Download Introduction to genetics

INTRODUCTION TO
GENETICS PART II
Mrs. Stewart
Honors Biology
Central Magnet School
Bell work
 Describe the relationship between genotype and phenotype
STANDARDS
CLE 3210.4.1 Investigate how genetic
information is encoded in nucleic acids.
CLE 3210.4.3 Predict the outcome of
monohybrid and dihybrid crosses.
OBJECTIVES
Analyze the law of segregation
Create a punnett square using the genotypes
of parents
Predict the outcome and probability of
monohybrid crosses
DECIDE WITH YOUR PARTNER
WHAT IS HEREDITY?
 Why do children look like their parents?
 Why do brothers and sisters resemble each other?
 We inherit traits from our parents
 Heredity = the passing of genetic traits from parents to offspring
TRAITS AND GENES
 Genes carry the instructions that define our traits
 Genes = segments of the DNA sequence that code for a
particular trait
 Traits = genetically determined characteristics (qualities)
 Example: natural hair color, eye color, skin tone, etc.
 The environment we live in can also help define our traits
 Example: a person’s genes may code for a certain hair color,
but exposure to dyes, chemicals, sunlight, etc can change
that color
 Characteristic = can be altered by the environment
DOGS
Tell your CAT another example of a characteristic
– (a trait that can be altered by the environment)
HOW DO WE GET TRAITS FROM OUR
PARENTS?
 Human body cells (somatic
cells) have 2 complete sets of
23 chromosomes
 2 x 23 = 46 chromosomes
 One set of 23 comes from
sperm (Dad)
 One set of 23 comes from egg
(Mom)
 Each parent contributes one
complete set to the child,
giving the child a “mix” of
genes
FERTILIZATION
 Fertilization – one
sperm fuses with an egg to
form a zygote
 The zygote now has 2 sets
of 23 chromosomes (46
total)
 This cell will begin dividing
and will ultimately become
a child.
Zygote
CATS
Tell your DOG how we inherit “traits” from our
parents
PARENTS CONTRIBUTE ONE OF EACH
CHROMOSOME PAIR TO THE CHILD
 On a karyotype, there are 2
chromosomes at each site.
 These represents the 2
chromosomes received from
the parents. One from mom,
one from dad.
 During meiosis, these will
separate into different
gametes (sex cells).
LAW OF SEGREGATION
(Pairs) Homologous chromosomes are separated
during the formation of gametes
DOGS
Explain the law of segregation to your CAT
CATS
Explain the law of segregation to your DOG
SIBLINGS
 Since parents contribute chromosomes randomly, every child inherits a
“unique” combination of traits.
 Some may resemble mom; some may resemble dad; others will be
completely unique
 They may be resemble each other or be totally different.
CATS AND DOGS
How can we predict the inheritance of
traits?
HOW CAN WE PREDICT THE INHERITANCE OF
TRAITS?
 Punnett Squares use genotypes to predict inheritance
 Punnett Squares show the law of segregation in action
M
o
m
Dad
DOES IT MATTER WHICH SIDE YOU PUT
THE PARENT’S GENOTYPE ON?
b
b
B
Bb
Bb
B
Bb
BB
No, the results are the same.
MONOHYBRID CROSS
Monohybrid = a cross between two organisms
that predicts the inheritance pattern/probability of
only one characteristic/trait
PRACTICE
Trait = fur color
B = brown fur
b = white fur
Which trait is dominant? Brown Fur = B
Cross a homozygous dominant with a heterozygous
dominant
What are the genotypes of the parents? BB and Bb
What percentage of the offspring will have white fur? 0
B
B
B
b
BB
Bb
BB
Bb
CHECK FOR UNDERSTANDING
 A one-eyed purple people eater is crossed with a two-
eyed purple people eater. All of their offspring have
two eyes. Which trait is dominant? Two-eyed
 Use the letter E or e to represent the alleles
(variations) for this gene. What is the genotype of the
offspring if you cross a purebred one-eyed purple
people eater with a homozygous two-eyed purple
people eater?
Ee
 What generation are the offspring of this cross part
of?
F1
 If you crossed the offspring with each other, how many
of the resulting offspring would have two eyes?
1 out of 4 or 25 %