Genetic Diagrams Noadswood Science, 2012. Genetic Diagrams To understand how to be able to construct...
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Transcript of Genetic Diagrams Noadswood Science, 2012. Genetic Diagrams To understand how to be able to construct...
Genetic Diagrams• To understand how to be able to construct genetic diagrams
BB bb
B B b b
Bb Bb Bb Bb
Wednesday, April 19, 2023
Genetic Diagrams• Genetic diagrams show the possible genes for offspring
• Alleles are different versions of the same gene, and most of the time there are two copies for each gene (one from each parent)
• If they’re different alleles one might be ‘expressed’ by the organism (dominant allele)
• In genetic diagrams letters are used to represent genes – dominant alleles are always shown with CAPITAL LETTERS, whilst recessive alleles are shown with lower case
Genetic Diagrams – Example• Hamster can be either normal or crazy – in this example
normal is dominant (B) and crazy is recessive (b)
• Hamster normal gene – B• Hamster crazy gene – b
• A crazy hamster (recessive characteristic) must have both alleles as recessive – bb
• A normal hamster (dominant characteristic) can have two combinations: either both dominant – BB, or one dominant and one recessive – Bb
Hamster Cross Example• Crossing a thoroughbred crazy hamster (bb) and a
thoroughbred normal hamster (BB)
B B
b Bb Bb
b Bb Bb
Normal hamster
Cra
zy
ham
ster
Hamster Cross Example• Crossing a thoroughbred crazy hamster (bb) and a thoroughbred
normal hamster (BB) (both homozygous) – all offspring normal
Parents Normal Crazy
Parent’s alleles
Gamete’s alleles
Possible combinations
BB bb
B B b b
Bb Bb Bb Bb
Hamster Cross Example• If two of the heterozygous offspring were then crossed (Bb x
Bb) then we would have 3x normal (75%) and 1x crazy (25%)
Parents Normal Normal
Parent’s alleles
Gamete’s alleles
Possible combinations
Bb Bb
B b B b
BB Bb Bb bb
Genetic Diagrams – Question• Complete the genetic cross to show the possible
combination of gametes: -▫ Female produces two X gametes (XX)▫ Male produces one X gamete (X) and one Y gamete (Y)
X Y
X XX XY
X XX XY
Male
Fem
ale
Sex Cross Example• Probability of male / female offspring – 50:50
Parents Male Female
Parent’s alleles
Gamete’s alleles
Possible combinations
XY XX
X Y X X
XX XX XY XY
Genetic Diagrams – Question• Eye colour can be brown and blue (simplistic) – in this
example brown is dominant (B) and blue is recessive (b)
• Brown gene – B• Blue gene – b
• An individual with blue eyes (recessive characteristic) must have both alleles as recessive – bb
• An individual with brown eyes (dominant characteristic) can have two combinations: either both dominant – BB, or one dominant and one recessive – Bb
Eye Colour – Homozygous• Crossing a homozygous blue-eyed person (bb) and a
homozygous brown-eyed person (BB)
B B
b Bb Bb
b Bb Bb
Brown-eyed - homozygous
Blu
e-e
yed
-
hom
ozy
gou
s
Eye Colour• Crossing a homozygous blue-eyed person (bb) and a homozygous
brown-eyed person (BB) – all offspring brown-eyed
Parents Brown-eyed Blue-eyed
Parent’s alleles
Gamete’s alleles
Possible combinations
BB bb
B B b b
Bb Bb Bb Bb
Eye Colour – Heterozygous• Crossing two heterozygous brown-eyed individuals (Bb)
B b
B BB Bb
b Bb bb
Brown-eyed - heterozygous
Bro
wn
-eye
d -
h
ete
rozy
gou
s
Eye Colour• Crossing two heterozygous brown-eyed individuals (Bb) –
3x brown-eyed (75%) and 1x blue-eyed (25%)
Parents Brown-eyed Brown-eyed
Parent’s alleles
Gamete’s alleles
Possible combinations
Bb Bb
B b B b
BB Bb Bb bb
Eye Colour – Hetero & Homozygous• Crossing one heterozygous brown-eyed individual (Bb) and
one homozygous blue-eyed individual (bb)
b b
B Bb Bb
b bb bb
Blue-eyed – homozygous
Bro
wn
-eye
d -
h
ete
rozy
gou
s