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Genetics
Objectives
• d. Describe how flowering plants
reproduce sexually
• . Identify chromosomes as cellular
structures that occur in pairs that carry
hereditary information in units called
genes
Objectives
• b. Recognize and describe how when
asexual reproduction occurs, the same
genetic information found in the parent cell
is copied and passed on to each new
daughter cell
• c. Recognize and describe how when
sexual reproduction occurs, genetic
material from both parents is passed on
and combined to form the genetic code for
the new organism
• Recognize and describe when asexual
reproduction occurs, the daughter cell is
identical to the parent cell
• b. Recognize and describe when sexual
reproduction occurs, the offspring is not
identical to either parent due to the
combining of the different genetic codes
contained in each sex cell
I. What is genetics?
i. Genetics
The study of heredity
(how traits are passed
from parents to
offspring)
Think about the picture
matching activity.
Everyone in the class is
alike, but different.
How are we alike?
How are we different?
Click here and then on “Find out more
about Heredity!”
ii. Heredity
How an organism passes traits from one
generation to the next.
More definitions
iii. Trait
A characteristic or
quality of an organism
iv. Traits that are advantageous are more
likely to get passed on
• The code for traits is contained in the nucleus of
each cell of our body.
• Inside the nucleus are chromosomes which are made of
DNA. This is the code to make you you.
Nucleus
Cell
Chromosome
DNA: One
section of
DNA is a
gene
• Defined: Tightly
coiled DNA
• Form when cells
divide
– Chromosomes
created for the new
cells
• 2 Parts:
– 1) Chromatids:
two identical parts
of a chromosome
– 2) Centromere:
Joins chromatids
together
• Chromosomes are very small.
• Here is what they look like when you
see them through a microscope.
Chromosome
smear
One section
of DNA is a
gene
One Makes Two
• One makes two, asexual
reproduction only one parent cell is
needed for reproduction.
• The parent cell just simply divides
producing newcells that are exact
copies of the parent cell.
• Most single-celled organisms
reproduce asexually and they do this
by mitosis. Our body cells also are
formed this way.
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• Sexual reproduction two parent cells join
together to form a new individual.
• Parent cells, known as sex cells, are
different from ordinary body cells.
• Human body cells have 46 chromosomes
(or 23 pairs)
• The chromosomes in each pair are called
homologous chromosomes.
• But human sex cells only have 23
chromosomes-half the usual number
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• Each parent donates one half
of the homologous pair. This
ensures that the offspring will
have a normal number of
chromosomes(46).
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• Sex chromosomes carry genes
that determine whether the
offspring is male or female.
• In humans, females have two X
chromosomes (the matching
pair), and males have one X
chromosomes and one Y
chromosome (the unmatched
pair).
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Male Vs Female Chromosomes
• Females have 23 matching pairs. Males
have 22 matching pairs of chromosomes.
Female
Male
Images believed to be in the Public Domain
1. Before a body cell divides it copies every
one of the chromosomes.
2. When the body cell divides, each new
body cell gets a copy of each
chromosomes.
3. The new body cell is exactly like the
original cell!! They have the same
number and same type of chromosomes.
Click here to see an
animation of this.
Normal Number of Body Cell
Chromosomes
Organism
Human
Chromosome
numbers
46
Chimpanzee
48
House Mouse
40
Maize
20
© 2007 Paul Billiet ODWS
II. Who is Gregor Mendel?
II. Who is Gregor Mendel?
• An Augustinian monk
who taught physics to
high school students.
• As a young man
worked as a gardener
and continued to work
with plants in his life
as a teacher and as a
monk.
II. Who is Gregor Mendel?
i. Mendel became
known as the father of
Genetics for his work.
ii. In the 1860s, Mendel
studied variation
using the traits of pea
plants.
II. Who is Gregor Mendel
iii. Plants
a. A flower is a
structure that contains
a plant’s reproductive
organs.
1. The stamen is
the male organ
that produces
pollen (sperm).
II. Who is Gregor Mendel?
2, The pistil is the
female organ that
contains egg cells.
b, During selfpollination, pollen is
transferred to the top
of the pistil (stigma)
within the same plant
this leads to
fertilization (union of
sperm and egg)
II. Who is Gregor Mendel?
b. During cross-pollination, pollen is transferred
to the stigma of another plant (fertilization)
II. Who is Gregor Mendel?
iv. Mendel found
patterns in the way
traits were inherited.
a. organisms contain
two genes per trait
(one from each
parent)
II. Who is Gregor Mendel?
b. Genes are units of heredity; determines
traits in offspring.
c. Dominant genes will mask (hide) other
genes; “stronger”
d. a recessive gene is hidden by a
dominant gene; “weaker”
II. Who is Gregor Mendel?
e. Purebred refers to an organism with a
pair of the same genes for a given trait
(either dominant or recessive); this is
known as being homozygous.
II. Who is Gregor Mendel?
e. Purebred refers to an organism with a
pair of the same genes for a given trait
(either dominant or recessive); this is
known as being homozygous.
f. Hybrid refers to an organism with two
different genes for a trait (one dominant
and one recessive); this is known as
being heterozygous.
II. Who is Gregor Mendel?
g. In genetics, each trait is noted by a
single letter (i.e. “T” for tall plants)
II. Who is Gregor Mendel?
g. In genetics, each gene is noted by a
single letter (i.e. “T” for height)
h. Capital letters are used to show which
is the dominant allele (copy of the gene)
1. i.e. T = the tall allele (dominant)
t = the short allele (recessive)
III. Are Genes Always Dominant
and Recessive?
III. Are Genes Always Dominant
and Recessive?
i. No, in some gene pairs, the genes are neither
dominant nor recessive. During incomplete
dominance, neither gene hides the other (each
gene blends with the other).
IV. What are Phenotype and
Genotype?
i. Phenotype – the
visible characteristics
(traits).
Genotypes and Phenotypes
Phenotype
• Genotype: Indicates
the alleles that the
organism has
inherited regarding a
particular trait.
• Phenotype: The
actual visible trait of
the organism.
Genotype
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•The resulting alleles show
all the possible genotypes
for the offspring.
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