Mendelian Genetics

Genotype Tongue Rolling (Dominant) roll/not roll     Widow's Peak (D) - just like Eddie Munster yes/no     Wet ear wax (D) - stick your finger in to check wet/dry     L/R interlocking finger (D) - without thinking, clasp your

hands together, is the right thumb over the left, or vice versa? L/R or R/L    

Attached earlobes (r) - ask a neighbor or check out the mirror yes/no    

Natural Red Hair(r) – Not dyed hair yes/no   Hitchhiker Thumb (r) - does it bend back at a 90 angle

yes/no           Darwin tubercle (D) - little bump on the inside of the ear

yes/no       Pigmented iris (D) - any color but blue yes/no     Freckles (D) yes/no     Polydactyl (D) - more than five fingers and/or toes yes/no     Dimples (D) yes/no       Long eyelashes (> 1cm; D) yes/no          

What Traits do you Have?

Genetics

The study of heredity:

Passing genetic traits from one generation to next.

Two basic questions about heredity:

1. What determines the traits that an organism has?

Examples: hair color, behavior

2. How are traits transmitted from one generation tothe next? (Why do we resemble our parents?)

Answer: Genes (of course)

Gregor Mendel

“Father of Genetics”Austrian MonkStudied heredity in

1850sUsed garden peas

Mendel studied peas because their phenotypes were easy to identify.

Phenotype - the outward, physical appearance of a particular trait

Mendel's pea plants exhibited the following phenotypes: - round or wrinkled seeds- yellow or green seeds- Colored or white flowers- tall or short plants

Mendel’s Peas

Mendel’s Experiment

He cross pollinated a tall plant with a short plant

Results

In the 1st filial (F1) generation all of the offspring showed the same trait – all tall.

F1 generation – children of the parents.

Next, he let the F1 generation self-pollinate.Results: ¾ of the F2 generation showed the

dominant trait & ¼ showed the recessive trait.F2 generation – grandchildren of the parents.

P (parent) generation were “pure-bred” for traits…they only carried the trait they showed!

Mendel did not know about chromosomes, genes or DNA!

He suggested that some “factors” were passed from parents to offspring.

“Factors” that Mendel talked about were actually alleles (versions of a gene) that show as traits.

“Factors” (alleles) are inherited from your parents.

You get 1 allele for each trait from each parent.

Ex – You have 1 GENE for tongue rolling. You can have 2 alleles for the ability to roll the tongue, 2 alleles for inability to roll, or 1 of each allele.

Mendel’s laws

1) Law of Dominance – some alleles show and some alleles are “hidden”. The traits show dominance.

EX: Tall plant X Short plant all offspring are TallTall is the dominant trait!

Use capital letter to represent dominant allele

Use lower case letter to represent recessive allele

EX: T = Tall t = short

REMEMBER…

Each organism has a pair of alleles (genes) for each trait (diploid)

TT =Homozygous dominant (tall)Tt = Heterozygous (tall, but carries an allele

for short)tt = homozygous recessive (short)

2) Law of Segregation – during meiosis, one member of a gene pair separates into different gametes.

Therefore, each gamete only carries one member of the gene pair.

3) Law of Independent Assortment – Gametes unite at random. This union produces the combination of genes that we are looking at.

The combination is irrespective of the other gene pairs involved. In other words – MOST of our genes don’t depend on other genes – they are Separate!

• Inheritance follows the rules of probability.– The rule of

multiplication and the rule of addition can be used to determine the probability of certain events occurring

Mendel’s principles reflect the rules of probability

F1 GENOTYPES

Bb female

F2 GENOTYPES

Formation of eggs

Bb male

Formation of sperm

1/2

1/2

1/2

1/21/4

1/41/4

1/4

B B

B B

B B

b

b b

b

b b

Figure 9.7

We demonstrated Mendel’s laws in lab and saw how inherited traits are… well… inherited and how that relates to how you look when you are born (and subsequently look as an adult).

Today, we will describe how to use Mendel’s laws on paper, and will figure out probabilities by doing sample problems.

Review from lab and notes:

What is a phenotype? Outward, PHYSICAL

appearance (what you can see)

What is a genotype? The alleles that make

up the gene that someone has (you MAY not be able to tell exactly what alleles… why?)

How do we show a dominant allele (on paper)? Capital Letter

How do we show a recessive allele (on paper)? Lower-case Letter

Using symbols we can depict the cross of tall and short pea plants in the following manner:

Reminder: Allele - one alternative form of a given gene pair.

Example: Tall and dwarf are the alleles for the height of a pea plant.

More than two alleles can code for any specific gene, but only two will be found within any individual. We will cover this in a future class

Punnet Squares

Way to determine inherited traitsSquare used to show all the possible

combinations of gametesUsed to predict the outcome of offspring.

P1 Monohybrid Cross

R

R

rr

Rr

RrRr

Rr

Genotype:

Phenotype:

FATHER

M O T H E R

R = Dominant Allele (Round)r = Recessive Allele (Wrinkled)

Round

Rr

Note: When filling in the punnett square, always write the capital letter first!

F1 Monohybrid Cross

R

r

rR

RR

rrRr

Rr

Genotypes:

Phenotypes:

FATHER

M O T H E R

R = Dominant Allele (Round)r = Recessive Allele (Wrinkled)

Round

Wrinkled

RR

Rr

rr

Genetic Problem Example 1

A blue-eyed mother (recessive) mates with a homozygous brown eyed father. What is the probability that they will have a brown-eyed child?

Where do you start?

What is the dominant allele? B (stands for brown)

What is the recessive allele? b (stands for blue)

What are the genotypes of the parents? Mother: bb Father : BB

Monohybrid Cross

B

B

bb

Bb

Bb

Bb

Bb

Genotype (%):

Phenotype (%):

FATHER

M O T H E R

B = Dominant Allele (Brown Eyes)b = Recessive Allele (Blue Eyes)

Brown

Bb 100%

100%

Genetic Problem Example 2

A blue-eyed mother (recessive) mates with a heterozygous brown eyed father. What is the probability that they will have a brown-eyed child?

Where do you start?

What is the dominant allele? B (stands for brown)

What is the recessive allele? b (stands for blue)

What are the genotypes of the parents? Mother: bb Father : Bb

Monohybrid Cross

B

b

bb

Bb

bbbb

Bb

Genotypes (%):

Phenotypes (%):

FATHER

M O T H E R

B = Dominant Allele (Brown Eyes)b = Recessive Allele (Blue Eyes)

Brown

Blue

Bb

bb

50%

50%

50%

50%