Download - 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