Genetics and Cell Division: Chromosomes, Mitosis, Meiosis, and Inheritance

Chromosomes

Composed of DNA, the genetic blueprint of a cell. Exists as chromatin when the cell is not dividing.

Chromatin

Loosely arranged DNA wrapped around proteins. Condenses to form chromosomes prior to the start of cell division.

Sister Chromatid

Two identical copies of a chromosome.

Homologous Chromosome

Pairs of chromosomes with different versions of the same trait.

Somatic Cells

Any cell of a living organism other than the reproductive cells.

Gametes

A reproductive cell, also known as a sex cell, that contains half the genetic information of a parent. Always a haploid.

Diploid

(2n) all of the pairs of chromosomes. Humans diploid number is 46 (44 autosomes and 2 sex chromosomes).

Haploid

(n) half of the chromosomes. Humans haploid number is 23 (22 autosomes and 1 sex chromosome).

Cell Theory

All cells reproduce.

Binary Fission

Simplest process that occurs in bacteria and some eukaryotes.

Mitosis

Division of the nucleus that occurs in most eukaryotes including plants, animals, and fungi.

Cell Cycle

Comprised of two main phases: Interphase and Mitosis.

Interphase

The normal life of the cell where DNA is duplicated in S phase.

M phase

Mitosis and Cytokinesis.

Cytokinesis

Division of the cytoplasm. In animal cells, it occurs through formation of a cleavage furrow; in plant cells, it occurs through formation of a cell plate.

Prophase

Chromosomes start to condense, nuclear envelope disappears, spindle forms.

Metaphase

Chromosomes align in the center of the cell.

Anaphase

Centromeres split and sister chromatids move to opposite ends of the cell.

Telophase

Cytokinesis occurs (division of the cytoplasm), nucleus reforms, chromosomes decondense.

Karyotype

Picture of the chromosomes.

Autosomes

Same in both male and female, is not a sex chromosome. Humans have 22 pairs of these.

Sex Chromosomes

Different between sexes and determine gender. Humans have 2 of these chromosomes (X and/or Y).

Meiosis

A process that produces four haploid daughter cells through two rounds of division.

Prophase I

Synapsis and crossing over occur, homologous chromosomes exchange segments of DNA, adding to genetic variation in the daughter cells.

Metaphase I

Homologous chromosomes pair off at the center of the cell.

Anaphase I

Homologous chromosomes separate to each end of the cell.

Telophase I

Cytoplasm divides, producing 2 haploid daughter cells.

Spermatogenesis

Produces sex cells called sperm in males.

Oogenesis

Produces sex cells called eggs in females.

Meiosis I and Meiosis II

Two divisions of meiosis that result in 4 daughter cells and reduce the chromosome number from diploid to haploid.

Nondisjunction

A failure of the chromosomes to separate during meiosis.

Trisomy

One extra chromosome (3 total instead of 2).

Monosomy

One less chromosome (1 total instead of 2).

Down Syndrome

A condition caused by having 3 copies of chromosome 21.

Turner Syndrome

A condition characterized by having only 1 X chromosome and an underdeveloped reproductive system.

Klinefelter Syndrome

A condition in males with an extra X chromosome (XXY) resulting in underdeveloped testes and prostate.

Jacobs Syndrome

A condition characterized by having an extra Y chromosome (XYY), often resulting in taller stature and some reading and speech delays.

Gregor Mendel

An Austrian monk who studied inheritance in pea plants and described a basic process of simple inheritance.

Alleles

The different versions of a specific gene trait, such as eye color or hairline.

Locus

The location of the allele on the chromosome.

Dominant

An allele that is expressed over a recessive allele, e.g., B is the allele for brown eyes.

Recessive

An allele that is only expressed if no dominant allele is present, e.g., b is the allele for blue eyes.

Genotype

The combination of alleles a person has.

Homozygous genotype

Two of the same alleles, e.g., BB (homozygous brown eye) or bb (homozygous blue eye).

Heterozygous

Two different alleles, e.g., Bb (heterozygous brown eyes).

Phenotype

The physical expression of the trait, e.g., BB (genotype) = Brown eyes (phenotype).

Genes

A segment of DNA that carries the instructions for specific traits and functions, inherited from parents to offspring.

Monohybrid Cross

Some traits are inherited in a simple dominant/recessive fashion.

Punnett Square

Used to determine the potential offspring of a cross (mating) of two individual parents.

Steps used to solve a genetic cross

Determine the genotype of each parent (P generation), List the possible gametes from each parent, Combine all possible gametes, Determine the genotypes and phenotypes of all offspring (F1 generation) and the ratio in which they might occur.

Law of Independent Assortment

The alleles separate independent of any other genes alleles, creating genetic variation in the gametes produced in meiosis.

Pedigree

A chart of a family's history of a particular genetic trait.

Squares

Represent males in a pedigree chart.

Circles

Represent females in a pedigree chart.

Shaded shape

Indicates an individual has the trait.

Non-shaded

Indicates an individual does not have the trait.

Autosomal Recessive Traits

Child might have the trait but neither parent has the trait; the parents are heterozygous so they express the dominant.

Autosomal Dominant Traits

For the child to have the trait, both parents will have it.

Law of Segregation

The two alleles separate during gamete formation; each gamete gets 1 of the 2 alleles from the parent.

Incomplete Dominance

Heterozygous genotype gives an intermediate phenotype instead of the dominant.

Multiple Alleles

When a trait has more than two possible alleles; each person still only has 2 of these possible alleles.

Codominance

Sometimes, both alleles are expressed so neither is recessive to the other.

Blood type

An example of multiple alleles and codominance.

Polygenic Inheritance

Traits controlled by multiple genes, each with multiple alleles; human height is an example.

Environment

Can affect the expression of a trait, leading to multifactorial traits.

Nature vs. Nurture

How much of us is genetic versus our environmental exposure?

Skin color

Polygenic inheritance AND a multifactorial trait; Over 100 genes involved.

More dominant alleles

Darker skin.

Recessive alleles

Lighter skin.

Sunlight

Effects melanin production which also influences skin color.

X-linked traits

Carried on the X chromosome; Effect males more since their Y chromosome is non-homologous so lacks a 2nd allele.

Colorblindness

Possible alleles in humans.

XB

Normal Color Vision (dominant).

Y

Does not contain an allele for this trait.

XBXB or XBXb

Woman with normal color vision.

XbXb

Woman who is colorblind.

XBY

Man with normal color vision.

Nucleotide

Contains a sugar, a phosphate, and a nitrogen base.

DNA

A nucleic acid composed of double strand of nucleotides in a helix shape.

Complementary base pairing

Allows DNA to copy itself.

Adenine

Pairs with Thymine.

Thymine

Pairs with Adenine.

Cytosine

Pairs with Guanine.

Guanine

Pairs with Cytosine.

DNA replication

Before cells divide the DNA has to be copied; 1 DNA molecule produces 2 DNA molecules.

DNA polymerase

Reads the template bases and adds complimentary bases to form a new strand.

Replication

Is semi-conservative; Each new DNA molecule has one old strand and one new strand.

RNA

Is a nucleic acid but different from DNA; Single strand of nucleotides.

Ribose sugar

The different sugar in RNA.

Uracil

The base in RNA instead of Thymine.

Codon

3 bases in a row in mRNA.

Start codon

AUG.

Transcription

making RNA from DNA

Translation

making protein from mRNA

Transcription location

occurs in the nucleus

Translation location

occurs in the cytoplasm (on ribosomes)

Starting material for Transcription

DNA

Starting material for Translation

mRNA

mRNA

A copy of DNA

End product of Transcription

mRNA (end product)