Genetics Powerpoint - Liberty Union High School District

Download Report

Transcript Genetics Powerpoint - Liberty Union High School District

MENDELIAN GENETICS
Gregor Mendel? “Father of Genetics”
Heredity  the study of how traits are passed from
parent to offspring
Mendel CROSSED pea plants
Cross = breed 2 different individuals
Tracking Generations
P1 Generation = parent
F1 Generation = 1st offspring
F2 Generation = 2nd offspring
Dominant: always expressed
– TT = tall
– Tt = tall
Recessive: expressed when not with a dominant
– tt = short
GENOTYPE: genetic makeup of genes
– TT
– Tt
– tt
PHENOTYPE: physical expression of genes
– Tall pea plant
– Short pea plant
You can see phenotype,
not genotype
Law of Dominance:
• Some alleles are dominant, others are recessive
– an organism with at least one dominant allele will
display the effect of the dominant allele
– dominant = uppercase
– recessive = lowercase
Example: Straight thumb is dominant to hitchhiker thumb
T = straight thumb t = hitchhikers thumb
Straight thumb = TT
Straight thumb = Tt
Hitchhikers thumb = tt
* Must have 2 recessive alleles
for a recessive trait to “show”
Traits are determined by the genes
gene = segment of DNA that determines a trait
allele – different genes (possibilities) for the same trait
Law of Segregation:
2 alleles that code for a trait separate during
gamete formation (meiosis)
• Both genes are the same – homozygous
AA – homozygous dominant
aa – homozygous recessive
• 1 dominant 1 recessive gene - heterozygous
Aa – heterozygous
AA – Black
Aa – Black
bb – White
Gamete Formation
1) Bb X Bb
B
B b
b
#2) bb x BB
b
bB
B
B
How to Make a Punnett Square
1. Parent genotypes
2. Parent phenotypes
3. Segregate  set up Punnett square
4. Fill  Offspring genotypes
5. Genotype Ratio
6. Phenotype Ratio
Sample Problems
A. PP x pp
B. YY x yy
C. Yy x Yy
Probability Notes
Probability is the likelihood of a particular
event or offspring …given as percent (25%),
ratio (1:4), or fraction (¼)
Mendel’s Laws follow the same probability as
flipping a coin or rolling dice
Formula:
# of one kind of possible outcome
total # all possible outcomes
Rule of Addition
• Chance an event can
occur in 2 or more
different ways
• Use when the word OR
is used
• ADD separate
probabilities
Example:
What’s the
probability of
rolling a 1 or 6?
1/6 + 1/6 = 2/6
Rule of Multiplication
• Chances 2 more
independent events can
occur together
• Use when the word
AND is used
Example:
If you roll 2 dice,
what’s the
probability of rolling
a 1 and 6?
1/6 x 1/6 = 1/36
• Multiply separate
probabilities
You Try:
Work on the problems on your notes
handout
Show work
Answers
• Boy  ½
• Boy or girl  Addition  ½ + ½ = 1
• Boy and girl  Multiplication  ½ x ½ = ¼
• 3 heads in row  Multiplication  ½ x ½ x ½ = 1/8
• Rolling a 6 on a die  1/6
• Rolling a 6 or a 5 on a die  Addition  1/6 + 1/6 = 2/6
• Rolling a 6 and a 5  Multiplication  1/6 x 1/6 = 1/12
• Pulling out Queen of Hearts  1/52
• Pulling hearts as the suit  ¼
• Queen Hearts of heart as suit  heart as suit
• Pulling Queen and Heart  Multiplication  1/52 x ¼ = 1/208
Class Practice
If you toss a penny into the air, what’s the probability
that it will land heads up?
What’s the probability of rolling a 6
with one die?
What’s the probability of pulling the
ace of hearts out of a deck of 52
cards?
What’s the probability of pulling any
ace from a deck of cards?
RULE?
A bag of beans contains 100 white
beans and 100 red beans. What is
the probability of reaching into the
bag and pulling out a white bean?
What’s the probability of tossing 2
coins and having them both land
heads up?
RULE?
What’s the probability of rolling a pair of
dice and getting snake eyes (double 1s)?
Rule?
What’s the probability of rolling a pair
of dice and getting any doubles at all?
Rule?
What’s the probability that a woman’s
first child will be a baby girl?
What’s the probability a family with 3
kids will have 3 daughters?
RULE?
Testcross
Purebred
– Describes a homozygous
trait
– Purebred dominant = AA
– Purebred recessive = aa
– “homozygous”
Hybrid
– Describes a
heterozygous trait
– Aa
– “heterozygous
What do you do if you don’t know
the genotype of the dominant
parent?
TESTCROSS!
Dominant parents can be
homozygous dominant or
heterozygous AA or Aa
 You have to do a TEST to
determine the type of
dominance
HOW?
Breed mystery dominant
parent to a homozygous
recessive parent
If any offspring show the
recessive trait, the
dominant parent HAD to
be heterozygous
Sample
A black mouse is mated with a brown mouse
(black is dominant to brown).
They have 10 black offspring.
What is the genotype of the black mouse?
Several black mice of the same genotype are mated
and produce 29 black and 9 brown offspring.
What are the genotypes of the parents?
Start by thinking of different possibilities!
BB x BB
BB x Bb or Bb x BB
Bb x Bb
Then do a backwards cross [called backcross]