masks the effects of the B allele.
Copyright © McGraw-Hill Education
Complex Patterns of Inheritance

49. Include such traits as skin color, height, and eye color
Polygenic Traits
Polygenic traits arise from the interaction of multiple pairs of genes.
Include such traits as skin color, height, and eye color
Copyright © McGraw-Hill Education
Complex Patterns of Inheritance

52. Skin Color

53. Multiple Alleles Blood groups in humans
Some forms of inheritance are determined by more than two alleles, referred to as multiple alleles.
The ABO blood group has three forms of alleles, sometimes called AB markers.
Copyright © McGraw-Hill Education
Complex Patterns of Inheritance

54. Blood Types About half of us are blood group O
Next most common is blood group A.
Few people have type B
Least common type AB.

55. Blood Types
Phenotype
Genotype A
AA or Ai B
BB or Bi AB O ii

56. Rh The Rh blood groups are the next most familiar types.
People whose red cells have a particular feature called the “ D antigen” are Rh positive. People who lack the factor are Rh negative.
Most people are Rh positive.

57. Who Can You Donate Too? Blood Type Video