B1 Understanding Ourselves

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B1 Understanding Ourselves

• Text in Green is relatively easy, everybody needs
  to know this information to get a satisfactory
  grade.
• Text in blue is a bit more difficult everybody
  who wants to get a good grade at foundation level
  needs to know this information.
• Text in red only needs to be learnt if you are
  doing the higher tier
• If you click on the pink text it will take you to
  a relevant web page or to the definition of that
  particular term.

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G Gene Control
B1 Understanding Ourselves
H Who Am I?
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G1 Gene Control Chromosomes

• Chromosomes are found within the nucleus of the
  cell.

Most chromosomes are arranged in matching pairs.
Humans have 46 chromosomes in each body cell,
Other species will have a different number of
chromosomes in their cells. (Bananas have 22!)
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Gene Control questions 1

• Chromosomes
• Page 40 Qs 1-4.

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G2 - DNA and Genes

• Chromosomes are made of a molecule called DNA.
• DNA contains a set of coded instructions called
  the genetic code.
• The genetic code controls the activities of a
  cell and therefore controls some of the
  characteristics of the organism.
• Sections of DNA that control a particular
  characteristic are called genes e.g. the section
  of DNA that controls eye colour is called the
  Gene for Eye Colour.

• http//www.pbs.org/wgbh/nova/genome/dna.html
• - relationship between the nucleus, chromosomes
  and DNA

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G3 Genes on a Chromosome
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Gene Control questions 2

• DNA
• Page 41 Qs 5-7.

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G4 - Bases and the Genetic Code

• DNA molecules contain chemicals called bases and
  that there are four different bases.
• The 4 bases are A, C, G and T
• Each gene contains a different sequence of bases.
  This is what makes one gene different to another.
  The different sequence of bases is what makes the
  genetic code.

• http//news.bbc.co.uk/1/shared/spl/hi/sci_nat/03/d
  na50/dna_in_3d/html/default.stm - 3D DNA
• http//www.pwc.k12.nf.ca/wadey/biotech/dna1.swf -
  structure of DNA.

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G5 - How Genes Work

• Every body cell has a complete set of genes. Only
  the genes that are needed are switched on in
  any particular cell e.g. the gene controlling eye
  colour is only switched on in the cells within
  the iris.

• The genetic code is actually a set of
  instructions on how to make different proteins.
• Each gene tells our cells to make a particular
  protein.
• The colour of our iris depends on the amount and
  type of protein found there.
• Many of these proteins are enzymes which control
  chemical reactions.
• In this way the DNA controls how the cell
  functions.

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Gene Control questions 3

• How genes work
• Page 41 Qs 8-10.

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G6 - Reproduction
There are two types of reproduction

• Sexual Reproduction
• Is the joining of the sperm and the egg.
• Needs two parents
• A new, unique individual is produced.
• Half of the genes in the new individual come from
  the mother, the other half come from the father.

• Asexual Reproduction
• Does not involve sperm or egg.
• Needs only one parent.
• A clone is produced
• All the genes come from one parent

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G7 - Gametes or sex cells

• For sexual reproduction to work chromosomes from
  the mother in the egg, and chromosomes from the
  father in the sperm, must join.
• Question If the sperm and egg each had the
  normal number of chromosomes, how many
  chromosomes would the babys first cell contain?
• Answer 464692, does this fit in with what we
  know about human cells?
• When gametes are made in the testes or ovary the
  pairs of chromosomes are separated into different
  cells.
• This means that each gamete only has half the
  normal chromosome number (23).
• When the gametes meet during fertilisation the 23
  chromosomes in the egg pair up with the 23
  chromosomes in the sperm.
• 23 23 46

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G8 - Sexual Reproduction
The human egg and sperm cell (GAMETES) contain
23 chromosomes each.
When fertilisation happens the gametes fuse
together to make a single cell. This cell has 46
chromosomes (23 pairs).
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G9 - Pairs of Genes

• Pairs of chromosomes have the same set of genes
  as each other.

Gene for blood group
Gene for blood group
Blood Group A
Blood Group B
However the pairs may contain different forms of
the same gene, (alleles). The eye colour gene on
one chromosome may code for blue eyes, but the
other chromosome in the pair may code for blue
eyes. What eye colour you have is decided by
which gene is dominant.
Gene for Eye colour
Gene for Eye colour
Blue Eyes
Brown Eyes
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G10 - Separating Chromosomes

• When gametes are made the pairs of chromosomes a
  separated.
• One chromosome from each pair ends up in each
  gamete.
• Question 1 How many chromosomes in a human sperm
  cell?
• Answer 46/223
• Question 2 if a cow has 60 chromosomes in its
  body cells how many chromosomes are in a cow egg?
• Answer 60/230

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G11 - Different Gametes
Blue Eyes

• If you had the following chromosomes in a body
  cell

Brown Eyes

• How many gametes with different combinations of
  chromosomes could you make?

Clue Remember one chromosome from each pair must
be in each gamete
Blonde hair
Brown hair
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G12 Variation in Gametes
Brown Eyes
Blue Eyes
Brown hair
Brown hair
Blue Eyes
Brown Eyes
Blonde hair
Blonde hair
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G13 - Lots of Variation

• Four variations!
• Gamete 1 brown hair, brown eyes
• Gamete 2 blonde hair, blue eyes
• Gamete 3brown hair, blue eyes
• Gamete 4 blonde hair, brown eyes
• What if you had three pairs of chromosomes?
• What if you had 23 pairs of chromosomes?
• Question Why are brothers and sisters different
  from each other when they should both have half
  their fathers genes and half their mothers?
• Answer The gametes that joined together to make
  them, contained different combinations of
  chromosomes and therefore genes, giving different
  characteristics.

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G14 - Variation
The mixing of parents genes and the different
combinations of genes found in the gametes are
the reasons why sexual reproduction leads to
variation even between brothers and sisters!
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H Who Am I? Inherited and Environmental
Characteristics
Some characteristics may be affected by inherited
and environmental factors
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H2 Inherited, Environmental or Both?
Place each of the following characteristics in a
Venn diagram to show whether they are controlled
by the Environment, Inheritance or
both. Scars Eye colour Height Nose
shape Language Earlobe shape Body
mass Intelligence
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H3 Inherited, Environmental or Both?
There is an ongoing debate over the importance of
genetic and environmental factors. Especially
with characteristics like intelligence, sporting
ability and health.
Environmental
Inherited
Both
Eye colour
Scars
Height
Environmental!
Genetic!
Body Mass
Language
Nose shape
Intelligence
Earlobe shape
Can you think of one more characteristic to go
into each category?
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H4 Inherited Disorders

• Some times disorders or diseases can be
  inherited.
• These disorders are caused by faulty genes.
• Inherited disorders include

Red-green colour blindness
Sickle cell anaemia
Cystic Fibrosis
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H5 - Mutations

• Sometimes changes to genes occur. These changes
  are called mutations.
• Mutations are usually harmful but sometimes they
  may be beneficial.
• Mutations can be caused by radiation, chemicals
  or they can just happen spontaneously.
• Mutations are another factor, (along with gamete
  formation and fertilisation), that cause genetic
  variation.
• Mutations change the sequence of the bases on
  DNA.
• This alters or stops the production of the
  protein that the gene coded for.

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H6 Sex Inheritance
From this picture of someone's chromosomes can
you tell if the person is male or
female? Remember look at the 23rd pair of
chromosomes!

• Whether you are male or female is controlled by
  the 23rd pair of chromosomes.
• In females this pair is identical, both
  chromosomes are X chromosomes.
• Therefore the 23rd pair in females is XX
• In males the 23rd pair has one X chromosome and
  one smaller Y chromosome.
• The 23rd pair in males is XY
• The 23rd pair of chromosomes are called Sex
  Chromosomes

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H7 Sperm and Eggs

• Remember when gametes are made chromosomes are
  separated.

When eggs are produced the 23rd pair separate and
each egg that is produced gains an X
chromosome. Therefore all eggs contain the X
chromosome
When sperm are produced the 23rd pair
separate. Half the sperm end up with a X
chromosome and half with the Y chromosome.
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H8 Boy or girl?
XY
XX
Body cells
Equal (50) chance of being a boy or a girl!
X
X
Gametes
Fertilisation, (F.O.I.L.)
XX
XX
XY
XY
Babies cells
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H9 - Another method
Place the possible gametes in a grid called a
Punnett square
Mother
Father
XX
XX
XY
XY
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H10 - Dominant and Recessive
Characteristics that come sometimes be hidden
even if their genes are present on the
chromosomes - are called recessive
characteristics. Characteristics that always show
up when their genes are present on the
chromosomes are called dominant
characteristics. Question A brown eyed cat and a
blue eyed cat mate and have 11 kittens. 8 of the
kittens have brown eyes and 3 have blue eyes.
Which characteristic do you think is dominant,
blue or brown eyes? Answer Brown eyes! Because a
dominant characteristic is more likely to show
itself than a recessive one.
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H11 - Eye colour
In eye colour the brown eye allele is dominant,
so give it the capital letter B, and the blue eye
allele is recessive, so we give it the small
letter b. We use the term Homozygous if both
alleles are the same And Heterozygous if the
alleles are different
Homozygous brown-eyed parent
Heterozygous brown-eyed parent
Blue-eyed parent
What would the offspring have?
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H12 - Eye Colour Diagrams
X
X
Parents
Gametes
(FOIL)
Offspring
All offspring have brown eyes
25 chance of blue eyes
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H13 - Eye Colour Diagrams
Equal (50) chance of being either brown eyed or
blue eyed.
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H14 - Punnett Squares
Example 3 A heterozygous brown-eyed father and a
blue-eyed mother
Father
Mother
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H15 - Example questions
1) In mice, white fur is dominant. What type of
offspring would you expect from a cross between a
heterozygous individual and one with grey fur?
Explain your answer with a genetic diagram.
2) A homozygous long-tailed cat is crossed with
a homozygous short-tailed cat and produces a
litter of 9 long-tailed kittens. Show the
probable offspring which would be produced if two
of these kittens were mated and describe the
characteristics of the offspring (hint work out
the kittens genes first).
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H16 - Inherited diseases
Inherited disorders are caused by faulty
alleles. Most of the alleles that cause disease
are recessive
E.g. Cystic fibrosis a disease that causes
thick and sticky mucus to coat the lungs, gut and
pancreas. Its caused by recessive
alleles Question 1 Two parents both with the
genes Nn, (N normal, n cystic fibrosis) have
a history of cystic fibrosis in their family and
they are worried about passing the disease on to
their children. What advice would you give
them? Question 2 two parents with the genes Nn
and nn desperately want to have a baby. What do
you think they should do?
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Glossary - allele

• A different form of the same gene.
• The eye colour gene has a number of different
  alleles
• Blue
• Brown
• Green
• Hazel

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Glossary - base

• Part of DNA. The sequence of the four different
  bases, (A, C, G, T), within the DNA molecule make
  up the genetic code.

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Glossary - Characteristic

• A feature of a living thing
• e.g eye colour, language spoken, blood group,
  whether a person suffers from cystic fibrosis or
  not.
• Different characteristics may be inherited,
  caused by the environment or influenced by both
  genes and the environment.

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Glossary Chromosome

• Tightly coiled sections of DNA that occur in
  pairs (except for the male sex chromosomes).
• There are 46 chromosomes in human body cells.
• The chromosome pairs separate when sex cells are
  made giving 23 chromosomes in sperms and eggs.

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Glossary clone

• A genetically identical individual, (I.e. has the
  same genes)
• Normally produced via asexual reproduction

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Glossary DNA

• Molecule that carries the genetic code, and
  controls the production of proteins and therefore
  the workings of a cell and an organisms
  characteristics.

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Glossary Dominant

• A gene that always shows itself when present on a
  chromosome.
• Dominant alleles show themselves in heterozygous
  individuals.

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Glossary environmental characteristic

• A characteristic that is caused by our
  surroundings e.g. scars, spoken language, sun tan.

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Glossary - fertilisation

• Joining of a sperm and egg cell, (Gametes).

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Glossary Gamete

• A sex cell the male gamete is the sperm cell
  and the female gamete the egg cell, (or ovum)

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Glossary Gene

• A section of DNA the controls a particular
  characteristic. The section of DNA that controls
  what colour your eyes are is called the gene for
  eye colour

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Glossary Genetic Code

• DNA contains a set of coded instructions called
  the genetic code.
• The genetic code controls the activities of a
  cell and therefore controls some of the
  characteristics of the organism.
• The genetic code consists of the sequence of
  bases on the DNA molecule

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Glossary heterozygous

• When both alleles of a gene are different.
• A persons cells may contain both the brown eyed
  gene and the blue eyed gene (Bb).
• That person is said to be heterozygous for eye
  colour.

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Glossary homozygous

• When both alleles of a gene are the same.
• A persons cells may contain two brown eyed genes
  (BB)
• or two blue eyed genes (bb).
• In both cases that person is said to be
  homozygous for eye colour.

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Glossary inherited characteristic

• A characteristic that is caused by a persons
  genes I.e. the characteristic has been inherited
  from the persons parents.
• e.g. eye colour, hair colour, blood group.

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Glossary mutation

• Sometimes changes to genes occur. These changes
  are called mutations.
• Mutations are usually harmful but sometimes they
  may be beneficial.
• Mutations can be caused by radiation, chemicals
  or they can just happen spontaneously.
• Mutations are another factor, (along with gamete
  formation and fertilisation), that cause genetic
  variation.
• Mutations change the sequence of the bases on
  DNA.
• This alters or stops the production of the
  protein that the gene coded for.

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Glossary nucleus

• Part of the cell that contains DNA, (and
  therefore chromosomes and genes)

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Glossary Punnett square

• A way of linking two parents genes to calculate
  the possibility of a certain characteristic in
  their children.

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Glossary recessive

• A characteristic that only shows itself if both
  chromosomes have that particular gene
• Recessive alleles do not show themselves in
  heterozygous individuals.

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Glossary sex chromosomes

• Chromosomes that control the sex of an
  individual. In humans the 23rd pair of
  chromosomes are the sex chromosomes.
• Females have identical sex chromosomes XX
• Males have different sex chromosomes - XY