Download Chapter 9 - Fundamentals of Genetics

Chapter 9 - Fundamentals of Genetics
Heredity - the transmission of characteristics from parents to
offspring
Genetics - the study of how characteristics are transmitted from
parents to offspring
I. Gregor Mendel (father of genetics)
A. Garden Peas
1. observed 7 characteristics of pea plants
a. each had 2 contrasting traits (p. 165)
2. seeds from purple flowered plants produced purple
flowered plants but some white flowered plants also were
produced (why?)
3. to document traits of each generation, he controlled the
pollination
a. pollination - pollen grains from anthers transferred
to stigma
b. self-pollination - pollen from anther to stigma of same
flower (normal method)
c. cross-pollination - involves flowers of two separate plants
B. Why Did Mendel use pea plants?
 Easy to care for
 Short generation time
 Many offspring each generation
 Can control mating between plants
 Require little space to grow
 Several contrasting traits
C. TERMS Mendel used:
1. P1 generation (parental) - a pure strain plant for some trait
2. F1 generation (first filial) - offspring of the P1 generation
3. F2 generation (second filial) - offspring of F1 generation
4.factors - something in pea plants controlling traits
a. hypothesized each characteristic controlled by separate
factor
b. since each characteristic had 2 alternative forms, must
be pair of factors for each trait
5. Law of dominance
a. trait appearing in F1 must be controlled by dominant
factor (prevents other factor from having an effect)
b. trait not appearing in F1 but reappearing in F2 must be
controlled by recessive factor (factor hidden by
dominant)
6. Law of Segregation
a. a pair of factors is segregated, or separated, during the
formation of gametes
b. describes what happens in meiosis
7. Law of Independent Assortment
a. P1 yellow seed, round seed X green seed, wrinkled seed
1) F1 all yellow, round
2) F1 yellow, round X yellow, round (offspring F1)
F2: yellow, round
green, wrinkled
round, green
yellow, wrinkled
b. factors for different characteristics are distributed to
gametes independent of each other
1) dominant factors don't have to appear together nor do
recessive
c. described by tetrads lining up randomly in metaphase I
D. Molecular Genetics
1. study of structure and function of chromosomes and genes
2. gene is segment of DNA on chromosome controlling a trait
a. chromosomes in pairs, so genes are in pairs
3. allele - the alternative forms of a gene
E. symbols and terms
1. dominant allele represented by capital letter (G)
2.recessive allele represented by lower case same letter (g)
3. homozygous (pure strain) - both alleles of pair are
alike
GG - homozygous dominant
gg - homozygous recessive
4. heterozygous (hybrid) - two alleles of pair are different- Gg
5. genotype - genetic makeup of organism
(alleles it possesses for a trait) GG, Gg, gg
6. phenotype - the appearance of an organism as a result of
its genotype
7. genotypic ratio - ratio of genotypes appearing in offspring
8. phenotypic ratio - ratio of offspring's phenotypes
II. Genetic Crosses and Probability
A. Probability
1. the fraction or percentage that describes the chance of an
event taking place
2. probability = # of times an event is expected to happen
# of opportunities for an event to happen
a. predicts what should happen mathematically, not what will
happen (chance)
b. the larger the sample size (# of trials) the closer expected
and observed results should be
3. flipping a coin, throwing a die, spinner activity
4. flipping 2 coins 1/2x1/2=1/4:
throwing 2 dice: 1/6X1/6=1/36
Occurring together = 1/4x1/36=1/144
a. product rule - probability of 2 or more independent
events occurring together, is the product of their
individual probabilities
B. Predicting Results of Monohybrid Crosses
* cross involving one pair of contrasting traits
Punnett square - diagram to predict probability that certain traits
will be inherited by offspring
P
P
1. Key: PP/Pp = purple flower
pp = white flower
p
genotypic ratio
p
phenotypic ratio
2. Key: B= black coat
b = brown coat
genotypic ratio
BB x Bb
phenotypic ratio
3. Key: B= black coat
b = brown coat
Bb x Bb
genotypic ratio
phenotypic ratio
4. Key: B= black coat
b = brown coat
Bb x bb
genotypic ratio
phenotypic ratio
Sample Problems
5. How do you know if a black guinea pig is homozygous or
heterozygous?
a. test cross - organism of unknown genotype is mated
with a homozygous recessive organism
6. incomplete dominance - two or more alleles influence
phenotype, resulting in intermediate phenotype
between dominant and recessive
Key: RR= red flowers
rr = white flowers
Rr = pink flowers
Rr X Rr
genotypic ratio
phenotypic ratio
7. codominance - neither allele dominant or recessive,
nor do allele blend
a. both alleles expressed in heterozygous
individual
Key:
RR = red coat
R'R’ = white coat RR’ x RR’
RR' = roan coat
genotypic ratio
phenotypic ratio
C. Predicting Results of Dihybrid Crosses(NOTES)
cross involving 2 pairs of contrasting traits
1. Key: R= round seeds
r = wrinkled seeds
Y = yellow seeds
y = green seeds
RRYY X rryy (P1)
(RY) x (ry)
RrYy (F1)
RrYy X RrYy
(one trait)
# genotypes
# phenotypes
(two trait)
# genotypes
# phenotypes
Genotypic ratio:
RRYY : RRYy : RRyy : RrYY : RrYy : Rryy : rrYY : rrYy: rryy
Phenotypic ratio:
Round Yellow : Round Green : Wrinkled Yellow : Wrinkled Green
III. Human Genetics
A. Studying Human Inheritance
1. pedigree - family record showing how trait is inherited
over several generations (to find how traits are inherited)
a. show patterns of inheritance
b. carriers - have one recessive allele but don’t
express it (can pass it on to offspring)
http://www.youtube.com/watch?v=eYlJH81dSiw