Genomic Organization and Meiosis in Eukaryotes

Chromosome number

A distinguishing characteristic of a species.

Diploid cells

Cells that have an even number of chromosomes.

Chromosome numbers in humans

46 chromosomes.

Chromosome numbers in chimpanzees

48 chromosomes.

Karyotype

The description of the chromosomes as seen in the karyogram.

Karyogram

An image of chromosomes arranged in a standard format.

Autosome

The first 22 pairs of homologous chromosomes in humans that do not contain genes that determine biological sex.

Sex chromosome

The 23rd pair of chromosomes in humans, which includes two versions: X and Y.

Typical female chromosomes

Two homologous chromosomes (XX).

Typical male chromosomes

One of each, nonhomologous chromosomes (XY).

Genome

The whole of the genetic information of an organism, including the entire base sequence of each DNA molecule.

Gene

A sequence of DNA bases that codes for a functional RNA or protein product; the basic functional unit of inheritance.

Allele

Variations of a gene that occupy the same locus on the chromosome.

Single-nucleotide polymorphisms (SNPs)

Differences in a base between two genes that vary by one to a few base pairs.

Variation in genomes

Genomes vary in overall size and base sequence, with variation between species being much larger than variation within a species.

Genome size measurement units

Base pairs (bp)

Number of Chromosomes & Complexity Relationship

The number of chromosomes in a species has no specific significance nor does it indicate any relationship between two species. The number of chromosomes does NOT correlate to the number of genes.

Whole genome sequencing

Determining the entire base sequence of an organism.

Technological improvements in DNA sequencing

Technological improvements have sped the DNA sequencing process.

Applications of genome sequencing

Investigation of evolutionary origins and could lead to personalized medicine.

Ethical considerations of genome sequencing

Breach in privacy -> An individual's genome contains an extensive amount of personal information.

If mishandled or disclosed, it could lead to genetic discrimination by employers, insurance companies, or other entities.

Meiosis

Maintains correct number of chromosomes by reducing by half.

Cross-breeding between species

Cross-breeding between closely related species is unlikely to produce fertile offspring if parent chromosome numbers are different.

Mule

A sterile offspring produced by mating a donkey and a horse due to differences in parent chromosome numbers.

DNA barcode

Short sections of DNA from one gene.

Environmental DNA

Collected from water, soil, or any other part of the abiotic environment.

DNA barcoding

Identify species from small pieces of tissue that might otherwise be difficult to recognize.

Applications of DNA barcoding

Species identification for conservation.

Structure of a nucleosome

A DNA molecule wrapped around a core of eight histone proteins held together by an additional histone protein attached to linker DNA.

Linker DNA

nucleosome are joined by DNA that runs between them.

What is the basic structural unit of DNA packaging?

Nucleosome

What does a nucleosome consist of?

A length of DNA coiled around a core of eight proteins called histones.

Histones

A family of small, positively charged proteins.

Charge of DNA

Due to the phosphate groups in nucleotides, DNA is negatively charged. DNA binds tightly to the histone proteins using electromagnetic attraction

Gene knockout

A technique for investigating the function of a gene by changing it to make it inoperative.

Gene expression

The mechanism by which information in genes has effects on the phenotype.

Genotype

Combination of alleles present.

Phenotype

The characteristics of an organism.

Stages of gene expression

Transcription, translation, and the function of a protein product, such as an enzyme.

Sex chromosomes

Typical female: two homologous chromosomes (XX); Typical male: one of each, nonhomologous chromosomes (XY).

SRY gene

A gene on the Y chromosome that becomes active at about two months of development, causing immature gonads to develop into testes.

Testis-Determining Factor (TDF)

The protein coded by the SRY gene that activates processes causing a fetus to develop testes.

Gene locus

Where on the chromosome a gene is located.

Cytokinesis

The division of cytoplasm during cell division, which is usually equal but can be unequal.

Unequal cytokinesis in oogenesis

In humans, cytokinesis divides the cytoplasm unequally, producing one large cell (oocyte) and one small polar body.

Mitochondrion requirement

Both daughter cells must receive at least one mitochondrion and any other organelle that can only be made by dividing a pre-existing structure to survive.

Budding in yeast

Yeast cells reproduce asexually by dividing their nucleus by mitosis and receiving one of the nuclei with only a small share of the cytoplasm.

Oogenesis

The process in humans where usually only one egg cell (oocyte) is produced at a time, with enough stored food to sustain the developing embryo.

First division in oogenesis

Produces one large cell (with most of the cytoplasm) and one small polar body that does not develop further.

Second division in oogenesis

Only the large cell undergoes the second division, again unequally, resulting in one mature oocyte and another small polar body.

Human sex determination

Biological sex includes structural and functional characteristics determined by sex chromosomes and genes.

Chromosome pairs in humans

The 23rd pair of chromosomes in humans determines sex, with more genes carried by the X chromosome than the Y chromosome.

Knockout strain development

Develop several thousand knockout strains, each lacking one gene.

Gene function investigation

Predict which base sequences in a genome are games by characteristic base sequence patterns.

Budding process

Yeast cells carry out this budding process repeatedly and do not have to double in size between each division.

Nuclear division

Nuclear division is needed before cell division to avoid production of anucleate cells.

Mitosis

Mitosis maintains the chromosome number and genome of cells.

Meiosis definition

Meiosis is nuclear division that results in reduction of the chromosome number and diversity between genomes.

Chromosome condensation

Chromosomes condense during meiosis to separate & move elongated molecules without knots, tangles, or breaks.

Microtubules

Microtubules are hollow cylinders of tubulin proteins that can be rapidly assembled or disassembled to move chromosomes.

Kinetochores

Kinetochores are protein structures assembled on the centromere of each chromatid that link growing microtubules.

Diploid

Diploid is a homologous pair of each chromosome, with one copy of paternal and maternal chromosomes.

Human cell diploid number

The human cell diploid number is 46.

Haploid

Haploid is a single copy of each chromosome, with no chromosome pair.

Human cell haploid number

The human cell haploid number is 23.

Example haploid cells

Human sperm and egg cells are examples of haploid cells.

Meiosis I

Meiosis I is a reduction division where homologous chromosomes are separated to halve the chromosome number from diploid to haploid.

Interphase

During interphase, DNA replicates, and each chromosome (2n = 4) replicates to form sister chromatids, totaling 8 chromatids.

Homologous chromosomes

Homologous chromosomes share the same structural features and genes at the same loci positions, though alleles may differ.

Chromatid

A chromatid is one half of a duplicated chromosome, formed during DNA replication.

Segregation in meiosis

Meiosis involves two rounds of segregation to produce four haploid nuclei from one diploid nucleus.

Homologous Chromosome

Chromosomes that are homologous share same size, same banding patterns, and same centromere positions.

Nucleosomes

Nucleosomes are formed by wrapping the double helix of DNA around histones.

Prophase I

Diploid -> nuclear membrane begins to break down, spindle fibers begin to form, DNA condense/supercoil -> chromosomes, homologous chromosomes pair up, crossing over.

Metaphase I

Homologous chromosomes are independently aligned/line up @ the cell, Diploid (2n).

Anaphase I

Homologous pairs separate & each chromosome move towards opposite end of cells -> sister chromatids NOT separated, Diploid (2n).

Telophase I & Cytokinesis

Occurs simultaneously, new nuclei form around chromosomes @ each pole, DNA uncoils chromosomes -> chromatin, spindle fibers break apart, results in two haploid cells.

Meiosis II

Sister chromatids are separated.

Prophase II

Spindle fibers begin to form, DNA condenses/super coils again into chromosomes, nuclear membrane begins to break down, Haploid (n).

Metaphase II

Aligned @ cell equator, Haploid (2n).

Anaphase II

Sister chromatids pull apart & move towards opposite poles of cell, Haploid (2n).

Telophase II & Cytokinesis

Occurs simultaneously, spindle fibers break apart & DNA uncoils from chromosome to form chromatin, results in four haploid daughter cells, all genetically unique.

Chromosomes in Humans

46 chromosomes in humans

Meiosis I Reductive Division

Meiosis is known as the reductive division because it reduces the number of chromosomes in the daughter cell by half.

Haploid Cells After Meiosis I

2 haploid daughter cells at the end of meiosis I.

What is the main purpose of meiosis I?

To separate homologous chromosomes, promoting genetic diversity and evolution.

What is the result of mitosis?

Two genetically identical haploid daughter cells from a single parent cell.

How many divisions occur in meiosis?

One division.

What is the main purpose of meiosis II?

To separate sister chromatids.

What is the result of meiosis?

Four haploid daughter cells that are genetically unique from the parent.

How does the DNA amount in daughter cells compare to the parent cell in mitosis?

Daughter cells have half the amount of DNA compared to the parent cell.

Prophase I Events

Diploid -> nuclear membrane begins to break down, spindle fibers begin to form, DNA condense/supercoil -> chromosomes, homologous chromosomes pair up, crossing over.

Metaphase I Events

Homologous chromosomes are independently aligned/line up @ the cell, Diploid (2n).

Anaphase I Events

Homologous pairs separate & each chromosome move towards opposite end of cells -> sister chromatids NOT separated, Diploid (2n).

Telophase I Events

New nuclei form around chromosomes @ each pole, DNA uncoils chromosomes -> chromatin, spindle fibers break apart, results in two haploid cells.

Prophase II Events

Spindle fibers begin to form, DNA condenses/super coils again into chromosomes, nuclear membrane begins to break down, Haploid (n).

Metaphase II Events

Aligned @ cell equator, Haploid (2n).

Anaphase II Events

Sister chromatids pull apart & move towards opposite poles of cell, Haploid (2n).

Telophase II Events

Spindle fibers break apart & DNA uncoils from chromosome to form chromatin, results in four haploid daughter cells, all genetically unique.

Nondisjunction

The failure of chromosomes to separate during either anaphase I/II of meiosis (error).