Chapter 11 Meiosis and Sexual Reproduction

Autosome Diploid 2n

Everything but sex chromosomes

Represented as homologous pairs

1 Mom, 1 Dad

Sex Chromosomes Haploid 2n

Sex determining chromosomes

xx Female

XY Male

Non-homologous

Ploidy

A measure of the number of sets of chromosomes

Diploid (2n)

Humans have 23 pairs of chromosomes or 46 total

2n=46

Haploid (n)

Single set of chromosomes

found in gametes

n=23

Meiosis

Cell division found in sexually reproducing organisms , results in production of gametes

1: Reduce diplod-haploid

: Divide from duplicated to unduplicated

Meiosis Results

4 haploid daughter cells with half the number of chromosomes non genetically identical

Meiosis Purpose

Reduces chromosome number by half

prevents chromosome doubling each generating

DNA replication Timing

Before meiosis 1 not before meiosis 2

Meiosis 1

Reduction phase

Sister Chromatids remain attached

2 haploid daughter cells form

Meiosis 2

Results in 4 genetically unique daughter cells

Asexual reproduction

Ospring genetically identical to parent

Budding, Binary Fission, Cloning,vegatative propagation, Parthenogenesis

Asexual reproduction Advantages

Population can rapidly increase when needed

Only 1 parent needed

Time and energy efficient

no mate needed

Faster than sexual reproduction

Disadvantage of Asexual reproduction

No genetic variation

Sexual reproduction Advantages

allows for genetic variation, allowing the next generation to do more than its parents, increasing survival.

Sexual reproduction

Reproduction arising from the fusion of two gametes

Unique combinations of genes inherited from each parent

Diploid Dominant life cycle

Humans and most animals use this to maintain species characteristic chromosome numberwhere the diploid stage is the most prominent phase.

Gametes

Only haploid cells are gametes

meiosis creates how many gametes?

Humans: 2n=46 > n=23

How many diploid cells does fertilization create?

2 haploid cells from a diploid zygote through mitosis

sperm (n=23) + egg (n=23) = zygote 2n= 46

What produces gametes?

Via meiosis by the gonads (testes in males, ovaries in females).

2n>n

Gametes

Not genetically identical

offspring inherits half the traits from each parents mailing variability within a population

Recombinant Chromosomes

Crossing over during meiosis 1, prophase 1

individual chromosomes that carry genes from two different parents : genetic variation

Chiasmata

Visible structures at cross over points within recombinant chromosomes

Who is responsible for most of the genetic variation

The behavior of chromosomes during meiosis and fertilization

Independent Assortment of Chromosomes

Meiosis 1 maternal and paternal homologs are sorted into daughter cells independently of each other :genetic variation

Random Fertilization

Any of the genetically unique sperm from the Male may fertilize the genetically unique egg from the female.70 trillion combinations

Eggs

fewer and more energetically expensive

1 million at birth

Sperm

Smaller and abundant, energetically cheap

250,000,000 sperm/mL

Spermatogenesis

generation of sperm cells

Spermatogonia

Diploid cells embedded into walls of seminiferous tubes within the testes become spermatocyte 2n

Oogenesis

generation of egg cells

Oogonium

2n cell in the outer cortex of ovary becomes primary oocyte

Mitosis

genetically identical cells with the same number of chromosomes

DISCO PUG

Divisions

Independent Assortments

Synapsis

Crossing Over

Outcome

Ploidy

Use

Genetics