Unit 3 exam study

Chromatin

The uncoiled or unraveled form of chromosomes found in the nucleus.

Chromosome

Organized DNA that carries genes; chromatin condenses into chromosomes during cell division.

Sister Chromatids

Two identical copies of a duplicated chromosome.

Centromere

The region that joins two sister chromatids together.

DNA Replication

The process of copying DNA before cell division.

Cell Cycle

The sequence of events in which a cell grows and divides.

Three Main Phases of the Cell Cycle

Interphase, mitosis, and cytokinesis.

Interphase

The stage when a cell grows, performs its normal functions, and duplicates its DNA; it is not part of mitosis.

Prophase

Chromatin condenses into chromosomes, the nucleolus and nuclear membrane break down, and spindle fibers form.

Metaphase

Chromosomes line up at the middle (equator) of the cell.

Anaphase

Sister chromatids separate and move toward opposite poles; each chromatid is now considered a chromosome.

Telophase

Chromosomes begin to relax into chromatin, and new nuclear membranes form.

Order of Mitosis

Prophase, Metaphase, Anaphase, Telophase (PMAT).

Spindle Fibers

Fibers that help move and separate chromosomes during cell division.

Cytokinesis in Animal Cells

The cell membrane pinches inward, forming a cleavage furrow.

Cytokinesis in Plant Cells

A cell plate forms between the two new cells.

Purpose of Mitosis

Growth, repair, and replacement of cells; it produces two genetically identical daughter cells.

Cancer

Uncontrolled cell division and growth caused by cells dividing at the wrong time or place.

Benign Tumor

A group of abnormal cells that grows without invading neighboring tissues.

Malignant Tumor

A cancerous tumor that grows and invades neighboring tissues.

Metastasis

The spread of cancer cells to other parts of the body through the blood or lymph system.

Somatic Cells

Body cells that do not produce sperm or eggs; they are diploid (2N).

Germ Cells

Specialized diploid cells that undergo meiosis to produce gametes.

Diploid (2N)

A cell with two sets of chromosomes, one set from each parent.

Haploid (1N)

A cell with one set of chromosomes; human sperm and egg cells are haploid.

Human Somatic Cell Chromosome Number

46 chromosomes: 22 pairs of autosomes and 1 pair of sex chromosomes.

Autosomes

The 22 pairs of human chromosomes that are not sex chromosomes.

Sex Chromosomes

The chromosomes that determine biological sex; typically XX in females and XY in males.

Karyotype

A numbered display of chromosomes arranged in matching pairs by size and type.

Homologous Chromosomes

A matching pair of chromosomes, one inherited from each parent; they carry the same genes but may have different alleles.

Meiosis

Two rounds of cell division that produce four genetically different haploid cells from one diploid cell.

Purpose of Meiosis

To produce haploid gametes for sexual reproduction and create genetic variation.

Mitosis vs. Meiosis

Mitosis produces two genetically identical cells; meiosis produces four genetically different haploid cells.

Meiosis I

Homologous chromosomes pair up and then separate, reducing the chromosome number by half.

Meiosis II

Sister chromatids separate, resulting in four haploid cells.

Result of Meiosis in Humans

One diploid germ cell with 46 chromosomes produces four haploid cells with 23 chromosomes each.

Fertilization

The fusion of a haploid sperm and haploid egg to form a diploid zygote.

Zygote

The diploid cell formed when a sperm and egg unite.

Independent Assortment

Homologous chromosome pairs line up independently during meiosis, creating different chromosome combinations.

Crossing Over

The exchange of DNA between homologous chromosomes during meiosis, creating new combinations of genes.

Random Fertilization

The random union of one sperm and one egg, increasing genetic variation.

Three Sources of Genetic Variation

Independent assortment, crossing over, and random fertilization.

Nondisjunction

The failure of chromosomes or sister chromatids to separate properly during meiosis.

Down Syndrome

A genetic condition caused by having three copies of chromosome 21; also called trisomy 21.

Genetics

The study of heredity and how traits are passed from parents to offspring.

Heredity

The passing of traits from parents to offspring.

Trait

A characteristic of an organism.

Protein Synthesis

The process by which cells produce proteins; genes contain instructions used to make proteins.

Genotype

The combination of alleles an organism has for a particular gene.

Phenotype

An organism's observable characteristics.

Allele

An alternative form or version of a gene.

Genotype and Environment

An organism's genotype interacts with its environment to produce its phenotype.

Dominant Allele

An allele that is expressed in the phenotype when at least one copy is present.

Recessive Allele

An allele that is expressed in the phenotype only when two recessive copies are present.

Homozygous

Having two identical alleles for a gene, such as AA or aa.

Heterozygous

Having two different alleles for a gene, such as Aa.

Carrier

An individual who has one recessive disease allele but usually does not show the disease.

Gregor Mendel

The scientist who first correctly described basic patterns of inheritance through experiments with pea plants.

Why Mendel Used Pea Plants

They were easy to breed and manipulate, could self-fertilize, and had traits with clear variations.

P Generation

The original parent generation in a genetic cross.

F1 Generation

The first generation of offspring produced by crossing the parent generation.

F2 Generation

The offspring produced when members of the F1 generation are crossed.

True-Breeding Organism

An organism that consistently produces offspring with the same trait when self-fertilized or bred within its line.

Monohybrid Cross

A genetic cross that studies the inheritance of one trait.

Dihybrid Cross

A genetic cross that studies the inheritance of two traits.

Punnett Square

A chart used to show possible allele combinations in offspring from a genetic cross.

Mendel's Principle of Segregation

The two alleles for a gene separate during gamete formation, so each gamete receives only one allele.

Dominant vs. Recessive Inheritance

A dominant allele can be expressed in AA or Aa; a recessive trait requires aa.

Mendel's Monohybrid Cross Results

Crossing two heterozygotes (Aa × Aa) produces a 1:2:1 genotype ratio and a 3:1 phenotype ratio when dominance is complete.

Genotype Ratio

The ratio of different allele combinations among offspring.

Phenotype Ratio

The ratio of observable traits among offspring.

Testcross

A cross between an individual with an unknown dominant genotype and a homozygous recessive individual to determine the unknown genotype.

Wild Type

The trait or phenotype most commonly found in nature.

Homologous Chromosomes and Alleles

Homologous chromosomes carry the same genes at the same locations, but may have different alleles.

Gene Locus

The specific location of a gene on a chromosome.

Autosomal Genetic Disorder

A genetic disorder caused by a gene on an autosome, or non-sex chromosome.

Recessive Genetic Disorder

A disorder that usually appears when an individual inherits two recessive disease alleles.

Cystic Fibrosis

An inherited recessive disorder that affects mucus production and can cause problems in the lungs and digestive system.

Dominant Genetic Disorder

A disorder that can appear when an individual inherits just one disease-causing dominant allele.

Incomplete Dominance

An inheritance pattern in which a heterozygote has an intermediate phenotype between the two homozygotes.

Example of Incomplete Dominance

Red and white flowers can produce pink flowers when the heterozygote has an intermediate appearance.

Codominance

An inheritance pattern in which both alleles are fully expressed in a heterozygote.

ABO Blood Type

An example of codominance involving three alleles: IA, IB, and i.

ABO Blood Type Alleles

IA and IB are codominant; i is recessive.

Blood Type A Genotypes

IAIA or IAi.

Blood Type B Genotypes

IBIB or IBi.

Blood Type AB Genotype

IAIB.

Blood Type O Genotype

ii/oo

Multiple Alleles

When a gene has more than two possible alleles in a population, such as the ABO blood group.

Family Pedigree

A diagram used to trace how a trait is inherited through generations of a family.

Pedigree Symbols

A square represents a male; a circle represents a female; shaded symbols represent individuals who show the trait.

Pleiotropy

When one gene affects two or more different phenotypic traits.

Polygenic Inheritance

When two or more genes contribute to one phenotype, such as human height or skin color.

Sex-Linked Trait

A trait controlled by a gene located on a sex chromosome, often the X chromosome.

Sex Determination in Humans

Typically, an egg contributes an X chromosome; a sperm contributes either X or Y.

Sexual Reproduction

Reproduction involving the fusion of sperm and egg.

Genetic Variability

The genetic differences among individuals; sexual reproduction increases genetic variability.

Hermaphrodite

An organism that has both male and female reproductive systems.

External Fertilization

Fertilization that occurs outside the female's body, such as in frogs.

Internal Fertilization

Fertilization that occurs inside the female's body.