Transcript Fundamentals of Genetics

Fundamentals of Genetics
Introduction to Genetics
1. GREGOR MENDEL - “Father of Genetics”
• Austrian monk, teacher, scientist, gardener
• Formulated basic laws of heredity in the early 1860s
• Simplified problems; was meticulous with data collection;
think quantitatively
2. Worked with garden peas because:
• Easy to grow and had a short generation time
• Could be self-pollinated
3. Chose true-breeding varieties for his experiments
• Means no genetic variation for a trait
• Studied 7 simple traits
4. Mendel cross-pollinated plants
•
•
•
P1 = parental generation
F1 = first-generation
(sons/daughters)
F2 =second-generation
5. Principle of Dominance and Recessiveness
• F1 plants resembled only one of the parents
• F1 hybrids contained two factors for each trait
• one dominant; (stronger, masks recessive);
• one recessive; (seems to disappear)
6. Principle of Segregation
• Organism contains two factors for each trait.
• Factors segregate during formation of gametes.
• Each gamete contains one factor for each trait.
7. Principle of Independent Assortment
•
Each trait is independent of another
•
Genes of one pair of traits assort
independently
•
All combinations of genes occur in gametes
STOP
IN: P12
• Why did Mendel select pea plants to
study?
OUT: P 12
Pick any dominant and recessive trait.
Complete and diagram the 3 types of
.
monohybrid crosses below.
1. Homozygous x Homozygous
2. Homozygous
x Heterozygous
.
3. Heterozygous x Heterozygous .
.
Chromosomes, Genes, and Genetic Crosses
1. Homologous
Chromosomes contain
genes (locations) for
the same traits
2. Traits are controlled by
alleles (alternative
forms of a gene).
3. Genotype refers to the
alleles an individual
receives at fertilization
4. Phenotype refers to
the physical
appearance
of the individual.
5. Homozygous dominant genotypes =
two dominant alleles for a trait. (BB)
6. Homozygous recessive genotypes =
possess two recessive alleles for a trait (bb)
7. Heterozygous genotypes =
one of each allele for a particular trait (Bb)
8. Punnett Squares
• Show probabilities of future offspring
• Monohybrid crosses = crosses between
individuals that involve one pair of contrasting traits.
9. Monohybrid Crosses (Examples)
Ex 1: Pure Tall x Pure Short
TT=Tall
tt =short
F1
T
t
t
F2
T
Tt
Tt
Tt
Tt
100% Tall
T
t
T
TT
Tt
t
Tt
tt
25% pure tall
50% hybrid tall
25% pure short
(Homozygous x Homozygous)
(Heterozygous x Heterozygous)
10. Test Crosses
• A cross of an individual of unknown genotype with an
individual of known genotype
• Tells if individual is heterozygous or homozygous
• Very important to breeders
STOP
Dominance Has Degrees
1. Incomplete dominance
• Offspring are intermediate
between two parental
phenotypes
• Neither allele is completely
dominant over the other
• Both alleles influence
phenotype
• 3 phenotypes
• Ex: Japanese Four o’clocks
RR = red RR’ = pink R’R’ = white
R
R
R’
RR’
R’
RR’
RR’
RR’
All Pink
R
R’
R
RR
RR’
R’
RR’
R’R’
1 red : 2 pinks : 1 white
2. Codominance
• Both alleles of a
gene are expressed.
• A person with AB
blood has both A and
B antigens on their
red blood cells.
• Neither allele is
dominant or
recessive
RED
WHITE
ROAN
• Ex: Red Coat - RR
White Coat – WW
White & Red Mixed – RW (“roan”)
W
W
R
R
RW
RW
RW
RW
All Roan – both red and white
hair
R
W
R
W
RR
RW
RW
WW
1 red : 2 roan : 1 white
STOP
IN: P 28
My Steps for Dihybrid Crosses
• 1. Underline: What’s dominant, recessive,
and the parents
• 2. Genotype and phenotype possibilities
• 3. Write genotypes of parents
• 4. Diagram possible gametes
X
• 5. Do cross
• 6. Answer question asked
OUT: P 28
•
•
•
•
Prepare Data Table
Count Kernels (C or D)
PREDICT GENOTYPE of PARENTS
purple and smooth are Dominant
Purple
Smooth
Purple
Wrinkled
Yellow
Smooth
Yellow
Wrinkled
Dihybrid Cross
Feather color = ORANGE or blue
CREST or no crest
A cross involving two pairs of
contrasting traits
• Example:
Dominant
Recessive
Yy, YY = yellow yy = green
Rr, RR = round rr = wrinkled
Example cont.
P1 RRYY
x
round, yellow
(homozygous)
rryy
wrinkled, green
(homozygous)
RY
RY
ry
RrYy
RrYy
ry
RrYy
RrYy
Offspring are all heterozygous
RrYy X RrYy
• Law of Independent Assortment
Genes for different traits are inherited
independently
R, r, Y, y go to sperm/egg independently of
each other
Can recombine in four ways:
RY, Ry, rY, ry
RY
RY
Ry
rY
ry
Ry
RRYY
rY
ry
.
9 round,yellow :
3 round, green :
9:3:3:1
3 wrinkled, yellow :
1 wrinkled ,green
RY
Ry
rY
ry
RY
RRYY
RRYy
RrYY
RrYy
Ry
RRYy
RRyy
RrYy
Rryy
rY
RrYY
RrYy
rrYY
rrYy
ry
RrYy
Rryy
rrYy
rryy