B1 Revision Notes

Here are some of my notes, pretty much covering the topic B1- You and Your Genes:)

hope this helps you, feel free to ask me anything about it and tell me anything that i may have missed out.

Enjoy :)

HideShow resource information
  • Created by: Cleo
  • Created on: 23-04-13 19:07
Preview of B1 Revision Notes

First 524 words of the document:

Cleona Aston B1 REVISION
Genes are found in our chromosomes, which parents pass on to offspring in their sex cells in
reproduction. Different versions of the same gene are called alleles, and these can determine
features like eye colour, and the inheritance of disorders such as cystic fibrosis.
The nucleus controls the activities of a cell. The instructions for how an organism develops are found
in the nuclei of its cells. Chromosomes are structures found in the nucleus of most cells. They consist
of long strands of a substance called DNA.
A section of DNA that has the genetic code for making a particular protein is called a gene. The
proteins can either be: structural proteins such as the ones found in muscles and hair- Used for
growth and repair. Functional Proteins such as enzymes. These speed up chemical reactions (such as
Individuals differ in all sorts of ways, even when they are offspring of the same parents. These
differences are called variation. Most characteristics, such as height, are determined by several
genes working together. They are also influenced by environmental factors.
When an egg and sperm cell come together, the now fertilised egg contains 23 pairs of
chromosomes. Sex chromosomes are responsible for certain genetic traits.
Human body cells each contain 23 pairs of chromosomes. Parents pass on their genes to their
offspring in their sex cells.
Female sex cells are called egg cells, or ova
Male sex cells are called sperm.
A pair of chromosomes carries the same genes in the same place, on each chromosome within the
pair. However, there are different versions of a gene called alleles. These alleles may be the same
(homozygous) on each pair of chromosomes, or different (heterozygous), for example, to give blue
eyes or brown eyes.
Sex cells only contain one chromosome from each pair. When an egg cell and sperm cell join
together, the fertilised egg cell contains 23 pairs of chromosomes. One chromosome in each pair
comes from the mother, the other from the father.
Which chromosome we get from each pair is completely random. This means different children in the
same family will each get a different combination. This is why children in the same family look a little
like each other and a little like each parent, but are not identical to them.
Females have the combination of XX
Males have the combination of XY
When sex cells form, the pairs of sex chromosomes (XX and XY) are separated. Remember that
females carry XX, males XY. This means that all normal egg cells produced by a human ovary have an X
chromosome and half the sperm carry an X chromosome, and half a Y.
So a human baby's gender is determined by the sperm that fertilises the egg cell. The baby will be a
girl if it carries an X chromosome. It will be a boy if the fertilising sperm carries a Y chromosome.

Other pages in this set

Page 2

Preview of page 2

Here's a taster:

Cleona Aston B1 REVISION
Different versions of the same gene are called alleles. They can be either recessive or dominant.
Genetic testing can determine whether a person is carrying the alleles that cause genetic disorders.
A recessive allele only shows if the individual has two copies of it. For example, the allele for blue
eyes is recessive. You need two copies of this allele to have blue eyes.
A dominant allele always shows, even if the individual only has one copy of it.…read more

Page 3

Preview of page 3

Here's a taster:

Cleona Aston B1 REVISION
There are two types of stem cells:
Adult stem cells - these are unspecialised cells that can develop into many (but not all) types
of cells
Embryonic stem cells - these are unspecialised cells that can develop into any type of cell.
During the development of an embryo, most of the cells become specialised (cells with modifications
to structure according to the task they have to perform). They cannot later change to become a
different type of cell.…read more

Page 4

Preview of page 4

Here's a taster:

Cleona Aston B1 REVISION
Summarise different views that might be held. For instance, some people think that destroying
human embryos this way is murder. Others believe it is furthering our knowledge of science for the
benefit of everyone
Identify and develop arguments based on the idea that the right decision is the one that has the best
outcome for the majority of the people involved.…read more


No comments have yet been made

Similar Science resources:

See all Science resources »See all resources »