INTRODUCTION TO GENETICS - PART II Mrs. Stewart Honors Biology
Central Magnet School
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Bell work Describe the relationship between genotype and
phenotype
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STANDARDS CLE 3210.4.1Investigate how genetic information is
encoded in nucleic acids. CLE 3210.4.3 Predict the outcome of
monohybrid and dihybrid crosses.
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OBJECTIVES Analyze the law of segregation Create a punnett
square using the genotypes of parents Predict the outcome and
probability of monohybrid crosses
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DECIDE WITH YOUR PARTNER
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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
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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 persons 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
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DOGS Tell your CAT another example of a characteristic (a trait
that can be altered by the environment)
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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
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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
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CATS Tell your DOG how we inherit traits from our parents
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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).
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LAW OF SEGREGATION (Pairs) Homologous chromosomes are separated
during the formation of gametes
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DOGS Explain the law of segregation to your CAT
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CATS Explain the law of segregation to your DOG
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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.
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CATS AND DOGS How can we predict the inheritance of
traits?
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HOW CAN WE PREDICT THE INHERITANCE OF TRAITS? Punnett Squares
use genotypes to predict inheritance Punnett Squares show the law
of segregation in action MomMom Dad
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DOES IT MATTER WHICH SIDE YOU PUT THE PARENTS GENOTYPE ON? bb
BBb B BB No, the results are the same.
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MONOHYBRID CROSS Monohybrid = a cross between two organisms
that predicts the inheritance pattern/probability of only one
characteristic/trait
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PRACTICE Trait = fur color B = brown fur b = white fur Which
trait is dominant? Cross a homozygous dominant with a heterozygous
dominant What are the genotypes of the parents? What percentage of
the offspring will have white fur? Brown Fur = B BB and Bb BbBb B B
BB Bb 0
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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? 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?
What generation are the offspring of this cross part of? If you
crossed the offspring with each other, how many of the resulting
offspring would have two eyes? Two-eyed Ee F 1 1 out of 4 or 25
%
