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Inheritance
Why are you unique?
Inheritance
• What we are like
depends on the
genes we inherit
from our parents
• The study of
inheriting
characteristics is
called genetics
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choose the section you want to work on from this page
About
variation
How genes work
About cells
Start at the top and work round clockwise!
About genes
Boys and girls
What is Variation?
• Individuals
within a species
have different
characteristics
• Variation
ensures survival
Two types of variation
1. discontinuous
Number of
people
Tongue rolling ability
100
50
0
1
2
number who cannot or can roll their tongue
• A
characteristic
you either
have or you
don’t!
Two types of variation
2. Continuous
• Produces a range
of differences for a
single
characteristic
within a population
• Variation in height
is an example of
this…
Does variation always happen?
• Sexual
reproduction
• needs two parents
• produces offspring
with a mixture of their
characteristics
• Asexual
reproduction
• needs only one
•
parent
produces identical
offspring called
clones
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•
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understanding
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need to look at the
information again ……
About cells
• Dividing and growing!
Cell division
•
•
•
•
Cells
Cells
Cells
Cells
divide
divide
divide
divide
to make new cells
when we are growing
during repair of the body
to make eggs and sperms
Cell division by mitosis
• Mitosis is cell
•
•
division of body
cells
Mitosis produces 4
exact copies of the
parent cell
The new daughter
cells have the
diploid number of
chromosomes
Cell division by meiosis
• Meiosis produces
sex cells or
gametes
• Sex cells have
half, the haploid
number, of
chromosomes
How many chromosomes?
• Humans have 23 pairs of
chromosomes like these
• The diploid number of
chromosomes is
23x2 = 46
• Sex cells (gametes) have
23 single chromosomes the haploid (half) number
What’s the point?
• An egg cell has 23 chromosomes
• A sperm cell has 23 chromosomes
• When they join at fertilisation there are
46 chromosomes
• This makes a full set of instructions to
make a new human being!
What can you remember so far?
• Click the brain box picture to
check your knowledge and
understanding
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worksheet
• Or go back to the start again if
you need to look at this
information again ……
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Boys or girls?
• What will your baby be?
What are little girls made of?
•XX
What are little boys made of?
•XY
Predicting the chances:
• Will it be a boy?
• Will it be a girl?
• We can work out
the chances….
Mums and Dads!
• Mums produce
only and
chromosomes
• Dads produce
or
chromosomes
Now work it out!
…and the babies?
• Half will be
girls
• Half will be
boys!
• 50% of each
sex
What can you remember?
• Try out the worksheet
exercise…
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what you have learnt
• Or return to the main
menu
Why am I unique?
• It’s down to your genes!
It’s all down to your parents!
• At fertilisation two
•
•
•
gametes join
A gamete has half a set
of instructions – the
haploid number
A zygote is a fertilised
egg cell
It has has a full set of
instructions - the diploid
number
What causes variation?
All living cells contain a complex protein called DNA
Long strands of DNA forms chromosomes inside cells
Chromosomes are long strings of genes
What is a gene?
• Genes are short
•
•
sections of
chromosomes
Genes are groups of
bases on DNA
molecules
All genes are made of
just 4 bases
Adenine
Thymine
Guanine
Cytosine
Pairs of bases!
• The four bases are
arranged in pairs on
chromosomes
• A always pairs with T
• C always pairs with G
A–T
G–C
T–A
C-G
Amazing spirals
• The arrangement
of bases forms a
double helix
shape – like a
twisted ladder!
• This is a
chromosome
So why do you look like
that??
Phenotype
• The physical
•
appearance of
individuals within a
species varies
The genes that are
inherited from parents
control the phenotype
of each individual
Genotype
• The different genes
•
•
that each individual
has is their genotype
Every body cell
carries pairs of
genes on the paired
chromosomes
Genes can be
dominant or
recessive
What have you learnt from this
section?
• Test yourself here
• Or go back and look
at this section again
• Or select a new topic
from the menu
So how do your genes work?
Gene competitions?
• This rabbit’s
genotype is BB –
the black fur gene
is dominant
This rabbit’s
genotype is bb –
the white fur
gene is recessive
How do the genes work?
BB?
Homozygous two genes the
same
Bb?
Heterozygous two different
alleles
bb?
Homozygous
How do they work?
• Dominant genes are
•
•
•
‘stronger’
They are written as
capital letters -‘B’
Recessive genes are
‘weaker’
They are written as
small letters – ‘b’
This rabbit may have a
genotype of either Bb or
BB
Genes in conflict?
• B + B =BB
Phenotype Black fur
Genotype BB
• B + b = Bb
Phenotype Black fur Genotype - Bb
• b + b = bb
Genotype - bb
Phenotype White fur
Now work it out…..
parent
parent
gametes
offspring
What are the off spring like?
• All the offspring have the same
•
genotype
They all have one dominant gene
• They all have one recessive gene
• The dominant gene ‘wins’ so the
offspring all have black fur!
What is their genotype?
• Offspring have a mixture of their parents’
genes:
• They are heterozygous
• They each have one allele for white
fur and one allele for black fur
What about the next
generation?
parents
gametes
3:1
offspring
What are their genotypes?
heterozygous
homozygous
homozygous
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