genetics teks 6f: predict possible outcomes of various genetic combinations such as monohybrid...

GeneticsGeneticsTEKS 6F: TEKS 6F: Predict possible outcomes of various Predict possible outcomes of various genetic combinations such as monohybrid genetic combinations such as monohybrid crosses, dihybrid crosses, and non-Mendelian crosses, dihybrid crosses, and non-Mendelian inheritance.inheritance.

Gregor MendelGregor MendelFather of Modern GeneticsFather of Modern Genetics

• Performed experiments with pea plants

• Helped determined how traits are passed from one generation to the next.

How are offspring influenced by How are offspring influenced by genetic combinations? genetic combinations?

• Parents pass on units of information called genes.

• These genes produce traits, which are characteristics that make up an organism. Ex: height, hair color, blood type, intelligence.

• For each trait, an individual has two alleles (different forms of a gene). Alleles are represented as letters (ex: TT can stand for the trait of tallness). How are these passed along?

Where she get that booty from?Where she get that booty from?She get it from her momma…She get it from her momma…and her daddyand her daddy

• Traits are passed on from parents.

• You inherit ½ of your genes from your mom and the other ½ from your dad.

• These come from the sperm and the egg when an egg is fertilized.

Mendel’s principle of Mendel’s principle of dominancedominance

• Mendel’s principle of dominance states that some alleles are dominant and others are recessive.

• Dominant alleles are written with capital letters (ex: TT, Tt)

• Recessive alleles are always written in lower case letters (ex: tt)

• The recessive allele is exhibited only when the dominant allele is not present.

1. How do I know if it’s dominant?• If there is even one big letter,

it is dominant. (TT and Tt)2. Why is Tt dominant if it has a

small letter?• Because there is a big letter

next to it. Dominant will always overpower recessive!

3. How do I know if it’s recessive?• If it has two little letters, it is

recessive. (tt)

Homozygous vs. Homozygous vs. HeterozygousHeterozygous

• When both alleles (letters) are the same, the individual is homozygous for that trait. This is also called true-breeding.

• When the alleles are different, the individual is heterozygous for the trait. This is also called hybrid.

1. What if the letters are both big, like SS or TT?• It is Homozygous.

2. What if the letters are both little, like ss or tt?• It is Homozygous.

3. What if one letter is big and one letter is little, like Ss or Tt?• It is Heterozygous because

they are different sizes.

Genotype vs. PhenotypeGenotype vs. Phenotype

• The genetic makeup of an organism is called its genotype. Write this as letters, like TT.

• The organism's physical traits are its phenotype. Write this as a description, like tall, red..

1. Is Aa a genotype or phenotype?• Genotype! Because it’s just

the letters.2. Are purple, tall, short, white, and

round genotypes or phenotypes?• Phenotypes! Because it’s a

physical description.3. What is an organism’s genotype if

it receives two recessive alleles for height (T=tall, t=short)?• tt. Because little letters are

recessive. The phenotype would be short.

How can you predict which traits How can you predict which traits will be expressed using will be expressed using monohybrid crosses?monohybrid crosses?

• When doing a genetic cross, the parent organisms are the P, or parental generation.

• The offspring are called the F1, or first filial generation.

• A monohybrid cross is a cross in which there are two contrasting alleles for a single trait.

• A Punnett square is a diagram that helps predict combinations in genetic crosses. Punnett squares are easy to construct.

• Do this animation: http://www.siskiyous.edu/class/bio1/genetics/monohybrid_v2.html

• You can watch this for more practice and explanation: http://biology-animations.blogspot.com/2011/07/punnett-square-animation.html

http://www.siskiyous.edu/class/bio1/genetics/monohybrid_v2.html



http://biology-animations.blogspot.com/2011/07/punnett-square-animation.html



Practice with monohybrid Practice with monohybrid crosses on the whiteboard!crosses on the whiteboard!

What if you are using more What if you are using more than one trait, like someone than one trait, like someone that has that has blue eyes blue eyes andand isis

short?short?• You would use a dihybrid cross

instead of a monohybrid cross.• A dihybrid cross is a cross that

shows the possible offspring for two traits.

How do you predict the outcomes How do you predict the outcomes of dihybrid crosses?of dihybrid crosses?

Let’s do an example!

Fur Color:B: Black b: White

Coat Texture:R: Roughr: Smooth

In this example, we will cross:

A heterozygous black/heterozygous rough individual with another heterozygous black/heterozygous rough individual. Their genotypes will be: __________.

BbRr x BbRr

BbRr x BbRrFirst, you must find ALL possible gametes that can be made from each parent.Remember, each gamete must have one B and one R.

BR, BrbR, br

BR, BrbR, br


BbRr x BbRr

Possible gametes:BRBrbRbr

Next, arrange all possible gametes for one parent along the top of your Punnett Square, and all possible gametes for the other parent down the side of your Punnett Square…



Coat Texture:R: Roughr:

Smooth

BbRr x BbRr

BR

bR

br

bR

Br

BR

br

Br

Then, find the possible genotypes of the offspring




Smooth

BbRr x BbRr

BR

bR

br

bR

Br

BR

br

Br

BBRR

BbRR BbRr

BBRr BBrr BbRr Bbrr

BbRR BbRr bbRR bbRr

BbRr Bbrr bbRr bbrr

BBRr


BR bR

br

bR

Br

BR

br

Br

BBRR

BbRR

BbRr

BBRr BBrr BbRr Bbrr

BbRR

BbRr bbRR

bbRr

BbRr Bbrr bbRr bbrr

BBRr

How many of the offspring would have a black, rough coat?

How many of the offspring would have a black, smooth coat?

How many of the offspring would have a white, rough coat?

How many of the offspring would have a white, smooth coat?



Smooth


BR bR

br

bR

Br

BR

br

Br

BBRR

BbRR

BbRr

BBRr BBrr BbRr Bbrr

BbRR

BbRr bbRR

bbRr

BbRr Bbrr bbRr bbrr

BBRr

How many of the offspring would have black, rough coat?

How many of the offspring would have a black, smooth coat?

How many of the offspring would have a white, rough coat?

How many of the offspring would have a white, smooth coat?

Phenotypic Ratio

9:3:3:1


In pea plants, yellow seeds (Y) are dominant over green seeds (y), and rounded peas (R) are dominant over wrinkled peas (r).

1. Cross a plant that is heterozygous for both traits with a plant that is homozygous recessive for both traits. Draw a Punnett square to show all possible offspring, and determine the genotypic and phenotypic ratios.

More dihybrid practice..More dihybrid practice..

YyRr X yyrrYyRr X yyrr

YR yR

yr

yr

yr

yr

yrYr

YyRr yyRr yyrr

YyRr Yyrr yyRr yyrr

YyRr Yyrr yyRr yyrr

YyRr Yyrr yyRr yyrr

Yyrr

Non-mendelian genetics: Non-mendelian genetics: What are some other What are some other patterns of inheritance?patterns of inheritance?Some forms of inheritance are distinctly non-Mendelian inheritance because they do not follow the principles described by Gregor Mendel.

Incomplete DominanceIncomplete Dominanceandand

CodominanceCodominance

Incomplete DominanceIncomplete Dominance

• Neither allele is dominant, so the traits blend together.• Phenotypes combine to create a separate trait.• Example, red and white snapdragons = offspring pink

snapdragons

• You can use two different letters now!

• RR (red) X WW (white)

RR RR

WW RWRW

pinkpinkRWRW

pinkpink

WW RWRW

pinkpinkRWRW

pinkpink

Incomplete DominanceIncomplete Dominance

Incomplete Dominance Incomplete Dominance PracticePractice

• Cross of two purple flowers (what 2 colors make purple?)____ X ____

• What are the genotype ratios? 1RR : 2RB : 1BB1RR : 2RB : 1BB• What are the phenotype ratios? 1red : 2 purple : 1 blue1red : 2 purple : 1 blue• Can you have a

heterozygous red orhybrid blue flower? ___

B

R

R B

BBRB

RR RBred

purple

purple blue

RBRB RBRB

nono

CodominanceCodominance

• Expression of both alleles equally• Phenotype of both traits are seen in

heterozygous individuals• Example black rooster and white chicken produce offspring with both

black and white feathers.

Punnett Square of Codominant Punnett Square of Codominant crosscross

• Expressed as two separate traits in a Punnett Square Cross

• BB (black) X WW (white)

BB BB

WW BWBW

(Black and (Black and white)white)

BWBW

(Black (Black and and white)white)

WW BWBW

(Black and (Black and white)white)

BWBW

(Black (Black and and white)white)

genetics teks 6f: predict possible outcomes of various genetic combinations such as monohybrid...

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