1. Patterns of Heredity and Human Genetics
Chapter 12
Patterns of Heredity
and Human Genetics

3. Chapter 12.1 Scientific Terms
Pedigree
Carrier
Fetus

4. 1. What is a pedigree? How do you make one?
Pedigree  graphic representation of genetic inheritance
- looks like a “family tree”
It is made of a set of symbols that identify:
- male or female
- the trait being studied
- the relationships between the members 

6. 2. Describe how you would analyze a pedigree. Why are these useful?
Pedigrees show “carriers”, which are heterozygous individuals
You can follow a trait through generations by looking at a pedigree
Helpful for knowing the possibility of genetic disorders, or any recessive trait 

7. 3. Describe what “simple recessive heredity” refers to
3. Describe what “simple recessive heredity” refers to. Describe the three recessive disorders that the book discusses.
Genetic disorders caused by a homozygous recessive situation (rr or tt, etc)
Cystic fibrosis  1 in 28 white Americans carry the recessive allele (Rr)
- 1 in 2500 white kids born with it
Tay-Sachs  common in Amish people and Jewish people from eastern Europe
Phenylketonuria  common in descendants of Norway and Sweden 

8. 4. Describe what “simple dominant heredity” refers to
4. Describe what “simple dominant heredity” refers to. Overview the several dominant traits that the book discusses.
A trait is inherited with at least one dominant allele (RR or Rr)
Tongue rolling
Free hanging ear lobes
Hitchhiker’s thumb
Almond shaped eyes
Full lips
Hair on middle section of fingers
Huntington’s disease 

9. Section Assessment
Answer questions (1-4) on page 314.

12. Chapter 12.2 Scientific Terms
Incomplete dominance
Codominant allele
Multiple allele
Autosome
Sex chromosome

14. 5. Describe the concept of “incomplete dominance” and describe an example.
When the phenotype of the heterozygote is a blending of the two homozygotes
Ex: If a red flower (RR) is crossed with a white flower (R’R’), the resulting offspring are heterozygotes (RR’) which look pink 

16. 6. Describe the concept of codominance. Show an example.
Codominant alleles cause the phenotypes of both homozygotes to be produced in the heterozygote
Both alleles are expressed equally, not combined
When a black chicken is crossed with a white chicken, the offspring are NOT gray, they are black and white 

18. 7. Describe the concept of multiple phenotypes from multiple alleles
7. Describe the concept of multiple phenotypes from multiple alleles. Describe the book’s example.
It is common for more than 2 alleles to control one trait
Traits controlled by more than 2 alleles have “multiple alleles”
In pigeons, a single gene that controls feather color has 3 alleles
Ex: BA makes red feathers
B makes blue feathers
b makes chocolate colored feathers 

20. 8. What is the difference between autosomes and sex chromosomes
8. What is the difference between autosomes and sex chromosomes? How do the sex chromosomes affect sex-linked inheritance? Can you think of any sex-linked traits in humans?
Autosomes  the 22 pairs of homologous chromosomes besides the sex chromosomes
Sex chromosomes  the 2 chromosomes that determine the sex of an individual
Sex-linked traits  traits controlled by genes located on the sex chromosomes
- the Y chromosome has no corresponding allele to some traits on the X chromosome
Ex: color blindness, male pattern baldness 

23. Review… write answers with SAQs
1. A blue fish and a yellow fish have all green babies! What inheritance pattern does fish color follow?
2. A red cow and a white cow have red & white calves. What inheritance pattern does this follow?
3. What is a chart of chromosomes called?
4. What is II-2’s genotype? 
5. What is most likely II-1’s 
genotype?

24. Types of Inheritance… Complete dominance Incomplete dominance
Codominance
Multiple Alleles
Sex Determination
Sex-linked inheritance
Polygenic inheritance
Environmental Influences

25. Chapter 12.2 & 3 Terms Sex-linked trait Polygenic inheritance
Karyotype
*Turn in terms
sheet*

26. 9. Describe what polygenic inheritance is and describe an example.
It is the inheritance pattern of a trait that is controlled by two or more genes
Ex: skin color (AABBCC)
- the CAPITAL letters are darkness
- the lowercase letters are lightness
AABBCC AaBbCc aabbcc AAbbCc
very dark medium very light medium 

28. 10. How does the environment influence genetic expression
10. How does the environment influence genetic expression? Describe the influence of the external and internal environments.
The genetic makeup at fertilization is the potential
Many factors can influence how the gene is expressed (internal and external factors)
External  temperature, nutrition, light, chemicals, infections
- Ex: tree leaves, height
Internal  male vs female due to hormones and structural differences
- Ex: horn size, male baldness, peacock feathers 

30. 11. Describe what disorder exhibits codominance in humans, and why this is actually an advantage.
Sickle-cell anemia
Most common in African-Americans and white Americans from the Mediterranean
About 1 in 12 are heterozygous (RR’) and produce both normal RBCs and sickle ones
Advantage in malaria 

31. 12. Describe how multiple alleles govern human blood types, and why this is important to know.
ABO blood group
Determined by the presence or absence of surface proteins on RBCs
Three alleles for the “I” trait  IA, IB, i 

32. Section Assessment
Answer questions (1-4) on page 322

33. Turn in your Ch 12.2 sheet

34. Types of Inheritance… Complete dominance Incomplete dominance
Codominance
Multiple Alleles
Sex Determination
Sex-linked inheritance
Polygenic inheritance
Environmental Influences

35. 13. Describe the two sex-linked traits talked about in your book
13. Describe the two sex-linked traits talked about in your book. Why do males usually get these disorders?
Red-Green color blindness
- caused by two recessive alleles at two gene sites on the X chromosome
Hemophilia
- problem with blood clotting
- 1 in 10,000 males
- 1 in 100,000,000 females
- inherited on X chromosome from mother carriers
- treated with blood transfusions and Factor VIII (a blood clotting enzyme) 

36. 14. Describe how skin color is considered polygenic inheritance.
There aren’t just light and dark people, there are intermediates also
Ex:
light person + dark person = medium people
medium + medium = dark, medium, light
The “AABBCC” idea from before 

37. 15. What happens when there are changes in the chromosome numbers in humans?
Many abnormal phenotypes result from changes in chromosome numbers
Missing information
Too much information
Usually results in disorders 

38. 16. How do scientists figure out if someone has an unusual number of autosomes?
Normal: 23 pairs (46 chromosomes)
22 pair are autosomes; 1 pair are sex
If unusual autosome number, can have 47 or more chromosomes
A “karyotype” is a chart of chromosome pairs from an individual’s cells 

40. 17. What happens when an individual has an extra chromosome 21?
Usually disorders of chromosome number cause problems so severe the fetus dies
Down syndrome  the only autosomal trisomy where the individual survives into adulthood (1 in 700 births)
It is a trisomy of chromosome 21
Higher incidence in mothers over 40 years 

42. 18. Describe the abnormalities that occur when there is an unusual number of sex chromosomes.
The 2 sex chromosomes
XX if female and XY if male
An X chromosome can be missing and be XO
An X may be extra and be XXY or XXX
An extra Y could be added and have XYY
There is not enough information in the Y to have no X at all  YO won’t happen 

43. MiniQuiz Which inheritance pattern is exhibited by the following:
Red flowers + white flowers = pink flowers
Red, blue, and chocolate pigeon feathers
Black chicken + white chicken = checkered chicken
Red-green colorblindness & hemophilia
Cystic fibrosis & Tay-Sachs disease

44. Section assessment
Answer questions (1-4) on page 329
The End!