Download File

Introduction to Genetics
Are some traits more common in men or
women?
Human chromosomes exist in pairs: 23 pairs for a total of
46 chromosomes
The 23rd pair of chromosomes are the SEX
CHROMOSOMES and determine gender:
XX = female
XY = male
Genes that are carried on the X chromosome are said to
be SEX-LINKED. These
include male pattern baldness and colorblindness.
Since males only have one X chromosome, they have a
greater chance of expressing a sex-linked trait than females
do!
How are traits passed
from parent to offspring?
• Traits
– Traits are physical
or physiological
characteristics of an
organism
– Ex. Height or blood
type
– Picky Eater????
How are traits passed
from parent to offspring?
• Traits
– The term
phenotype is used
to describe the
physical expression
of the trait
– Ex. Short/tall or
Type A/Type B
Chemical basis of traits
• DNA is the
molecule that
contains the
information to
make proteins,
which control our
traits
Chemical basis of traits
• A section of DNA
that is used to
make a protein is
called a gene.
• There are many
genes (hundreds)
on a single
chromosome.
Fill It In …
How are the following terms related?
gene, DNA, chromosome
Chemical basis of traits
• Eukaryotic organism’s
chromosomes exist in
pairs.
• One is inherited from the
sperm and one is inherited
from the egg.
• Each chromosome, in a
pair, contains genes for the
same traits.
• This is why we call them
homologous pairs.
Chemical basis of traits
• Although the genes on
homologous
chromosomes may
code for the same
trait, slight differences
in the DNA sequences
may lead to different
forms of the protein.
Chemical basis of traits
• This creates slightly
different versions of
the same trait.
• Each version is called
an allele.
– Ex. Blue and brown
are two alleles of the
eye color trait.
Fill It In …
• Draw a homologous pair of
chromosomes showing a different
allele for eye color on each:
Chemical basis of traits
• Genotype is the term
used to describe the
combination of alleles
present in an organism’s
chromosomes.
• An allele is usually
represented by a single
letter.
• Thus a genotype is usually
represented by two
letters.
Chemical basis of traits
• If an individual inherits
identical copies from
each parent the
individual is considered
homozygous (pure
breeding)
– Ex. AA or aa
• If an individual inherits
a different copy from
each parent the
individual is considered
heterozygous
(hybrid)
– Ex. Aa
Fill It In …
WORD HELP:
Pheno - ________________
Geno - _________________
Homo - _________________
Hetero - _________________
Check Yourself!
1. Give an example (not in the notes) of a human
trait.
2. What is a phenotype?
3. From where did you get each of the
chromosomes in the homologous pair?
4. What is an allele?
5. What is a genotype?
Check Yourself!
1. Give an example (not in the notes) of a human
trait. ANSWERS WILL VARY
2. What is a phenotype?
3. From where did you get each of the
chromosomes in the homologous pair?
4. What is an allele?
5. What is a genotype?
Check Yourself!
1. Give an example (not in the notes) of a human
trait. ANSWERS WILL VARY
2. What is a phenotype? PHYSICAL
EXPRESSION OF A TRAIT
3. From where did you get each of the
chromosomes in the homologous pair?
4. What is an allele?
5. What is a genotype?
Check Yourself!
1. Give an example (not in the notes) of a human
trait. ANSWERS WILL VARY
2. What is a phenotype? PHYSICAL
EXPRESSION OF A TRAIT
3. From where did you get each of the
chromosomes in the homologous pair? ONE
FROM MOM AND ONE FROM DAD
4. What is an allele?
5. What is a genotype?
Check Yourself!
1. Give an example (not in the notes) of a human
trait. ANSWERS WILL VARY
2. What is a phenotype? PHYSICAL
EXPRESSION OF A TRAIT
3. From where did you get each of the
chromosomes in the homologous pair? ONE
FROM MOM AND ONE FROM DAD
4. What is an allele? DIFFERENT VERSIONS OF
A PARTICULAR TRAIT
5. What is a genotype?
Check Yourself!
1. Give an example (not in the notes) of a human
trait. ANSWERS WILL VARY
2. What is a phenotype? PHYSICAL
EXPRESSION OF A TRAIT
3. From where did you get each of the
chromosomes in the homologous pair? ONE
FROM MOM AND ONE FROM DAD
4. What is an allele? DIFFERENT VERSIONS OF
A PARTICULAR TRAIT
5. What is a genotype? COMBINATION OF
ALLELES FOR AN ORGANISM
How was the path of
inheritance discovered …
• in a garden in Austria?
• Gregor Mendel
– The father of genetics
• Using pea plants, Mendel
proved experimentally the
link between meiosis,
genes, and inheritance
(long before we knew about
DNA!)
• He developed 3 basic
conclusions:
The Principle of
Dominance
• Certain alleles (forms of
a trait) can hide/mask
other alleles.
• These alleles are called
dominant alleles and
are represented by a
capital letter (A).
• The alleles that may be
hidden are called
recessive alleles and
are represented by the
lower case of the same
letter (a)
The Principle of
Dominance
• Thus, homozygous
dominant is AA and
will express the
dominant phenotype.
• Heterozygous
individuals are Aa and
will also express the
dominant phenotype.
• Only homozygous
recessive (aa).
individuals will express
the recessive
phenotype
Fill It In …
Draw a picture of a dominant and recessive
trait. Write the possible genotypes under
each:
The Principle of
Segregation
• Alleles are not passed in
pairs from one parent to
an offspring.
• Each parent only
donates half of each
offspring’s genotype
(typically one allele per
trait).
The Principle of
Segregation
• This is because
during meiosis only
one of each
homologous pair of
chromosomes is
passed to the
gamete (sperm or
egg)
Fill It In …
Based on the parent cell:
A
a
What are the possible gametes (after
segregation in meiosis)?
The Principle of
Independent Assortment
• The way one pair
of chromosomes is
separated during
meiosis does not
affect the way the
next pair
separates.
The Principle of
Independent Assortment
• A gene for one trait
is only passed in
connection with a
gene for a different
trait if the two
genes are on the
same chromosome.
• Genes on separate
chromosomes are
passed
independently of
each other.
Fill It In …
Mendel’s Three Laws:
1. D_______________
2. S_______________
3. I_______________
A_______________
Check Yourself!
1. Name Mendel’s three principles of heredity:
2. What cell process allows the principle of
segregation to take place?
3. When would a gene for one trait be passed
with a gene for a different trait?
Check Yourself!
1. Name Mendel’s three principles of heredity:
PRINCIPLE OF DOMINANCE
PRINCIPLE OF SEGREGATION
PRINCIPLE OF INDEPENDENT ASSORTMENT
2. What cell process allows the principle of
segregation to take place?
3. When would a gene for one trait be passed with
a gene for a different trait?
Check Yourself!
1. Name Mendel’s three principles of heredity:
PRINCIPLE OF DOMINANCE
PRINCIPLE OF SEGREGATION
PRINCIPLE OF INDEPENDENT ASSORTMENT
2. What cell process allows the principle of
segregation to take place?
MEIOSIS
3. When would a gene for one trait be passed with
a gene for a different trait?
Check Yourself!
1. Name Mendel’s three principles of heredity:
PRINCIPLE OF DOMINANCE
PRINCIPLE OF SEGREGATION
PRINCIPLE OF INDEPENDENT ASSORTMENT
2. What cell process allows the principle of
segregation to take place?
MEIOSIS
3. When would a gene for one trait be passed with
a gene for a different trait?
INDEPENDENT ASSORTMENT