biology

genes, DNA, asexual reproduction and sexual reproduction

HideShow resource information

DNA

A gene is a section of DNA that carries the code for a particular protein. Different genes control the development of different characteristics of an organism. Many genes are needed to carry all the genetic information for a whole organism. Chromosomes, found in the cell nucleus, contain many genes.chromosome, showing gene as section of DNA (http://www.bbc.co.uk/schools/gcsebitesize/science/images/cell_chrom_dna.jpg)

The number of genes and chromosomes varies from species to species. For example, cells in human beings have 46 chromosomes that carry about 30,000 genes in each cell; and cells in fruit flies have eight chromosomes that carry about 13,600 genes.

1 of 3

sexual reproduction

Sexual reproduction happens when a male gamete and a female gamete join. This fusion of gametes is called fertilisation. Sexual reproduction allows some of the genetic information from each parent to mix, producing offspring that resemble their parents, but are not identical to them. In this way, sexual reproduction leads to variety in the offspring. Animals and plants can reproduce using sexual reproduction.

In human beings, each gamete contains 23 chromosomes, half the number found in the other cells of the body. When the male and female gamete fuse, the new embryo contains the full 46 chromosomes – half from the father and half from the mother.

the female egg and the male sperm fuse to create a zygote cell which then turns into an embryo. 23 chromosomes from the male and female each make 46 chromosomes in 23 pairs (http://www.bbc.co.uk/schools/gcsebitesize/science/images/9_sex_cells.gif)

2 of 3

asexual reproduction

Asexual reproduction only needs one parent, unlike sexual reproduction, which needs two parents. Since there is only one parent, there is no fusion of gametes and no mixing of genetic information. As a result, the offspring are genetically identical to the parent and to each other. They are clones.

Plants

Asexual reproduction in plants can take a number of forms. Many plants develop underground food storage organs that later develop into the following year’s plants. Potato plants and daffodil plants are examples that do this.

the flower bud is at the centre of the bulb, and a lateral bud is at the side (http://www.bbc.co.uk/schools/gcsebitesize/science/images/bulb_1.gif)remains of leaves are now where the flower bud was, and a new plant has begun to grow from the lateral bud  (http://www.bbc.co.uk/schools/gcsebitesize/science/images/bulb_2.gif)

Some plants produce side branches with plantlets on them. Busy Lizzy does this. Other plants, such as strawberries, produce runners with plantlets on them.

3 of 3

Comments

No comments have yet been made

Similar Biology resources:

See all Biology resources »See all resources »