Download PowerPoint - The Science Queen

Whose got Genes?
Genes, Heredity, & DNA
Baker 2003/2004
What are genes?
Genes are a segment of DNA
on a chromosome that
controls a particular trait.
Genes are located on the
chromosomes in the nuclei. Each
organims has a fixed number of
chromosomes.
Humans have 23 pairs (46)
chromosomes.
Genetics is the study of how
traits are passed on from one
generation to another
Baker 2003/2004
So what is DNA?
DNA is a complex
molecule (polymer) found
in all living things.
The primary function of
DNA is to store and
transmit genetic
information that tells
cells which proteins to
make and when to make
them.
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DNA TRIVIA
An idea about size:
An average cell nucleus is about 6
micrometers in diameter.
The total length of the DNA in the human
genome is 1.8 meters.
There must be several levels of coiling and
super coiling in DNA
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Who was Gregor Mendel?
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Who was Gregor Mendel?
Austrian monk who studied
mathematics and science
As a boy he could predict the
possible types of flowers and
fruits that would result from
crossbreeding two plants in his
father’s garden
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Who was Gregor Mendel?
Curiosity about the connection
between the color of a pea flower
and the type of seed that same
plant produced inspired him to begin
experimenting with garden peas in
1856.
Made careful use of scientific
methods, which resulted in the first
recorded study of how traits pass
from one generation to the next.
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What is GENETICS?
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What is GENETICS?
The study of how traits are
inherited through the
interactions of genes.
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What is a GENE?
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What is a GENE?
The material that
controls which traits are
expressed in an organism
Genes come in pairs and
offspring inherit one copy
of each gene from each
parent
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Define the following terms:
Heredity
Allele
Trait
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Define HEREDITY
The passing of traits
from parent to
offspring
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Define ALLELE
The different forms of a
trait that a gene may
have
One form of a gene
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Define TRAIT
Ways of looking,
thinking, or being
Traits that are genetic
are passed down through
the genes from parents
to offspring
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Describe RECESSIVE
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Describe RECESSIVE
A trait that is covered over,
or dominated, by another
form of that trait and
seems to disappear
Hidden when the other copy
of the gene contains the
dominant allele.
A recessive allele shows up
only when there is no
dominant allele present
Shown with a lower-case
letter Baker 2003/2004
What is HOMOZYGOUS?
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What is HOMOZYGOUS?
Both alleles [forms of the gene]
are the same
When offspring inherit two
dominant genes, (one dominant
gene from each parent) they are
said to be homozygous dominant
When offspring inherit two
recessive genes, (one recessive
gene from each parent) they are
said to be homozygous recessive
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What is
HETEROZYGOUS?
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What is
HETEROZYGOUS?
When alleles occur in
different forms
When offspring inherit one
dominant gene and one
recessive gene, they are said
to be heterozygous
Since the dominant gene will
be expressed, they are said to
be heterozygous dominant
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Describe DOMINANT
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Describe DOMINANT
A trait that covers over, or
dominates, another form of that
trait
Trait that always shows up, even
when only one of the two alleles is
in the dominant form
Shown by a capital letter
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Define GENOTYPE
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Define GENOTYPE
An organism's genetic
makeup
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Define PHENOTYPE
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Define PHENOTYPE
Outward physical appearance
and behavior of an organism
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What is a PUNNETT
SQUARE?
A tool to predict the probability of
certain traits in offspring that
shows the different ways alleles
can combine
A way to show phenotype &
genotype
A chart that shows all the possible
combinations of alleles that can
result when genes are crossed
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What is a PUNNETT
SQUARE?
Letters stand for dominant and
recessive alleles
An uppercase letter stands for
a dominant allele
Lowercase letters stand for
recessive alleles
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Introduction to
Punnett Squares:
A Punnett Square is a chart drawn to
determine the probable results of a
genetic cross. To be able to draw a
Punnett Square, you must know the
genotype of both parents.
R
R
r
r
RR Rr
RR rr
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Punnett Squares
Sample Problem 1. In roses, red
flowers are dominant over white flowers.
What are the possible offspring when a
homozygous red rose is crossed with a
homozygous white rose.
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Generation 1
homozygous red
rose = RR
homozygous
white rose = ww
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Generation 2
homozygous red
rose = RR
heterozygous red
rose = Rw
homozygous
white rose = ww
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Generation 3
homozygous red
rose = RR
heterozygous red
rose = Rw
homozygous
white rose = ww
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List the 3 Principles of
Heredity
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List the 3 Principles of
Heredity
Traits are controlled by alleles on
chromosomes
An allele’s effect is dominant or recessive
When a pair of chromosomes separate
during meiosis the different alleles for a
trait move into separate sex cells
Baker 2003/2004
References
Slideshow adapted from
http://www.scienceclass.net/PowerPoints/Genetics.htm
Baker 2003/2004