Genetics

Review of Probability

To find the overall probability of 2 independent events,

Example:

Heads twice = ______________ Tails twice = ________________ One heads and one tails = ____________ (__________________________________ _______________________)

multiple the probability of each.

Genetics

Gregor Mendel conducted a series of genetic experiments with pea plants in the mid- 1800’s.

Advantages: • Control of pollination • ____________________ • ____________________

Mendel removed the stamen (male reproductive organ) to prevent self pollination. He conducted a series of controlled experiments, in which he cross- pollinated plants with specific traits.

Purebreds (True-breeding)

A purebred strain produces offspring that always have the same trait (with large number of offspring).

Mendel knew that some strains of pea plants were purebreds for a trait, others were not.

Purebred Short

Parents:

Offspring: All Short

Purebred Tall

Parents:

Offspring: All Tall

Not Purebred

Parents:

Offspring: Mix Tall and Short

Mendel studied 7 different traits in pea plants. Looking at individual patterns for a trait as well as combinations of traits.

Mendel’s Results

● In the F1 generation (1st generation of offspring), _____________was expressed. _____________ trait

● Mendel crossed purebred plants with different characteristics in the parental generation.

● In the F2 generation, some (___ ) of the offspring exhibited the trait that had disappeared in the F1 generation. _________________ trait

Recessive Trait: can be hidden and reappear from

parents who do not have the trait.

Dominant Trait: can not be hidden.

Law of Segregation

From his experiments, Mendel concluded that each plant had ____ _______ of the information for a trait and that those copies segregate (or____________ ) when inheritance is passed down.

We now know this is due to meiosis.

Alleles Allele = a_________________ . Alleles are found on ___________________ of a chromosome and control the same trait but can be different forms.

Example: the purple flower allele and the white flower allele are two alleles for the flower color gene in pea plants.

Video: Mendel’s Experiments Overview

http

s://w

ww

.yo

utu

be

.co

m/w

atc

h?

v=

MW

kF

xW

XH

Tn

w&

fea

ture

=c4

-ove

rvie

w-

vl&

list=

PL

D2

55

C11

CF

27

A7

68

2

Dominant/Recessive Alleles The dominant allele (gene form) is the allele that

is expressed in the F1 generation. It is represented with a ___________ letter.

The recessive allele is the allele that can be hidden by a dominant allele.

It is represented by the ______________ form of the _______ letter.

Example: Spherical seed (dominant) S Wrinkled seed (recessive) s

Phenotype/Genotype Phenotype:

The___________________________________.

Examples: Long ears

Sickle cell anemia

Genotype:

The combination of _________________ contained in an organism.

Examples: LL, Ll, ll

Homozygous/Heterozygous Genotypes

Homozygous:

2 of the ______ allele

___ is homozygous dominant

___ is homozygous recessive

Heterozygous: 2 _________ alleles Bb

Two individuals with the dominant trait have the same____________ , but could have different ___________.

__ __

Discuss with your table partner:

The long-tail allele (L) is dominant in cats.

The short-tail allele (l) is recessive.

Can 2 long-tailed cats have a short-tailed offspring? Explain why or why not. Hint- think of possible genotypes of parents.

X

______________________________________________________________________________________

Also discuss the question on the next slide with your table partner.

Can 2 short-tailed cats have a long-tailed offspring? Explain why or why not. Hint- think of possible genotypes of parents. X _________________________________________________________________________________________________________________________________

Analyzing Mendel’s Results

• True breeding plants are _____________ for the trait.

• The F1 generation was ________________.

• In the F2 generation, 3 out of 4 (75%) received

• _____________________________________.

• 25% chance of receiving ______________________

_______________________________.

Punnett Squares Punnett squares can be used to determine the

possible offspring from two parent genotypes, and

the probabilities.

• The alleles from __________are written on the sides.

• _________ is written above each square (when looking at a single trait) since only _____________ _____________________________________.

• Filling in the squares shows the probability of each genotype combination

Example: Dd x dd

Phenotype Ratio Phenotype Ratio=The probable number of offspring with dominant trait to the probable number of offspring with the recessive trait.

Written-

____________________

In this example- ___________________________ ________________________________________.

A child from these parents has a _______ chance of inheriting the dimple trait.

Genotype Ratio

Genotype Ratio-

There may be three possible genotypes for a trait.

Written-

Homozygous Dominant: Heterozygous Dominant: Recessive (Homozygous)

Example

____________________

Heterozygotes

When an offspring possibility in a Punnett square

inherits a dominant allele from one parent and a

recessive allele from the other, write the dominant

allele first.

If written bB, it would be the same genotype. But

Bb is the standard way to write out the genotype.

B b

B Bb

b Bb

Work together to solve the Punnett Square

problems on the next three slides and provide

the phenotype and genotype ratios

Review with your table partner:

Heterozygous Cross Both parents are heterozygous for the tongue

rolling gene. (Tongue rolling is dominant R,

non tongue rolling is recessive r) Rr x Rr

_

_

_

_

__ __

__ __

Phenotype Ratio: _________________________ __ out of 4 receive at least one dominant allele from heterozygous parents.

Genotype Ratio: __________________ ______________________________________________________________________

More Fun with Punnett Squares

The allele for long eyelashes is dominant (L).

The allele for short eyelashes is recessive allele (l).

One parent is heterozygous for long eyelashes (Ll), and the other parent has short eyelashes(ll)

(Ll x ll)

What are their probabilities of having children with long eyelashes or short eyelashes?

_ _

_

_

__ __

__ __

Phenotype ratio: ___________

If one fruit fly is homozygous dominant for normal wings (WW) and the other has vestigal wings (ww), what are the possible offspring?

x

______________________________, ________

_________________________________.

WW ww

Punnett Square Disclaimer

Remember that probabilities are more accurate with a ____________ sample size.

Actual outcomes are often different from expected probabilities especially when the sample size is ___________ , due to ________________________.

Additional online review problem sets:

http://www.biology.arizona.edu/mendelian_genetics/problem_sets/monohybrid_cross/monohybrid_cross.html

http://www.ksu.edu/biology/pob/genetics/mono.htm