1. Mendelian Genetics Patterns of inheritance chp 12
how characteristics (traits) pass from parents to offspring

2. Early Ideas of Heredity
Botanists in the 18th and 19th centuries produced hybrid plants.
When the hybrids were crossed with each other, some of the offspring resembled the original strains, rather than the hybrid strains.
This evidence contradicted the idea that traits are directly passed from parent to offspring.

3. Gregor Mendel
- A monk who studied peas in his garden and developed our basic understanding of heredity.

4. Why pea plants?
1. other research showed that pea hybrids could be produced
2. many pea varieties were available
3. peas are easy to grow
4. peas can self-fertilize
or be cross-fertilized

5. Allele Mendel’s term for Alternate forms of a trait.
Most traits have 2 alleles
Ex. Yellow or green pea

6. Blue eye or brown eye allele

7. Mendel said traits could be Dominant or recessive
Dominant – The trait that is stronger or masks the other trait
Recessive – The trait that is weaker or hidden in presence of dominant one

8. If there are both a dominant and recessive traits together, only the dominant one appears

9.                                                   
Ex. Dominant gene
Black fur is dominant to white

10. Ex. Recessive genes Blue eyes and blond hair

11. What Mendel did NOT know?
Genes
DNA
Chromosomes
Meiosis
He still figured out how it worked with out knowing the details

12. Genes
A discrete unit of hereditary information located on a chromosome

13. Locus (loci)
A gene’s specific location on a chromosome

14. Mendel’s experimental method:
1. produce true-breeding strains for each trait he was studying
2. cross-fertilize true-breeding strains having alternate forms of a trait
-perform reciprocal crosses as well
3. allow the hybrid offspring to self-fertilize and count the number of offspring showing each form of the trait

16. True Breeding Or True Breeding
When pollinated or fertilized, all the offspring have the same trait
Crosses always produces same traits
The genes are all the same
“Pure bred”

17. Hybrid When an organism has both forms of the gene (both alleles)
Ex. Heterozygous pepper has one gene for yellow and one gene for red

18. Genotype vs Phenotype Genotype are the genes an organism has
Phenotype is the expression of those genes (which trait shows)
Ex aa X AA
Genotype = Aa Phenotype = Yellow

19. Monohybrid cross Looks at one single trait Cross RR X rr  get all Rr
Cross Rr X Rr  get 1RR + 2Rr + 1rr
3:1 ratio of
dominant phenotype

20. Generations of a monohybrid cross
P1 Generation – The original parents
F1 Generation – The first offspring
(Children)
F2 Generation – The offspring from the F1 gen. (grandchildren)

21. F1 generation (1st filial generation):
offspring produced by crossing 2 true-breeding strains
For every trait Mendel studied, all F1 plants resembled only 1 parent
-no plants with characteristics intermediate between the 2 parents were produced

23. F2 generation
:offspring resulting from the self-fertilization of F1 plants
dominant: the form of each trait expressed in the F1 plants
recessive: the form of the trait not seen in the F1 plants

25. F2 patterns: ¾ plants with the dominant form
¼ plant with the recessive form
ratio was 3 : 1.
Mendel discovered the ratio is actually:
1 true-breeding dominant plant
2 not-true-breeding dominant plants
1 true-breeding recessive plant

27. Mendel’s Law of segregation
Offspring can only receive one allele or the other. They segregate from each other
When gametes (sperm and egg) form, only one of the 2 possible genes for each trait will be in each gamete

30. Mendel’s Law of independent assortment
Alleles separate independently.
During meiosis, each of the homologous pairs of chromosome separates independently. Different combinations possible

33. Dihybrid cross
Look at 2 traits at same time when crossing 2 hybrids

34. DiHybrid example

35. 9 : 3 : 3 : 1 ratio 9 Dom / Dom Tall/Red 3 Dom / res short/Red
3 res / Dom Tall/yellow
1 res / res short/yellow

36. Testcross
a cross used to determine the genotype of an individual with dominant phenotype
cross the individual with unknown genotype (e.g. P_) with a homozygous recessive (pp)
the phenotypic ratios among offspring are different, depending on the genotype of the unknown parent

38. Mendel’s model of inheritance assumes that:
-each trait is controlled by a single gene
-each gene has only 2 alleles
-there is a clear dominant-recessive relationship between the alleles
Most genes do not meet these criteria.

39. Other inheritance patterns

40. Polygenic inheritance
When there is more than one gene for a trait. Ex. Eye color, human height
The phenotype is an accumulation of contributions by multiple genes.
These traits show continuous variation and are referred to as quantitative traits

42. Pleiotropy
Refers to an allele which has more than one effect on the phenotype.
This can be seen in human diseases such as cystic fibrosis or sickle cell anemia.
In these diseases, multiple symptoms can be traced back to one defective allele.

43. Incomplete dominance
When a the heterozygous phenotype is a mixture of the two alleles
Ex: Red and White make Pink

44. Incomplete dominance symbols
Note:
CR = red
CW = white

45. Incomplete dominance snap dragons
Red Cr Cr X white Cw Cw
Yields pink Cr Cw

46. Co Dominance When both parent traits show up in heterozygotes
Co dominant chickens – have both color feathers
White FwFw x black FBFB
Yields FwFB black and white

47. Codominance in cattle
Red and white make roan

48. Blood is CoDominant AND has multiple alleles (more than 2)
3 Blood type alleles
IA – A gene – A antigen
IB – B gene – B antigen
i – O gene – no antigen
codominance: IA and IB are dominant to i but codominant to each other

49. Blood types A B
AB - Universal receiver
0 - Universal donor

51. Environment effects
The expression of some genes can be influenced by the environment.
Ex. coat color in Himalayan rabbits and Siamese cats
-an allele produces an enzyme that allows pigment production only at temperatures below 30oC

52. Norm of reaction The range of phenotype reaction to environment.
Ex. corn that grows in high temps has a range of temperature it will grow in
Tall genes have a range of tallness

53. Epistasis
When the effects of one gene are modified by another gene (s).
Not at same locus
Ex. - Albinism overrides other genes that determine color

54. Labrador retriever – Polygenic
           
           
Black is dominant to chocolate B or b Yellow is recessive epistatic (when present, it blocks the expression of the black and chocolate alleles) E or e
Phenotype Possible
Genotypes
BBEE BbEE BBEe BbEe
bbEE bbEe
BBee Bbee bbee

55. Task: Determine the number of chocolate labs produced from a black female and a yellow male (BbEe x bbee)
           
           
BBEE BbEE BBEe BbEe
bbEE bbEe
BBee Bbee bbee

56. X - linked traits When a trait is carried on the X chromosome
Females (XX) need both genes for recessive trait
Males (XY) need only one gene to have trait, even if recessive
Women are often carriers

57. Mendel’s Laws summary
Alternate versions of genes (alleles) account for different traits.
An individual inherits 2 alleles for each character. (one from each parent)
If 2 alleles differ, then one (the dominant allele) is fully expressed in the organisms appearance; the recessive allele is masked.
The law of segregation (only one allele from each parent)
Law of independent assortment – each pair separates independently