Transcript Train your brain

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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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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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!
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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
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exercise…
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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
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section?
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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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