Sexual reproduction in plants Strawberry plants can also produce new individuals by forming seeds. Plants which reproduce sexually by forming seeds are called flowering plants. This is a type of sexual reproduction because male and female gametes are required to produce seeds. There are some plants, like ferns and mosses, which reproduce sexually without forming seeds but most of the plants that we are familiar with are flowering plants.
Fig. 4 Flowering plants reproduce sexually.
Sexual reproduction in animals Animals are multicellular. While there are a few types of animal that can reproduce asexually, for example greenfly, most species of animal can only reproduce sexually.
Genetic inheritance in sexual reproduction Our genes carry a code which determines many of our characteristics. These genes are found on the chromosomes that are in every cell of our bodies. The chromosomes are found in the nucleus of each cell. Chromosomes contain the genetic instructions for the cells. Chromosomes are usually in pairs. For example, humans have 46 chromosomes (23 pairs), cats have 38 chromosomes (19 pairs) and cabbages have 18 (9 pairs). One of each pair comes from the mother and one from the father. Chromosomes are made of a material called
Cell Nucleus
DNA. Each chromosome contains a long strand of DNA. Sections of the DNA form structures called genes. Genes provide instructions which control the activities of cells. Genes can also influence the way that an entire organism develops. For example, genes have a very strong influence over eye colour. Human sperm and eggs contain 23 chromosomes.
At fertilisation the sperm and egg form a zygote with 46 chromosomes. Each new individual will have chromosomes that came from both of their parents. The offspring from sexual reproduction are similar to their parents but are not genetically identical to either of them.
128 Chromosome
DNA
Fig. 5 The nucleus of each cell contains chromosomes which are made of DNA.
