Download gene - MrSimonPorter

Can you stick the
sheets in please?
Do now!
In the right order!
Tests!
• Check Mr Porter has added your marks up
correctly
• Calculate the percentage mark for each
test by multiplying the out of 25 mark by 4
• Fill in the “Science assessment tracker” on
the front of your folder
• In your books write a target for the next
unit.
Last lesson
• Understand the
difference
between species,
breeds, varieties
Read pages 6 to 9 and write 10 multiple choice
questions (each with 4 possible answers) on the
subject of species, breeds, varieties, selective
breeding and cross-breeding
Today’s lesson
• How genetic information is transferred
• How genes work
How is genetic information
transferred?
I dunno.
I’m a
sheep.
How is genetic information
transferred?
Sex!
Let’s start at the very beginning
Sexual reproduction
• Requires two parents, a male and female.
Sexual reproduction
• Both have sex organs
Sexual reproduction
• The sex organs make sex cells (gametes)
Sexual reproduction
• In male animals the sex cells are called
sperm, made in sex organs called testes
(testis is singular)
I can stay alive in the
vagina for up to 3
days waiting for an
egg to be released.
Sexual reproduction
• In female animals the sex cells are called
eggs, made in sex organs called ovaries.
An egg is released
from the ovaries about
every 28 days. This is
called ovulation.
Sexual reproduction
• During sexual reproduction the sperm and
egg join together (fertilisation)
I will die after about
2 days if not
fertilised.
External fertilisation
In some animals fertilisation takes place
outside the body.
External fertilisation
In some animals fertilisation takes place
outside the body.
Some sperm may get
washed away so I
produce a lot of eggs so
at least some get
fertilised.
External fertilisation
In some animals fertilisation takes place
outside the body.
I don’t look after my
eggs either so many get
killed before they have
chance to develop into
fish.
Mendelian genetics
Mendelian genetics
Gregor Mendel (1822 – 1884) was a monk
who was very interested in plant breeding.
Peas
Mendel took one pea plant that always
produced wrinkled peas and used this
plant to pollinate another pea plant that
always produced smooth peas
Peas
He found that the plants produced (called the F1
generation) all had smooth peas.
F1 Generation
He called this (smooth) the dominant
characteristic
Peas
When two plants of the first generation
(F1) were cross-pollinated, 75% of the
offspring (F2 plants) had smooth peas and
25% had wrinkled peas.
F1 Generation
F2 Generation
He said the wrinkled peas had the
recessive characteristic.
Genes
We can now explain Mendel’s results
using what we know about genes.
A gene can be defined as a region of DNA that
controls a hereditary characteristic.
Chromosomes, genes & DNA
Chromosomes are X-shaped objects found in the
nucleus of most cells. They consist of long strands of a
substance called deoxyribonucleic acid, or DNA for
short. A section of DNA that has the genetic code for
making a particular protein is called a gene.
Genes
Our DNA contain two genes (one from our
mother and one from our father) for each
characteristic (eye colour, hair colour etc.)
Obviously the best looking
Alleles
Different genes for the same characteristic (e.g.
eye colour) are called alleles.
Pron: “Al – eels”
For example, you all have two genes (alleles) for
eye colour
Which colour eyes?
Which colour eyes?
Your eye colour depends on which genes
you have. Lets look at the genes for brown
and blue eyes.
The brown eye gene (B) is dominant and
the blue eye gene (b)is recessive
(heterozygous)
Which colour eyes?
If you have the alleles for eye colour of Bb,
you will have brown eyes (because the
brown gene is dominant).
(homozygous)
Which colour eyes?
If you have BB, you will also have brown
eyes.
(homozygous)
Which colour eyes?
Only if you have bb will your eyes be blue
(both genes are recessive)
Which colour eyes?
Your combination of genes (BB, Bb or bb)
is called your genotype.
Cats don’t eat
their own poo,
dogs do!
The colour of eyes you actually have is
called your phenotype
An example
Let’s imagine your mother has Bb
genotype and your father also has Bb.
Bb
Bb
An example
Half your mother’s eggs will have B genes
and half b (eggs are gametes and only
contain one of each pair of genes)
eggs
B
b
An example
Half your father’s sperm will have the B
gene and half the b gene too.
B
b
Sperm!
Gene diagram (Punnett square)
We can look at the
possible combinations
on a gene diagram
Sperm Sperm
with B with b
Egg
with B
Egg
with b
Gene diagram (Punnett square)
Here are all the
possible combinations
for a fertilised egg
Sperm Sperm
with B with b
Egg
with B
BB
Bb
Egg
with b
Bb
bb
Gene diagram
This means that there
is a 75% chance the
baby will have brown
eyes (BB or Bb) and
only a 25% chance
the baby will have
blue eyes (bb)
Sperm Sperm
with B with b
Egg
with B
BB
BROWN
Egg
with b
Bb
BROWN
phenotype
genotype
Bb
BROWN
bb
BLUE
Pure breeding
If one parent has both
dominant genes(BB),
any baby will have to
have brown eyes. We
say the parent is pure
breeding.
Sperm Sperm
with B with B
Egg
with B
BB
BROWN
Egg
with b
Bb
BROWN
phenotype
BB
BROWN
Bb
BROWN
WARNING!
WARNING!
This is a simplified explanation. In reality
eye colour is a little more complex than
this. Please do not go home and accuse
your mother of sleeping with the cable guy
if both your parents have blue eyes and
you have green or brown!
Let’s try some questions!