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?

1. Code the alleles and identify which is dominant/recessive

2. Determine parental (or given) genotypes3. Determine parental (or given) gametes4. Draw Punnett square5. 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 1Code 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 2Determine 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 3Determine 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 4Draw 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 5Re-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