Cell Division and Genetics Overview

Cell Division

The heart of the reproduction of cells and organisms because cells originate only from preexisting cells.

Single Cell Division

Reproduction process exemplified by yeast.

Multicellular Division

Involves development, growth, and repair in organisms like people.

Asexual Reproduction

Producing offspring that are all genetic copies of the parent and identical to each other.

Sexual Reproduction

Creates a variety of offspring.

Binary Fission

A method of asexual reproduction in prokaryotic cells meaning dividing in half.

Cell Cycle

An ordered sequence of events from the time a cell is first formed from a dividing parent cell until its own division.

G1 Phase

Phase of the cell cycle characterized by lots of growth.

S Phase

Phase of the cell cycle known as 'Synthesis', where DNA replication occurs.

G2 Phase

Phase of the cell cycle involving growth and preparation for mitosis.

M Phase

Phase of the cell cycle where mitosis occurs, distributing duplicated chromosomes into two daughter nuclei.

Interphase

The phase of the cell cycle that includes G1, S, and G2, excluding mitosis.

Prophase

Phase of mitosis where chromatin condenses into visible chromosomes and the nuclear envelope begins to break down.

Metaphase

Phase of mitosis where chromosomes line up along the metaphase plate and spindle fibers attach to the centromere.

Anaphase

Phase of mitosis where sister chromatids are pulled apart by spindle fibers toward opposite poles of the cell.

Telophase

Phase of mitosis where chromosomes arrive at the poles, decondense back into chromatin, and two new nuclear envelopes form.

Cytokinesis in Animal Cells

Occurs when a cell constricts, forming a cleavage furrow, and microfilaments constrict to completely pinch the cell.

Cytokinesis in Plant Cells

A membranous cell plate forms and then splits the cell into two.

Effect of Environment on Cell Division

Most normal cells divide only when attached to a surface and continue dividing until they touch one another.

Growth Factors

Signals that affect critical checkpoints in the cell cycle and are usually necessary for cell division.

Cancer

Characterized by growing out of control, producing malignant tumors that can invade other tissues.

Benign Tumors

Tumors that do not metastasize (spread to new areas).

Difference between Mitosis and Meiosis

Meiosis divides twice to form four daughter cells, while mitosis produces two genetically identical diploid somatic daughter cells.

Meiosis

Produces four genetically unique haploid gametes.

Diploid

Cells with two sets of homologous chromosomes.

Haploid

Eggs and sperm are haploid cells with a single set of chromosomes.

Sexual life cycles

Involve the alternation of haploid and diploid stages.

Variation in Meiosis

Random arrangements of chromosome pairs at metaphase I lead to many different combinations of chromosomes in egg and sperm.

Random fertilization

Greatly increases genetic variation as any sperm can fuse with any egg, totally by chance.

Independent assortment

During the formation of gametes, different genes independently separate from one another.

Inheritance of traits

The inheritance of one trait doesn't automatically affect the inheritance of another trait.

Crossing over

An exchange of corresponding segments between nonsister chromatids of homologous chromosomes that increases genetic variability.

Nondisjunction

Abnormal chromosome count resulting from the failure of homologous chromosomes or sister chromatids to separate during meiosis.

Karyotype

A photographic inventory of an individual's chromosomes.

Preparation of a karyotype

Involves isolating white blood cells, stimulating them to grow, arresting them at metaphase, and photographing under a microscope.

Abnormal Chromosome numbers

An extra copy of chromosome 21 causes Down syndrome.

Trisomy 21

The most common chromosome number abnormality resulting in Down syndrome.

Alterations to chromosomes

Can cause birth defects and cancer through chromosome breakage leading to deletions, duplications, inversions, or translocations.

Law of Segregation

Each individual has two alleles for each trait that separate during the formation of gametes.

Law of Independent Assortment

Genes for different traits separate independently when gametes are formed, creating genetic variation.

Law of Dominance

When two different alleles are present, one is dominant and masks the effect of the other (recessive).

Dominant allele

A dominant allele masks the effect of a recessive allele when both are present.

Recessive allele

A recessive allele only expresses its trait when both alleles for a gene are recessive.

Homozygous

An individual is homozygous for a gene if they have two identical alleles for that gene.

Heterozygous

An individual is heterozygous for a gene if they have two different alleles for that gene.

Allele

Alternative versions of genes that account for variations in inherited characters.

Character

Variation among individuals.

Traits

Variations in a character.

Punnett square

Shows the four possible combinations of alleles that could occur when these gametes combine.

Mendel's work

Revolutionary because he used experiments, math, and clear evidence to show that traits are inherited through discrete units, not by blending.

Blending Theory of Inheritance

The idea that traits from parents simply mixed in their offspring, like mixing paint colors.

Genotype

The genetic constitution of an individual, represented by alleles.

Phenotype

The physical appearance of an organism as a result of its genotype.

PP

Example of homozygous dominant alleles.

pp

Example of homozygous recessive alleles.

Pp

Example of heterozygous alleles.

Locus

The specific position of an allele on a chromosome.

Gametes

Reproductive cells that carry alleles from each parent.

Medium-height child

An example of the blending theory where a tall parent and a short parent produce an offspring.

Purple flowers

The phenotype expressed when at least one dominant allele (P) is present.

White flowers

The phenotype expressed only when both alleles are recessive (pp).

Two recessive alleles

Required for a recessive trait to show up in the phenotype.

Allele combinations

The result of combining alleles from each parent in a Punnett square.

Interpret the Results

The process of determining the possible genetic combinations and phenotypes based on the filled squares in a Punnett square.

Genotype

The genotype refers to the genetic makeup of an individual - the specific alleles (versions of a gene) that an organism inherits from its parents.

Phenotype

The phenotype refers to the observable characteristics or traits of an organism, which result from the interaction between its genotype and the environment.

Law of Independent Assortment

States that the alleles of a pair segregate independently of other allele pairs during gamete formation.

Law of Segregation

The Law of Segregation relates to Anaphase I of Meiosis I, and it ensures that only one allele for each gene goes into each gamete.

Anaphase I of Meiosis I

During Anaphase I of meiosis, homologous chromosomes (one from mom, one from dad) separate and move to opposite sides of the cell.

Testcross

Mating between an individual of unknown genotype and a homozygous recessive individual can reveal the unknown genotype.

Family Pedigrees

Genetic traits in humans can be tracked through family pedigrees.

Recessive Disorders

Many inherited traits in humans are controlled by a single gene.

Carrier Screening

Carrier screening, fetal testing, fetal imaging, and newborn screening can provide information for reproductive decision, but may create ethical dilemmas.

Complete Dominance

Mendel's pea crosses always looked like one of the two parental varieties, which is called complete dominance.

Incomplete Dominance

Incomplete dominance results in intermediate phenotypes.

Codominance

Many genes have more than two alleles that may be codominant.

ABO Blood Group

ABO blood group phenotype in humans is controlled by three alleles that produce a total of four phenotypes.

Pleiotropy

Pleiotropy refers to the phenomenon where one gene influences multiple phenotypic traits.

Heterozygous

An individual with two different alleles for a specific gene.

Alleles

Different versions of a gene that can exist at a specific locus.

Gamete

A reproductive cell that carries half the genetic information of an organism.

Phenotypic Traits

Observable characteristics of an organism that result from the genotype and environment.

Mendel's Law of Assortment

The principle that alleles for different traits are segregated independently during gamete formation.

F1 Hybrids

Offspring resulting from the cross of two different parental varieties.

Homozygous Recessive

An individual with two identical recessive alleles for a specific gene.

Normal Parents

Parents who do not exhibit a trait but may carry a recessive allele for that trait.

Intermediate Phenotypes

Phenotypes that are a blend of the parental traits, seen in incomplete dominance.

Pleiotropy

Occurs when one gene influences multiple characters.

Sickle cell disease

An example of pleiotropy that affects the type of hemoglobin produced, the shape of red blood cells, and causes anemia and organ damage.

Codominant alleles

Sickle-cell and nonsickle alleles are codominant.

Carriers of sickle-cell disease

Have increased resistance to malaria.

Polygenic inheritance

A single phenotypic character results from the additive effects of two or more genes.

Human skin color

An example of polygenic inheritance.

Multiple allele system

A gene that exists in three or more different forms (alleles) within a population.

Alleles in a population

While an individual can only have two alleles for a specific gene, the population can have many different allele combinations.

Environmental effects on gene expression

The environment affects many characters and traits are influenced by both genetic and environmental factors.

Linked genes

Genes on the same chromosome that tend to be inherited together.

Bateson and Punnett's study

Studied plants that did not show a 9:3:3:1 ratio in the F2 generation.

Crossing over

Produces new combinations of alleles between homologous chromosomes.

Recombinant gametes

Gametes that contain linked genes separated by crossing over.