Transcript What Did Mendel Find?

He
discovered different
laws and rules that
explain factors affecting
heredity.
The
two alleles for a
trait must separate when
gametes are formed
A parent randomly passes
only one allele for each
trait to each offspring
The
genes for different
traits are inherited
independently of each
other.
Each
organism has two
alleles for each trait
Alleles - different forms of
the same gene
Genes - located on
chromosomes, they control how
an organism develops

The
trait that is observed
in the offspring is the
dominant trait (uppercase)
The trait that disappears
in the offspring is the
recessive trait (lowercase)
Phenotype
- the way an
organism looks

red hair or brown hair
Genotype
- the gene
combination of an organism

AA or Aa or aa
Heterozygous
- if the two
alleles for a trait are
different (Aa)
Homozygous
- if the two
alleles for a trait are the
same (AA or aa)
A
Punnett square is a chart which
shows/predicts all possible gene
combinations in a cross of parents (whose
genes are known).
 Punnett squares are named for an English
geneticist, Reginald Punnett. He discovered
some basic principles of genetics, including
sex linkage and sex determination.
 Setting
up and using a Punnett square is
quite simple once you understand how it
works. You begin by drawing a grid of
perpendicular lines:
 Next,
you put the genotype of one parent
across the top and that of the other parent
down the left side. For example, if parent
pea plant genotypes were YY and GG
respectively, the setup would be:
Note that only
one letter goes
in each box for
the parents. It
does not matter
which parent is
on the side or
the top of the
Punnett
square.
 Next,
all you have to do is fill in the boxes by
copying the row and column-head letters
across or down into the empty squares. This
gives us the predicted frequency of all of the
potential genotypes among the offspring
each time reproduction occurs.
 What
is the phenotype?
 What is the genotype?
 What is homozygous?
 What is heterozygous?
 What do we call the trait that is
observed?
 What case (upper or lower) is it written
in?
 What about the one that disappears?
 What case is it written in?
1. In pea plants, spherical seeds (S) are
dominant to dented seeds (s). In a cross of
two plants that are heterozygous for the
seed shape trait, what percentage of the
offspring should have spherical seeds?
75%