Mendelian Genetics 11.1 Gregor Mendel

Who was Gregor Mendel?  Austrian monk  Also “high school” science/math teacher  One of the first to use statistics to analyze results  Studied garden peas  Attempted to refute Blended Inheritance belief

What was Mendel’s experimental design?  Create true-breed strains  Selected for phenotypic traits  Genotype vs. phenotype  Crossed true-breed plants  Kept track of offspring phenotypes

What is Mendel’s law of segregation?  Traits segregate independently  Today we now know  What alleles are  What a locus is  How genotype influences phenotype  Why traits segregate independently  Remember independent assortment in meiosis I?

What is the difference between dominant and recessive?  Dominant is phenotypically expressed  To be expressed, a recessive must be paired with ________

How can I describe an individual’s genotype?  Use capital letter for ____________ allele  Use small case letter for _________ allele  Homozygous dominant____________  Homozygous recessive_____________  Heterozygote_________________  If a disease, then is a CARRIER

What’s the relationship of genotype to phenotype?  Genotype _________ phenotype  If T = tall and t = short, then  TT is a _________ plant  Tt is a _________ plant

Mendelian Genetics 11.2 Mendel’s experiments

So can you tell me more about Mendel’s monohybrid cross?  F1 and F2 generations showed something interesting  Ratio: _______ Punnett square

What were the F2 offspring like?  Ratio:

What did Mendel think about this ratio?  He determined traits (AKA alleles) are either ________ or _______

What happened when Mendel followed two traits?  Dihybrid cross  Ratio of cross of two heterozygotes is:  Thus, the traits assort ___________ of each other when making gametes

Mendelian Genetics 11.3 Solving genetics problems

How do we know a trait is dominant (or recessive) in humans?  Can’t do breeding experiments like Mendel!  Pedigrees  Carriers

So what do I do with all this information?  Solve genetics problems!  Use the five steps to solving a genetics problem…

What are the five steps to solving a genetics problem? 1. Code the alleles and identify which is dominant/recessive 2. Determine parental (or given) genotypes 3. Determine parental (or given) gametes 4. Draw Punnett square 5. Re-read problem to be sure you are answering the question correctly.

Let’s try it!  In humans, being able to roll your tongue is dominant (R). If a heterozygous woman marries a man who can’t roll his tongue, what are the chances a child of theirs also won’t be able to roll its tongue?  First step…

Step 1 Code the alleles and identify which is dominant/recessive In humans, being able to roll your tongue is dominant (R). If a heterozygous woman marries a man who can’t roll his tongue, what are the chances a child of theirs also won’t be able to roll its tongue?

Step 2 Determine parental (or given) genotypes In humans, being able to roll your tongue is dominant (R). If a heterozygous woman marries a man who can’t roll his tongue, what are the chances a child of theirs also won’t be able to roll its tongue?

Step 3 Determine parental (or given) gametes In humans, being able to roll your tongue is dominant (R). If a heterozygous woman marries a man who can’t roll his tongue, what are the chances a child of theirs also won’t be able to roll its tongue?

Step 4 Draw Punnett square In humans, being able to roll your tongue is dominant (R). If a heterozygous woman marries a man who can’t roll his tongue, what are the chances a child of theirs also won’t be able to roll its tongue?

Step 5 Re-read problem to be sure you are answering the question correctly.  In humans, being able to roll your tongue is dominant (R). If a heterozygous woman marries a man who can’t roll his tongue, what are the chances a child of theirs also won’t be able to roll its tongue?  Answer:

Now you try!  If a homozygous tongue roller and a non-tongue roller marry, what are the chances their child will be able to roll its tongue?  USE THE 5 STEPS!!!!

Here’s the solution:  If a homozygous tongue roller and a non-tongue roller marry, what are the chances their child will be able to roll its tongue?

Now practice with the genetics problems…  You will be expected to know and use the 5 steps on your exam!

Mendelian Genetics 11.4 Human genetic disorders

What are autosomal recessive disorders?  Autosome = ________  Examples  Tay-Sachs disease  Cystic fibrosis  Phenylketonuria

What are autosomal dominant disorders?  Only need one copy of the allele to have the disease  Examples  Neurofibromatosis  Huntington’s disease  Achondroplasia

Mendelian Genetics 11.5 Beyond Mendelian genetics

Is complete dominance the only kind of dominance?  No!  Incomplete dominance  Dominant allele cannot fully mask the recessive allele  Sickle cell anemia  Curly vs. straight hair

 Codominance  Multiple alleles  Blood types demonstrates both Is complete dominance the only kind of dominance?

What is polygenic inheritance?  More than one gene affects phenotype  Skin color in humans  Human height  Eye color  Seed color in wheat

What is epistasis?  One gene affects many traits  Marfan Syndrome  Defective collagen gene  Affects tendons, ligaments, bone, heart tissue, etc.

Can environment affect phenotype?  Yes!  Himalayan rabbits  Epigenetics