1. Patterns of Inheritance

2. Mendelian Genetics
Mendelian Genetics refers to a pattern of inheritance that Gregor Mendel observed when studying traits in pea plants at the turn of the 20th century.
Gregor Mendel was able to breed pea plants in a controlled way so that he could observe:
That some traits are dominant over a recessive trait.
Usually, the dominant allele codes for an enzyme that works (meaning it produces a protein that makes a trait)
The recessive allele codes for an enzyme that doesn’t work (meaning it does produce a protein and the absence of the protein makes a different form of the trait)

3. NonMendelian Genetics
Incomplete Dominance occurs when heterozygous genotypes do not fully produce the dominant phenotype.
Incomplete Dominance – dominant allele does not completely cover up the recessive allele
R = red carnations R’ (or r) = white carnations
RR x R’R’
RR’ x RR’
4 out of 4 would be… R R R R’
1 red : 2 pink : 1 white RR
RR’
RR’
RR’ R R’
PINK!- a color in between white and red R’
RR’
R’R’ R’
RR’
RR’

5. Codominance is when two alleles are equally dominant and heterozygous individuals will show both alleles.
Codominance – a condition in which both alleles of a trait will be expressed equally in heterozygous individuals
Codominance differs from incomplete dominance because both alleles are active in heterozygous individuals
Symbols for codominant alleles are different than those for dominant/recessive alleles (cannot use different cases of letters because both alleles are dominant)

7. Multiple Alleles mean that a trait can come in more than two forms.
Multiple alleles – a series of three or more alternative or allelic forms of a gene, only two of which can exist in any normal, diploid individual
Heterozygous individuals with multiple alleles will usually express both phenotypes like codominant traits.
Blood type in humans is the most common form of multiple alleles.

8. Possible Allele Combinations
Blood Type
Possible Allele Combinations
Type A
Type B
Type AB
Type O
IA IA, IA i
IB IB, IB i
 IA IB ii

9. NO offspring could have blood type O between these two parents.
The alleles for blood type are: IA, IB, and i
Could the second parent be the parent of a child with a blood type of O?
IAi x ii
ii x IAIB IA i i i
IAi
IAi i
IAi ii IA i IB
IBi
IBi
IAi ii
NO offspring could have blood type O between these two parents.
50% would have blood type A and 50% would have blood type O

10. Polygenic Inheritance is when more than one gene controls a single trait.
Polygenic Inheritance – occurs when one characteristic is controlled by two or more genes
Usually polygenic inheritance allows for a wide diversity of phenotypes depending on the inheritance of the number of alleles for a given trait.

12. Sex-linked inheritance leads to traits that are inherited on sex chromosomes
Sex-linked inheritance – traits are located on genes on the sex chromosomes
Sex-linked inheritance leads to a unequal inheritance of traits between genders (typically, a trait will be inherited more often in males than females)
Sex-linked inheritance usually involves genes found on the X chromosome as there aren’t many genes for traits expressed in both males and females on the Y chromosome.

13. XN = normal vision Xn = color blindness Y= male chromosome
The symbols USUALLY will be represented as the letter of the chromosome the trait is found on with a superscript letter for the trait
XN = normal vision Xn = color blindness Y= male chromosome
XNXn x XNY
Mother is a carrier because she has the gene but doesn’t show the trait XN Xn XN
XNXN
XNXn Y
XNY
XnY
½ males ½ females
½ OF females would be carriers, none would be color blind
½ OF males would be color blind