Download GENETICS

GENETICS
HEREDITY and
CHROMOSOMES
INSTRUCTIONS
• Please define vocabulary words and answer
questions
• Turn-in for a grade
VOCABULARY
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Chromosome
Allele
Dominant
Homozygous
Genotype
Karyotype
Sex chromosomes
XX , XY
Gene
Gamete
Recessive
Heterozygous
Phenotype
Mutation
Autosomes
CHROMOSOMES
• Contain genetic information for organism
• Made of DNA
GENES
• Encode for traits of an organism
• Alternate form of a gene is an allele
• You have 2 alleles for each trait- one from
your mother and one from your father
ALLELES
• Alleles can be dominant or recessive.
• Your genotype includes all of the alleles
that you carry.
• Your phenotype
is the visible
evidence of your
alleles.
Ex: EYE COLOR
• Brown eyes are dominant over lighter colored
eyes.
• In order for brown
eyed parents to
have a blue
eyed child, they
both need to
carry the
recessive allele
for blue eyes.
Dominant vs. Recessive
• Dominant alleles are expressed in the
organism’s phenotype.
• Recessive alleles are only expressed in
the organism’s phenotype if there are two
copies of the recessive allele.
PUNNETT SQUARES
Monohybrid Cross (One Trait)
• You are given the genotype of the male
and the female of a species. You should
be able to predict likely phenotypes and
genotypes of the offspring.
• Example: Fur color of mice
– T-dominant tan
– t-recessive white
– Female Tt, Male Tt
• Genotypes: What
are the allele
combinations?
TT,Tt,Tt,tt
What is the genotype
ratio?
1:2:1
Phenotypes: What
are the colors of
the mice?
Tan, white
What is the phenotype ratio?
3:1
YOUR TURN!
• B-dominant gray cheeks
• b-recessive pink cheeks
• 1. What are the
genotypes?
• 2. What are the
phenotypes?
HOMOZYGOUS VS.
HETEROZYGOUS
To be homozygous for 2 alleles
means: 2 copies of the
same allele.
Homozygous dominant:
2 copies of dominant allele.
Homozygous recessive:
2 copies of recessive allele.
• To be heterozygous for a trait:
One copy of the dominant allele,
and one copy of the recessive one.
The organism will
display dominant
traits, but still
carry the
recessive.
INTERPRETING GENOTYPES
• Remember-you can interpret the genotype from
the description.
• G-dominant green feathers
• g-recessive yellow feathers
• L-dominant long beak
• l- recessive short beak
• Given: ggLl(female) X Ggll(male)
• 3. What are the phenotypes of the parents?
PREDICTING OFFSPRING in
DIHYBRID CROSSES
• Separate traits into separate Punnett
squares: GgLl(female)X Ggll(male)
MOM
G
DAD
G
g
GG
Gg
(green)1
g
3
Gg
(green)
2
(green)
L
l
l
ll
Ll
DAD
(long)
1 2 (short)
3
l
4
MOM
4
Ll
ll
(long)
(short)
gg
(yellow)
1. Green feathers, long beak 2. Green feathers, short beak
3. Green feathers, long beak
4. Yellow feathers, short beak
QUESTIONS!
• 4. What is the percentage of short beaked
offspring?
• 5. Is there a single trait visible in all
offspring?
• 6. Can you ever have a recessive
phenotype when both of the parents have
a dominant allele for the trait?
• Using the following information, create a
genotype for the male and female birds:
• 7.Homozygous dominant color, and
heterozygous beak (female)
• 8.Heterozygous color, and homozygous
recessive beak (male)
WHERE DO THE ALLELES COME
FROM?
• Gametes-sex cells with half the amount of
genetic information.
• In animals, the male sex cell is the sperm
and the female is the egg.
KARYOTYPES
• Karyotypes are a map of the chromosomes of an
individual.
• This is a karyotype of a male human.
• Note that there
are 23 pairs of
chromosomes.
• The last pair are the
sex chromosomes,
and for a male, they
are XY.
• Note that this is the karyotype of a female.
• There are 23 pairs of chromosomes, the
last pair being XX, a genetic female.
• There are 22 pairs of chromosomes that
encode for every trait that the organism
will possess, but only 1 pair that indicates
the sex of the organism.
• These chromosomes encode for
autosomes, (body cells).
• You might also see them
referred to as somatic cells.
GENETIC DISORDERS
• Some genetic disorders are a result of
extra chromosomes being present, or
deletion of some chromosomes.
• Extra chromosome at the
• 21st= Down Syndrome
• Turner Syndrome is a result of only one X
chromosome.
MUTATIONS
• Mutations occur as a result of a change in
a protein sequence.
• Some mutations are deleterious, and
some are fatal, but some are not.
• Changes in the protein sequence can occur in
various ways. Some examples are:
• Deletion-where one base is missing
– Ex: ATTGCGAAA  ATGCGAAA
• Insertion-where an extra base is added
– Ex: ATTGCGAAA  ATTGCGAAGA
• All mutations can alter the
amino acids in a protein
sequence, thus possibly
changing the protein
produced.
• The only mutations that can be passed to
offspring are the mutations that occur in
the gametes. (Sex cells)
PRACTICE QUESTIONS
• 1. Overexposure to ultraviolet light causes
mutations in the DNA of skin cells. The mutated
DNA has no effect on offspring because:
– A. Changes in skin cell DNA are homozygous
recessive.
– B. Mutations must occur within the RNA codons.
– C. Offspring reject parental skin cells.
– D. Only changes to gamete DNA can be inherited.
• 2. Mutations in DNA molecules occur
when:
– A. Replication of DNA is exact.
– B. A DNA enzyme attaches to an RNA codon.
– C. RNA codons are replaced by DNA
nucleotides.
– D. A change occurs in a DNA nucleotide
base.