asexual reproduction - wca life sciencewcalifescience.weebly.com/.../lifesciencechapter20ppt.pdf ·...

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