Meiosis and Genetic Diversity

Genetics

The study of heredity and hereditary variation

Heredity

The transmission of traits from one generation to the next

Genes

Segments of DNA that code for basic units of heredity

Asexual Reproduction traits

• Single individual

• No fusion of gametes

• Clones

• Produce through mitosis

Source of variation for asexual reproduction

Mutations

Sexual reproduction traits

• Two parents (male/female)

• Offspring are unique combinations of genes from parents

• Genetically varied from parents and siblings

Homologous chromosomes

A pair of chromosomes that carry the same genetic info (mom + dad)

Karyotypes

A display of chromosome pairs ordered by size and length

Somatic (body) cells

Diploid (2n) - two complete sets of chromosomes

Gametic (sex) cells

Haploid (n) - one set of each chromosome

Autosomes

Chromosomes that do not determine sex

Sex chromosomes

X and Y

Life cycle

Sequence of stages in the reproductive history of an organism from conception to its own reproduction

Fertilization and meiosis

Alternate in sexual life cycles

Meiosis

A process that creates haploid gamete cells in sexually reproducing diploid organisms

Result of meiosis

daughter cells with half the number of chromosomes as the parent cell

Interphase

Cell goes through G1, S (DNA is copied), and G2

Prophase 1

• Synapsis: homologous chromosomes pair up and physically connect to each other, forming a tetrad

• Crossing over (recombination) occurs at the chiasmata and DNA is exchanged between the homologous pairs

Metaphase I

Independent orientation: tetrads line up at the metaphase plate

Anaphase I

pairs of homologous chromosomes separate (sister chromatids are still attached)

Telophase I and Cytokinesis

• Nuclei and cytoplasm divide

• Now haploid set of chromosomes in each daughter cell

Prophase II

• No crossing over

• Spindle forms

Metaphase II

• Chromosomes line up at the metaphase plate

• Because of crossing over in meiosis I, the chromatids are unique

Anaphase II

Sister chromatids separate and move towards opposite poles

Telophase II and Cytokinesis

• 4 Haploid cells

• Nuclei reappear

• Each daughter cell is genetically unique

Crossing over

Produces a recombinant chromosomes: they exchange genetic material

Independent assortment of chromosomes

Chromosomes are randomly oriented along the metaphase plate during Metaphase I (maternal or paternal chromosomes)

Random fertilization

Any sperm can fertilize any egg