Genetics Chapter 3-Chromosomes and Inheritance

Mitosis

cell division resulting in 2 daughter cells with the same number and type of chromosomes as the original parent cell. It preserves genetic info through all these generations of cells. 

Meiosis

cell division resulting in 4 daughter cells with only 1 chromosome from each pair; how diploid cells form haploid cells 

Diploid

zygotes carrying 2 matching sets of chromosomes (2n)

Haploid

zygotes carrying 1 set of chromosome (n)

Metaphase

individual chromosomes have duplicated and condensed and are aligned in the center of the cell

Sister chromatids

2 identical halves of the same chromosome

Centromere

specific location at which sister chromatids are attached to each other

Metacentric chromosomes

centromere is in the middle

Acrocentric chromosomes

centromere is close to one end

Homologous chromsomes

chromosomes that match in size, shape, and banding patterns

Karyotype

arranging homologous pairs of chromosomes from large to small

Human male karyotype

46 chromosomes arranged in 22 matching pairs and 1 non-matching pair

Autosomes

the 44 chromosomes in matching pairs

Aneuploidy

missing or additional chromosomes

Chromatin

chromosomes that resemble a mass of extremely fine tangled string surrounded by nuclear envelope

Chromatid

chromosome condensed into rods

Cell Cycle

repeating pattern of cell growth (increase in size) followed by division

Interphase

period between divisions, most of the cell spends its time in interphase

G1

GROWTH! It lasts from the birth of a new cell until the onset of chromosome replication. Period when chromosomes are growing the most but neither duplicating nor dividing

S (synthesis)

DOUBLES! Each chromosome doubles to produce identical sister chromatids

G2

INTERVAL! It is the interval between chromosome duplication and the beginning of mitosis

Mitosis Phases

Prophase, Prometaphase, Anaphase, Metaphase, Telophase, Cytokinesis

Prophase

Condensation of individual chromosomes from the mass of chromatin marks the beginning of mitosis. Nucleoli begin to break down and disappear, and replicated centrosomes move apart.

Prometaphase

It begins with the breakdown of the nuclear envelope, allowing microtubules from the centrosomes to attach to kinetochores on the chromosomes in the nucleus.

Kinetochore

structure in the centromere region of each chromatid that is specialized for conveyance. 

Kinetochore microtubules

microtubules that extend between the centrosome and the kinetochore of a chromatid 

Polar microtubules

microtubules from each centrosome directed toward the middle of the cell

Astral microtubules

microtubules that extend out of from the centrosome toward the cell’s periphery

Metaphase

Chromosomes move toward an imaginary equator halfway between the two poles (metaphase plate) so that they are in balanced equilibrium maintained by tension across the chromosomes. 

Anaphase

Separation of sister chromatids allows each chromatid to be pulled toward the spindle pole to which it is linked by kinetochore microtubules

Telophase

Spindle fibers disperse, nuclear envelope forms around the group of chromatids at each pole, and nucleoli appear. 

Cytokinesis

parent cell separates into two smaller independent daughter cells with identical nuclei. Usually begins during anaphase but not completed until after telophase.

Cytokinesis in animals 

contractile ring pinches the cell into 2 equal halves

Cytokinesis in plants

cell plate forms inside the cell near the equator, growing rapidly outward, dividing the cell in two

Regulatory checkpoints

moments where the cell evaluates the results of previous steps and allows the sequential coordination of cell-cycle events. 

Germ cells

set aside for specialized role in production of gametes

Recombination

non-sister chromatids exchange parts and produce new combinations of alleles via crossing over 

Prophase I

chromatin condenses, homologous chromosomes pair and cross over

Metaphase I

kinetochores of sister chromatids fuse, so each chromosome contains only a single functional kinetochore; chromosomes align at metaphase plate 

Anaphase I 

separation of homologous chromosomes when chiasmata dissolves and maternal/paternal homologs are pulled to opposite sides. Note that sister centromeres don’t separate

Telophase I 

when nuclear membranes form around chromosomes that have moved to opposite poles. cytokinesis typically follows. 

Interkinesis

NO S PHASE! brief interphase between meiosis I and II 

Prophase II

chromosomes recondense and nuclear envelope breaks down

Metaphase II

attachment of kinetochores to microtubule fibers; chromatids are ½ of that in mitotic metaphase

Anaphase II

separation of sister chromatids, severing connection between sister centromeres

Telophase II

membranes form around each of the 4 daughter nuclei and cytokinesis follows. 

1st aspect of meiosis

CHANCE governs which parental homolog migrates to the two poles during first meiotic division, contributing to gene diversity 

2nd aspect of meiosis

reshuffling of genetic info via crossing over during prophase I contributes to gene diversity 

Independent assortment in Meiosis

genes carried on different chromosomes of two bivalents will assort into gametes independently 

Mendelian Laws and Meiosis

meiosis ensures that each gamete will contain only a single chromatid of a bivalent so only a single allele of any gene on that chromatid