Download 11 3 exploring - guided reading

11-3: Exploring Mendelian
Genetics
Pgs 272 - 273
Honors Biology
Block 1
Independent Assortment –
Figure 11-9
• P generation
• round yellow x
wrinkled green
• RRYY x rryy
• F1 generation are all
genotype RrYy.
Independent Assortment –
Figure 11-10
• RrYy x RrYy
• Results in a 9:3:3:1
phenotype ratio.
• This cross shows alleles
for seed shape segregated
independently of those
for color – independent
assortment.
Mendel’s Principles:
• Genes determine biological characteristics and
are passed parent to offspring.
• When two or more genes determine a trait some
forms may be dominant and some may be
recessive.
• Organisms that reproduce sexually receive half of
their genes from each parent.
• Alleles for genes usually segregate independently
of each other.
Genetic Interactions
• Until today we have discussed simple
dominant recessive interactions. If a
dominant allele is present with a
recessive, the recessive will be hidden
and not show in the phenotype of the
offspring.
• There are many genes that have more
than one allele that is neither dominant
or recessive.
Incomplete Dominance
• Neither allele is
completely dominant.
• The genes seem to
mix with one another.
• Examples: fouro’clock flower,
shorthorn cattle, and
andalusian fowl.
Codominance
• Both alleles combine and each affect
the phenotype of the offspring.
• Examples: roan horses and erminette
chickens.
Multiple Alleles
• Genetics is a complex
subject because many
traits in nature involve
genes that contain
multiple alleles.
• Examples: coat color
on many animals,
human – hair color, eye
color, blood type.
Genetics of Blood Type
• A and B are codominant and O is
recessive.
Blood Type
Possible Genotypes
A
AA (homozygous)
AO (heterozygous)
BB (homozygous)
BO (heterozygous)
OO
AB
B
O
AB
Polygenic Traits
• Traits that are
controlled by more
than one gene.
• Examples: human
skin color, shape
of human mouth,
ear position.
Clarification
• DNA is the molecule that makes up the chromosome.
• Genes are different locations on the chromosomes.
These can be small or large.
• Alleles are the coding sequences or letters used to
express a given genotype.
Thomas Hunt Morgan
• American geneticist that
worked in the 1900s to
further the work of Gregor
Mendel.
• Came to the conclusion
that Mendel’s principles
applied to people and other
organisms.
Morgan’s fruit flies:
• Small and easy to store.
• Reproduce in large
numbers
• Many generations can
be observed over a short
period of time.
• Simple genetic system –
haploid number of 8.
Genetics and Environment
• Genetics provides
the plan but how the
plan unfolds
depends on
environment.
• Environment refers
to things like
nutrition, sanitation,
medical care, etc.