AP Bio Unit 5

Heredity

the study of how traits are passed from parents to offspring

Genes

a fundamental unit of heredity, essentially a specific segment of DNA that carries instructions to build functional products, usually proteins, which determine an organism's traits

Mutations

a permanent change in an organism's DNA sequence, creating new alleles and providing the raw material for evolution, which can alter the genotype and phenotype, ranging from silent (no effect) to harmful (disease) or beneficial (adaptation).

Homologous Chromosomes

pairs of chromosomes in a diploid organism that are similar in size, shape, and gene content.

Asexual Reproduction

a form of reproduction where a single parent produces genetically identical offspring (clones) without the fusion of gametes (sperm/egg) or sexual processes

Sexual Reproduction

involves two parents contributing genetic material via specialized haploid cells (gametes like sperm and egg) that fuse during fertilization to form a unique, diploid offspring, introducing significant genetic variation through meiosis, crossing over, and random assortment, driving evolution.

Karyotype

a visual map or photograph of an organism's complete set of chromosomes, organized by size, shape, and banding patterns (from largest to smallest), used to identify genetic conditions by revealing extra/missing chromosomes or structural changes like deletions, duplications, or translocations, and determine biological sex

Somatic Cell

any cell in a multicellular organism that is not a reproductive cell (gamete).

Gametic cell

specialized reproductive cell (such as a sperm or egg) that contains half the number of chromosomes of a normal body cell.

Diploid

a cell or organism having two complete sets of chromosomes, one inherited from each parent, forming homologous pairs

Haploid

one that contains a single, or one, complete set of chromosomes.

Autosome

the non-sex chromosomes (numbered 1-22 in humans) that carry genes for most body traits, differing from the sex chromosomes (X and Y) that determine biological sex.

Sex Chromosome

specialized chromosomes that determine the biological sex of an organism

Life Cycle

the series of developmental stages an organism goes through from its formation (often as a zygote) to reproduction, ensuring continuity, involving growth, reproduction (sexual/asexual), and death, with key variations like alternation of generations in plants and complex stages in animals.

Zygote

the diploid cell formed by the fusion of two gametes (a sperm and an egg) during fertilization.

Genetics

the study of heredity, focusing on how traits are passed from parents to offspring, driven by DNA, genes, and alleles, involving Mendelian laws (segregation, independent assortment) but also complex patterns like linked genes, gene regulation, and variations (codominance, polygenic traits)

Clones

an exact genetic replica of a DNA fragment, cell, tissue, or organism, created artificially or naturally, meaning they have identical genetic material.

Meiosis

a specialized cell division that reduces a diploid cell into four genetically unique haploid cells (gametes like sperm/egg) for sexual reproduction.

Synapsis

the crucial process during Prophase I of meiosis where homologous chromosomes (one from each parent) pair up lengthwise, forming a structure called a bivalent or tetrad, held together by the synaptonemal complex, allowing for genetic recombination (crossing-over) to occur, which shuffles alleles and increases genetic diversity in gametes. 

Tetrad

a tetrad is a structure of four chromatids (two homologous chromosomes, each with two sister chromatids) that forms during Prophase I of meiosis, allowing for crossing over (genetic recombination) and increasing genetic diversity in gametes, leading to four unique haploid cells at the end of meiosis.

Chiasmata

the visible, X-shaped points where non-sister chromatids of homologous chromosomes cross over and physically exchange genetic material during Prophase I of meiosis, creating genetic recombination and ensuring proper chromosome separation for genetic diversity in gametes.  

Crossing Over

the crucial process during Prophase I of meiosis where homologous chromosomes (one from each parent) physically exchange segments of their DNA, creating new, "remixed" chromosomes with unique combinations of parental alleles

Independent Assortment

a principle of genetics where alleles for different traits segregate independently during gamete formation

Prophase 1

the crucial first stage of Meiosis I where homologous chromosomes pair up (synapsis) to form tetrads, allowing for genetic recombination through crossing over at points called chiasmata, significantly increasing genetic diversity for gametes, unlike mitosis where homologs don't pair.

Prophase 2

chromosomes (each with two chromatids) re-condense, the nuclear envelope breaks down (if it reformed), the spindle apparatus forms, and microtubules attach to the kinetochores, preparing the sister chromatids for separation in Anaphase II to produce four unique haploid gametes, with no DNA replication or homologous pairing. 

Metaphase 1

the stage of meiosis where homologous chromosome pairs (tetrads), after pairing and crossing over in Prophase I, align randomly along the cell's equatorial plate (metaphase plate), with spindle fibers attached to opposite poles, preparing to separate into two haploid cells in Anaphase I, ensuring genetic diversity through independent assortment. 

Metaphase 2

the second stage of meiosis II, where the now-haploid cells align their individual chromosomes (each still made of two sister chromatids) along the cell's equator, or metaphase plate, preparing for anaphase II when these sister chromatids will finally separate, resulting in four unique haploid gametes. 

Anaphase 1

the crucial stage where homologous chromosome pairs separate and are pulled to opposite ends (poles) of the cell, but sister chromatids stay together, reducing the chromosome number by half

Anaphase 2

the stage of meiosis where the sister chromatids, previously joined at the centromere, are pulled apart by spindle fibers and move to opposite poles of the cell, effectively becoming individual chromosomes, ensuring each of the four resulting haploid gametes receives one complete set of chromosomes.

Telophase 1

the final stage of meiosis I where separated homologous chromosomes arrive at opposite poles, the nuclear envelope reforms around each set, and cytokinesis divides the cell into two genetically unique, haploid (1n) cells, each still containing duplicated chromosomes (2c).

Telophase 2

the final stage of meiosis where the separated sister chromatids reach opposite poles, nuclear envelopes re-form around the two new chromosome sets, chromosomes decondense back to chromatin, and cytokinesis (cytoplasm division) finishes, resulting in four genetically unique, haploid daughter cells (gametes) from one original diploid cell. 

Cytokinesis

the final stage of cell division where the cytoplasm of the parent cell physically divides to form two separate, genetically identical (mitosis) or diverse (meiosis) daughter cells, completing the cell cycle and ensuring each new cell gets essential organelles and cytoplasm.

True Breeding

organisms that, when self-pollinated or mated with others of the same type, consistently produce offspring with the exact same traits (phenotype and genotype) as the parents, because they are homozygous for the genes controlling those traits

P Generation

the original, true-breeding parents in a genetic cross, used by Mendel to study inheritance

F1 Generation

the first filial generation, the offspring that results from a cross between two parent organisms

F2 Generation

the offspring resulting from crossing two individuals from the F1 generation (first filial), which themselves came from a cross of two true-breeding parental (P) generations

Punnett Squares

a diagrammatic tool used to predict the probability of offspring inheriting specific genotypes (allele combinations) and phenotypes (observable traits) from a parental genetic cross

Monohybrid Cross

a genetic cross between two parents differing in only one specific trait (controlled by a single gene, like pea color or height) to study its inheritance

Dihybrid Cross

genetic cross that examines the inheritance of two different traits simultaneously

Phenotype

the set of all observable characteristics of an organism, resulting from the interaction between its genetic makeup (genotype) and environmental influences.

The Multiplication Rule

calculates the probability of two or more independent events happening together by multiplying their individual probabilities

Law of Segregation

during gamete (sperm/egg) formation, the two alleles for a single gene separate (segregate) from each other, so each gamete ends up with only one allele, ensuring offspring receive one allele from each parent, maintaining genetic variation.

Law of Independent Assortment

alleles for different traits segregate and are inherited independently of one another during gamete formation.

The Addition Rule

calculates the probability of either one of two mutually exclusive events happening by adding their individual probabilities

Recessive

only shows up in an organism's appearance (phenotype) when two copies are present, one from each parent; it's masked by a dominant allele if present, making the individual a "carrier" without showing the trait

Alleles

a variant form of a gene that determines a specific trait.

Heterozygous

an individual with two different alleles for a specific gene, one inherited from each parent.

Genotype

the specific combination of alleles (gene versions) an organism inherits for a particular trait

Dominant

is one that masks the effect of a recessive allele

Homozygous

an organism has two identical alleles for a specific gene, one inherited from each parent.

Pedigrees

a diagram that shows the presence or absence of a specific trait across multiple generations of a family.

Incomplete dominance

a non-Mendelian inheritance pattern where the heterozygote's phenotype is an intermediate blend of the two homozygous parents' phenotypes, not a complete masking;

Polygenic Inheritance

an AP Biology concept where a single trait is controlled by multiple genes, resulting in a wide range of possible phenotypes rather than distinct categories.

Multiple alleles

the concept that a single gene can have three or more different allelic forms (versions) within a population.

Epistasis

when one gene masks or modifies the expression of a different, non-allelic gene, leading to altered Mendelian ratios (like 9:3:4 or 12:3:1) in offspring, showing that multiple genes interact to control a single trait, such as coat color or fruit color.

X-linked

describes traits determined by genes on the X chromosome, leading to different expression patterns in males (XY) and females (XX) because males only have one X, making recessive traits more apparent (hemizygous).

Codominance

a non-Mendelian inheritance pattern where both alleles for a gene are fully and separately expressed in the heterozygote, resulting in a distinct phenotype showing both parental traits, rather than a blend (like roan cattle with red and white spots) or one masking the other, exemplified by human AB blood type (both A and B antigens present). 

Y-linked

determined by genes on the Y chromosome and is passed exclusively from a father to all of his sons.

Hemizygous

describes having only one copy of a gene instead of the usual two, most commonly seen in males for X-linked genes because they have one X and one Y chromosome (XY)

Barr body

a densely packed, inactivated X chromosome visible in the nucleus of female somatic cells, formed through X-inactivation to equalize gene expression between sexes

Recombinants

new combinations of genetic material (DNA, alleles) created either through natural processes like crossing over during meiosis (producing recombinant gametes) or by artificial methods (recombinant DNA technology) where DNA from different sources is joined, leading to unique genetic makeup in organisms or cells, increasing diversity. 

Linkage map

a diagram showing the relative positions and order of genes or genetic markers on a chromosome, built using the frequency of recombination (crossing-over) between them during meiosis

Chi square

a statistical tool to see if observed experimental results (like offspring from a genetic cross or species distribution) significantly differ from expected results

Phenotypic plasticity

the ability of a single genotype (genetic makeup) to produce different phenotypes (observable traits/characteristics) in response to varying environmental conditions

Nondisjunction

the failure of chromosomes or sister chromatids to separate properly during cell division (mitosis or meiosis)