1. Inheritance Patterns & Human Genetics
Chapter 12

2. Chromosomes & Inheritance
Section 12.1

3. What makes human males different than females?
Sex chromosomes (X and Y)
Male: XY
Female: XX
Gametes:
Egg: carry only X
Sperm: carry either X or Y

4. Who Discovered Sex Chromosomes?
Thomas Morgan
Early 1900s
Columbia University (USA)
Worked with fruit flies

5. Sex Linkage: When genes are found on the sex chromosomes
X-linked Genes: genes on the X chromosome
Y-linked Genes: genes on the Y chromosome

6. Sex Linked Traits Most sex linked genes are found on the X chromosome
Only genes on the Y chromosome are for male reproductive organ development

7. Sex Linked Genetic Problems
In flies: R = red eyes, r = white eyes
Gene located on the X chromosome X X X Y

8. Example 1: White eye male mates with a red homozygous dominant female
XrY x XRXR Xr Y
XRXr
XRY XR
100 % red female
0 % white female
100 % red male
0 % white male
XRXr
XRY XR

9. Example 2: Red eye male mates with a red heterozygous female
XRY x XRXr XR Y
XRXR
XRY XR
100 % red female
0 % white female
50 % red male
50 % white male
XRXr
XrY Xr

10. Example 3: White eye male mates with a red heterozygous female
XrY x XRXr Xr Y
XRXr
XRY XR
50 % red female
50 % white female
50 % red male
50 % white male
XrXr
XrY Xr

11. Linkage Groups
Genes located on the same chromosome and therefore inherited together
Goes against Mendel’s Law of Independent Assortment

12. How do linked genes get “unlinked”?
Crossing Over
The frequency of crossing over between certain genes is used to make a chromosome map

13. Which two genes have the highest probability of crossing over
Which two genes have the highest probability of crossing over? The lowest? a A b B
Highest: A & C
Lowest: A & B c C

14. Chromosome Map:
Diagram of the linear order of genes on a chromosome

16. Sex Linkage Problems!!!!
Use these genotypic symbols for the sex linked trait of red-green color blindness in humans to solve the problems that follow.
"Normal" female = XBXB
Carrier female = XBXb
Color-blind female = XbXb
Normal male = XBY
Color-blind Male = XbY

17. 1) A normal female marries a color blind male
1) A normal female marries a color blind male. What are the chances that the offspring will be color blind if they are females? What are the chances that the offspring will be color blind if they are males?

18. 2) A color blind female marries a normal male
2) A color blind female marries a normal male. How many of the female offspring will be carriers of the color blind allele?

19. 3) A man whose mother is color blind marries a woman with normal vision. What is the genotype of the husband? What percent of their offspring can be expected to be color blind? What percentage of their offspring can be expected to be carriers?

20. How do biologist keep track of inherited traits over generations in a family?
Pedigree (page 241)

21. Pedigree Key Normal male Marriage Affected male Unmarried
Normal female
Dead
Affected female

22. Let’s try some pedigree problems!

23. R = Tongue Roller r = No Tongue Roller
John Jones, a tongue roller, marries Jill Smith, a woman that cannot roll her tongue. John and Jill have four children that can each roll their tongue: John Jr., Alice, Lisa, and Sean. John Jr. later marries non-tongue roller Pamela, and they have four children: Jessica, Sherri, Mary, and John III. Sherri and Mary both can roll their tongues, and Jessica and John III are non-tongue rollers. Sean marries Robin, a non-tongue roller. Both Robin’s parents are non-tongue rollers also. Sean and Robin have four children: Nicholas, Harry, Donna, and Sean Jr. Nicholas, Harry and Donna each have the ability to roll their tongues. Sean Jr. cannot.

24. Human Genetics
Section 12.2

25. Human genetics is not as easy as Mendel’s peas!
Many patterns of inheritance

26. Human Patterns of Inheritance
Single allele trait
Multiple allele trait
Polygenic trait
X-linked trait
Nondisjunction

27. 1. Single Allele Trait
A trait that is controlled by a single allele of a gene
Normal dominant-recessive (Mendel)
Example Genetic Disorders:
Huntington’s Disease (autosomal dominant)
Cystic Fibrosis (autosomal recessive)

28. 2. Multiple Allele Trait
3 or more alleles of the same gene code for a single trait
Example: ABO Blood Type
IA = type A (dominant)
IB = type B (dominant)
i = type O (recessive)

29. Blood Type Problems
If a person is type A blood….what is his/her genotype?
IAIA or IAi
If a person is type B blood….what is his/her genotype?
IBIB or IBi
If a person is type O blood….what is his/her genotype? ii
If a person is type AB blood….what is his/her genotype?
IAIB

30. Blood Type Problems
A mother gives birth to a type O child. The mother is type A blood. The two potential fathers are type A (father 1) and type AB (father 2).
Who’s the daddy?

31. 3. Polygenic Trait Trait that is controlled by 2 or more genes
Range of phenotypes
Influenced by environmental factors too
Examples:
skin color
eye color
human height

32. 4. X-Linked Trait Trait controlled by a gene on the X chromosome
Examples:
colorblindness (recessive)
hemophilia (recessive)

33. Hemophilia Pedigree

34. 5. Nondisjunction
The failure of chromosomes to separate during meiosis resulting in one gamete with too many chromosomes and one gamete with too few chromosomes
Monosomy
Trisomy

35. Trisomy: cell with 3 copies of a chromosome (too many chromosomes)
Monosomy: cell with 1 copy of a chromosome (too few chromosome)
Example Genetic Disorders:
Down Syndrome (Tri-21)
Klinefelter’s Syndrome (XXY)
Turner’s Syndrome (X__)

36. Blood Typing Lab! Background
Blood is a tissue comprised of 4 components: plasma, red and white blood cells, and platelets. Plasma is a clear straw-colored liquid portion that makes up 55% of the blood. It contains a number of blood-clotting chemicals that help stop bleeding. Red and white blood cells and platelets make up the remaining 45% of the blood. Red blood cells are tiny biconcave discs. Each red blood cell contains the oxygen-binding protein, hemoglobin. Hemoglobin contains 4 iron ions with bind with oxygen and carbon dioxide.

37. Blood functions principally as a vehicle with transports gases, metabolic waste products and hormones throughout the body. As blood passes through the lungs, oxygen molecules attach to the hemoglobin. As blood passes through the body’s tissues in capillary beds, the hemoglobin releases the oxygen. Carbon dioxide and other waste gases are, in turn, transported by the hemoglobin back to the lungs. Thereafter the process is repeated.

38. Mutations that Lead to Genetic Disorders:
Mutation: a change in the DNA of an organism
Can involve an entire chromosome or a single nucleotide
Can lead to genetic disorders

40. Mutation Types Germ-cell mutation: occurs in the germ cells (gametes)
Does not affect the organism
Does affect the organism’s offspring
Somatic-cell mutation: occurs in the organism’s body cells
Does affect the organism
Does not affect the organism’s offspring
Lethal mutation: causes death, often before birth

41. Chromosome mutation: change in the structure of a chromosome
a. Deletion
b. Inversion
c. Translocation
d. Nondisjunction

42. Deletion
Inversion
Translocation
Nondisjunction

43. 5. Gene mutation: involves large segments of DNA or a single nucleotide of DNA
a. Point mutation: single nucleotide mutation within a codon
b. Frame shift mutation: cause the misreading of codons during translation thus making the wrong protein

44. Detecting Human Genetic Disorders
Before Pregnancy:
Genetic Screening
Genetic Counseling
During Pregnancy:
Amniocentesis
Chorionic Villi Sampling
After Birth: