Genetics - Mitosis + Meiosis

Cell Division

The asexual reproduction of cells

1 parent cell divides and forms 2 daughter cells

INTERPHASE takes up __% of a cell's life

90

MITOSIS AND CYTOKINESIS takes up __% of a cell's life

10

Mitosis

Cell division in SOMATIC cells

INTERPHASE 3 parts

G1 phase, S phase, G2 phase

G1 Phase

Growth phase, DNA grows to a certain point to be duplicated

Synthesis (S) Phase

DNA is replicated

G2 Phase

Second growth phase, DNA continues to grow

Prophase

- Chromatin condenses into Chromosomes

- Nuclear membrane breaks down

- Nucleolus disintergrates

Metaphase

- Chromosomes align at the middle of the cell (equatorial plate)

Anaphase

- Replicated chromosomes split into 2 separate sister chromatids (now become unreplicated chromosomes)

Telophase

- Nucleus splits

- Nuclear membrane and Nucleolus reforms

Cytokinesis

- Division of Cytoplasm

- Clevage furrow (Ani.) or Cell plate (Pla.) forms

Important Reasons for Mitosis (3)

Reproduction, Maintenance/Growth, Repair

Reproduction

Zygote divides to become trillions of cells

Maintenance/Growth

Replacing old cells with new ones

Repair

Regenerating damaged tissue

Meiosis

Cell division that produces haploid gametes by halving the amount of chromosomes

Meiosis I

reduction

Prophase I

Homologous chromosomes undergo synapsis and cross-over at the chiasmata. Spindle fibres extend and attach to chromosome tetrads (4 chromosomes in homologous pairs)

Homologus Pairs

Matching pairs of chromosomes with the same: length, genes (that control the same alleles), gene loci, centromere position

Crossing-over

Process where homologous chromosomes share genetic information between their non-sister chromatids

Synapsis

Pairing of homologous chromosomes

Chiasmata

X-shaped regions where crossing over occurs

Metaphase I

Paired homologous chromosomes line up across the center of the cell

Anaphase I

Homologous chromosomes are separated and pulled to opposite poles.

Telophase I + Cytokinesis

The cytoplasm divides and two new cells form. Each new cell has one duplicated chromosome from each similar pair.

Meiosis II

division of sister chromatids

Prophase II

The duplicated chromosomes and spindle fibers reappear in each new cell. Almost identical to Prophase in Mitosis

Metaphase II

Chromosomes line up at the equator.

Anaphase II

Sister chromatids are separated by spindle fibers

Telophase II + Cytokinesis

Nuclear membrane reforms, cytoplasm divides, 4 daughter cells formed

Alleles

Different versions of the same gene

Law of Segregation

Pairs of homologous chromosomes separate in meiosis so that only ONE CHROMOSOME from each pair is present in each gamete

Gametogenesis

production of gametes

Spermatogenesis

production of sperm, occurs throughout life

Oogenisis

the production or development of an ovum, occurs in the womb

Random Fertilization

Source of genetic variation caused by the unlimited number of possible sperm & egg combinations

Law of Independent Assortment

Homologus pairs can arrange themsleves in more than one way, leading to different gamete types

Mutations

Change in the genetic composition of the gamete

Karyotype

A display of the chromosome pairs of a cell arranged by size and shape.

Autosomes

non-sex chromosomes

Chromosome Abnormality - Chromosome Number

too many/too few chromosomes

Aneuploidy

Having an abnormal amount of chromosomes (not a multiple of n)

Monosomy

missing a chromosome

Trisomy

extra chromosome

Chromosome Abnormality - Chromosome Structure

correct amount, some are damaged (results in developmental abnormalities), usually occurring due to errors in crossing-over

Inversion

Fragments on chromosomes are in reverse order (least severe)

Translocation

Chromosomes contain segment of DNA that they should not have due to non-homologous chromosomes crossing-over

Deletion

Fragments of chromosome are lost (most severe)

Duplication

Fragment of chromosome is replicated

Prenatal Testing - Fetal Cells

Cells are taken from placenta/amniotic fluid to diagnose chromosomal abnormalities

Prenatal Testing - Multiple Marker Screening

Drawing blood from mother to test for different hormones

ARTs

Artificial Reproductive Technologies: can enhance reproductive success

Fertilization problems - M

- poor sperm quality + production

- blockage in epididymis

Fertilization problems - F

- poor/reduced egg

- blockage in falopian tubes