inheritance looking at how and what we inherit a couple of things before we start 1.sex...
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InheritanceLooking at how and what we inherit
A couple of things before we start
1. Sex determination2. How to use a punnet square
Spot the difference… What is the one difference between the male and female sets of chromosomes?
Male chromosomes Female chromosomes
Do you notice any similarities?
An example A father with dimples (Dd) and a mother with no dimples, what are the chances of their child having dimples
Parents Father with dimples x Mother no dimples
Parents alleles Dd x dd
(the genes they have)
Gametes (egg/sperm) D or d d or dPossible offspring
D d
d Dd
dd
d Dd dd
50% Dd (dimples)
50% dd (no dimples)
How are genes inherited?
The parentsHomer has straight hair Marge has curly hair
The families
Is hair curliness controlled by genes or by the environment?
Homer
• Homer has straight hair
• Every cell in Homer has two sets of
genes
• Homer’s cells have two straight hair
genes
• We can show the straight hair gene
with a capital H
• Homer’s genes: HH
Marge
• Marge has curly hair
• Every cell in Marge has two sets of
genes
• Marge’s cells have two curly hair
genes
• We can show the curly hair gene with
a small h
• Marge’s genes: hh
Making a new Simpson
• Homer makes sperm
• Each sperm has one gene for hair type
• Homer only has straight hair genes
• So all of his sperm have straight hair
genes
Homer’s Sperm
H H
Making a new Simpson
• Marge makes eggs
• Each egg has one gene for hair type
• Marge only has curly hair genes
• So all of her eggs have curly hair
genes
Marge’s Eggs
h h
Making a new Simpson
hh
H
H
Hh
HhHh
Hh
Making a new Simpson
Hh HhHhHh
• All of the Simpson babies have one gene for curly hair and
one gene for straight hair
• So what type of hair do they have?
Making a new Simpson
Hh
THEY ALL HAVE STRAIGHT HAIR!
• The straight hair gene is DOMINANT
• Just one copy of this gene will give the characteristic
• The curly hair gene is RECESSIVE
• TWO copies of this gene are needed to have the characteristic
Liking donuts
• Homer likes donuts
• Every cell in his body has two ‘liking’
donut genes.
• His genes are: D D
Homer’s sperm
D D
Liking donuts
• Marge doesn’t like donuts.
• Every cell in her body has two ‘non-
liking’ donut genes
• Her genes are: d d
Marge’s Eggs
d d
Making a new Simpson
d d
D
D DD
D D dd
d d
Making a new Simpson
Dd DdDdDd
• Liking donuts is dominant
• Do the Simpson children like donuts?
Weight
• Marge has normal weight.
• Both of her weight genes are for
normal weight
• Her genes are: N N
Marge’s Eggs
N N
Weight
• Homer does not have normal weight.
He is obese.
• Both of his weight genes are for
obesity (not normal weight)
• His genes are: n n
Homer’s sperm
n n
Making a new Simpson
Nn NnNnNn
• Normal weight is dominant
• What weight do all the Simpson children have?
PracticeHomer’s
characteristicHomer’s genes Marge’s
characteristicMarge’s genes
Likes beer Bb Doesn’t like beer bb
Plays sports Ss Doesn’t play sports ss
Burps Bb Doesn’t burp bb
Lazy Ll Not lazy ll
Can’t dance dd Can dance Dd
No musical ability mm Musical ability Mm
The next generation?
• Lisa has straight hair
• Every cell in Lisa has two sets of genes
• Lisa has one gene for straight hair,
which is dominant.
• She also has one gene for curly hair,
which is recessive.
• Lisa’s genes: Hh
The next generation?
• Milhouse has straight hair
• Every cell in Milhouse has two sets of
genes
• Milhouse has one gene for straight
hair, which is dominant.
• He also has one gene for curly hair,
which is recessive.
• Milhouse’s genes: Hh
The next generation?
• Milhouse’s genes: Ss
S s
S s
• Lisa’s genes: Ss
The next generation?
H
hh
H
h
H
h H h
h
H
h
The next generation
Hh hhHhHh
• Straight hair is dominant
• How many children have straight hair?
• How many have curly hair?
The next generationLisa’s
characteristicLisa’s genes Milhouse’s
characteristicMilhouse’s genes
Likes School Ss Likes School Ss
Good eyesight EE Bad eyesight ee
Brave Bb Not brave bb