Download Biology 105

Biology 105
Chapter 11: Principles of
Heredity
Pgs 237-261
Student Outcomes
 Describe Mendel’s principles of
segregation and independent
assortment
 Solve genetic problems involving
monohybrid, dihybrid, and test crosses
 Use probability to predict outcomes of
genetic crosses.
Student Outcomes
 Define linkage and how it occurs in meiosis
 Describe the genetic determination of sex
and the inheritance of X-linked genes in
mammals
 Use methods other than
dominance/recessive to explain genetic
problems.
Key Terms
Heredity-the passing of genetic information
from parent to offspring
Genetics – the study of heredity
Genetic variation – differences between
parents and offspring or among individuals of
a population.
History of Genetics
Mid 1800’s Gregor Mendel worked with pea
plants and proposed the basic principles of
genetics.
This was unaccepted by many for several
decades. However, in the early 1900’s,
after science advancements, Mendel’s ideas
gained momentum
History of Genetics
 Burbank - in late 1800’s created over
800 new breeds of plants
 Thomas Morgan - fruit fly studies in
1908
 Watson, Wilkins and Crick - DNA
structure in 1953
History continued
 Genetics proceeded through the 1900’s with
developments in crops (large yield,
resistance to disease)
 In the 1990’s an exponential growth occurred
with the location of several genetic diseases
(cystic fibrosis)
 Has continued with the Human Genome
Project (HGP) through the 21st century.
More key terms
Dominant-factor being expressed
Recessive-factor being hidden (masked)
Phenotype – physical appearance of an organism
Genotype–genetic makeup of an organism
Gene-factors determining a trait (30,000 for human)
Allele-alternative forms of a gene
Homozygous–having similar allele makeup (purebred)
Heterozygous–having dissimilar allele makeup (hybrid)
Locus-the location of a gene on a chromosome.
Punnett square-chart used to predict outcomes
Mendel’s principles
• Principle of segregation
• Before sexual reproduction occurs, the
two alleles carried by an individual parent
must separate. Each sex cell carries only
one allele for each trait.
Mendel’s principles
 Principle of independent assortment
Gene pairs separate independent of each
other
Monohybrid Cross
 A single trait is studied (from one
locus)
 Tall vs short
TT, Tt, tt
Test Cross will determine the parent
genotype – test cross must be homozygous
recessive. (tt)
Dihybrid Cross
 Two traits located at two loci
*TTEE, TtEe
Linked Genes
 If different genes are located very
close to each other on a chromosome,
they may be ‘linked’ and inherited
together.
Sex Linked traits
 Found on Sex chromosomes (X, Y)
 Hemizygous - have only 1 chromosome
so only 1 allele
Sex Chromosomes
 X and Y
XX - female
XY- male
X0??
XXY??
 More than 1/2 of conceived babys are
male - Why??
Dosage compensation
 When a single X chromosome has as
much influence as two (XX) as in the
female.
Exceptions to the rule
 Incomplete dominance - blending of alleles
(white and red flower color)
 Codominance- both are expressed
 Multiple Alleles - Three of more alleles code
for a trait.
Pleiotropy
 Ability of a single gene to have
multiple effects. (CF)
Polygenic inheritance
 Multiple gene pairs at different
locations affect a trait
 Example skin color