AP Biology Unit 5: Heredity

Genetics

The study of genes, heredity, and how traits are passed from one generation to the next

Gene

Section of DNA that codes for characteristics of life forms

Alles

Alternative forms of genes (one letter)

Genotype

Refers to the alleles an individual receives at fertilization

Phenotype

Physical appearance based on genotype (protein produced from alleles)

Homozygous

Genotype with the same alleles

Heterozygous

Genotype with different alleles

Dominant allele

DNA that produces fully functioning protein

Recessive allele

DNA that produces a protein with little or no function

Law of Dominance

In genetics, the principle that states the dominant allele will mask the effect of the recessive allele in the phenotype

Law of Segregation

During the formation of gametes, the two copies of each gene seperates so that each gamete gets only one copy

Law of Independent Assortment

Genes for different traits are passed on to offspring independently of each other

Monohybrid cross

Cross of a single trait

Locus

Location of gene on homologous chromosomes

Dihybrid cross

Cross between two different traits

Traits

Characteristics that are passed from parents to offspring, often influenced by genes

Recombinant DNA

Gebes where crossing over has occured between them

Linked genes

Genes located on the same chromosome (the closer two genes are together, the more likely they will be inherited together)

Unlinked genes

Genes are different chromosomes (the further two genes are apart, the more likely that will be recombined)

Autosomal recessive disorder

individual needs both recessive genes (aa) to have disorder

Carrier

Heterozygous , individuals carry , but does not have disorder (skips generations/rare in populations)

Autosomal dominant disorder

Only needs one of two alleles (AA or Aa) to have the disorder (doesn’t skip generation/very rare)

Sex-linked gene

Any gene that is located on a sex chromosome

Sex-linked recessive disorder

Males only need one copy, while females need two

Sex-linked dominant disorder

Affects both females and males (X^HY/ X^HX^H/ X^HX^h)

Y-linked disorders

Conditions caused by mutations in genes on the Y chromosome, affecting only males (passed on from father to son only)

Multiple allele traits

Traits controlled by more than two alleles, allowing for a variety of expressions

Incomplete dominance

Both alleles of a gene are partially expressed, resulting in a blend of a phenotype (neither allele is dominant or recessive)

Codominance

Several alleles are dominant. Both are fully expressed in the phenotype (White and black bunny create offspring with white fur and black spots)

Polygenetic inheritance

Several genes contribute to a single phenotype (eye color, height)

Variable expressivity

Refers to the range of signs and symptoms that can occur in different people with the same genetic condition

Incomplete penetrance

An individual may have the genotype, but won’t express the phenotype

Pleiotropy

Occurs when a single mutant gene affects two or more distinct and seemingly unrelated trait (albinism)

Epistasis

Interaction of two or more genes that affect a single trait, where the presence of one gene can mask or modify the effects of another (gene a controls gene b)

Pedigrees

Family tree that records and traces the occurrence of a trait

Males

Square

Females

Circles

Shaded circles and squares in a pedigree…

Are affected individuals (watch 5.10 for more context if needed)

Environmental factors

Influence gene expression and can lead to phenotypic plasticity

Phenotypical plasticity

Occurs when individuals with the same genotype exhibit different phenotypes in response to varying environmental conditions