AP Bio unit 5: Genetics & Patterns of Inheritance

Gregor Mendel

father of genetics, monk, experimented with peas

genetics

the scientific study of inheritance, which is the passing of traits from parents to offspring

Principle of Dominance & Recessiveness

when one allele masks the other

Law of Segregation

alleles separate into eggs and sperm

Law of Independent Assortment

the alleles for different traits are inherited independently of each other

Trait

Specific Characteristic

Fertilization

when sperm and egg fuse together to form a zygote

Pure-breeding (homozygous)

with each cross, always getting the same trait; alleles are the same

Hybrid (heterozygous)

crossed homozygous plants

alleles

different forms of genes

How do dominant alleles hide recessive ones (ex. in flowers)?

when present, purple allele codes for functional enzyme

Phenotype

description of an organism’s trait

Genotype

description of organisms’s genetic makeup

Monohybrid cross

follows the inheritance of single characteristics

Dihybrid cross

follows the inheritance of 2 different characteristics

Incomplete Dominance

The phenotype of the heterozygote differs from the phenotypes of both homozygotes.

Codominance

both alleles are expressed at the same time

Epistasis

when 1 trait hides another (red hair is hidden by brunette hair, red heads are actually blonde)

Polygenic inheritance

1 trait controlled by >1 gene

Pleiotropy

1 gene controls >1 trait

Karyotype

photomicrograph of chromosomes used to detect genetic abnormalities

Huntington’s Disease

autosomal dominant

Cystic fibrosis

autosomal recessive

Tay-Sachs

Albinism

autosomal recessive

male-patterned baldness

Hemophilia

sex-linked

Linked Genes

genes that sit together on a chromosome, making them likely to be inherited together (hair and eye color)

test cross

One individual has the dominant phenotype and the other has the recessive phenotype. A testcross is an experiment performed to determine whether the genotype of an organism with a dominant phenotype is homozygous or heterozygous.

penetrance

the extent to which a particular gene or set of genes is expressed in the phenotype of individuals carrying it, measured by the proportion of carriers showing the characteristic phenotype