AP Biology Unit 6: Heredity — Questions and Answers

40 in-depth question-and-answer cards covering the Schoology Unit 6 plan, expanded with the linked OpenStax Biology for AP Courses textbook. Each front is a question; each back is the answer. Use Knowt Practice Test for automatic multiple-choice options.

What is the main result of meiosis in a diploid organism?

Haploid cells for sexual reproduction

What separates during meiosis I?

Homologous chromosomes

How does crossing over increase variation?

Homologous chromosomes exchange DNA segments

What is independent assortment?

Random orientation of homologous chromosome pairs in meiosis I

What does Mendel's law of segregation describe?

Two alleles separate into different gametes

Why are recessive X-linked traits often more visible in XY individuals?

They usually have only one X chromosome

What can recombination frequency estimate for linked genes?

Distance between genes on a chromosome

What is a polygenic trait?

A trait influenced by multiple genes

What is one source of extranuclear inheritance?

Mitochondrial DNA

What is phenotypic plasticity?

One genotype can produce different phenotypes in different environments

What is a homologous chromosome pair?

Two chromosomes with the same genes, one from each parent

What is the difference between haploid and diploid cells?

Haploid cells have one chromosome set; diploid cells have two

When does DNA replication occur before meiosis?

During S phase before meiosis I

What is synapsis?

Pairing of homologous chromosomes in prophase I

What is a tetrad?

A paired set of homologs containing four chromatids

When does crossing over occur?

During prophase I of meiosis

What separates during anaphase II?

Sister chromatids

How many divisions follow one DNA replication in meiosis?

Two divisions

How many haploid cells can one diploid meiotic cell produce?

Four

Why are meiotic products genetically different?

Crossing over and independent assortment reshuffle alleles

How does fertilization restore diploidy?

Two haploid gametes fuse

What is a genotype?

An organism's allele combination for a trait

What is a phenotype?

An observable expression of a trait

What does homozygous mean?

Having two identical alleles for a gene

What does heterozygous mean?

Having two different alleles for a gene

What is a test cross used to determine?

The genotype of an individual with a dominant phenotype

What ratio is expected from Aa x Aa for a complete-dominance phenotype?

Three dominant to one recessive

What fraction of offspring from Aa x Aa are expected to be aa?

One fourth

What is incomplete dominance?

The heterozygote has an intermediate phenotype

What is codominance?

Both alleles are expressed in the heterozygote

What does a dihybrid cross test?

Inheritance of two traits at once

When does a 9:3:3:1 phenotype ratio apply?

Independent assortment with complete dominance for both genes

Why can linked genes violate independent assortment?

They lie on the same chromosome and tend to travel together

What does a 1 percent recombination frequency represent?

One map unit or centimorgan between genes

How can a pedigree reveal an autosomal recessive trait?

Two unaffected carriers can have an affected child

What is nondisjunction?

Failure of chromosomes or chromatids to separate properly

What can nondisjunction produce?

Gametes with extra or missing chromosomes

What is aneuploidy?

An abnormal number of individual chromosomes

How is mitochondrial DNA often inherited in animals?

Through the maternal line

How can environment influence a polygenic trait?

Conditions can change the measured phenotype without changing the genotype