1. Complex Inheritance and Human Heredity
Chapter 11

2. We inherit traits from our parents, we get half of our genes from mom, and half from dad
Alleles are either recessive (lowercase) or dominant (uppercase)
Homozygous recessive, homozygous dominant, heterozygous
Let’s review!

3. Autosome/Autosomal: Any chromosome other than the sex chromosomes (X & Y). Chromosomes designated
Carrier: An individual who is heterozygous for a recessive disorder
Pedigree: A diagram that traces the inheritance of a particular trait through several generations of the same family
New Words!

4. Basic patterns of inheritance
Genetic Disorders

5. An abnormal condition that a person inherits through their genes
Can be caused by either changes in DNA, or an extra or missing chromosome
Genetic disorders can be recessive or dominant
Genetic Disorders

6. Recessive Disorders Two recessive alleles, one from each parent
If an individual is heterozygous, they are a carrier (this means they could pass it on even if they don’t have it!)
BB – Normal
Bb – okay, but a carrier
bb – disease
Often skips a generation
Recessive Disorders

7. Affects cell membrane protein, water cannot diffuse from cells
the body produces an abnormally thick mucus in the lungs
Chromosome 7
Medication, strict diet, enzyme replacement
Death is usually caused by lung complications
Cystic Fibrosis

8. Tay-Sachs Absence of enzyme that breaks down fatty substances
Chromosome 15
Buildup of fatty acids in brain
Cherry red spot on back of eye
Causes deafness, blindness, severe retardation, and death usually by age 4
Most carriers choose to avoid birth because there is no cure
Brain on top is normal, brain on bottom has lipid accumulation (is “clogged”)
Tay-Sachs

9. Caused by altered genes, resulting in the absence of the skin pigment melanin in hair and eyes
White hair
Very pale skin
Pink pupils
Albinism

10. Recessive genetic disorder characterized by the inability of the body to digest galactose.
People with this disorder should avoid milk products
Galactosemia

11. The mutation for cataracts (c) occurs on a gene represented by the letter E. Owls that are homozygous for the mutation (EcEc) exhibit cataracts. Owls that are homozygous for normal eyes are EE and owls that are carriers of the mutation but do not exhibit cataracts are EEc. What percentage of the offspring in a cross between parents with the genotypes EE and EcEc will exhibit cataracts? A. 0% B. 25% C. 50% D. 75%
OGT

12. Dominant Disorders Caused by dominant alleles
Those who do not have the disorder are homozygous recessive.
BB – have disease
Bb – have disease
bb – normal
Dominant Disorders

13. Huntington’s Disease Affects the nervous system
Deterioration of brain tissue, usually begins between age 30 and 40
Chromosome 4
No cure, but have medications to cope with symptoms
People usually die years after onset of degeneration
Huntington’s Disease

14. causes small body size and limbs that are comparatively short, most common type of dwarfism
Chromosome 4
75% born to parents of average size
When this happens it is due to a gene mutation
Achondroplasia

15. Genetic disorders
To Test or Not to Test?

16. Choosing Thomas You will need one worksheet and one index card
Find the rest of your family based on the number on your cards
Complete the worksheet as a group and be prepared to discuss your answers as a class
Choosing Thomas

17. Pedigrees

18. A diagram that traces the inheritance of a particular trait through several generations of the same family
Allows us to use family trees and affected individuals to predict the risk of disease in future offspring
Pedigrees

19. Symbols Male: Mating: Female: Siblings: Affected Individual:
Divorced/Separated:
Deceased:
Male:
Female:
Affected Individual:
Carrier:
Symbols

20. Individuals are numbered Generations are numbered with roman numerals
Individuals are in birth order from left to right (oldest at left, youngest on right)
Individuals are numbered
Generations are numbered with roman numerals
When referring to an individual, use the generation number and then the individual number
II-4

21. Example of a Pedigree I II III Do any disorders run in this family??
Grandparents
Grandparents I
Parents II
Aunts, Uncles
Aunts, Uncles
III
Brother
You
Do any disorders run in this family??

22. What can you tell from a pedigree?
Whether a family has an autosomal or sex-linked disease or disorder
If the trait is dominant or recessive
Autosomal: appears in both sexes equally
Sex-linked disorder: allele is located only on the X or Y chromosome. Most sex-linked genes are on the X chromosome and are recessive
So who would have an X-linked disorder more often, boys or girls?
What can you tell from a pedigree?

23. Complex patterns of inheritance

24. Let’s Review! Basic patterns of inheritance involve…
The passing of dominant or recessive traits
Disorders that are recessive require:
2 recessive alleles, 1 from mom, 1 from dad
A normal person who carries the gene could pass it on
Disorders that are dominant require:
2 dominant alleles, 1 from mom, 1 from dad OR
1 dominant allele (heterozygous)
There are no carriers for these disorders, you either have it or you don’t!
Let’s Review!

25. Let’s Review! These disorders are autosomal
Chromosomes 1-22
Geneticists use a diagram called a pedigree to trace familial traits and predict the inheritance of the trait in future offspring
Let’s Review!

26. Sometimes the laws and principles of genetics established by Gregor Mendel do not always explain the inheritance patterns seen in an organism.

27. Neither allele is completely dominant nor completely recessive
Heterozygous phenotype is a blend of the two homozygous phenotypes
a mix in physical appearance between the dominant and the recessive
Incomplete Dominance

28. Both alleles are completely expressed in the heterozygous condition.
Sickle Cell
Codominance

29. Abnormal hemoglobin causes a person’s red blood cells to be sickle shaped
The shape causes clots and blockages, they also carry less oxygen
The allele for the disease is codominant with the normal allele (heterozygous)
People who are heterozygous for sickle cell also have a higher resistance to malaria
Consequently, fewer people with sickle cell die from malaria, so the gene continues to pass
Sickle Cell Anemia

30. Sickle Cell rr – all sickle shaped cells Rr– mixture of both
RR– normal shaped cells
Sickle Cell

31. Codominant or Incomplete?

32. Multiple Alleles 1 gene, more than 2 alleles
Sometimes, there are 3 or 4 alleles that code for a single trait
Blood Groups
This doesn’t mean a person has more than 2 alleles for the trait, just that more than 2 exist in the population
1 gene, more than 2 alleles
Multiple Alleles

33. Blood Groups 3 forms of the allele i is recessive to IA and IB
IA – type A
IB – type B
i – type O
i is recessive to IA and IB
IA and IB are codominant
IAIB – type AB
Blood Groups

34. Blood Groups IAi – type A IBi – Type B IAIB – type AB IAIA – Type A
Heterozygous
Homozygous
IAi – type A
IBi – Type B
IAIB – type AB
IAIA – Type A
IBIB – Type B
ii – Type O
Blood Groups

35. A scientist uses a microscope to examine two slides of living bacteria
 A scientist uses a microscope to examine two slides of living bacteria. Each slide contains a different type of bacteria. While the cells on the first slide are moving rapidly, the cells on the second slide are stationary.
Based on these observations, the cells on the second slide most likely have no
A. nucleus
B. flagella
C. chloroplasts
D. mitochondria
OGT

36. Sex-Linked Traits Genes that are found on the X chromosome
Expressed more in males because they only have one X chromosome (XY) compared to females (XX)
Sex-Linked Traits

37. Hemophilia Recessive sex-linked disorder
Takes a long time for blood to clot (body lacks proteins involved in clotting)
Very rare in females because she would need to have both X chromosomes with the recessive trait.
Hemophilia

38. Patricia is a healthy carrier of hemophilia and Sam is completely healthy. Complete the Punnett square below.
Mom’s genotype:
Dad’s genotype:
What is the probability of getting:
Daughter with hemophilia?
Son with hemophilia?
Carrier?
Healthy child?

40. Red-Green Colorblindness
Recessive X-linked trait
Male only needs one copy of this allele in order to be colorblind.
Female would need to have two copies of the recessive allele.
It is very rare to find a color blind female.
Mothers pass this to their sons
Father pass it to their daughters
Red-Green Colorblindness

41. Judy is homozygous recessive for colorblindness and Dennis is healthy
Judy is homozygous recessive for colorblindness and Dennis is healthy. Complete their Punnett square below.
Mom’s genotype:
Dad’s genotype:
What is the probability of getting:
Colorblind daughter?
Color blind son?
Carrier?
Heterozygous child?

42. Baldness Baldness is X-linked Recessive
Grandpa bald = XbY X Grandma = XBXB
Daughter = XBXb marries Male = XBY
Sons?
50% XB(normal)
50% Xb(bald)
This is why men should look to their mom’s dad for probability of baldness. But beware grandma could be a carrier too!
Baldness

43. At 25°C, water has a density of 1
At 25°C, water has a density of 1.0 g/mL and vegetable oil has a density of 0.90 g/mL.
How would a substance with a density of 0.95 g/mL behave when placed in both oil and water?
A. a decrease in air quality.
B. a decrease in biodiversity.
C. an increase in deciduous tree species.
D. an increase in nighttime temperatures.
OGT

44. What’s different?

45. Cell division during which sister chromatids fail to separate properly
If this occurs during Meiosis I or II then the resulting gametes will not have the correct number of chromosomes
Nondisjunction occurs in both autosomes (body cells) and in gametes
Trisomic: one extra chromosome (only 3 trisomies that result in survival after birth)
Monosomic: one missing chromosome (usually lethal, except in Turner’s Syndrome)
Nondisjunction

47. Down Syndrome Chromosome 21 Can be moderate or severe
Trisomy
Can be moderate or severe
Short stature, heart defects, and mental disability
Correlated with mother’s age, can be from nondisjunction of father’s chromosome 21
Down Syndrome

48. Other Examples Autosomal Sex Chromosomes Patau Syndrome: Trisomy 13
serious eye, brain, circulatory defects as well as cleft palate. 1:5000 live births. Children rarely live more than a few months
Edwards’s Syndrome: Trisomy 18
almost every organ system affected 1:10,000 live births. Children with full Trisomy 18 generally do not live more than a few months.
Klinefelter Syndrome: XXY
Male sex organs; unusually small testes, sterile. Breast enlargement and other feminine body characteristics. Normal intelligence.
Trisomy X: XXX
1:1000 live births - healthy and fertile - usually cannot be distinguished from normal female
Monosomy X: Turner’s Syndrome
1:5000 live births; the only viable monosomy in humans - women with Turner's have only 45 chromosomes!!! XO individuals are genetically female, however, they do not mature sexually during puberty and are sterile. Short stature and normal intelligence. (98% of these fetuses die before birth)
Other Examples

50. Environmental Factors
The environment can have an influence on how genes are expressed
Toxic agents
Diet and exercise
Sunlight and water
Temperature
Medications
Conditions can cause a gene to shut down or turn on
I got the “fat” gene.
Environmental Factors

51. Additional Vocabulary
Karyotype: an image that shows homologous chromosomes arranged in decreasing size
Telomere: caps on the ends of chromosomes, have a protective function
Additional Vocabulary

52. Epistasis BBC: The Ghost in Your Genes
Epistasis: When the one gene hides the effects of another gene
Epigenetics
Epistasis

53. A driver traveling from the coniferous region to the tundra region would most likely observe
A. sink in both oil and water
B. sink in oil and float on water
C. float on oil and sink in water
D. float on both oil and water  
OGT