1. PATTERNS OF HEREDITY AND HUMAN GENETICS
CHAPTER 11
☺ You will compare the inheritance of recessive and dominant traits in humans.
☺ You will analyze the inheritance of incompletly dominant and codominant traits.
☺ You will determine the inheritance of sex -
linked traits.

2. Mendelian Inheritance of Human Traits
Making a Pedigree
Pedigrees illustrate inheritance: a graphic representation of genetic inheritance.
Made up of a set of symbols that identify males, females and the trail being studied and family relationships.
☐= male; ❍ = female
☐┬❍ = parents ▄ affected male
┌┴┐ ●affected female
☐ ❍ = siblings Half shaded square or circle means a carrier of trait

3. Simple Recessive Heredity
Most genetic disorders are caused by recessive alleles. Allele must be inherited from both parents.
Many of the alleles are relatively rare.
Few are common in certain ethnic groups
Cystic fibrosis - most common genetic disorder among white Americans. 1 in 20 carry, 1 in 2000 inherit disorder.
Tay-Sachs - Amish and Ashkenzic Jews. Disorder of the central nervous system.
Phenylketnuria (PKU) - Norway, Sweden. Disorder that results from the absence of an enzyme that converts an amino acid to another amino acid.

4. Simple Dominant Heredity
Trait only has to be inherited from one parent
Simple dominant traits - Tongue rolling, hitchhiker’s thumb, attached earlobes, and Hunington’s disease.

5. When Heredity Follows Different Rules
Complex Patterns of Inheritance
Incomplete dominance: a third genotype: A dominant red flower and a dominant white flower produce a pink flower.
Both flowers have incomplete dominance patterns, neither allele is dominant.
Codominance: Expression of both alleles.
The phenotype of both homozygotes to be produced in heterozygote individuals. Both alleles are expressed equally.
Traits controlled by more than two alleles have multiple alleles.

6. Sex Determination 1:1 Ratio; 50 - 50 Chance
22 pairs of matching homologous chromosomes called autosomes; look exactly alike.
23rd pair differ in males and females. Females have a “XX” pair males have a “XY” pair.
These are the chromosomes that control the inheritance of sex characteristics.
Females only produce the “X” gamete while males produce both the “X” and the “Y” gamete.

7. Sex-linked Traits & Polygenic Inheritance
Traits carried on the 23rd pair
Traits dependent on genes that follow the inheritance pattern for a sex chromosome.
Color blindness
Traits that are controlled by two or more genes
May be on the same chromosome or on different chromosomes
Skin color, height .

8. Environmental Influences
External and Internal
External influences: Temperature, nutrition, light, chemicals, infection all can change the way a gene is expressed.
Internal influences: hormones and structural differences, organisms age can change a gene’s expression.

9. Complex Inheritance