inheritance looking at how and what we inherit a couple of things before we start 1.sex...

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


• 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


hh

H

H

Hh

HhHh

Hh


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?


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


d d

D

D DD

D D dd

d d


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


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


• 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


• Milhouse’s genes: Ss

S s

S s

• Lisa’s genes: Ss


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

inheritance looking at how and what we inherit a couple of things before we start 1.sex...

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