Genetics (Chromosomal theory of inheritance and The Cell Cycle)

Personal reviewer for midterm exam

chromosomes

Where genes are located

chromosome theory of inheritance

the idea that genes are located on chromosomes

Drosophila melanogaster (fruit flies)

The **chromosome theory of inheritance**, or the idea that genes are located on chromosomes, was proposed based on experiments by Thomas Hunt Morgan using

sex-linkage

inheritance of genes that are on the sex chromosomes (X and Y).

true

This inheritance pattern means that a male with the recessive allele will always show the recessive trait

G1 Phase

Metabolic changes prepare the cell for division. At a certain point – the restriction point – the cell is committed to division and moves into the S phase.

S Phase

DNA synthesis replicates the genetic material. Each chromosome now consists of two sister chromatids. 

G2 Phase

Metabolic changes assemble the cytoplasmic materials necessary for mitosis and cytokinesis. 

M Phase

 A nuclear division (mitosis) followed by a cell division (cytokinesis).

Interphase

The period between mitotic divisions – that is, G1, S and G2 – is known as

Meiosis

the form of eukaryotic cell division that produces haploid sex cells or gametes (which contain a single copy of each chromosome) from diploid cells (which contain two copies of each chromosome).

Meiosis I

 separates the pairs of homologous chromosomes; a special cell division reduces the cell from diploid to haploid.

Prophase I

The homologous chromosomes pair and exchange DNA to form recombinant chromosomes.

Leptotene

chromosomes start to condense.

Zygotene

homologous chromosomes become closely associated (synapsis) to form pairs of 

chromosomes (bivalents) consisting of four chromatids (tetrads). 

Pachytene

crossing over between pairs of homologous chromosomes to form chiasmata (sing. chiasma). 

Diplotene

homologous chromosomes start to separate but remain attached by chiasmata.

Diakinesis

homologous chromosomes continue to separate, and chiasmata move to the ends of the chromosomes.

Prometaphase I

Spindle apparatus formed, and chromosomes attached to spindle fibres by kinetochores.

Metaphase I

Homologous pairs of chromosomes (bivalents) arranged as a double row along the metaphase plate. The arrangement of the paired chromosomes with respect to the poles of the spindle apparatus is random along the metaphase plate.

Anaphase I

The homologous chromosomes in each bivalent are separated and move to the opposite poles of the cell. 

Telophase I

The chromosomes become diffuse and the nuclear membrane reforms. 

Cytokinesis

The final cellular division to form two new cells, followed by Meiosis II. Meiosis I is a reduction division: the original diploid cell had two copies of each chromosome; the newly formed haploid cells have one copy of each chromosome. 

Meiosis II

separates each chromosome into two chromatids