Chapter12:Patterns of Heredity and Human Genetics

Section12.1 Mendelian Inheritance of Human Traits

• Interpret a pedigree.

• Identify human genetic disorders caused by inherited recessive alleles.

• Predict how a human trait can be determined by a simple dominant allele.

Making a Pedigree

• Pedigree(系谱， P 309)– A graphic representation of genetic inheritance. – Track Genotypes by looking at their phenotypes– Genotype- allele combination for genes that

express a trait (ex. AA, Aa, aa)– Phenotype- physical traits caused by a

genotype( ex. AA= red flowers, aa= white flowersCarrier- person who can pass on a disease but it not effected by it

Reading a Pedigree

• Is this a dominate or recessive disease?• Which individuals MUST be carriers?• I-1,2; II-1,2; III-3,4• What are the possible genotypes for III-1?• AA or Aa

Aa Aa

aa

aa

AaAa

Aa Aa

aa

Recessive (aa)

AA orAa

Reading a Pedigree• Is this a dominate or recessive disease?• Which individuals MUST be carriers?

-None. Cannot have carries for a simple dominate disease

• What are the possible genotypes for IV-1?

-Aa

aaAA

aa

aa

Aa

Aa Aa

Aa

Dominate (AA, Aa)

• Recessive traits can remain dormant and can appear suddenly; carriers• Tend to skip generations• Some recessive disease are fatal and have late onset

Simple Recessive Heredity

Simple Recessive Heredity

• Cystic fibrosis disease囊性纤维化– 1/28 Americans are carriers– Thick mucus builds in the lungs– Makes physical activity difficult– Must be treated with medication

Simple Recessive Heredity

• Phenylketonuria (PKU)– Body lacks enzyme to change phenylalanine to tyrosine– Build up in the body leads to a damaged nervous system– Fetuses are tested to treat with diet

Simple Dominant Heredity

• Heredity of many physical characteristics– Widow’s peak hairline

– Darwin earlobes– Hitchhiker’s thumb

• Traits appear in every generation and is equally spread between males and females

• Distinguish between alleles for incomplete dominance and codominance.

• Explain the patterns of multiple allelic and polygenic inheritance.

• Analyze the pattern of sex-linked inheritance.• Summarize how internal and external

environments affect gene expression.

Section12.2/12.3 When Heredity Follows Different Rules

Complex Patterns of Inheritance

• Incomplete dominance(不完全显性 ):

Appearance of a third phenotype （ P 31

5）– When traits are inherited in an incomplete

dominance pattern, however, the phenotype of

heterozygous individuals is intermediate

between those of the two homozygotes.

Complex Patterns of Inheritance

• Codominance(共显性 ): Expression of both

alleles （ P 316）– Codominant alleles cause the phenotypes of both

homozygotes to be produced in heterozygous

individuals.

– In codominance, both alleles are expressed

equally.

Complex Patterns of Inheritance

• Multiple phenotypes from multiple alleles

(多重等位基因造成多种表现型， P 317）– Traits controlled by more than two alleles have

multiple alleles.

Complex Patterns of Inheritance

• Polygenic inheritance(多基因遗传 ,P 320）

– Polygenic inheritance is the inheritance pattern of a

trait that is controlled by two or more genes.

– Alleles are not dominate or recessive; they represent

degrees of expression

– All heterozygotes are intermediate in phenotype.

Complex Patterns of Inheritance

• Sex determination (性别决定， P318):

– chromosomes, which determine the sex of an

individual, are called sex chromosomes (性染色体 ).

– 22 other chromosomes are called autosomal

chromosomes (常染色体 )。

Complex Patterns of Inheritance

• Sex-linked inheritance(伴性遗传， P 318）

Complex Patterns of Inheritance

• Sex-linked traits(伴性性状， P 319）– Traits controlled by genes located on sex

chromosomes are called sex-linked traits.

– Red-green color blindness

– Hemophilia

Complex Patterns of Inheritance• Environmental Factors:Environmental Factors:

– Temperature, nutrition, light, etc… can effect the phenotype of an individual by changing the expression of the genes

– Ex. Arctic Fox

• Internal Factors:Internal Factors:

– Hormones regulate gene expression so a genotype may not express the same phenotype it different individualsHormones regulate gene expression so a genotype may not express the same phenotype it different individuals

– Ex. PeacocksEx. Peacocks