Transcript Genetics introduction

Heredity
• The genetic passing of characteristics
(traits) from parent to offspring
– Hereditary traits are determined by
specific genes
– Genes are on chromosomes
What cells pass on genetic information?
 gametes!
Offspring looking like their
parents
Alleles
Two alleles for every gene
Alleles
• Alleles are on chromosomes
• Alleles for the same trait are found in
the same location on homologous
chromosomes
• One chromosome can carry hundreds
of alleles
Chromosomes carry alleles
Complete dominance
• Alleles: dominant or recessive
– Dominant alleles will overpower recessive
alleles in appearance
• Represented by a CAPITAL letter
– Recessive alleles will stay masked by
dominant alleles in appearance
• Represented by a lowercase letter
Genetics: complete dominance
• Pea plants: Purple flowers are
dominant over white flowers
• This trait (color) is governed by only
two alleles
• Purple is represented by
P
• White is represented by p
Homozygous traits vs
heterozygous traits
PP
Pp
p p
Homozygous vs Heterozygous
• Homo: same
• Hetero: different
• Homozygous dominant:
PP
• Homozygous recessive: pp
• Heterozygous:
Pp
Genotype vs Phenotype
• Genotype: genetic makeup, what
type of alleles are present in the cell
• Phenotype: the outward physical
appearance from the alleles
• Lets go back and look at flowers
Genotype
Phenotype
Homozygous
or
Heterozygous
PP
Homozygous
dominant
Pp
heterozygous
pp
Homozygous
recessive
Gregor Mendel
• 1822 –1884 was an Austrian monk and
scientist
• “father of modern genetics”
– groundbreaking work on theories of
heredity
• Used pea pod plants
Mendels experiment with flower
color
Do Now: 1/12/12
(made up example!)
The color red in flowers is dominant over
the color yellow.
•What letters would you use to represent these
alleles?
•What is the genotype of a flower that is
homozygous dominant? Heterozygous?
Homozygous recessive?
•What is the phenotype of a flower that is
homozygous dominant? Heterozygous?
Homozygous recessive?
Do Now continuation:
A heterozygous red flower crossfertilizes with a yellow flower. What are
the possible genotypes for the
offspring?
Complete dominance
practice
Suppose black noses are dominant over pink
noses in a certain breed of dogs. A homozygous
dominant black-nosed dog is bred with
homozygous recessive pink-nosed dog.
•Genotype of each parent?
•What is the genotypic ratio?
•What is the phenotypic ratio?
•What percentage of the F1 generation will have
a heterozygous genotype?
•What is the probability that the 5th puppy will
have a pink nose?
Complete dominance:
going backwards
Use the dog example from
the previous slide:
A litter of puppies was born!
Out of the 6 puppies4 have black noses and 2
had pink noses.
•What were the genotypes
of the parents?
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Dihybrid punnett squares
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Dihybrid punnett square
Circle is dominant-C
Square in recessive- c
Black is dominant- B
White is recessive- b
Cross: C c B b x C c B b