Topic: Modeling Inheritance

TOPIC: MODELING INHERITANCE

EQ: How can inheritance be modeled?

Tt

T

t

T

t

¼

OBJECTIVE

THE STUDENT WILL DEMONSTRATE AN UNDERSTANDING OF HOW INHERITANCE CAN BE MODELED

STUDENTS WILL DEMONSTRATE HOW TO USE A PUNNETT SQUARE TO MODEL INHERITANCE

STUDENT EXPECTATIONS

Understand how to make predictions about possible outcomes of genetic combinations using an organisms inherited genotypes.

T t

T

T

TT Tt

For each monohybrid cross, Mendel cross-fertilized true-breeding plants that were different in just one character—in this case, flower color. He then allowed the hybrids (the F1 generation) to self-fertilize.

Mendel’s Conclusions of how often traits are passed!!!! Mendel found that

traits usually passed with the following ratios.

This was used to predict expected genetic outcomes

He found that for every cross these results were found.

¾

75%

3:1 (usually there were 3 traits

for every one trait seen

What controls traits?

ChromosomesHomologous chromosome: one of a matching pair of chromosomes, one inherited from each parent.

Sister chromatids are identical

Genes

Factors that are passed from one generation to the next…

Genes come in different forms called alleles: ex: tall and short

Some are seen and some are not

DOMINANT/RECESSIVE_____________ allele is represented by a ____________ letter.(usually the first letter of the trait)

____________ allele is represented by the SAME

_________________ letter.

EX: Tall = ______

Short =______

capital

lower-case

T

tNOT S for short

Dominant

Recessive

Important: You will only see a recessive trait if you inherit two recessive traits. If not you will always see the dominant trait

Phenotype– An organism’s physical traits

1. Tall or short• Genotype

– An organism’s genetic makeup

1. Letters Tt or Tt

HOMOZYGOUSHETEROZYGOUS

When both alleles in the pair are

the _______, the organism is _______________ or __________

EX: ____ or ___When both alleles in the pair are

_____________, the organism is_________________ or _____________

Ex: ____

HETEROZYGOUS HYBRID

HOMOZYGOUS PUREBREDSAME

TT tt

DIFFERENT

Tt

It can be written as a:Fraction

Percent ____Ratio

____________________is the __________ that a particular _________________

PROBABILITY

1/4

25%

1:3

likelihood

event will occur

COIN FLIPThere are 2 possible

outcomes:HEADS TAILS

capital

http://www.arborsci.com/CoolStuff/CoinFlip.jpg

The chance the coin will land on either one is:____ ____ ____

Alleles segregate randomly just like a coin flip. . . So can use probability to predict outcomes of genetic crosses.

1/2 50% 1:1

TOOLS FOR MODELING INHERITANCE

A PUNNET SQUARE IS A TOOL USED TO PREDICT THE POSSIBLE GENOTYPES FOR THE OFFSPRING OF TWO KNOWN PARENTS.

PARENT’S GENES

PA

RE

NT

’S G

EN

ES

How Does it Work?

1. ___________ what _________________ are2. ________correct__________ square __________3. ______ possible_______________________4. ______ boxes with _____________________5. Determine ____________of_____________& ____________

STEPS FOR MAKING CROSSES using Punnett Squares!

Figure out parent alleles (genotypes)Choose Punnett sizePut in parent alleles (genotypes)Fill in offspring combinations probabilities phenotypes

genotypes

IN PEA PLANTS

Tall is dominant over short

TALL = ____ SHORT = ____

Tt

LET’S MAKE A CROSS!

PURE TALL PURE SHORT

X

PURE TALL parentWhat are the parent alleles?

T T _________

T T

HOMOZYGOUS

What gametes can it make?

PURE SHORT parent What are the parent alleles?

t t _________

t t

HOMOZYGOUS

What gametes can it make?

GENOTYPE _____ PHENOTYPE _______

_____ of the offspring

____ % ___/4 will be

T T

t

t

T t T t

T t T tTt

TALL

ALL

100

4

HOW TO USE A MONOHYBRID (ONE TRAIT) PUNNETT SQUARE

THE PARENTS’ ALLELES GO ON THE OUTSIDE OF THE SQUARE B B

b

b

B B

B B

DROP THE LETTERS ON THE TOP, INTO EACH SQUARE

MOVE EACH LETTER ON THE SIDE, INTO EACH SQUARE

THE ORDER DOES NOT MATTER IN THE BOXES, BUT UPPERCASE FIRST IS A GOOD RULE

b b

b b

HOW TO USE A MONOHYBRID (ONE TRAIT) PUNNETT SQUARE

THE PARENTS’ ALLELES GO ON THE OUTSIDE OF THE SQUARE B B

b

b

BB X bb

HOW TO USE A MONOHYBRID (ONE TRAIT) PUNNETT SQUARE

B B

b

b

Bb Bb

Bb Bb

WHAT DO THE RESULTS SHOW?

IF B IS THE DOMINANT ALLELE FOR BLACK

AND b IS THE RECESSIVE ALLELE FOR BROWN

THEN WE CAN MAKE PREDICTIONS ABOUT THE OUTCOMES

RESULTS:

PHENOTYPIC: 100% BLACK

4:0 RATIO, BLACK TO BROWN

GENOTYPIC:

100% Bb

4:0 ALL Bb

HOW TO USE A PUNNETT SQUARE

T t

T

t

WHAT ARE THE RESULTS?

PHENOTYPIC: 75% TALL 25% SHORT

3 TO 1 RATIO: TALL TO SHORT

GENOTYPIC:

1TT: 2Tt: 1tt 1:2:1 RATIO

25 %TT, 50% Tt, 25% tt

LET’S LOOK AT ANOTHER PUNNETT SQUARE AND PREDICT THE OUTCOME T T

T t

T t

t t

T IS THE DOMINANT ALLELE FOR TALLNESS

t IS THE RECESSIVE ALLELE FOR SHORTNESS

B b

B

b

BB

Bb

Bb

bb

TAKS FORMATTED ITEMS

3. IF B IS THE ALLELE FOR BLACK FUR AND b IS THE ALLELE FOR WHITE FUR, WHAT PERCENT WOULD BE BLACK?

A. 25%B. 50%C. 100%D. 75%

4. WHAT FRACTION IS HOMOZYGOUS DOMINANT IN THE ABOVE CROSS?

A. 1/2B. 1/4C. 1/3D. 3/4

TERMS TO KNOW

ALLELES DIFFERENT FORMS OF A TRAIT THAT A GENE MAY HAVE T,t

HOMOZYGOUS AN ORGANISM WITH TWO ALLELES THAT ARE THE SAME TT, tt

HETEROZYGOUS AN ORGANISM WITH TWO DIFFERENT ALLELES FOR A TRAIT Tt, Gg

TERMS TO KNOWHYBRID SAME AS

HETEROZYGOUS Tt, GgDOMINANT A TRAIT THAT

DOMINATES OR COVERS UP THE OTHER FORM OF THE TRAIT

REPRESENTED BY AN UPPERCASE LETTER

T OR GRECESSIVE THE TRAIT BEING

DOMINATED OR COVERED UP BY THE DOMINATE TRAIT

REPRESENTED BY A LOWER CASE LETTER

t or g

Topic: Understanding Inheritance EQ: How can

inheritance be modeled?

TERMS TO KNOW

PHENOTYPE THE PHYSICAL APPEARANCE OF AN ORGANISM(WHAT IT LOOKS LIKE)

Tall, short, etc..

GENOTYPE THE GENE ORDER OF AN ORGANISM(WHAT ITS GENES LOOK LIKE)

TT, GG, Tt, ggGg, tt

RATIO THE RELATIONSHIP IN NUMBERS BETWEEN TWO OR MORE THINGS

3:1, 2:2, 1:2:1

PRACTICAL APPLICATION OF PUNNETT SQUARES

THE ALLELES OF A PARTICULAR SPECIES OF DOG CAN BE EITHER D (NORMAL HEIGHTH) OR d (DWARF). THE HETEROZYGOUS (Dd) AND HOMOZYGOUS DOMINANT (DD) FORM OF THIS DOG LOOK THE SAME (TALL). IF YOU FOUND A STRAY DOG OF THIS BREED, HOW COULD YOU DETERMINE ITS GENOTYPE?

PRACTICAL APPLICATION OF PUNNETT SQUARES

COULD A DOG BE CROSSED WITH ANOTHER DOG TO DETERMINE IF HE WAS PUREBRED FOR TALLNESS?

WHAT GENOTYPE SHOULD THE DOG HAVE THAT IS BEING USED FOR THE CROSS?

PRACTICAL APPLICATION OF PUNNETT SQUARES

IF THE DOG IS PUREBRED (DD), IT DOESN’T MATTER WHAT YOU CROSS IT WITH, THE OFFSPRING WILL ALWAYS LOOK LIKE THE DOMINANT.

D D

D

DD

D D

D

D

D

d d

dDD

D

Dd Dd DdDd

Dd Dd

DD

DD

DD

DD

PRACTICAL APPLICATION OF PUNNETT SQUARES

WHAT WOULD BE THE MOST EFFECTIVE CROSS FOR DETERMINING IF THE DOG IS HETEROZYGOUS (Dd) ? CROSSING IT WITH A PUREBRED (DD) WILL NOT HELP.

D

WHAT WOULD THE RESULTS BE IF YOU CROSSED IT WITH ANOTHER HETEROZYGOUS?

d

D

d

D d

d

d

WHAT WOULD THE RESULTS BE IF YOU CROSSED IT WITH A HOMOZYGOUS RECESSIVE (dd)?

DdDD

Dd dd

Dd

Dd

dd

dd

PRACTICAL APPLICATION OF PUNNETT SQUARES

D d

D

d

DdDD

Dd dd

D d

d

d

Dd

Dd

dd

dd

THE HETEROZYGOUS CROSS WOULD ONLY GIVE YOU A 25% CHANCE OF THE RECESSIVE TRAIT APPEARING.

THE MOST EFFECTIVE CROSS WAS USING THE HOMOZYGOUS RECESSIVE. THIS WOULD GIVE A 50% CHANCE OF THE RECESSIVE TRAIT APPEARING.

THIS PROCESS IS CALLED A TEST CROSS. IN A LITTER OF DOGS, IF A RECESSIVE DOG APPEARS, THEN YOU KNOW THAT THE ORIGINAL DOG WAS NOT A PUREBRED.

TAKS FORMATTED ITEMS

IN DROSOPHILA MELANOGASTER (FRUIT FLIES), RED EYE COLOR (R) IS DOMINANT OVER BROWN EYE COLOR (r). IF THE FLIES IN THE PICTURE WERE CROSSED, WHAT PERCENT OF THEIR OFFSPRING WOULD BE EXPECTED TO HAVE BROWN EYES?

ANSWER: 50%

TAKS FORMATTED ITEMS

H h

H

h

4

3

1

2

1. WHICH OF THE FOLLOWING HAS THE hh GENOTYPE?

A. 1 & 3B. 2C. 4D. NONE

2. WHICH OF THE FOLLOWING IS A TRUE STATEMENT?

A. INDIVIDUAL 4 IS RECESSIVEB. INDIVIDUALS 1 & 3 ARE HETEROZYGOUSC. INDIVIDUAL 2 IS DOMINANTD. ALL INDIVIDUALS ARE FEMALE

B B

B

b

BB

Bb

BB

Bb

TAKS FORMATTED ITEMS

5. IN THIS CROSS, WHAT IS THE RATIO OF BB TO Bb?

A. 3 : 1B. 4 : 1C. 2 : 2D. 0 : 4

BIBLIOGRAPHY

• Mendel picture provided by wikipedia.com

• Dog and tree pictures provided by Microsoft ClipArt

• Graphics from TEA/ TAKS information booklet Middle School Science Grade 8

• Dice graphic from Microsoft Clipart