1. INHERITANCE PATTERNS AND HUMAN GENETICS Chapter 12

2. Quick review…
Genetics is the field of biology devoted to understanding how characteristics are transmitted form parents to offspring.

3. Generations:
P Tall x Short
F1 Tall (tall is dominant)
F Tall : 1 short
The DOMINANT factor/gene masks the effect of the other factor in the F1 generation.
Use CAPS ex. T for tall
The RECESSIVE factor/gene’s effect can only be seen in the P generation or F2 generation when the DOMINANT gene is absent.
Use lower case ex. t for short

4. MENDEL’S 2 LAWS: #1 LAW OF SEGREGATION:
A pair of factors is segregated, or separated, during the formation of gametes.
Factors for different characteristics are distributed to gametes independently.
#2 LAW OF INDEPENDENT ASSORTMENT:

5. PHENOTYPE is the physical appearance of that organism.
Ex. Tall or short
GENOTYPE is the genetic makeup of the organism.
TT = homozygous dominant
Tt = heterozygous
tt = homozygous recessive
MENDELIAN INHERITANCE- DOMINANCE…. 2 phenotypes only.
If someone has the dominant phenotype but you aren’t sure of
Their genotype… use a pedigree (humans) or do a test cross.

6. Other Patterns of Inheritance:
Incomplete Dominance- blending seen in heterozygote (ex. pink flowers, brown hair)
Codominance- both dominant and recessive phenotypes seen in heterozygote. (ex. type AB blood, roan horse fur color)
Polygenic- more than 1 gene determines the phenotype. (Ex. Eye color, Hair color aabbcc)
Multiple alleles- more than just 2 alleles
(Ex. Blood type = A allele, B allele, O allele is recessive.)

7. EX. Polygenic Inheritance- when the trait is controlled by multiple genes so many phenotypes are possible.
AaBbCc x AaBbCc
Huge variety in possible
Phenotypes of the offspring
- skin, hair, eye color
- foot size
- nose length
- height

8. Multiple alleles- trait controlled by three or more alleles.
-Ex.
ABO blood groups:
- TYPE A
- TYPE B
- TYPE AB Shows Codominance!
- TYPE O

9. The process of using phenotypes to deduce genotypes
When someone has the DOMINANT phenotype you are uncertain of their genotype.
TT or Tt
When someone has the recessive phenotype you can be sure of their genotype. tt

10. DIRECTIONS:
For each of the following single gene/ Mendelian traits, write your phenotype on the line.
Write as much of your genotype as you can be certain.
- both alleles if RECESSIVE (rr)
- one allele if DOMINANT (R __)
Repeat the process by studying two blood relatives (parents work the best)
Use a pedigree.

11. 1. HAIR TYPE very curly or straight TT, Tt tt

12. 2. Hair Color Dark or Light DD, Dd dd

13. 3. Hair Line Continuous or Widow’s Peak WW, Ww ww

14. 4. Iris Color Pigmented or Blue EE, Ee ee

15. 5. Lens of Eye Astigmatism or Normal AA, Aa aa

16. 6. Nose Shape Roman (convex) or Concave NN, Nn nn

17. 7. Ear Lobe Free/Long or Attached LL, Ll ll

18. 8. P.T.C. Taster Taster or Nontaster RR, Rr rr

19. 9. Tongue Curling Can curl or Can not curl CC, Cc cc

20. 10. Point of chin Dimpled or NO dimple II, Ii ii

21. 11. Number of Fingers Polydactylism or Normal # PP, Pp pp

23. 12. Little Finger Bent or Straight FF, Ff ff

24. 13. Hypermobility of Thumb Loose Jointed or Not so HH, Hh hh

25. 14. Thumb Extension Hitchhiker’s Thumb or Not H’H’, H’h’ h’h’

26. 15. Middigital Hair Present or Absent MM, Mm mm

27. 16. Palmar Muscle Normal (2) or Long (3) UU, Uu uu

28. 17. Allergies Tendency Or No tendency A’A’, A’a’ a’a’

29. 18. Veins Varicose or Normal VV, Vv vv

30. 19. White Skin Spotting Freckles or No freckles SS, Ss ss

31. 20. White Forelock

32. LIST OF STRANGE MENDELIAN TRAITS
Ear wiggling
Misshapen toes or teeth
Inability to smell musk or skunk
Lack or teeth, eyebrows, nasal bones or thumbnails
Whorl in the eyebrow
Tone Deafness
Hairs that are triangular in cross-section or that have multiple hues (colors)
Hairy knuckles, palms, soles, or elbows
Egg-shaped pupils
Magenta urine after eating beets
Sneezing fits in bright sunlight.

33. DNA in chromosomes contain information to make proteins.
Geneticists use their knowledge of DNA and the way chromosomes behave to study how traits are inherited and expressed.

34. The parent’s genotype can be a
gene pair of either:
- TT homozygous dominant
- tt homozygous recessive
- Tt heterozygous
The parent can make gametes (sperm or eggs), through the process of MEIOSIS, that have either one or the other of the gene pair in it.

35. SEX DETERMINATION MORGAN’s Fruit fly (Drosophila)
breeding experiments of
the 1900’s revealed the
identity of sex chromosomes.
In males they were different
XY; in females they were the
same XX.
The other chromosomes
(22 in humans) are AUTOSOMES.

36. The male determines the sex of the offspring…
<--The FEMALE XX can only make X gametes.
<--The MALE XY can make either X gametes or Y gametes.

37. SEX LINKAGE traits caused by genes found on a sex chromosome
X-LINKED GENES:
Genes located on the X chromosome.
Women can be carriers.
Ex. gene for ALD (Lorenzo’s Oil)
Y-LINKED GENES:
Genes located on the Y chromosome.
Only males show these traits.
Ex. SRY- triggers male development of testis.

38. Males exhibit X-linked traits more often than women because they only have ONE X chromosome.
Females have two XBXb or sex linked genes.
Females can be “carriers” of the bad gene yet not show the disease..
Males only have one X or sex linked gene since they are XbY.
Males have a higher chance of having the condition than if it were on an autosome.
THERE IS NO HETEROZYGOUS for men.

39. X-linked Examples: Eye color in Drosophila Red-green colorblindness
Male Pattern Baldness
Hemophilia
Duchenne Muscular Dystrophy
ALD (adreno leuko dystrophy)

40. What do you see in the circle? Do your bruises look like this?

41. If a carrier (woman) for hemophilia marries a normal man, what are the chances of having kids who are hemophiliacs? Who are not? What if the man is a hemophiliac???????

42. LINKAGE GROUPS
Genes located on the same chromosome are said to be linked.
Linked genes tend to be inherited together.
Examples: Hair color and intelligence are linked in humans.
fur color and deafness in cats are linked.

43. I’m kidding about intelligence and hair color being linked.
But if they were linked…
What would the phenotype(s) be of children of a dumb,blonde & smart,brunette

44. smart,brunette If that smart,brunette had kids w/ a dumb,blonde
What kinds of kids could they have?
What is the probability of each?

45. Parental Phenotypes:
Smart, brunette
Dumb, blonde
Recombinant Phenotypes:
Smart, blonde
Dumb, brunette

46. Linked genes result in traits that tend to be inherited together…
If you do a test cross of your
Heterozygote you can see if the genes
Are linked (5:5:1:1) or not (1:1:1:1).
If the intelligence and hair color genes were linked, we’d only see smart-brunettes and dumb-blondes. (HA HA)
So, since there are smart blondes- are these genes on separate chromosomes or on the same chromosome yet separated by crossing over?????

47. Chromosome maps can be created by conducting breeding experiments.
Linked genes that separate by crossing over X% of the time are X map units apart.
Compare 4 phenotype inheritance to 2 phenotype inheritance.
Genes can now be placed on a chromosome in some order.

48. Genes W and Z separate by crossing over 20% of the time.
Genes W and X separate by crossing over 5% of the time, and
genes Z and X are separated by crossing over 25% of the time.
CONSTRUCT A CHROMOSOME MAP.
Z W X
I I--5--I

49. Mutations, Disease, & Human Mendelian Traits
Where they occur/ significance.
Types: Chromosome or Gene
Diseases & Inheritance Patterns.
Using Phenotypes to deduce Genotypes

50. Germ cell mutation
occurs in the gametes
does not effect the organism
may be passed on to offspring if fertilized
Somatic mutation
occurs in the organism’s body cells & can affect the organism
ex. Skin cancer & leukemia
are not passed on to offspring
Lethal mutation
causes death (often before birth)
is not passed on if death occurs before reproduction
Beneficial mutation
result in phenotypes that are beneficial.
beneficial phenotypes lead to increased reproduction.

51. Mutation: a change in the DNA sequence.
A) chromosome mutations (affects many genes)
B) gene mutations (one gene)
A) Chromosome mutations:
Cross over errors:
Deletion- loss of a piece due to breakage.
Inversion- a piece is attached upside down.
Translocation- a piece reattaches to a non-homologous chromosome.
Segregation Error:
Nondisjunction- failure of homologous chromosomes to separate during meiosis.
ex. Down Syndrome = Trisomy 21 (egg usually has 2 of #21)

52. Chromosome Mutations
nondisjunction

53. B) Gene mutations/ point mutations-
are nucleotide differences.
Substitution- one nucleotide is switched for another.
- ex. sickle cell anemia
Frame shift mutations- occur when nucleotides are added or removed either more or fewer than 3 nucleotides at a time.
- addition
- deletion

54. GENE MUTATION: SUBSTITUTION
ex. Sickle Cell Gene- Hemoglobin

55. INHERITANCE OF GENETIC DISEASES follow different Patterns of Inheritance
Single allele Dominant
Single allele recessive
X-linked
Sex influenced

56. PEDIGREE ANALYSIS Humans have about 100,000 genes.
Most studies are of disease-causing genes.
- easy to track through generations..
A pedigree is a family record that shows how a trait is inherited over several generations.

57. Single allele DOMINANT- need only one gene to have the disease.
- huntington’s disease (1/10,000) Hh
- dwarfism Dd
- cataracts Cc
- polydactyly Pp
PATTERN: effected individuals in every generation of both male and female sex.

58. Single allele recessive- The individual needs two genes to have the disease.
Albinism aa
Cystic fibrosis (1/200 whites) cc
Phenylketonuria (1/1800) pp
Hereditary deafness dd
Sickle cell anemia (1/500 African-Americans) sc sc
Tay-Sachs disease (1/1600 European Jews) tt
Pattern: 2 healthy parents have effected child of either sex.

59. X-Linked- women need two genes, men need only one gene.
- colorblindness XcXc XcY
-hemophilia (1/7000) XhXh XhY
-muscular dystrophy (1/10,000) XdXd XdY
-Icthyosis simplex
-ALD
Pattern: more common in males,
Can kip generations.