Reproduction

Question 1

What is reproduction

Answer 1

Process by which animals increase in number
Animals grow and develop until they reach maturity

Question 2

Asexual reproduction

Answer 2

Effectively cloning of tissues to produce a novel individual

Replication of cells takes place but these are clones of the original cells and these get organised into a smaller replica of the original animal, e.g. budding in hydra

Question 3

Fragmentation

Answer 3

involves development of a new animal from a fragment of an original – annelids, flatworms and echinoderms

Question 4

Which organisms reproduce by binary fission

Answer 4

Cnidarians (jellyfish, sea anemones, corals and hydroids) and tunicates (sea squirts)

Question 5

Parthenogenesis

Answer 5

asexual reproduction where unfertilised eggs develop naturally into adults without input from males (obligate parthogenesis)

Observed in hymenopterans, aphids, water fleas and some lizards
Egg cells are produced by mitosis so are diploid rather than haploid

Question 6

Cyclical parthenogenesis

Answer 6

life-cycle that alternates between asexual and sexual reproduction

advantage of cyclical parthenogenesis is that the population can be quickly increased by asexual reproduction so as to exploit prevailing conditions, such as a good food supply.

Question 7

Facultative parthenogenesis

Answer 7

arises when there is low frequency or absence of males for a long period for a species that normally reproduces sexually
Observed in crayfish and all vertebrate groups, except mammals

Triggers for spontaneous development are unclear – may involve environmental ‘shocks’

Question 8

Sexual reproduction

Answer 8

involves the fusion of two specialised haploid cells – gametes produced by meiosis in male and female animals
Male gametes are spermatozoa produced in a testis
Female gametes are ova produced in an ovary

Question 9

External fertilisation

Answer 9

Aquatic animals often release their gametes into the water (spawning) and fertilisation is external
This is a risky strategy so spawning is often synchronised to maximise the chances of fertilisation
Synchronised spawning can be triggered by environmental factors such as temperature, photoperiod, lunar periodicity or tidal cycles

Question 10

What triggers synchronised spawning

Answer 10

environmental factors such as temperature, photoperiod, lunar periodicity or tidal cycles

Question 11

Internal fertilisation

Answer 11

involves the introduction of the spermatozoa into the female’s body so that the zygote is formed in the oviduct
Internal fertilisation is obligate for those animals that retain their offspring as they develop

Question 12

Oviparous

Answer 12

animals release their eggs that have little or no embryonic development
Fertilisation can be external or internal
Embryonic development takes place outside of the female’s body

Question 13

Ovo-viviparity

Answer 13

involves the retention of large fertilised eggs in the female’s body and embryonic development takes place internally and is fuelled by the contents of the egg.

Question 14

Viviparity

Answer 14

involves the retention of small fertilised eggs in the female’s body and embryonic development takes place internally and is fuelled by an inter-change of nutrients from the maternal blood

Question 15

Semelparity

Answer 15

once a lifetime reproduction
Salmon spawn once before death
High risk if environmental conditions are not stable
High risk if life span of species is < 1 year

Question 16

Iteroparous

Answer 16

more than one-time investment in reproduction before death
Increases reproductive success in variable environment
Can be a single, extended mating season or multiple mating seasons

Question 17

Male reproductive anatomy

Answer 17

based around paired testes and vas deferens that connects to the urethra at the prostate gland, which then exits through an intromittent phallus
Therefore, mammals have moved from a common cloaca because there is a separate anus

Question 18

Spermatogenesis

Answer 18

takes place in the testes
In particular within the seminiferous tubules of the testes
Essentially sperm start their life as germ cells on the outer rim of the seminiferous tubule.
They move ‘inwards’ towards the lumen as they develop

Question 19

Female reproductive anatomy

Answer 19

based on paired ovaries that are connected to a uterus via Fallopian tubes
Uterus is the oviduct and is a fluid-filled muscular tube that is partially ciliated

The uterus is linked to the outside via a cervix and vagina
Ovulation releases the ovum into the body cavity and cilia waft it to the opening of the infundibulum and into the Fallopian tube

Question 20

Oogenesis

Answer 20

formation of the haploid ovum (female sex cell) within the ovaries within a follicle

Question 21

Vitellogenin

Answer 21

In many taxa yolk deposition is based around the production of vitellogenin by the liver. Vitellogenin is commonly found in vertebrates (except mammals) and it provides amino acids, lipids and ions. In the amphibian egg (shown) vitellogenin provides almost all of the protein and all of the lipid in the yolk.

The amount of yolk is crucial – small amounts only provide enough energy to have a brief period of embryonic development before the larva has to be free-living (fish and amphibians) or the embryo is provided with an external source of nutrition (mammals).

Question 22

Vitellogenesis in reptiles and birds

Answer 22

Yolk is the most abundant material stored in the ooplasm
In eggs with a macroscopic ovum, e.g. birds, there is an enlargement of the oocyte by deposition of yolk in large amounts

Oviparous vertebrates synthesise the lipoprotein VLDL in maternal liver and transported via the blood
VLDL:
60-70% of solids in fowl egg yolk
30% in Crocodylus porosus yolk
Absent in lizard eggs (?)

Question 23

Copulation

Answer 23

effectively the end result of courtship behaviour that typically bonds the male and female. This courtship bond can last a lifetime or be transitory. For those species with internal fertilisation copulation is essential to introduce the spermatozoa into the female’s reproductive tract.

Question 24

Fertilisation

Answer 24

process involves the binding of the sperm head to the surface of the ovum and the breakdown of the ovum plasmalemma by the acrosome reaction

Question 25

Stages of embryogenesis

Answer 25

Zygote
Cleavage
Blastoderm
Gastrulation
Segmentation
Organogenesis

Question 26

Holoblastic cleavage

Answer 26

entire egg divides during cleavage
small egg with little yolk
Daughter cells get progressively smaller

Question 27

Meroblastic cleavage

Answer 27

partial cleavage
Large eggs with large egg reserve
Larger cells at vegetal pole
Cells that divide are concentrated at the animal pole
Cytoplasm forms a “polar cap” at the site of nucleus following fertilisation – this begins to divide

Question 28

Cleavage in amphibians

Answer 28

Anuran cleavage pattern
- asymmetrical cleavage — more like the holoblastic pattern

Question 29

Metamorphosis

Answer 29

A biological process by which an animal physically develops after birth or hatching, involving a conspicuous and relatively abrupt change in the animal’s body structure through cell growth and differentiation.
Generally, illustrated in two quite disparate groups – insects and amphibians.

Question 30

Insect metamorphosis

Answer 30

Grasshoppers, bugs and cockroaches, lay eggs that hatch into neonate that has some resemblance to the adult. Over a series of moults the nymphs increasingly resemble the adult (imago)
Butterflies, flies, beetles, lay eggs that hatch into neonate that bear little resemblance to the adult. The larva undergoes moult that largely keeps the same form but the final moult is into a pupa. In this stage tissues are reorganised into an adult that is very different to the larval form

Question 31

Genetic sex determination

Answer 31

Associated with heteromorphic (sex) chromosomes
XX/XY – male = heteromorphic sex
ZZ/ZW – female = heteromorphic sex

Question 32

Temperature dependent sex determination in reptiles

Answer 32

Gender of the offspring is not determined by heteromorphic chromosomes
Zygote at conception has no fixed gender and the incubation environment determines the sex of an individual

Question 33

Types of sex determination

Answer 33

Genetic
Temperature dependent

Question 34

Can you get high temperature induced female crocodiles?

Answer 34

low and high temperature females and males at intermediate temperatures

Question 35

What are females sex cells called?

Answer 35

Ova

Question 36

What is the difference between semelparity and iteroparity?

Answer 36

Semelparity- once a lifetime reproduction
Iteroparity- more than once

Question 37

Do birds lay fertilised eggs that undergo holoblastic cleavage?

Answer 37

No- meroblastic cleavage

Question 38

What is gastrulation?

Answer 38

proliferation of cells and their migration into the blastocoel to form a multi-layered embryo

Question 39

Eutherian mammal ova

Answer 39

very small and contain almost no yolky cytoplasm so development is impossible unless the developing embryo implants into the uterine wall and so can gain additional nutrients

Question 40

What is vitellogenin

Answer 40

commonly found in vertebrates (except mammals) and it provides amino acids, lipids and ions

Question 41

What type of ova undergo holoblastic cleavage

Answer 41

Small cells