Understanding Inheritance through Pedigree Analysis

1. 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. 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. 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. 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? 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? 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. 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. 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  14. Describe how skin color is considered polygenic inheritance.

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!