Sexual reproduction facts for kids

Sexual reproduction is how most animals and plants make new living things. Some tiny living things called protists and fungi also reproduce this way. Living things that reproduce sexually have two different types: male and female. New living things (offspring) are made when a male cell called a sperm joins with a female cell called an ovum. This joining is called fertilization. Many steps are involved in this process.

How Cells Help with Reproduction

Most cells in animals and plants have two sets of chromosomes. We call these cells diploid. But when special cells for reproduction, called gametes (or sex cells), are made, they only have one set of chromosomes. These cells are called haploid.

Gametes are made through a special type of cell division called meiosis. Meiosis makes sure that the new living things are different from their parents and from each other. This happens in two main ways:

Mixing Chromosomes

When gametes are made, the two sets of chromosomes become one set. For each pair of chromosomes, it's completely random which one goes into a gamete. Since the tiny parts of genes (called alleles) on each chromosome are not always the same, this mixing creates lots of differences between gametes. This idea was first described by Gregor Mendel.

Swapping Parts

During meiosis, parts of chromosomes can swap places. This is called crossing over. It makes the chromosomes even more unique and creates new combinations of genes.

Because of this mixing and swapping, it's almost certain that no two offspring from the same mother and father will be exactly alike. The only exception is identical twins, who start from the same fertilized egg.

Good and Bad Sides of Sexual Reproduction

Sexual reproduction has both good points and not-so-good points, especially when compared to asexual reproduction (making copies of yourself without a partner).

• Good points: Having more differences among offspring helps them survive. If a dangerous sickness spreads, a greater variety means some offspring might be strong enough to live through it. This increases the chance that some of the family will survive.

• Bad points: You need two parents. If a population reproduced sexually, it would make only half as many offspring as a population reproducing asexually, assuming the same total number of eggs.

Important Terms to Know

Here are some important words you might hear when learning about sexual reproduction:

• Gonads are special body parts where gametes are made. In males, these are the testes. In females, they are the ovaries.

• Gametes are the special sex cells made in the gonads. This process is called gametogenesis. The male gamete is the sperm, and the female gamete is the ovum.
  • Spermatogenesis: This is the process that makes haploid sperm cells.
  • Oogenesis: This is the process that makes haploid egg cells.

• Hermaphrodite: This is a living thing that has both male and female sex organs. Examples include earthworms, snails, and hydra.

• Fertilization: This happens when a sperm cell enters and joins with an ovum. The single cell that forms after this joining is called a zygote.

• Cleavage: This is an early stage in the development of a new living thing (an embryo). The number of cells quickly increases through cell division.
  • 1. Morula: A solid ball of cells.
  • 2. Blastula: A hollow ball of cells with fluid inside.
  • 3. Gastrulation: The blastula keeps growing, and cells keep dividing. Cells on one side begin to move inward, forming a new structure. This eventually leads to an embryo with three main layers of cells.

• Ectoderm: This outer layer of cells develops into the nervous system, which includes the brain, spinal cord, and nerves. It also forms the lining of the mouth, anus, nostrils, and the outer layer of skin (epidermis), including sweat glands, hair, and nails.

• Mesoderm: This middle layer of cells develops into bones, muscles, the reproductive system, kidneys, blood, blood vessels, and the inner layer of skin.

• Endoderm: This inner layer of cells develops into the lining of the digestive system, respiratory system, liver, pancreas, and bladder.

• Growth and differentiation: This is when unspecialized cells in the embryo change into specialized cells. These specialized cells then form different tissues and organs in the body.

Related pages

• Asexual reproduction
• Gender
• Sex

Images for kids

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  An Australian emperor dragonfly laying eggs, with a male nearby.

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  Puffballs releasing their spores.

See also

In Spanish: Reproducción sexual para niños