Transcript Mendelian Genetics

CST Review Genetics Part II.
Mendel’s Principle of Dominance
and Punnett Squares
Standards: Meiosis
» BI2. Mutation and sexual reproduction lead to
genetic variation in a population. As a basis for
understanding this concept:
» BI2. a. Students know meiosis is an early step in
sexual reproduction in which the pairs of
chromosomes separate and segregate randomly
during cell division to produce gametes containing
one chromosome of each type.
» BI2. b. Students know only certain cells in a
multicellular organism undergo meiosis.
» BI2. c. Students know how random chromosome
segregation explains the probability that a particular
allele will be in a gamete.
Standard Explanations
• BI2. a. Meiosis produces sex cells,
chromosomes pairs are separated randomly
during this process, producing gametes
containing one chromosome of each type
(haploid).
• BI2. b. Only sex cells (gametes) are produced
meiosis.
• BI 2.c.-Chromosomes segregate randomly
during meiosis.
Standards:Meiosis and Punnett
Squares
» BI3. A multicellular organism develops from a single zygote,
and its phenotype depends on its genotype, which is
established at fertilization. As a basis for understanding this
concept:
» BI2. d. Students know new combinations of alleles may be
generated in a zygote through the fusion of male and female
gametes (fertilization).
» BI2. e. Students know why approximately half of an individual’s
DNA sequence comes from each parent.
» BI2. f. Students know the role of chromosomes in determining an
individual’s sex.
» BI2. g. Students know how to predict possible combinations of
alleles in a zygote from the genetic makeup of the parents.
» BI3. a. Students know how to predict the probable outcome of
phenotypes in a genetic cross from the genotypes of the parents
and mode of inheritance (autosomal or X-linked, dominant or
recessive).
» BI3. b. Students know the genetic basis for Mendel’s laws of
segregation and independent assortment.
Standards Explanation-Meiosis and
Punnett Squares
• BI 2.d.-New combination of genes (alleles) are
produced from fertilization.
• BI 2.e.-Half of an organisms chromosomes
come from each parent because of Meiosis.
• BI 2.f.-XX-female, XY-male
• BI 2.g.,3.a.-Punnett Squares
• BI 3.b.-Mendel’s Laws-chromosome pairs
separate, and genes for different traits are
inherited independently of each other.
Objectives:
SWBAT
• explain the genetic factors that influence
the way we look.
• recognize that DNA contains the genetic
information that determines the way we
look.
• explain the structure and function of DNA.
• predict the physical characteristics of
an organism based on its genetic make
up.
Mendel’s Principle of Dominance
• Some alleles (diff. forms of gene) are
dominant and some are recessive
• Organisms with dominant alleles will
always show that form of the trait (YY, Yy)
• Organisms with recessive alleles will only
show that form of the trait when there are
no dominant alleles present (yy)
Allele Combinations
• Homozygotes- two identical alleles for a
certain trait (YY,yy)
• Heterozygotes- two different alleles for the
same trait (Yy)
What are Punnett Squares?
• Punnett Squares are…
• a grid system for predicting all possible
genotypes resulting from a cross.
• The sides of the square represent the
possible gamete genotypes of each
parent.
• Shows all possible genotypes of offspring
Punnett Squares
What’s actually happening?
What is probability?
• Probability-the likelihood that an event will
occur
• P= # of ways an event can occur
________________________
# of total possible outcomes