Mendelian Genetics

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 • 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? • Code the alleles and identify which is dominant/recessive • Determine parental (or given) genotypes • Determine parental (or given) gametes • Draw Punnett square • 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

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

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

Mendelian Genetics