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Asexual Reproduction
• involves mitosis
• results in offspring that are genetically identical to the parent
Sexual Reproduction
• offspring receive one set of genes from each parent
• results in genetic variety
gamete a special reproductive cell designed to transfer or receive chromosomes
meiosis the process of special cell divisions that produces cells with only one set of an organism’s chromosomes
1 2
3 4
1
2
3 4
1 2
3
4
1 2
3 4
1
2
3 4
1 2
3
4 1 2
3 4
1 2
3 4
1 2
3 4
1 2 3 4
gametes
haploid having only one of each type of chromosome normally found in the cells of an organism
• Gametes are haploid cells that transfer or receive chromosomes.
• Meiosis is the process that produces haploid gametes.
Animal Number of
Chromosomes Haploid
Gametes
fruit fly 4 pairs (8) 4
cat 19 pairs (38) 19
horse 32 pairs (64) 32
Plant Number of
Chromosomes Haploid
Gametes
pea 7 pairs (14) 7
water-melon 11 pairs (22) 11
Gametes
• eggs = female gametes
• ova, ovum
• sperm = male gametes
Testes • the male reproductive
organs that produce sperm
Ovaries • the female reproductive
organs that produce eggs (ova)
fertilization the union of two haploid gametes to form a zygote
zygote—the cell that forms from the union of two gametes
diploid having two of each type of chromosome in the cells of an organism
egg sperm
fertilization
zygote
meiosis meiosis
female male
Fertilization • the union of two haploid
gametes to form a diploid zygote
• two types of fertilization
• external
• internal
= outside
= inside
external fertilization occurs as the egg and sperm unite outside of the parents’ bodies
internal fertilization occurs as the egg and sperm unite inside of the female parent’s body
External
• fish
• frogs
Internal
• sharks
• reptiles
• birds
• mammals
External Fertilization
• occurs in the water
• involves jelly-like eggs
External Fertilization
• involves thousands of gametes
• not all of the eggs are fertilized
• even fertilized eggs may not survive
spawning the laying of eggs in water by aquatic animals
milt the sperm-containing fluid released by males during external fertilization
fry newly hatched fish
external • outside
• in the water
• jelly-like covering
internal • inside
• on land
• hard shell
• low survival rate
• many eggs
• little care before birth
• higher survival rate
• few eggs
• more care before birth
external internal
Internal Fertilization
• animals that lay eggs
• animals that give birth to live young
Egg • a female gamete
• a zygote with a shell around it
Egg-Laying Animals
• birds
• reptiles
• snakes/turtles ➜ leathery shells
• alligators ➜ hard shells
➜ thick, hard shells
• sharks and rays
• monotremes
➜ tough cases
➜ leathery shells
Egg-Laying Animals
yolk the stored food that will nourish the growing embryo
nucleus
yolk
Albumin • the egg white
• a liquid environment that contains water and proteins plus some vitamins and minerals
albumin
shell lining shell
Pores • important for the exchange
of oxygen and carbon dioxide between the egg and the environment
• permeable to water and odors
incubation the maintaining of the conditions necessary to hatch an egg
• Birds sit on their eggs.
• Snakes and turtles dig holes for their eggs.
• Alligators and crocodiles cover their eggs.
Incubation Methods
embryology the study of how a young animal develops, either before hatching or before birth
Placental Animals
uterus • the special structure in
which an embryo develops in a mother that gives live birth
placenta • attached to the wall of the
uterus
• the structure where the mother’s blood vessels and the embryo’s blood vessels come in close contact
umbilical cord • a ropelike structure that
carries the blood vessels from the embryo’s heart to the placenta and back
placenta
embryo
umbilical cord
amnion
uterus (womb)
the fluid-filled sac that surrounds the embryo
Incubation • the period of time the
embryo is within the egg
Gestation • the period of time the
embryo is within the uterus
Gestation Periods of Various Animals
• rabbit—30 days
• dog—63 days
• cat—65 days
• tiger—107 days
• hippo—237 days
• cow—280 days
• dolphin—390 days
• elephant—645 days
Gestation Periods of Various Animals