1. Basic Patterns of Inheritance
Genetics
Basic Patterns of Inheritance

2. Genetics Recessive disorders Disorder/phenotype observed only
When the individual has no dominant alleles.
NN = homozygous dominant, no disorder
Nn = heterozygous, no disorder
nn = homozygous recessive, has disorder
Cystic fibrosis, albinism

3. Genetics Dominant Disorders Requires presence of dominant allele
NN = has disorder, homozygous dominant
Nn = has disorder, heterozygous dominant
nn = no disorder, homozygous recessive
Huntington’s disease

4. Genetics Pedigrees A map of a family history
Follows an inheritance pattern
A carrier has both alleles but presents the dominant phenotype.
Individual can pass on the recessive allele to the offspring.
By knowing family history, you can predict the future.
Boy and Girl Carriers = Recessive
No carriers = Dominant
Only girl carriers and no boy carriers = sex linked

5. Genetics Complex inheritance Incomplete dominance (mixing)
Both alleles offer some control.
RR = red r r= white Rr = pink

6. Genetics Codominance Both alleles present the phenotype
GG = gray gg = white
Gg = both gray and white show in the pony.

7. Genetics Polygenic traits O is recessive and also represented as ii
Multiple genes will influence the phenotype (hair color, skin color, eye color, height)
Multiple Allele traits
More than 2 allele variations for a gene.
Blood Type (A, B, O, AB)
O is recessive and also represented as ii
A and B are dominant
AB is codominant

8. Genetics ½ Male ½ Female Sex linked Traits
Alleles/genes are found on X or Y chromosomes
called sex chromosomes.
Found more frequently in males

9. Genetics Nondisjunction
Chromosomes don’t separate correctly during meiosis.
The chromosomes on the left have separated properly giving a normal set of gametes.
The chromosomes on the right did not separate properly giving 2 abnormal gametes.

10. Genetics Trisomy 21 = Down Syndrome 47 chromosomes
(3 copies of chromosome #21)
23 chromosomes from dad chromosomes from mom = 47