Meiosis

Meiosis

prduces gametes (sperm and egg cells) for sexual reproduction.

• done through cell division that produces haploid gametes from diploid cells

chromosome (n)

number of unique chromosomes in 1 set

what set of chromosome do humans have?

diploid (2n)

somatic cells

body cells (usually diploid)

gametes cells

sex cells (sperm, eggs)

homologous chromosomes

similar chromosome (one from each parent), same genes, different alleles

sister chromatids

identical copies of one chromosome made during DNA replication

asexual reproduction

one parent, offspring get copies of each parent’s genome, less genetic variation, less costly

sexual reproduction

usually 2 parents, offspring have different combonations, greater genetic variation, require more energy/resources

sexual reproduction components

fusion of 2 haploid gametes (fertilization)

produce genetically distinct offspring

increases genetic variation

importance of genetic variation

help population adapt to environment

help organisms respond to evolving parasites, pathogen (red queen hypothesis)

reduce buildup of harmaful mutations (muller’s ratchet)

meiosis I

separates homologous chromosomes

Reduces diploid to haploid

Crossing-over occurs in Prophase I

Meiosis II

Separates sister chromatids

Maintains haploid number

Crossing-over (Genetic Recombination)

• Happens during Prophase I.

• Homologous chromosomes pair up (synapsis).

• Nonsister chromatids exchange DNA.

• Creates new combinations of alleles.

• Chiasma (plural: chiasmata): Visible point where crossing-over occurs.

Independent Assortment

• Happens because homologous chromosome pairs can align in different orientations during Metaphase I.

• Maternal and paternal chromosomes are distributed randomly into gametes.

• Creates different chromosome combinations.

Mitosis

Growth, healing damaged tissues, replacing old cells, and asexual reproduction.

Synapsis

Homologous chromosomes pair up

whats crossing over?

The result of the exchange of homologous portions of nonsister chromatids is new combinations of genetic material (genetic recombination).

Genetic variation occurs when chromosomes are shuffled in fertilization and what other process?

meiosis

Homologous pairs of chromosomes are lined up independently of other such pairs during _____.

metaphase I

Crossing over, resulting in an increase in genetic variation, occurs between _____.

nonsister chromatids of homologous chromosomes

In human gamete production there is an average of _____ crossover events per chromosome pair.

2-3

What number and types of chromosomes are found in a human somatic cell?

44 autosomes and 2 sex chromosomes

In alternation of generations, what is the diploid stage of a plant that follows fertilization called?

sporophyte

The parent cell just before prophase I is __ploid

diploid

The daughter cells at the end of meiosis II are __ploid

haploid

Each daughter cell at the end of meiosis I has

of the DNA present in the parent cell just before prophase I

one half

Each daughter cell at the end of meiosis II has __ of the DNA present in the parent cell just before prophase I

one quarter