Sexual Reproduction and Meiosis (10/23-10/25)

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Asexual Reproduction (Hint: 3)

Single individual passes on all of its genes to its progeny

Progeny are genetically identical to the parent- a clone

Genetic differences rarely occur

Sexual Reproduction (Hint: 4)

2 parents give rise to progeny

Each passes on half of its DNA

Progeny have a unique combination of DNA

Greater genetic variation in the resulting population

The Cell Cycle (Hint: 2)

The process by which cells replicate their chromosomes and separate them into 2 new cells

The resulting cells contain the same genetic material as the original

Interphase (Hint: 2)

What happens before mitosis

G1, G0, S, and G2

G1 Phase (Hint: 2)

Gap (growth) phase

Normal cellular function/preparation for S

S Phase (Hint: 3)

Synthesis

DNA replication

Always go through, regardless of type (aka mitosis vs. meiosis)

G2 Phase (Hint: 2)

Gap (growth) phase

Preparation for M

Mitosis/M-Phase (Hint: 2)

Division of the nucleus

Cytokinesis

Cytokinesis

Division of the cytoplasm

G0 Phase (Hint: 2)

Cell cycle exit (arrest)

Cells go about normal function without dividing

Homologous Chromosomes (Hint: 2)

A pair of the same chromosome

Eukaryotic cells generally contain a pair of each chromosome (one maternal and one paternal)

Monad

1 DNA molecule and 1 Chromosome

Dyad

2 Sister chromatids, 2 DNA molecules, and 1 Chromosome

Sister Chromatids

Identical copies of a chromosome that are joined together by a centromere and are formed during DNA replication

Meiosis (Hint: 4)

A form of cell division that produces the haploid gametes

Start with a diploid cell

Involves 2 cell divisions

Known as reductive division

Gametes (Hint: 2)

Sex cells

Sperm and egg

Haploid (Hint: 3)

n

Carry 1 set of chromosomes

Humans: 23 chromosomes

Diploid (Hint: 4)

2n

Carry 2 sets of chromosomes

1 maternal/1 paternal

Humans: 46 chromosomes

Meiosis I (Hint: 2)

Homologous chromosomes are separated into 2 new cells

Reductive division, but still dyad

Meiosis II (Hint: 2)

Sister chromatids are separated into 4 new cells

Very similar to mitosis (separate dyad)

Prophase I

Chromosomes condense and nuclear envelope disintegrates

Synapsis (Hint: 4)

Homologous chromosomes pair with each other

Unique (only happens here)

Paternal and maternal chromosomes pair up

Called a bivalent or tetrad

Crossing Over (Hint: 4)

Occurs late in prophase I

Only happens here

Forms a structure called the chiasmata

Chiasmata (Hint: 2)

Specialized chromatin structures that link homologous chromosomes together until anaphase

Where crossing over occurs

Metaphase I (Hint: 2)

Homologous chromosomes line up on metaphase plate

Homologous chromosomes attach to meiotic spindle

Meiotic Spindle

A microtubule-based structure that separates chromosomes during meisosis

Cohesin In Mitosis (Hint: 3)

Holds the sister chromatids together

Cleaved by separase at anaphase

Allows chromatids to separate

Cohesin in Meiosis (Hint: 3)

Cohesins on the arms hold homologs together at the chiasmata

Protected by shugoshin (not cleaved by separase)

By Meiosis II, shugoshin destroyed and separase cuts cohesins and separates sister chromatids

Anaphase I

Homologous chromosomes are separated

Separase

Cuts cohesion and allows the sister chromatids to separate

Shugoshin (Hint: 2)

Protects the cohesins at the centromere during anaphase I

Degraded in anaphase II and separase can cleave the cohesins and the sister chromatids separate

Telophase I (Hint: 3)

Cell divides to form 2 cells and nuclei reform

Number of chromosomes per cell = 23 (humans)

Number of DNA molecules per cell = 46 (humans)

Interkinesis

The period between meiosis I and meiosis II

Prophase II

Chromosomes condense and nuclear envelope disintegrates

Metaphase II

Individual chromosomes line up on the equatorial plane

Equatorial Plane

The imaginary plane that runs directly through the center of a dividing cell, where all the chromosomes line up during the metaphase stage of mitosis or meiosis

Anaphase II

Sister chromatids separate and are pulled to the poles

Telophase II (Hint: 3)

Cells divide to form 4 haploid gametes

Number of chromosomes per cell = 23 (human)

Number of DNA molecules per cell = 23 (human)

Recombination (Hint: 2)

How crossing over happens

The process that makes 2 chromatids from a bivalent pair swap portions of DNA

Random Separation of Homologous Chromosomes (Hint: 4)

2^{haploid number of chromosomes}

During meiosis I the homologous pairs of chromosomes line up randomly and are separated

The sister chromatids are separated in meiosis II

The resulting gametes will have a random assortment of chromosomes

Independent Assortment

A genetic principle that describes how genes separate independently during the development of reproductive cells

Gametogenesis

Production of the haploid gametes

Fertilization

Fusion of the sperm and egg to form a diploid zygote

Zygote

A fertilized egg cell that contains the genetic information for a new individual organism

Spermatogenesis (Hint: 2)

The generation of sperm cells

Occurs in the testes

Spermatogonium (Hint: 2)

Starting cell

Can produce more spermatogonia by mitosis

Primary Spermatocyte

Enters meiosis I

Secondary spermatocyte

After meiosis I

Mature sperm cells

Developed from spermatids

Oogenesis (Hint: 2)

The generation of an egg cell

Occurs in the ovaries

Oogonium (Hint: 2)

Starting cell

Can produce more oogonia by mitosis

Primary oocyte (Hint: 4)

Enters meiosis I

Occurs in utero

Cell remains arrested in prophase I until puberty

Cell division is unequal- produces a secondary oocyte and a polar body

Secondary Oocyte

Produced in meiosis I by a primary oocyte because the cell division is unequal

Arrests at metaphase II until the egg is fertilized

Ovum (Hint: 2)

Mature cell that is created

Unequal division produces only 1 ovum and 1 polar body

List the 3 advantages of sexual reproduction

High genetic variability

Facilitates adaptation

“Speeds” up evolution

List the 3 disadvantages of sexual reproduction

Energy costly

Courtship is time/resource consuming

Usually sacrifices the fitness of one sex to the other

List the 3 advantages of asexual reproduction

Save energy

Courtship is a non-issue

Greatest increase in fitness for each individual

List the 3 disadvantages of asexual reproduction

Low genetic variability

Adaptation to environment is difficult

Slows down evolution

Describe Meiosis in its entirety

List the similarities and differences between mitosis and meiosis

What are the 2 sources of genetic variation during meiosis?

Crossing Over

Random Separation of Homologous Chromosomes