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Animal Reproduction

Chapter 46.

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Sexual & asexual reproduction Asexual

production of offspring with genes from oneindividual

Sexual formation of gametes & fertilization genetic recombination & variation

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Parthenogenesis Development of an unfertilized egg

honey bees drones = males produced through

parthenogenesis → haploid workers & queens = females produced from

fertilized eggs → diploid

queen worker drone

Honey bee eggs hatch regardless of whether the are fertilized. Thefemale bees--queens & workers--develop from fertilized eggs thatcontain 32 chromosomes. These 32 chromosomes consist of twosets of 16, one set from each parent. Hence female bees are said tobe diploid in origin. The males (drones) develop from unfertilized eggwhich contain only one set of 16 chromosomes from their mother.Drones are thus haploid in origin This reproduction by thedevelopment of unfertilized eggs is called parthenogenesisDrones develop by parthenogenesis from unfertilized eggs that thequeen produces by withholding sperm from the eggs laid in largedrone cells. Drones lack stings and the structures needed for pollencollection; in the autumn they are ejected by the colony to starve,unless the colony is queenless. New drones are produced in thespring for mating.Both queens and workers are produced from fertilized eggs. Queenlarvae are reared in special peanut-shaped cells and fed more of thepharyngeal gland secretions of the nurse bees (bee milk or royaljelly) than the worker larvae are. The precise mechanism for thiscaste differentiation is still uncertain. Although workers are similar inappearance and behavior to other female bees, they lack thestructures for mating. When no queen is present to inhibit thedevelopment of their ovaries, however, workers eventually begin to layeggs that develop into drones.

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Differentworlds…

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Hermaphrodites

flat worm

earth worms mating

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Fertilization External

usually aquatic animals Internal

usually terrestrial animals

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Development External

in water (eggs) on land (amniotic eggs) oviparous: lay eggs ovoviparous: live births from eggs

sharks & some snakes

Internal placenta viviparous:

live placental birth

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Adaptive advantages? What is the adaptive value of each

type of sexual reproduction number of eggs? level of parental of care habitat?

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Human reproduction Male reproductive system

over 100 million per day!

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Male reproductive system

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Testosterone regulated by

FSH & LH frompituitary

Hormonecontrol oftestes

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Spermatogenesis

Meiosisproducesgametes inseminiferoustubules

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spermatocytes

seminiferoustubule

sperm

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Female reproductive system

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Female reproductive system

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Sex hormones: female Estrogen

ovaries stimulates uterine lining growth 2° female sex characteristics regulated by FSH & LH from pituitary

Progesterone ovaries stimulates uterine lining growth regulated by FSH & LH from pituitary

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Hormoneregulationof femalecycleWhat happens in:pituitary glandovaryuterus

Menopause46-54ovaries lose

response toFSH & LH

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Oogenesis

state of eggwhen fertilized

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Ovarian cycle

Stages ofdevelopmentin ovary

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Fertilization

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Early development

blastocyst

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Placenta Materials exchange across membranes

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Fetal developmentamniotic sac

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BirthHormoneinduction

positive feedback

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Birth