Exercise 13:Reproduction

Meiosis

Spermatogenesis

Oogenesis

Ovarian cycle

Uterine cycle

Fertilization

Embryonic and fetal development

Meiosis• the process of nuclear division within a cell

that involves in a reduction of chromosome number from diploid to haploid, resulting in gamete formation– Human somatic (body) cells have 46

chromosomes• 22 pairs of autosomes and 2 sex chromosomes

– XX in females, XY in males

– Human gametes (sex cells – eggs and sperm) have 23 chromosomes

• Sperm cells carry either an X or a Y

Meiosis• Of the 46 chromosomes, there are 23

kinds - 2 copies of each kind– One copy from mother, one from father,

coming together when a sperm fertilizes an egg

• The 2 copies are called homologous chromosomes – they carry the same genes (although they might vary in the version – different alleles)– Exception: X and Y, although paired in males,

are not considered homologous

Meiosis

• First: review of mitosis

• Prior to mitosis– Replication of DNA– 46 chromosomes all copied

• Each copy = chromatid• ‘sister’ chromatids held together at centromere

Replicated chromosome

Review of Mitosis

• Stages of mitosis– Prophase: chromosomes condense and

nuclear membrane breaks down; mitotic spindle forms

– Metaphase: chromosomes align at equator– Anaphase: chromosomes divide– Telophase: chromosomes unpack; nuclear

membranes reassemble

Review of Mitosis

Stages of Meiosis

• Prior to meiosis: DNA replication, resulting in 46 chromosomes each with 2 sister chromatids held together at centromeres

• Meiosis occurs in 2 phases:– Meiosis I: Reduction division

• Separation of homologous chromosomes• Chromosome number now 23• Each chromosome still has 2 sister chromatids

– Meiosis II: Mitotic division• Separation of sister chromatids

Meiosis I

• In Prophase I, the homologous chromosomes pair up– This ensures that each daughter cell winds up

with exactly one copy of each of the 23 kinds– The sister chromatids of the 2 chromosomes

make 4 total copies of each DNA strand – a tetrad

• While paired up, they entwine (synapsis) and can break and reform, swapping parts (chiasmata and crossing over)

Stages of Meiosis I

synapsis

chiasma

Stages of Meiosis I

Stages of Meiosis II

Products of Meiosis

• Four daughter cells– Haploid (23 chromosomes)– Each has one copy of each kind of

chromosome– Identical, except for 2 things:

• In males, half X, half Y sex chromosomes• Crossing over results in different combinations of

alleles

Spermatogenesis

Testis: Low Power

• Seminiferous tubules: spermatogenesis• Interstitial cells: produce testosterone

Spermatogenesis

Spermatogenesis

Spermatogenesis

Oogenesis

Ovary

• Ovarian cycle– Follicular stage– Luteal stage

• Follicles secrete estrogens and house egg– Primordial– Primary– Secondary– Mature

Ovarian Cycle

Ovary: Low Power

Ovary: Early stages

Ovary: Mature Follicle

Ovary: Mature Follicle structures

Ovary: Corpus Luteum

Ovary: Corpus Luteum

Uterine cycle

• Corresponds with Ovarian Cycle– Synchronized by ovarian hormones

• Menstrual phase

• Proliferativie phase– Corresponds to ‘diestrous’ in other mammals

• Secretory phase– Corresponds to ‘estrous’ in other mammals

Uterus: Diestrous

Uterus: Diestrous

Uterus: Estrous

Uterus: Estrous

Embryonic and fetal development

• EmbryologyReproduction.ppt