Reproduction
Invertabrates – How do they “Do It”• Hydra – Budding - asexual• Earthworm – hemaphroditic and exchange
sperm with each other – the fertilized egg capsule gets dropped off in the soil
• Grasshopper – separate sexes -Female grasshoppers deposit fertilized eggs in batches in the ground, the female uses four horn-like appendages at the tip of the abdomen, and twists her body and forces her ovipositor into the ground - metamorphosis
Vocab
• Regeneration – lobster claw or sea star arm grows back
• Parthenogenesis – egg cells can become an organism without sperm – ie bees
• Haploid – n – one set of chromosomes (unfertelized egg)
• Diploid – 2n - two sets of chromosomes
Males
Side View
Male Reproductive system
• Major functions• Produces sperm• Produces semen – the fluid vehicle that acts
as nourishment for sperm as they make their way through the female reproductive system
• Produces Testosterone – male hormone for secondary sex characteristics and tells the body to make testosterone
Feedback Mechanism
Female Reproductive system
Side view
Meiosis
• How we get SEX CELLS• Gametogenesis• Two division stages – Meiosis I and Meiosis II• Meiosis I is the reduction phase – Meiosis II is
the division stage (similar to mitosis)
Gametogenesis
Meiosis I
• Interphase I – DNA replicates, sister chromatids are joined by a centromere
• Prophase I – Chromosomes line up in homologous pairs in a process called synapsis forming a tetrad – crossing over occurs during this stage.
• Metaphase I – Tetrads move to the “equator” or metaphase plate – attach to spindle fibers
• Anaphase I – homologous chromosomes separate (keeping chromotids intact)
• Telophase I – events occur in the reverse order from the events in prophase I…spindle broken down two new cells are formed, chromosome number reduced in half
Non disjunction
• During Meiosis I – an abnormality that can happen is that one pair of tetrads doesn’t separate so both chromosomes go to one side while the other side doesn’t get a copy of that chromosome at all – this is the cause of down’s syndrome.
• non disjunction animation
Meiosis II
• Meiosis II can occur immediately (in males) can be put on hold (in females)
• Names are the same – prophase II, metaphase II, anaphase II, telophase II
• Similar to mitosis the chromosomes line up in the middle (NOT tetrads) – chromotids separate to opposite poles – (only DNA doesn’t get replicated BEFORE this stage!)
Vocab
• Meiosis – making sex cells• Gametogenesis – making sex cells– Gamete = sex cell
• Spermatogenesis – making sperm– Sperm = male sex cell
• Oogenesis – making egg– Ova = female sex cell
The menstrual cycle
• The functioning of the reproductive system is dependent on the cyclical fluctuation of hormone levels that repeat regularly every 28 days.
Feedback Mechanism
If an egg is fertilized
• Must be fertilized in the oviduct• 24 – 48 hours after ovulation• Pregnancy occurs• Fertilized egg travels down oviduct and
implants into uterus• Most development occurs within the first
trimester (month 1 – 3)• The last trimester is mainly for growth
Genetic Variation
• If a plant has seven pairs of chromosomes – and there are two different ways it can line up at the equator…how many sperm are possible?
• 2n = 27 = 128 combinations of sperm – also then 128 combinations of egg how many possible zygote
• 128 x 128 = 16,384 possible outcome
Human variation
• We have 23 chromosome – 2n = 223 = over 8 million combinations
• 223 x 223 = 70 trillion different zygotes are possible.
In the Beginning
• Gastrulation
• More human Development
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