Reproduction

1
Reproduction Development I. Selective
Forces -- all of evolution is based on
reproduction -- to persist through evolutionary
time, animals must put copies of their genes into
the next generation -- for sexual reproduction,
fertilized egg must develop into surviving
offspring
2
Reproduction II. Asexual vs. Sexual
Reproduction A. Asexual reproduction --
only one parent -- no reproductive organs --
no meiotically produced gametes (sex cells) no
fertilization or zygote formation --
offspring are genetically identical to parents
(clones)
3
Reproduction II. Asexual vs. Sexual
Reproduction A. Asexual reproduction 1.
advantages -- pass on 100 of genome to
each offspring -- all individuals can
produce offspring directly -- can occur
rapidly rapid exploitation of resources
-- saves energy and resources (no gonads or
gametes, no finding mates, no
courtship, no STDs, no males) 2.
disadvantages -- no genetic variability in
offspring (except for random mutations) --
limited ability to respond to changing
environment
4
Reproduction II. Asexual vs. Sexual
Reproduction B. Sexual reproduction --
usually involves two parents -- reproductive
organs -- haploid gametes produced by meiosis
fertilization ? diploid zygote -- offspring are
genetically unique 1. disadvantages --
pass only 50 of genome to each offspring
-- energy expended for gonads and gametes
-- production of males (many fail to mate)
-- is complicated occurs more slowly --
requires finding mates, courtship, --
STDs 2. advantages -- increased
genetic variability in offspring --
ability to respond to changing environment, esp.
biotic environment
5
Reproduction II. Asexual vs. Sexual
Reproduction C. Combination of Asexual and
Sexual reproduction -- common in lower
invertebrates (Porifera Cnidaria
Platyhelminthes) -- asexual reproduction often
used for rapid build up in numbers to exploit
available resources -- sexual reproduction
often occurs when environment is changing (e.g.
seasonally) -- both methods may occur
simultaneously -- may alternate with different
stages of the life cycle
6
Asexual and Sexual Reproduction ex Obelia
(Class Hydrozoa)
asexual colony of polyps
sexual medusa
7
Asexual and Sexual Reproduction ex Fasciola
(sheep liver fluke)
miracidium
egg
Sexual adult in sheep liver
asexual redia in snail
metacercaria encysted on vegetation
Asexually produced cercaria leave snail
8
Reproduction III. Mechanisms of Asexual
Reproduction A. Fission animal divides by
mitosis
Binary fission Paramecium
Multiple fission Plasmodium
9
Reproduction III. Mechanisms of Asexual
Reproduction B. Budding new individual arises
from outgrowth of parent
10
Reproduction III. Mechanisms of Asexual
Reproduction C. Gemmulation -- formation of
new individual from aggregation of asexual cells
encased in resistant capsule ( gemmule)
11
Reproduction III. Mechanisms of Asexual
Reproduction D. Fragmentation -- formation
of new individual from fragments of parent
12
Reproduction IV. Mechanisms of Sexual
Reproduction A. Conjugation exchange of
genetic material without gender
13
Reproduction IV. Mechanisms of Sexual
Reproduction B. Separate sexes (dioecious)
14
Reproduction IV. Mechanisms of Sexual
Reproduction C. Hermaphroditism
(monoecious) -- common in sessile and burrowing
invertebrates -- common in endoparasites --
can be self-fertilizing, but usually cross
fertilize
15
Reproduction IV. Mechanisms of Sexual
Reproduction C. Hermaphroditism
(monoecious) sequential hermaphroditism
change sex during lifetime 1. protandry
male first female second oysters 2.
protogyny female first male second bluehead
wrasse
16
Reproduction IV. Mechanisms of Sexual
Reproduction D. Parthenogenesis development
of unfertilized egg 1. ameiotic
parthenogenesis -- egg formed by mitosis
(usually diploid) -- offspring genetically
identical to parent 2. meiotic
parthenogenesis -- haploid egg formed by
meiosis a. egg activated by sperm egg
and sperm dont fuse b. egg does not
require sperm for activation
Whiptail lizard
Aphid
Cladoceran
ameitoic
meitoic
ameitoic
17
Reproduction V. Gametogenesis formation of
gametes (mammals) A. Spermatogensis
formation of sperm -- occurs in seminiferous
tubules of testes
18
A. Spermatogensis formation of sperm

• spermatogonia (germ cells diploid) divide
• by mitosis
• each daughter spermatogonium enlarges
• and becomes a primary spermatocyte
• (diploid)
• undergoes first meiotic division ?
• secondary spermatocyte (haploid)
• undergo second meiotic division ?
• spermatids (haploid) each primary
• spermtocyte gives rise to 4 spermatids
• spermatids are nourished by Sertoli cell
• ? spermatozoa

19

• Reproduction
• V. Gametogenesis formation of gametes
  (mammals)
• B. Oogensis
• 1. formation of ova (singlular ovum)
• oogonia (germ cells diploid) divide by mitosis
• increase in size ? primary oocytes happens in
  early fetal development, then arrest

20

• Reproduction
• V. Gametogenesis formation of gametes
  (mammals)
• B. Oogensis
• 1. formation of ovum
• at puberty, primary oocyte finishes 1st meiotic
  division unequal division of cytoplasm results
  in secondary oocyte and first polar body

21

• Reproduction
• V. Gametogenesis formation of gametes
  (mammals)
• B. Oogensis
• 1. formation of ovum
• secondary oocyte released from follicle,
  initiates 2nd meiotic division ? 2nd meiotic
  division completed only when secondary oocyte
  penetrated by sperm ? ovum (haploid) ? zygote

22
Reproduction V. Gametogenesis formation of
gametes (mammals) B. Oogensis 2. hormonal
regulation review notes on menstrual cycle
23
Reproduction V. Gametogenesis formation of
gametes (mammals) B. Oogensis 3. yolk (
vitellin) -- produced by vitellaria (yolk
glands) many invertebrates -- supplied
by follicle cells insects vertebrates
24
Reproduction VI. Reproductive patterns A.
Oviparous eggs laid in the environment
25
Reproduction VI. Reproductive patterns B.
Ovoviviparous -- eggs retained in body --
embryo nourished by yolk from egg itself, not
directly from mothers body -- egg
hatches in body live birth
26
Reproduction VI. Reproductive patterns B.
Viviparous -- egg develops in oviduct or
uterus of female -- embryo derives
nourishment directly from mother
27
Reproduction VII. Sex Determination A.
Chromosomal some insects, most fish,
amphibians, most reptiles, birds, mammals
-- in human XX female XY
male Humans 1. Y chromosome contains
SRY (sex-determining region Y male determining
gene) -- organizes developing gonad
into testes 2. X chromosome contains SRVX
(sex-reversing X) -- promotes ovary
formation
28
Reproduction VII. Sex Determination B.
Haplodiploidy Class Insecta, Order
Hymenoptera -- fertilized egg (diploid) ?
female -- unfertilized egg (haploid) ?
male (meiotic parthenogensis)
In honey bees -- csd locus (complementary
sex determining locus) -- highly polymorphic
(18 alleles) -- if heterozygous (diploid) ?
female -- if hemizygous (haploid) ? male
29
Reproduction VII. Sex Determination C.
Environmentally determined 1. temperature
(alligators many turtles some lizards)
-- low nest temperature ? female --
high nest temperature ? male 2. social
environment -- many fish are
hermaphroditic change sex with social
situation -- Crepidula fornicata
30

• Development
• VIII. Genetic Regulation of Development
• -- pattern formation determination of body
  axes
• Anteroposterior (front-to-rear)
• Left-to-right
• Dorsoventral (back-to-front)
• -- development of limbs and organs
• -- controlled by gene products called morphogens
  that establish gradients and determine
  developmental patterns

31

• Reproduction
• VIII. Genetic Regulation of Development
• A. Pattern formation axes
• 1. Insects
• bicoid (gene) ? mRNA ? bicoid (protein
  morphogen)
• binds with other genes initiates cascade of
  genetic events that produces anteroposterior
  gradient
• short gastrulation ? ventral structures (nerve
  cord)
• 2. Vertebrates
• Pitx2 ? determines left-right gradient is a
  homologue for bicoid\
• chrodin ? contributes to early embryological
  events and development of dorsal nerve cord in
  vertebrates homologue of short gastrulation

32

• Reproduction
• VIII. Genetic Regulation of Development
• A. Pattern formation metammerism
• -- segmentation occurs along
  anteroposterior axis
• -- initially all segments are identical
  later activation of different genes cause
  segments to form different structures
• 1. segmentation genes
• Determine the number and orientation of segments
• Regulate expression of other genes, such that
  they are active only in certain segments

33

• Reproduction
• VIII. Genetic Regulation of Development
• A. Pattern formation metammerism
• 2. homeotic genes
• Regulated by segmentation genes
• Determine what structures/organs develop within
  each segment
• ex Antennapedia of insects
• -- controls development of legs
• -- typically active only in thorax
• -- if activated in head segment
• of larvae, adult will have legs
• instead of antennae

34

• Reproduction
• VIII. Genetic Regulation of Development
• A. Pattern formation metammerism
• 2. homeotic genes
• Contain a homeobox
• --180 DNA base pairs
• --produces part of the
• protein that attaches to DNA
• of other genes and alters their
• Expression
• -- evolutionarily highly conserved
• Hox genes
• Occur as clusters on one
• or a few chromosomes
• and determine the location
• where structures will develop
• along the anteroposterior axis

35

• Reproduction
• VIII. Genetic Regulation of Development
• B. Limb and organ formation
• -- controlled by Hox and other homeobox
  genes
• -- determine formation of limbs, brain
  regions, etc. by producing morphogen gradients
• Ex formation of limb bud in vertebrates
  (chick)
• Development induced by FGF (fibroblast growth
  factor)
• At anterior end ? wing at posterior end ? leg
• FGF is a morphogen forms proximal-distal
  gradient digits develop where FGF is highest
  (distal end) other genes determine dorso-ventral
  axis

36
Reproduction VIII. Genetic Regulation of
Development C. Evolutionary Developmental
Biology -- virtually all animals have
homologues for homeotic and Hox genes --
several genes that control ventral development
in protostomes control dorsal development in
dueterostomes (ex short gastrulation and
chrodin) -- genetic control of dorso-ventral
patterning is similar, except one is upside down
compared to the other -- Therefore, major
evolutionary changes may occur, not slowly
through the gradual accumulation of small
mutations in many genes, but rapidly through a
few mutations in developmental genes.