1. Review Questions
What is the difference between a genotype and a phenotype?
What are the terms for genotypes AA, aa, and Aa?
If a red flower (RR) is crossed with a white flower (rr), what will be the phenotype and genotype of the F1?
Genotype Alleles in DNA for a certain trait
Phenotype The physical trait expressed by a genotype
AA homozygous dominant
aa homozygous recessive
Aa heterozygous
Phenotype Red flower Genotype Rr

2. Chromosome Theory of Inheritance
Sum up what we have learned from Mendel:
Chromosomes occur in pairs in sexually reproducing, diploid organisms. Alleles for each gene are on these chromosomes
The chromosomes of each pair are separated and delivered to different gametes. This also separates alleles of genes
One-half of each chromosome pair after fertilization comes from the each parent.

3. Genetic Crossing

4. Monohybrid Crosses
Punnett Square method for organizing alleles during breeding that uses statics
Father on top; Mother on side
All possible offspring in the middle
All Statics probabilities are between 0-1
0impossible
1 completely possible
Product Rule events where both A and B will occur
Chance of heads vs. tails 0.5
Chance of heads twice 0.5x0.5= 0.25
Sum Rule when two or more possible ways exist to get the same outcome
Chance of getting head and tail in 2 tosses 0.5x0.5=0.25
Two ways (head and tail or tail and head) = 0.5

5. Practice Crosses P p Pp P G g Gg P G g Gg gg
What are the possible genotype ratios for a cross between homozygous dominate (purple) and homozygous recessive (white) garden pea plants? What is their phenotypes?
1.0 chance of heterozygous (Pp)
All purple flowers
What are all possible genotype ratios for a green seed X yellow seed? Green is dominate.
1.0 chance heterozygous (Gg)
0.5 chance heterozygous (Gg) and 0.5 homozygous recessive (gg)
All green seeds OR half green and half yellow seeds. Which is correct? P p Pp P G g Gg P G g Gg gg

6. How do We Know AA or Aa? G g Gg G g Gg gg
Test Cross determines if parent is AA or Aa based on cross with F1
F1 with recessive trait crossed with unknown parent
One of two possible results:
If parent is GG:
GG X gg 100% Ga offspring; 100% green
If parent is Gg:
Gg X gg 50% Gg and 50% gg offspring; 50% green and 50% yellow
F1 X P G g Gg
F1 X P G g Gg gg

7. Non-Mendelian Inheritance Patterns
Not all alleles follow dominant/recessive patterns; most do not
Incomplete dominance
Phenotype for heterozygous genotype is a blend of both homogenous traits
Recessive trait is not completely blocked because dominate trait is incomplete
CR red form of color allele
CW white form of color allele
CRCR x CWCW give what type of offspring ratios?
100% pink (heterozygous)
What about F2?
1 Red: 2 Pink: 1 White P CR CW
CRCW F1 CR Cw
CRCR
CRCW CW
CWCW

8. Non-Mendelian Inheritance Patterns
2) Codominance
Both alleles have equal chance expressed so heterozygotes show both traits
Mosaic Flowers
Cells express either Red or White allele
Both alleles are present, but one is randomly not expressed
Like flipping a coin; close to 50%
Same inheritance patterns as incomplete dominance
P= ARAR X AWAW 100% ARAW Mosaic (F1)
F2= ARAW X ARAW 1:2:1; AR, 2 ARAW, 1 A P AR AW
ARAW F1 AR AW
ARAR
ARAW
AWAW

9. Non-Mendelian Inheritance Patterns
3) Multiple Allele Inheritance
More than two alleles will code for different phenotypes
Human Blood-Types
Allele I IA, IB, or I
A Type (IAIA, IAi)
Mixes with A and O type
B Type (IBIB, IBi)
Mixes with B and O type
AB Type (IAIB)
Universal acceptor
Mixes with A, B, and O type
O Type (ii) 
Universal donor
Can be given to any type
IAIA
IBIB
IAIB ii

10. Sex-Linked Genes Any genes located on the sex chromosomes
X or Y in humans
All other 22 chromosomes are called autosomes (automatically inherited)
Y Chromosome
Sex-determining gene; SRY gene makes females into males
XY heterogametic
X Chromosome
Mostly codes for non-sex related traits (ex. Color vision)
XX homogametic

11. Sex-Linked Inheritance
Often when a trait is similar to Mendelian genetics (dominant/recessive) but offspring show patterns when divided by sex
Mice Body Color:
B black body
b white body
If Bb X bb, what should be the ratio of black to white mice?
1 : 1 ratio (50% Bb and 50% bb)
However you notice that females are only black and males are only white. What does this mean?
B and b alleles are on X-chromosome
XB Y x Xb Xb 100% XB Xb and 100% Xb Y P XB Y Xb
XBXb
XbY

12. Too Many Xs! Why do females need two Xs?
They Don’t! Two X chromosomes would mean double the genetic material necessary
What does the body do with the X chromosome?
It randomly shuts one X chromosome down
They are copied and passed on in mitosis but are never used to make proteins
How can this show us X-recessive traits?
Dominate X might be randomly deactivated so the X recessive is randomly present in cells
Female calico cats have a mix of orange and black fur but males are always black or orange

13. Following Sex-linked Traits
Pedigree map of parents and offspring in a family over generations
⃝ female
 males
 has trait
 carrier; has gene but not trait
Hemophilia platelets numbers so low person often bleeds to death from little body damage
X-linked recessive gene
Rare for XhXh why?
Most males with the disease do not reproduce
Lead to the Russian Revolution