Meiosis and Gamete Formation Gametes Gametes sex cells

Meiosis and Gamete Formation

Gametes • Gametes =sex cells • Gametes form from germline cells via meiosis – Male gamete =sperm – Female gamete =oocyte (egg) • A male and a female gamete come together to form a new individual – Somatic (non-gamete) cells have 46 chromosomes (diploid) – Gametes have 23 chromosomes (haploid) • ½ + ½ = 1 whole

Human Karyotype

Remember… A chromosome Replicated chromosome (2 sister chromatids connected at centromere) Figure 3. 2 Homologous pair of chromosomes Homologous pair of replicated chromosomes

Meiosis • Produces gametes (1 n or haploid) from somatic germline cells (2 n or diploid) from mother from father child too much! meiosis reduces genetic content Figure 3. 1

Meiosis overview • Produces gametes (1 n or haploid) from somatic germline cells (2 n or diploid) • Mixes up genetic information – Diversity is important! • Consists of 2 divisions – Meiosis II Meiosis I (reduction division) Meiosis II (equational division) Diploid Figure 3. 1 Haploid

Meiosis I • • • Interphase (CHROMOSOMES REPLICATE) Prophase I Metaphase I Anaphase I Telophase I

Interphase • Precedes Meiosis I • Cell grows and organelles are made • CHROMOSOMES ARE REPLICATED Homologous pair of chromosomes Homologous pair of replicated chromosomes

Prophase I • • • Pro =forward, forth Chromosomes condense Nuclear envelope breaks down – Membrane surrounding the nucleus • Centrioles move to opposite poles • Spindle fibers grow • Chromosomes synapse and crossing over occurs Q 4 Prophase

Crossing Over (Recombination) Q 7 • Replicated chromosomes pair up with their homologs – i. e. chromosome from mom and chromosome from dad get together • Genetic information is exchanged – Like shuffling a deck of cards and re-dealing Homologous pair of replicated chromosomes Synapsis New combinations of genetic info

Metaphase I Q 4 Metaphase • Meta =after, with • Homologous chromosome pairs line up at the midline – Line up is random so that INDEPENDENT ASSORTMENT takes place • Spindle attaches to chromosomes at the centromere – The centromere is where the sister chromatids are attached

Independent Assortment • Another way in which meiosis increases diversity • Chromosomes line up at the midline in a random way Q 3

Anaphase I • Ana =against • Homologous pairs split • Homologs are pulled to opposite poles by the shortening of spindle fibers Q 4 Anaphase

Telophase I • Telo =completion of a goal • Spindle breaks down • Nuclear envelope forms in each of the new cells Q 4 Telophase

Summary of Meiosis I INTERPHASE Prophase I (early) (diploid) Prophase I (late) (diploid) Metaphase I (diploid) Anaphase I (diploid) Telophase I (diploid)

Meiosis II • • • Interphase –Chromosomes DO NOT replicate! Prophase II Metaphase II Anaphase II Telophase II

Prophase II • Nuclear envelope breaks down – Membrane surrounding the nucleus • Centrioles move to opposite poles • Spindle fibers grow Q 4 PII

Metaphase II • Chromosomes line up at the midline • Spindle attaches to chromosomes at the centromere – The centromere is where the sister chromatids are attached Q 4 MII

Anaphase II • Centromeres split • Sister chromatids are pulled to opposite poles by the shortening of spindle fibers Q 4 AII

Telophase II • Spindle breaks down • Nuclear envelope forms in each of the new cells • Chromosomes decondense Q 4 TII

Summary of Meiosis II Q 2 Entire Overview Prophase II (haploid) Metaphase II (haploid) Anaphase II (haploid) Telophase II (haploid) Four nonidentical haploid daughter cells

Homologous chromosomes in germline cells Synapsis Square Dance Homologous pair of replicated chromosomes New combinations of genetic info

Males and Females are Different! Girls have a “flower” and boys have a “noodle”

Male Reproductive System • Gametes are made in the gonads – Sperm are made in the testes – Sperm are made and stored outside of the body • 200 -600 million sperm are released with each ejaculation!!! • Trillions of sperm are made in a lifetime vas deferens bladder urethra seminal vesicle prostate bulbourethral gland epididymis testis

Spermatogenesis Entire process starts at puberty Q 1

Female Reproductive System • Gametes are made in the gonads – Oocytes are made in the ovaries • A girl is born with just one million oocytes per ovary • Only 400 eggs will be uterine tube ovary ovulated between uterus cervix puberty and menopause vagina

Oogenesis Before birth Arrested in Prophase I After puberty (each month) Arrested in Metaphase II Upon fertilization

Polar Bodies • Three polar bodies are generated due to the developing egg hogging all of the cytoplasm – Polar bodies usually degenerate – If fertilized by a sperm, a blighted ovum develops and results in miscarriage