Transcript Lab Biology Chapter 9 - Genetics Mrs. Nemanic

Lab Biology
Chapter 9 - Genetics
Mrs. Nemanic
I. Mendel’s Legacy
Genetics – study of heredity
A. Gregor Mendel
1. Researched heredity – the passing of traits
from parents to offspring.
2. Observed 7 characteristics of garden peas.
a. when he planted seeds from purple
flowers, he noticed most offspring were
purple but some were white.
b. seeds from tall plants produced mostly tall
but some short.
3. Mendel’s Methods
a. pollination – occurs when pollen
grains produced in (anthers) male
reproductive parts of flower are
transferred to (stigma) female
reproductive parts.
b. Self-pollination – when flower is
pollinated by same plant.
c. Cross-pollination – when flower
is pollinated by a different plant.
B. Mendel’s Experiments
1. Trait – different forms for a
characteristic.
2. Pure – always produce offspring with
that trait.
3. Strain – denotes plants that are pure
4. P1 Generation – parental generation
5. F1 Generation – first filial generation
(offspring of P1)
6. F2 Generation – second filial
generation (offspring of F1)
C. Mendel’s Results & Conclusions
1. Recessive & Dominant Traits
a. Dominant – it “masked” the other
‘factor’ ( gene).
b. Recessive – it is not expressed if with
dominant gene.
Recessive traits did not appear in F1 but
reappeared in F2.
2. Law of Segregation – a pair of
‘factors’ ( genes) is segregated, or
separated, during gamete
formation.
3. Law of Independent Assortment –
‘factors’ ( genes) for different
characteristics are distributed to
gametes independently.
D. Chromosomes and Genes
1. Molecular Genetics – study of
structure & function of chromosomes
& genes
2. Gene – a segment of DNA that
controls a trait
3. Allele – alternate forms of a gene
(Mendel’s factors)
a. capital letters refer to dominant
genes
b. lowercase letters refer to recessive
genes
II. Genetic Crosses
A. Vocabulary
1. Genotype – genetic makeup of an
organism
- consists of alleles the organism
inherits
2. Phenotype – appearance of an
organism as a result of its genotype
3. Homozygous – when both alleles of
a pair are alike
a. dominant homozygous Ex: TT
b. recessive homozygous Ex: tt
4. Heterozygous – when 2 alleles in a
pair are different or hybrid

Ex: Tt
B. Probability
1. Probability – the likelihood that a specific
event will occur.
a. expressed as a decimal or percentage or
fraction.
b. probability =
# of times an event is expected to happen
# of opportunities for an event to happen
c. the results predicted by probability are more
likely to occur when there are many trials.
C. Predicting Results of
Monohybrid Crosses
1. Monohybrid – a cross between
individuals involving one pair of
contrasting traits.
2. Punnett Square – a diagram used to
predict results of crosses.
Homozygous x Homozygous
Ex: TT x tt
Homozygous x Heterozygous
Ex: TT x Tt
Heterozygous x Heterozygous
Ex: Tt x Tt
a. Ratios:
– Genotypic Ratio – ratio of genotypes in
offspring
– Phenotypic Ratio – ratio of phenotypes
in offspring
b. Testcross – individual of unknown
genotype is crossed with homozygous
recessive.
C. Dominance:

Complete Dominance – one allele is
completely dominant over another.
(Heterozygous and dominant
homozygous plants are
indistinguishable in phenotype)


Incomplete Dominance – two or
more alleles influence the phenotype,
resulting in intermediate phenotype.
Codominance – both alleles for a
gene are expressed in heterozygous
offspring. Neither allele is dominant
or recessive; nor do they blend in the
phenotype.
D. Predicting Results of
Dihybrid Crosses

Dihybrid Cross – cross between
individuals that involves 2 pairs of
contrasting traits.
a. Homozygous x Homozygous
Ex: RRYY x rryy
b. Heterozygous x Heterozygous
Ex: RrYy x RrYy
Likely to result in 9 different
genotypes & 4 different phenotypes