IB 140 L2

Semiconservative replication

Before dividing, cells must copy their DNA

Gene

Section of DNA that has the instructions for making one protein

Chromosome

One molecule of DNA wrapped around proteins, containing hundreds of genes

Chromosomes before cell division

Chromosomes are uncondensed

Sister chromatids

Duplicated chromosomes held together at the centromere

DNA replication

Process by which chromosomes are duplicated

The Cell Cycle

A series of events the cell undergoes throughout its life

G1 Phase

First period of growth and activity in the cell cycle

S Phase

Synthesis of DNA occurs (the amount of DNA within the cell doubles)

G2 Phase

Second period of growth and activity in the cell cycle

M Phase

Mitosis and cytokinesis occur; division of the cell nucleus and cytoplasm

Stages of Mitosis

1) Prophase, 2) Metaphase, 3) Anaphase, 4) Telophase

Meiosis

Specialized form of cell division in gonads to produce gametes

Chromosomes in somatic cells

22 pairs of autosomes, one pair of sex chromosomes

Haploid cells (gametes)

Cells that contain half the number of chromosomes (one member from each pair)

Diploid cells (somatic cells)

Cells that contain a full set of chromosomes (two copies of each chromosome)

Meiosis I

The first division in meiosis where homologous chromosomes are separated

Meiosis II

The second division in meiosis where sister chromatids are separated

Interphase

DNA is duplicated before meiosis begins

Prophase I (Meiosis I)

Homologous chromosomes pair up and may exchange segments (crossing over)

Metaphase I (Meiosis I)

Homologous chromosomes align on the central plane

Anaphase I (Meiosis I)

Homologous chromosomes are pulled apart to opposite poles of the cell

Telophase I (Meiosis I)

Homologous chromosomes gather at the poles, resulting in two haploid cells

Prophase II (Meiosis II)

New spindle forms to attach to chromosome clusters

Metaphase II (Meiosis II)

Chromosomes align along the central plane, spindle fibers attach to centromeres

Anaphase II (Meiosis II)

Sister chromatids are pulled apart to opposite poles

Telophase II (Meiosis II)

Nuclear envelope reforms around the four sets of daughter chromosomes

Gametogenesis

The process of forming gametes from diploid cells of the germ line

Spermatogenesis

The process of forming sperm cells by meiosis

Oogenesis

The process of forming an ovum (egg) by meiosis in ovaries

Meiosis vs Mitosis

Meiosis halves chromosomes, Mitosis produces two identical daughter cells

Genes

Segments of DNA that code for proteins

Alleles

Alternate versions of a gene inherited from each parent

Human Life Cycle

Adults produce gametes, fertilize, and undergo mitosis and differentiation to develop into an adult

Mutations

Mistakes in copying DNA that produce different versions of genes, resulting in diversity

Segregation (Meiosis)

One member of each homologous pair goes into a gamete

Independent Assortment

Randomly determines which member of a pair of chromosomes goes into a gamete

Random Fertilization

Produces diversity through the combination of gametes (64 trillion possibilities)

Parthenogenesis

Asexual reproduction where offspring are produced from an unfertilized egg (e.g., whiptail species)

Pluripotency in Germ Cells

Epigenetic slate is wiped clean in germ cells

Sexual Reproduction Strategies

Spawning/brooding vs. internal fertilization: different strategies in reproduction

Reproductive Strategies

Specialized membrane systems and placentae in female reproductive tract for reproduction