Reproduction in Animals

Reproduction

the process by which living organisms produce young ones of their own kind.

Important of Reproduction

ensures continuity of species
prevents extinction of species
plays important role in evolution → creates variations in organisms through genetic fusions.

Types of Reproduction

asexual
sexual

Asexual Reproduction

no fusion of gametes
no change in no. of chromosomes
only 1 parent
occurs in both unicellular or multicellular organisms
offspring inherits full set of parent’s genes (it is exact copy) → because only 1 parent’s genes are being inherited

Advantages:

fast process
only single parent involved
daughter cells are exact copies

Disadvantages:

If parent cell has a disease, it gets transferred to daughter cells. This could disrupt whole species.

Types of Asexual Reproduction

binary fission
budding

Binary Fission

asexual reproduction
in prokaryotes and few unicellular eukaryotes - amoeba, paramecium, euglena
parent cell divides into 2 new daughter cells
each daughter cell receives one copy of parent DNA
“fission” means division

Budding

asexual
new organism is developed from a small part of parent body
baby remains attached as it grows further
it is separated when it gets matured & leaves scar tissues behind
hydra, yeast, jellyfish

Sexual Reproduction

two parents
fusion of male-female gametes forms zygote
genes from both parents inherited & baby is not a total copy

Advantages:

genetic variation
disease is less likely to affect every single person in the species
diversity

Disadvantages:

slow process

Unisexual animals: male and female reproductive systems are present in different individuals

Hermaphrodite/Bisexual organisms: invertebrates (leeches, earthworms) have both male and female reproductive.

Fertilisation: process of fusion of male and female gametes + nuclei of sperm fuse with nuclei of the egg to form a single nucleus

Types of Fertilisation

1. Internal fertilisation

→ fertilisation occurs inside female +mostly in land (cows, dogs, cats, humans)

Advantages:

more probability of successful fertilization
low chances of dehydration of gametes
young one is protected against predators SO chances of survival are increased.

Disadvantages:

less number of offspring produced at a given time

2. External fertilisation

→ fertilisation occurs outside female body + mostly in water (fish, frogs)

Advantages:

produces a larger number of offsprings

Disadvantages:

A large quantity of gametes is wasted and left unfertilized.
young isn’t protected against environmental hazards and predators.
Eggs and sperms may not come in contact.

Gametes: special reproductive cells in males and females (male = sperm, female = ovum/egg)

Male Reproductive System:

located in the pelvic region
include a pair of testes, two sperm ducts and a penis
Sperm
single cell, consisting of the usual cell components + very small
has a head, a middle piece and a tail which is the longest part + propels it for swimming and aids in penetrating the egg.
The testes are present outside the abdominal cavity in a pouch called scrotum

PARTS

Testes:

produces sperms
present outside abdominal cavity in a pouch called scrotum
made up of coiled tubes called seminiferous tubules
endocrine glands

male reaches puberty → pituitary gland stimulates testes to produce male sex hormone testosterone

Sperm duct/Vas deferens:

narrow tube
transport sperms from testes to penis
fluids are secreted by different glands [the seminal vesicles, the prostate gland, and the bulbourethral glands (Cowper's glands)]. + mix with sperms to form semen

Penis:

transfers semen to vagina

Urethra:

tube within the penis through which semen and urine go out

Scrotum:

thick-skinned sac that surrounds and protects the testes.
maintains optimum temperature required for sperms

Epididymis:

a long coiled tube
transports and stores sperms

Female Reproductive System:

Ovaries:

located in the abdominal cavity
produces female ova
Either of the two ovaries releases 1 mature ovum in a cycle ranging from every 21 to 35 days

Oviduct or fallopian tubes:

oviduct has finger-like projections called fimbriae that capture mature egg & transport it to uterus
oviduct is tube leading to the uterus
oviduct transports the fertilised ovum (zygote) to the uterus.

Uterus:

ovum is fertilised by the sperm → the zygote travels to uterus → embeds itself in uterine wall, which thickens (cuz of increased blood supply) → zygote develops.

development of zygote takes place here + it expands to adjust the baby.

Cervix: narrow, neck-like passage + connects to the vagina.
Vagina:

muscular tube
“birth canal” bc it allows passage of the baby from the uterus.

Fertilisation

The fertilised egg is called a zygote.

ovum is released every month by an ovary during the process of ovulation → ovum moves into the oviduct → male transfers semen in vagina → The sperms travel through cervix into uterus and reach the oviduct → one of the sperms fuses with egg to form a zygote

fertilisation occurs in the oviduct

fertilised egg moves down the oviduct and reaches the uterus → The zygote divides further and gets implanted into the wall of uterus → The zygote develops to form an embryo → embryo develops different body parts and is called a foetus → growth of foetus is complete? mother gives birth

Development of Embryo

Repeated division in the zygote forms a ball of cells
cells form groups to create different organs of the body ==== EMBRYO
embryo to 16 cells == ==MORULA== ===
morula becomes hollow == ==BLASTULA== === implants in uterus
GASTRULATION ==== development of organs
PLACENTA ==== embryo receives nourishment from its mother's blood through placenta + it is a special tissue attached to uterus & connected to embryo through umbilical cord
growing embryo floats in an amniotic fluid, a clear yellow fluid enclosed in an amniotic sac + serves as a cushion, provides nourishment and protects the growing embryo from injury
The stage of the embryo in which all body parts can be recognised is known as the FOETUS

→ PARTURATION : baby delivering

→ GESTATION PERIOD : when baby is inside mom +++ longest is elephant (95 weeks)

In vitro fertilisation [IVF]

egg and the sperm are made to fuse in lab
when embryo in the multicellular stage its implanted into uterus
babies born through this are called test tube babies.

Sex determination

sex is determined by father's sperm.
male has X and Y sex chromosomes & female has X and X.
egg will have only X
if sperm has X and ova fuses with it, then baby will be a girl (XX)
if sperm has Y baby will be a boy (XY).

Oviparous and viviparous animals

The animals that lay eggs === oviparous animals (snakes, frogs and fish)
The animals that give birth === viviparous animals (cows, horses, dogs)

Reproduction in hens

internal fertilisation occurs in a hen BUT it don’t give birth
internal fertilisation → fertilised ovum undergoes divisions → moves down oviduct → protective layers are formed including a white hard shell → hen lays the egg → embryo inside hard shell takes 3 weeks to develop into a chick
hen sits on the eggs to provide sufficient warmth (incubation).
When chick is developed, it bursts open hard shell.

Metamorphosis

in some animals, newly-hatched organisms do not resemble their parents + they undergo a series of changes called metamorphosis after birth.
featuresin these young ones are different from adults of their species.
eg frog butterfly

Frogs

frogspawn → fertilised egg → embryo → larva/tadpole → tadpole w/ 2 legs → tadpole w/ 4 legs → froglet w/ short tail → adult frog
process of metamorphosis controlled by the hormone thyroxine.
tadpole/larva can survive only in water BUT adult frogs can survive both in water and on land.

Butterfly

fertilised egg → larva (caterpillar) → pupa → adult butterfly
metamorphosis controlled by two hormones: ecdysone hormone and juvenile hormone.