Unit 5: Heredity

Study Guide on Unit 5: Heredity for AP Biology

Blending Theory of Inheritance

Blending Theory of Inheritance

The idea that original parental traits are lost or absorbed by the offspring

Continuous Variation

The determination of a characteristic by the action of many genes

Discontinuous Variation

Traits that maintain their distinctiveness and can be passed on unchanged.

Hybridization

The process involving two true-breeding individuals with different traits.

Trait

A variation in the physical appearance of a heritable characteristic.

Reciprocal Cross

A paired cross where male and female traits in one cross become the respective traits of the female and male in the other cross.

Dominant Trait

A trait that remains unchanged when inherited from hybridization.

Recessive Trait

A trait that disappears when inherited from hybridization unless combined with another recessive allele.

Product Rule

States that the probability of two independent events occurring together is the product of their individual probabilities.

Sum Rule

States that the total probability of mutually exclusive events is the sum of their individual probabilities.

Importance of Large Sample Size

Larger sample sizes reduce deviations caused by chance

Gene Expression

The location of physical characteristics expressed through genes on chromosomes.

Alleles

Variants of a gene located at the same position on homologous chromosomes.

Phenotype

The observable physical or biochemical characteristics of an organism

Homozygous

Having two identical alleles for a specific gene (e.g.

Heterozygous

Having two different alleles for a specific gene (e.g.

Monohybrid

The offspring of two true-breeding parents differing in one characteristic.

Punnett Square

A diagram used to predict the outcomes of a genetic cross.

Test Cross

A technique to determine if a dominant-expressing organism is homozygous or heterozygous by crossing it with a homozygous recessive individual.

Pedigrees

Charts used to analyze inheritance patterns of traits within a family.

Autosomes

Non-sex chromosomes that make up 22 homologous pairs in humans.

X-linked

Refers to a gene located on the X chromosome but not the Y chromosome.

Hemizygous

The state of males having only one allele for X-linked traits due to their single X chromosome.

Dominant Lethal

An inheritance pattern where an allele is lethal in both the homozygous and heterozygous states.

Recessive Lethal

An inheritance pattern where an allele is lethal only in the homozygous state.

Asexual Reproduction, The process by which unicellular organisms and some multicellular organisms produce genetically identical clones of themselves without the involvement of gametes.

Sexual Reproduction, The process of creating a unique diploid cell through the fusion of two haploid gametes, one contributed by each parent.

Meiosis, A type of cell division that reduces the chromosome number by half, creating haploid cells essential for sexual reproduction.

Haploid Cell, A cell containing a single set of chromosomes.

Diploid Cell, A cell containing two sets of chromosomes, one inherited from each parent.

Somatic Cell, Body cells that are not involved in reproduction or gamete formation.

Homologous Chromosomes, Pairs of chromosomes in a diploid cell that are similar in size, shape, and genetic content, one inherited from each parent.

Interphase, The cell cycle stage comprising G1, S, and G2 phases, where the cell grows and prepares for division.

G1 Phase, The first gap phase of interphase, focused on cell growth.

S Phase, The phase of interphase where DNA is replicated, producing sister chromatids.

G2 Phase, The second gap phase of interphase, focusing on final preparation for mitosis.

Sister Chromatids, Identical copies of a chromosome connected by cohesin proteins.

Prophase I, The phase in meiosis I where homologous chromosomes pair up, undergo synapsis, and exchange genetic material through crossing over.

Synaptonemal Complex, A protein structure that forms between homologous chromosomes during synapsis, facilitating genetic recombination.

Chiasmata, The points where homologous chromosomes remain connected after crossing over.

Tetrad, A group of four chromatids formed by the pairing of two homologous chromosomes during meiosis I.

Prometaphase I, The stage where spindle fiber microtubules attach to kinetochores, and the nuclear membrane dissolves.

Metaphase I, The phase where homologous chromosomes align randomly at the metaphase plate, contributing to genetic diversity.

Anaphase I, The stage where homologous chromosomes are separated, while sister chromatids remain attached at the centromere.

Telophase I, The phase where separated chromosomes reach opposite poles, and the cell divides.

Cytokinesis, The division of the cytoplasm, resulting in two cells.

Interkinesis, A phase between meiosis I and meiosis II without DNA replication.

Prophase II, The stage where chromosomes condense again, and the nuclear envelope breaks down.

Prometaphase II, The stage where the nuclear envelope fully dissolves, and spindle fibers attach to sister chromatids.

Metaphase II, The phase where sister chromatids align at the cell’s equator.

Anaphase II, The phase where sister chromatids are pulled apart to opposite poles.

Telophase II, The phase where chromosomes decondense, and nuclear envelopes form around them.

Crossing Over, The exchange of genetic material between nonsister chromatids during prophase I of meiosis.

Genetic Diversity, The variation in genetic composition among individuals of a population, enhanced by random alignment and crossing over in meiosis.

Mitosis, A process of cell division resulting in two genetically identical daughter cells.

The Red Queen Hypothesis, A theory stating that species must continuously evolve to maintain fitness relative to co-evolving species.

Alternation of Generations, A life cycle in sexually reproducing organisms alternating between haploid gametophyte and diploid sporophyte stages.

Gametophyte, A multicellular haploid organism that produces gametes.

Sporophyte, A multicellular diploid organism that produces haploid spores via meiosis.

Zygote, A diploid cell formed by the fusion of two haploid gametes.