Transcript Mendelian Genetics Notes Powerpoint

Gregor Mendel
• Gregor Mendel
was a monk who
studied heredity
using pea plants
• He came up with a
couple of laws for
determining
heredity
F1: Yy (Yellow)
Where did the green
color go?
What if you cross the
F1?
http://www.dnaftb.org/dnaftb/4/concept/index.html
F1: Gametes
F2 Generation:
YY-Yellow
Yy – Yellow
yy - Green
The recessive
gene shows up in
the F2 generation
when both alleles
for green are
present.
Symbols of Heredity
• Homozygous (pure)
– Having a pair of identical genes for a trait
– Ex: Tall (T) = TT, or tt
• Heterozygous (hybrid)
– Having two different genes (alleles) for a
trait
– Ex: Tt
Mendel’s Laws
1. Law of Dominance:
• In a cross between 2 pure contrasting
traits (tall vs. short), only one of these
traits appear in the next generation
• This is called the DOMINANT
TRAIT
• The one that does not appear is called
the RECESSIVE TRAIT
The Punnett Square
• Determines the probability of
obtaining various results in
genetic crosses
• Ex: cross a homozygous tall
(TT) and a heterozygous tall
(Tt)
• 1:2:1 ratio
• 1TT (Homozygous Tall)
• 2 Tt (Heterozygous tall)
• 1 tt (homozygous recessiveshort)
TT
Tt
Tt
tt
Cross 2 Heterozygotes
1:2:1 Ratio for a
heterozygote
trait which is
what Mendel
observed.
1: AA
2: Aa
1: aa
Monohybrid Cross
• Crossing
one trait
Dihybrid Cross
•Crossing
2 traits
Let’s do some Punnett Squares!!!!
1. Cross a Pure Tall with a Pure short plant. (T=Tall t=short)
Give ratios for genotype and phenotype
2. What is the expected ratio of offspring produced in crossed between
hybrid tall pea plants and pure tall pea plants?
3. What ratios can be expected in the offspring of a cross between hybrid
tall and short pea plants?
4. Mendel found that pure wrinkled plants crossed with pure round led to
100% round. What ratio can be expected in crossed between
wrinkled and hybrid round? (R=round r=wrinkled)
Mendel’s Laws:
2. The Law of Segregation:
• The idea that genes separate
from each other during meiosis
(gamete formation) and then
recombine at fertilization
3. Law of Independent
Assortment
•Each Allele pair
segregates
•
independently
of
the other allele
pairs during
meiosis.
•This is true
ONLY if the
alleles are on
different
chromosomes.
Karyotype: A
visual layout of
all the
chromosomes in
the nucleus of a
cell.
Used to indicate
if there are any
genetic
abnormalities.
•Each member
of a homologous
pair assorts
independently
How can we use our knowledge of inheritance patterns to trace a
disorder through a family and predict what future offspring
might be like for a trait?
Some traits operate according to the Law of Dominance
Let’s see what your genotypes and phenotypes are!!!
What is your genotype and
phenotype?
Trait
Chromosome Dominant
location
Phenotype
Possible
Dominant
Genotypes
Recessive
Phenotype
Recessive
Genotype
Widow’s
peak
4
PP or
Pp
No
peak
pp
Peak
Trait
Chromosome
Dominant
Phenotype
Possible
Dominant
genotypes
Hitchhikers
thumb
17
Straight
TT or Tt Curved
Ear
Lobes
21
Free
LL or Ll Attached ll
Ability
RR or Rr No
ability
Tongue 22
Rolling
Recessive Recessive
Phenotype Genotype
tt
rr
Take the person next to you and perform a Punnett Square for 2 of
the traits described
1. Create a separate Punnett square for each trait.
2. Determine the genotypes of your children
3. Determine the phenotypes of your children.
Enrichment:
Can you perform a dihybrid cross? Using the traits of tongue
rolling and widow’s peak, create the possible gametes and use a
4X4 Punnett square to predict the outcomes for the offspring.
Cross: TtPp X TtPp
TP
Tp
tP
tp
Incomplete Dominance
(Blending)
• Crossing 2 homozygous
parents whose offspring
look totally different
than parents
• Ex: Cross a pure red
snapdragon (RR) and a
pure white snapdragon
(WW)
• Offspring Phenotype:
____________________
Codominance
• Two dominant alleles
are expressed at the
same time
• Ex: Roan cattle
• Cross a homozygous
red coat cow (RR)
and a homozygous
white coat cow (WW)
Multiple Alleles
Blood Type A: AA or Aa
Blood Type B: BB or Bb
Blood Type O: ii
Classic Dominance and
Recessive inheritance
Blood Type AB: What
type of inheritance is this?
Co Dominance: Both
surface antigens are
produced equally.
• Ex: Human blood
type
• Cross a man with AB
blood (IAIB) and a
woman with type O
blood (ii)
Summary: Types of Dominance
Complete
Incomplete
Codominance
Genotype:
AA/Aa
Phenotype:
Only dominant
allele is
expressed
Genotype:
Aa
Phenotype:
Intermediate
between both
alleles
Genotype:
Aa
Phenotype:
Both alleles
expressed equally
Sex-linked
•Referring to a gene that is part of a sex chromosome.
• Since all of the genes on a chromosome are inherited as a
package, they are essentially linked together.
sex-linked
Common Sex Linked
disorders:
Color blindness
Hemophilia
Pedigrees: A diagram that shows how
family members are related (genetically)
2 Individual 2 is most likely a:
A. normal male
B. normal noncarrier female
C. color-blind male
D. carrier female
E. color-blind female
If individual 8 is not color blind, what is the probability that this
individual is a carrier?
A. 0
B. 1/4
C. 1/2
D. 3/4
E. 1
4. Individual 11 must be a:
A. carrier female
B. color-blind male
C. color-blind female
D. normal male
E. A or C
5. Which of the following describes individual 17?
A. The daughter of individuals 10 and 11.
B. A carrier female
C. A mistake
D. The result of a one night stand between individual 11
and a color-blind man.
E. C or D
6. Let us say individual 12 marries a normal, non-carrier
female. What is the probability that one of his sons will be
color-blind?
A. 0
B. 1/4
C. 1/2
D. 3/4
E. 1
7. Individual 5 has just married a woman who is not color-blind. This woman
was previously married to a color-blind man, and together they had a colorblind son. As newlyweds, this couple seeks your help as a genetic counselor.
What advice could you give?
A. Go ahead and have children: there's no chance that any will be color-blind.
B. 50% of your daughters may be color-blind.
C. 50% of your sons may be color-blind.
D. 25% of your sons may be color-blind.
E. Sorry, I can't help. Anything I could tell you would just be a wild guess.
8. Individuals 4 and 6 can be best described as:
A. Twins
B. Brothers
C. Color-blind
D. Sisters
E. A and D