INTRODUCTION TO GENETICS - PART II Mrs. Stewart Honors Biology Central Magnet School

Bell work  Describe the relationship between genotype and phenotype

STANDARDS  CLE Investigate how genetic information is encoded in nucleic acids.  CLE 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 MomMom Dad

DOES IT MATTER WHICH SIDE YOU PUT THE PARENT’S GENOTYPE ON? bb BBb B 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?  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

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 %