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Chapter 10
 Father
of genetics –
the branch of biology
that studies heredity.
 Mendel
did his
experiments on pea
plants
 Mendel
carried out the first important
studies of heredity (the passing on of
characteristics from parent to offspring)
 Mendel
controlled the pollination of the
pea plants in his experiments.
 Characteristics
called traits.
that are inherited are
 Each
organism has two factors that
control each of its traits.
 These
 Genes
factors are called genes.
exist in alternate forms called
alleles (you have two alleles for each of
your traits – one coming from your mom
and one from your dad)
 Dominant
– the observed trait
(represented by a capital letter)
 Recessive
– the trait that disappeared
(represented by a lower case letter)
Ex. Tall plant (T)
short plant (t)
 The
dominant trait always wins out and is
the trait to show up if it is present.
 An
uppercase letter represents dominant
traits
Ex. Tall plant (T)
short plant (t)
TT = ?
Tt = ?
tt = ?
 The
appearance of an organism is called
its phenotype (ex. Tall plant, brown hair)
 The
gene combination of an organism is
called its genotype (ex. TT, Tt, tt)
 You
cant always know an organism’s
genotype by looking at its phenotype.
 If
both alleles for a trait are the same then
the organism is homozygous.
ex. TT = homozygous dominant
tt = homozygous recessive
 An
organism is heterozygous for a trait if
its two alleles are different.
ex. Tt
 Crosses
P
involving only “one” trait
generation = parents
F1 generation = first filial generation
F2 generation = second filial generation
 Cross
two parents to
get the F1 generation
 Cross
two F1 to
get the F2 generation
 Put
the alleles for
each parent on the
outside of the box.
Chapter 10.2
 In
the body cells of animals and most plants,
chromosomes occur in pairs.
 One
chromosome came from the male parent,
and the other came from the female parent.
A
cell with two of each kind of chromosome is
called a diploid (2n) cell.
 This
pairing supports Mendel’s conclusion that
organisms have two factors – alleles – for each
trait.
 Organisms
produce gametes (sperm and egg)
that contain one of each kind of chromosome.
A
cell with one of each kind of chromosome is
called a haploid (n) cell.
 Human
diploid cells have 46 chromosomes (23
from mom and 23 from dad)
 Human
 If
haploid cells have 23 chromosomes
a dogs diploid cells had 78 chromosomes,
how many chromosomes would its haploid cells
have?
 Meiosis
is the division of diploid cells to produce
gametes containing half the number of
chromosomes (haploid).
 If
meiosis didn’t occur, then the offspring would
have twice as many chromosomes as the parents.
 23
chromomes (sperm) + 23 chromosomes (egg)
= 46 chromosomes (zygote)
 Consists
of two separate divisions known as
Meiosis I and Meiosis II.
 Meiosis
starts with one diploid cell and ends
with 4 haploid cells.
 Everything
happens the same in the stages just
like mitosis, but what happens to the
chromosomes is different.
 The
exchange of genetic material
between chromosomes.
 Crossing
over can occur at any location
on a chromosome (happens randomly)
 Crossing
over results in new
combinations of alleles on a chromosome