1. Why we look the way we look...
Laws of Heredity
Why we look the way we look...

2. What is heredity?
Heredity: passing of characteristics (traits) from parents to offspring
Genetics: the study of heredity

3. ALLELES = alternative forms of the same gene
Important Terms
ALLELES = alternative forms of the same gene
Example: F-f, E-E, D-d. Make up the genotype.
alleles for a trait are located at corresponding positions on homologous chromosomes
HOMOLOGOUS CHROMOSOMES
genes as “bands” iin
in chromosomes A b C D E f B d

4. Important Terms GENOTYPE = the genes present in the DNA of an organism
Example: GG, Bb, tt
Homozygous = “PURE”: both alleles are identical
 GG (homozygous dominant) & tt (homozygous recessive)
Heterozygous = “HYBRID”: the two alleles are different
 Bb
PHENOTYPE = how the trait physically shows-up in the organism
Ex.: green seed coat, curly hair

5. Gregor Mendel
The first person to predict how traits are transferred from parents to offspring.
Called the “Law of Inheritance.”
Studied pea plants extensively

6. Why Study Pea Plants? Reproduce sexually
2. They have both male and female sex cells (gametes) on the same flower.
3. Their traits are easy to isolate.

7. Mendel crossed pea plants…
Fertilization: the uniting of male and female gametes
Cross: combining gametes from parents with different traits
Mendel’s cross:
transferred pollen
from plant to plant and studied
the resulting
offspring pea plants.
PUNNETT SQUARE
P: Parent Generation
F1 First Offspring Generation

9. 1. Law of Independent Assortment Alleles for different traits are distributed to sex cells (& offspring) independently of one another
2. Law of Segregation
During the formation of gametes (eggs or sperm), the two alleles responsible for same trait separate from each other.  Alleles for a trait are then "recombined" at fertilization, producing the genotype for the traits of the offspring.

10. Some alleles are dominant, others are recessive.
3. Law of Dominance
Some alleles are dominant, others are recessive.
Recessive traits: hidden whenever dominant allele is present; lower case letters
Dominant traits: cover or mask recessive traits; capital letters
G = green = dominant allele
g = white = recessive allele
Gg = green
gg = white

11. NON-MENDELIAN INHERITANCE Does NOT follow Mendel’s Laws of Inheritance: Incomplete Codominance Multiple-Allele Sex-Linked

12. Incomplete Dominance
genotype: heterozygous (hybrid)
phenotype: the mix or “in between” of the two parents
example: white flower x red flower  pink flowers

13. genotype: heterozygous (hybrid) phenotype:
Codominance
genotype: heterozygous (hybrid)
phenotype:
both alleles in the offspring are dominant;
parent traits show separately in same individual
example: black cow x white cow  checkered (roan) cow

14. Blood Type Inheritance
Multiple Alleles
Traits that are controlled by more than 2 alleles
example: height, skin color, hair color, eye color, blood type
Blood Type Inheritance
blood type determined by the presence or absence of proteins on the surface of red blood cells
types: A, B, AB, O
Note: AB blood type is codominant!

15. Antigen on red blood cell (UNIVERSAL RECIPIENT)
BLOOD TYPES
Phenotype
(blood type)
Genotype
Antigen on red blood cell
Safe Transfusions To
From A
AA or AO
A, AB
A,O B
BB or BO
B, AB
B, O AB
only AB
A and B
(UNIVERSAL RECIPIENT)
A, B, AB, O O
only O
none
(UNIVERSAL DONOR)

16. SEX-LINKED INHERITANCE
controlled by genes on sex chromosomes
found on the X chromosome
female are carriers because they have XX
for X-linked traits, males pass the trait to their daughters not their sons…why?
examples: colorblindness, hemophilia

17. H = does not have hemophilia
h = hemophilia
Xh Y XH Xh