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B1 Revision - You and Your Genes (OCR 21st Century)
- Most cells in your body have a nucleus
- This contains your
genetic material
- Your genetic material is
arranged into
chromosomes.
- There are 23 pairs of chromosomes in the human cell nucleus.
- Each chromosome is one very long molecule of DNA.
- A gene is a short length of a
chromosome.
- Genes control the development of
different characteristics - for
example, hair colour
- Genes can exist in different versions.
- Each version gives a different form
of a characteristic, like blue or brown eyes.
- The different versions of the
same gene are called alleles.
- The different versions of the
same gene are called alleles.
- Each version gives a different form
of a characteristic, like blue or brown eyes.
- Genes are instructions for
making different proteins.
- Proteins are the building blocks
of cells. Having different versions
of proteins means we end up
with different characteristics.
- Structural proteins: part of things like skin, blood, hair, and the cytoplasm in cells.
- Collagen is a structural protein that is found in tendons, bones and cartilage.
- Collagen is a structural protein that is found in tendons, bones and cartilage.
- Functional proteins: Enzymes are
proteins that help with digestion by
breaking down food molecules -
amylase is a digestive enzyme that
breaks down starch to maltose.
- Structural proteins: part of things like skin, blood, hair, and the cytoplasm in cells.
- Proteins are the building blocks
of cells. Having different versions
of proteins means we end up
with different characteristics.
- Genes control the development of
different characteristics - for
example, hair colour
- Each chromosome is one very long molecule of DNA.
- There are 23 pairs of chromosomes in the human cell nucleus.
- Your genetic material is
arranged into
chromosomes.
- This contains your
genetic material
- An organism's genotype describes the genes it's got.
- An organism's genotype is all the genes it has.
- The characteristics an organism
displays are it's phenotype.
- Some characteristics are controlled only by genes.
- This can only be one gene, or quite
often, the characteristic is controlled by
several genes working together: eg, eye
colour.
- This can only be one gene, or quite
often, the characteristic is controlled by
several genes working together: eg, eye
colour.
- However some characteristics
are controlled only by
environmental factors such as
scars. They have nothing to do
with genes.
- Some characteristics are
controlled by genes and the
environment, for example,
weight
- An organism's genotype is all the genes it has.
- Genes and variation
- In body cells (all your cells apart from sex cells),
chromosomes come in pairs.
- One chromosome in every pair has come from each parent.
- The sex cells (sperm and egg) are different
from ordinary body cells because they contain
just 23 single chromosomes - one from each
pair.
- When the
sperm
fertilises the
egg, the 23
chromosomes
from the egg
combine with
the 23 from
the sperm.
- The fertilised egg
now has 23 pairs of
chromosomes, just
like an ordinary
body cell.
- The two chromosomes in a pair
always carry the same genes.
- Each gene is
always found in
the same place on
the two
chromosomes.
- Because the two
chromosomes in a pair
came from different
parents, they might have
different alleles of these
genes. Alleles are different
versions of the same gene.
- Because the two
chromosomes in a pair
came from different
parents, they might have
different alleles of these
genes. Alleles are different
versions of the same gene.
- Each gene is
always found in
the same place on
the two
chromosomes.
- The two chromosomes in a pair
always carry the same genes.
- The fertilised egg
now has 23 pairs of
chromosomes, just
like an ordinary
body cell.
- When the
sperm
fertilises the
egg, the 23
chromosomes
from the egg
combine with
the 23 from
the sperm.
- The sex cells (sperm and egg) are different
from ordinary body cells because they contain
just 23 single chromosomes - one from each
pair.
- One chromosome in every pair has come from each parent.
- Children resemble both parents, but are
identical to neither.
- Half a child's
chromosomes come from
each parent. That means
children get some alleles
from each of their parents,
which is why some children
look like a bit of both of
their parents.
- Every child has a unique combination of
alleles, which is why no two people in the
world are the same - apart from identical
twins.
- Every child has a unique combination of
alleles, which is why no two people in the
world are the same - apart from identical
twins.
- Half a child's
chromosomes come from
each parent. That means
children get some alleles
from each of their parents,
which is why some children
look like a bit of both of
their parents.
- In body cells (all your cells apart from sex cells),
chromosomes come in pairs.
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