1. Chapter 12-2 When Heredity Follows Different Rules

2. I) Complex Patterns of Inheritance
Mendelian inheritance-inheritance that is controlled by dominant & recessive paired alleles.
Complex exceptions(i.e. incomplete dominance, codominance,etc.)
Incomplete Dominance
Incomplete dominance-def-pg315-phenotype of heterozygous individuals is an intermediate between those of the 2 homozygotes
Ex/ Red snapdragon (dominant) & white snapdragon (recessive)  pink snapdragon (intermediate phenotype)

3. I) Complex Patterns of Inheritance
Incomplete Dominance
Why does this happen?
Neither of the alleles are completely dominant
Flower pigment controlled by enzymes
Red flower (R) makes enzyme that produces red pigment
White flower (R’)makes enzyme that produces no pigment
b/c half the amt of pigment is made the flowers that result are pink in the F1 generation
F2 generation = 1:2:1 phenotypic ratio happens
1- red flower, 2-pink flowers, 1-white flower

4. I) Complex Patterns of Inheritance
ii) Codominance-Expression of both alleles
codominance-def-pg316- pattern where phenotypes of both homozygous parents are produced in heterozygous offspring so that both alleles are equally expressed
In other word-both alleles are expressed equally
when codominance is noted the alleles are 2 different uppercase ltrs
Ex/ Rooster color or horse fur color +

5. I) Complex Patterns of Inheritance
C) Multiple Alleles-Multiple Phenotypes due to Multiple Alleles
Common for more than (2) alleles to ctrl a trait in population
Although only (2) alleles of a gene exist w/in an individual diploid cell, multiple alleles for a single gene can be studied in a population
Multiple Allele-def-pg317-traits ctrl’d by more than (2) alleles
Pigeon Feather Color
3 alleles exist but any 1 pigeon only has (2) of the (3)
B allele ctrls an enzyme that activates pigment production
b allele lacks enzyme that activates pigment production
Color Types:
Ash-red feather color: pigeon has BA allele which is dominant to both B & b alleles
Genotype Possibilities: BA b/ BA BA / BA B
Wild type Blue feather color:Pigeon have B allele which is dominant to b but recessive to BA
Genotype Possibilities: Bb/ BB
Chocolate feather color:Pigeons have b alleles only
Genotype Possibilities: bb

6. I) Complex Patterns of Inheritance
D) Sex Determination
Autosomes-def-pg318-the 22 pairs of homologous chromosomes
Sex chromosomes-def-pg318-these are the (2) chromosomes that determine the sex of an individual org
In humans indicated by X & Y
XX = female
Means when females produce gametes they produce:
XY = males
Means when males produce gametes they produce:
Males determine sex of offspring = 50% change of male/female X X Y X

7. I) Complex Patterns of Inheritance
E) Sex-linked inheritance
Sex-linked traits-def-pg319-traits ctrl’d by genes located on sex chromosomes
Written notation for sex-linked traits XC
Any recessive allele on a male’s X chromosome is not masked b/c only (1) X chromosome found in males
i) Thomas Morgan & sex-linked traits
1910-Morgan discovered traits linked to sex chromosomes, using fruit flies

8. I) Complex Patterns of Inheritance
i) Thomas Morgan & sex-linked traits
Eye Color & sex chromosome experiment:
Morgan noticed male fruit flies with wht eyes instead of red eyes
Crossed wht eyed males fruit flies w/ homozygous red eyed females
F1 generation = all red eyed offspring  wht eyes recessive
F1 generation mated among themselves
F2 generation: all females = red eyes
males = ½ red eyes & ½ wht eyes

9. I) Complex Patterns of Inheritance
i) Thomas Morgan & sex-linked traits
Morgan noted wht eyes only happened in males
Morgan hypothesized:
Red eyes dominant & wht eyes recessive
Gene for eye color on X chromosome & not on Y
Morgan crossed:
Heterozygous red eyed female X White eyed male
½ males wht eyes
½ females wht eyes
Morgan’s conclusions: Allele for eye color carried only on X chromosome & y chromosome has no corresponding allele for eye color
X-linked traits- are traits that are found only on the X chromosome
Y-linked traits-are traits that are found only on the Y chromosome and are only passed from male  males

10. I) Complex Patterns of Inheritance
F) Polygenic inheritance
Polygenic inheritance(PG)-def-pg320-inheritance pattern of traits that is ctrl’d by (2) or more genes
Ex/human skin color, human height, corn cob length
polygenic inheritance genes can be on the same or different chromosomes
polygenic inheritance at each gene may have (2) or more alleles
uppercase ltr in PG doesn’t = dominant
All heterozygotes are intermediates in phenotype

11. I) Complex Patterns of Inheritance
How PG inheritance works?
Each allele contributes sm but equal portion to trait being expressed
Results in phenotypes equals continous range of variability from minimum value of trait  maximum value of trait
Stem Length example:
Plant stem length ctrl’d by genes: A, B, C
All genes are on diff chromosomes & each have (2) different alleles
Each diploid plant has total of (6) alleles for stem length
Results:
Homo short = aabbcc = 4 cm base height
Homo tall = AABBCC =16cm base height
Difference between short & tall plant= 12 cm  2 cm per each tall allele
Ex/ tall plant X short plant
(AABBCC) (aabbcc)
F1­ generation:
AaBbCc-intermediate height (~10 cm)

12. II) Environmental Influences
Many factors influence gene expression in org
2 types of Influences:
External influences:
Temperature
Nutrition
Light
Chemicals
Infectious agents
Ex/arctic fox & Siamese cat
Temperature has effect on expression of coat color
Ex/leaves
Leaves can have different sizes, thickness & shapes dependent on amt of light rec’d

13. II) Environmental Influences
B) Influence of internal environments
2.Internal environments:
Hormones
Structural differences
Internal differences occur due to differing sex hormones-these differences happen according to different genes
Differences in:
Male pattern baldness in humans
Feather color in peacocks
Mountain sheep horn development:
Org’s age can affect gene fxn but this is not well understood