Meiosis

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How are living organisms distinguished

By their ability to reproduce their own kind

• A living thing reproduces, if it doesn't, its not living

Genetics

Scientific study of HEREDITY & VARIATION

Heredity

Transmission of traits from one generation to the next

Variation

Demonstrated by difference in appearance that offspring show from parents & offspring

• Different between members of a species (eye color, ability to collect oxygen)

Genes

Units of heredity

• MADE UP OF SEGMENTS OF DNA (Spread throughout chromosomes)

Gametes

Sperm & egg

Locus

LOCATION of a gene on a chromosome

Asexual reproduction

• Benefit

• Disadvantage

1 parent , genetically identical offspring

• Faster & less energetically intensive

• Little to no genetic variation

Sexual reproduction

• Benefit

• Disadvantage

2 parents , offspring have unique combo of genes

• High variation

• Slower, needs more energy

Somatic cells

BODY

• 23 pairs of chromosomes

Karyotype

Ordered display of the pairs of chromosomes from a cell (picture)

Homologous Chromosomes

Homologs

• Same length & carry genes controlling the same inherited characteristics BUT not genetically identical

  • In contrast, sister chromatids are identical

• Same spots of traits BUT different traits

  • Brown vs blue eyes

Reduction division & what does it form

Another name for meiosis

• Reducing the chromosome # in half by DIVIDING TWICE

• Results in the formation of 4 genetically DISTINCT HAPLOID GAMETES

What does Meiosis I and Meiosis II consist of

• What is the difference between the two

Prophase I, Metaphase I, Anaphase I, Telophase I

Prophase II, Metaphase II, Anaphase II, Telophase/Cytokinesis

• I is for homologous , II is for separating SISTERS

Prophase I

• Synapsis

• Crossing over

• Chiasmata

Over 90% of the time required for meiosis

• Chromatin CONDENSE into chromoSOMES , Nuclear envelope fragments (Same as Mitosis)

• SYNAPSIS OCCURS ; Homologous Chromosomes loosely line up (aligned gene by gene) to form TETRADS

• CROSSING OVER occurs within the tetrads → nonsister (opposite) chromatids exchange DNA segments randomly

• Chiasmata - X-shaped regions where crossing over occurs

Metaphase I

• Independent Assortment

• How many combos occur

Tetrads line up at metaphase plate w/ 1 chromosome facing each pole

• Tetrads line up INDEPENDENTLY of one another (Source of variation)

  • Not all dad genes are on the same side

• 2n combos ; for humans 8 million

Anaphase I

HOMOLOGOUS CHROMOSOMES SEPARATE , moving towards poles (Tetrads split)

• Sister chromatids remain attached & move as one unit

Telophase I & Cytokinesis

Each half of the cell has haploid set of chromosomes , EACH CHROMOSOME STILL CONSISTS OF TWO SISTER CHROMATIDS

• Cytokinesis usually occurs simultaneously , forming 2 haploid daughter cells

Meiosis II

IDENTICAL to mitosis

• SISTER CHROMATIDS are separated , resulting in the formation of FOUR GENETICALLY NONIDENTICAL HAPLOID DAUGHTER CELLS (gametes)

6 sources of genetic variation

1- Mutations (Environmental & replication errors)

2- Crossing Over (Prophase I) (Sexual only)

3- Independent Assortment (Metaphase I) (Sexual only)

4- Random Fertilization (Sexual only)

5- Transformation (We don't do)

6- Transduction

Nondisjunction

AKA when things don't separate → During Anaphase I or II

• Result: Aneuploidy (Abnormal chromosome #)

  • Monosomy - 1 copy

  • Trisomy - 3 copies

Polypoid

Having more than 2 copies of EVERY chromosome (common in agriculture crops)

• 3n , 6n , 4n → n = # of chromosomes

Structural Abberations

In chromosomes

1- Duplication ; Section of chromosome repeated

2- Deletion ; Chromosome section missing

3- Inversion ; Reversal of a chromosome section

4- Translocation ; Moving a section to nonhomologous chromosome

• Reciprocal ; = exchange

• Nonreciprocal ; not = exchange