Transcript Genetics - sciencegeek

Genetics
Chapters 6 and 7
Introduction to Mendel’s Law of
Independent Assortment:
1. Use coins to represent 2 animals
– Heads = Dominant Allele (H)
– Tails = Recessive Allele (h)
2. Flip coins simultaneously to represent a
pairing of alleles. (Perform 100 tests)
3. Record Results as Homozygous
dominant (HH), Heterozygous (Hh), or
homozygous recessive (hh)
Recorded
Amount of
Genotypes
Offspring
Homozygous
Dominant
(HH)
Heterozygous
(Hh)
Homozygous
Recessive
(hh)
Genotypic
Percentage
Investigation Questions
1. Create a hypothesis of which scenario will
be the most common. Explain your
reasoning.
2. Which scenario ended up occurring the
most often? Why do you think that was?
3. What did the coins represent?
4. Why did we use 2 coins? Why not 1 or 3,
4, 5…?
5. How does this lab relate to real life?
Mendel’s 3 Theories
• Principle of Dominance and Recessive
• Principle of Segregation
• Principle of Independent Assortment
The law of segregation
• Each parent would contribute one
factor to the new individual.
• Random Segregation would occur
during the formation of the sex cells.
The law of independent
assortment
• Factors for different characteristics
are distributed to reproductive cells
independently.
• Example: seed shape and seed
color are inherited independently of
each other.
Incomplete Dominance/
Co-Dominance
• Some traits do not have one clear dominant
gene or one clear recessive trait
• Traits appear to blend together
• Ex: Red flower with white flower makes a
pink flower
• Ex: Blood Types A, B, O
Patterns of Inheritance
• Polygenetic Inheritance:
• genes that are controlled by multiple
genes that are located on different
chromosomes
–Examples: eye color, skin color,
height, and facial features.
Multiple Alleles
• Control Several Traits
• Human Blood: Blood Typing
• Possible Alleles: A, B, and O
• Rhesus Factor (RH): Antigen in Red
Blood Cells
– factor has cell markers that make
you positive (antigens present) or
negative (no antigens present)
• A and B are both dominant
over O
• A and B presence is never
masked
• O is a universal donor
• AB is a universal recipient
Blood Types
Genotype
• AA
• BB
• OO
• AO
• BO
• AB
Phenotype
A
B
O
A
B
AB
Punnet Square Practice:
• Round Seeds are dominant over wrinkled
seeds. Cross: Pure round seeds with
Pure wrinkled seeds.
• Green pods are dominant over yellow
pods. Cross: Hybrid green pods with
Hybrid Green pods.
• Axial flowers are dominant over terminal
flowers. Cross: Hybrid axial flowers with
Pure axial flowers.
• Colored seed coats are dominant over white
seed coats. Cross: Hybrid colored seeds
with Hybrid colored seeds.
• Horned cattle is dominant over the hornless
condition. Cross: Pure hornless with
Hybrid Horned.
• Black fur is dominant over white fur in guinea
pigs. Cross: Hybrid black with Hybrid
Black.
• Long wings aer dominant over curly wing in
fruit flies. Show all the idfferent crosses
that can produce hybrid long wing
individuals.
In Sheep, black wool is recessive to white wool.
What happens when you mate a black ram to
a heterozygous ewe? Use W to represent
dominant white, w for the recessive black allele.
•
•
•
•
•
What is the genotype of the ram?
What is the genotype of the ewe?
What are the genotypes of the offspring?
What is the genotypic ratio of the offspring?
What are the phenotypes of the offspring?
Cross a heterozygous black female angus
to a heterozygous bull (B = black; b = red)
•
•
•
•
•
What is the genotype of the female angus?
What is the genotype of the bull?
What are the genotypes of the offspring?
What is the genotypic ratio of the offspring?
What are the phenotypes of the offspring?
In cattle, the polled gene (P) is dominant
over the horned gene (p). A polled cow
with genotype (Pp) is mated to a horned
bull. ½ of the offspring were polled and ½
were horned?
• What is the genotype of the bull?
• Whare the genotypes of the offspring?
Cross a heterozygous polled black angus
bull (BbPp) to a heterozygous polled black
angus cow (BbPp).
• Use a punnet square to determine
genotype and phenotype of offspring.
Sex Linked Inheritance/Sex
Limited
• Males have XY sex chromosomes
• Females have XX sex chromosomes
• Humans have 23 pairs of chromosomes
–22 pairs are called autosomes
• Pairs of matching homologous
chromosomes
–1 pair is known as sex chromosomes
Sex-linked Traits
• Many genetic disorders are linked to the X
Chromosome
• Much more common phenotypically in males
• Females are typically carriers
• These traits become evident after puberty
due to the chemical production in the body
Common Sex Linked/Sex
Limited Disorders
• Color Blindness
– People with this disorder are unable to
see the full color spectrum
• Hemophilia
– Inability for blood to clot
• Muscular Dystrophy
– Deterioration of the muscles, early
death in males
Sex Influenced
• Traits controlled by hormones or
chemical in the body of one
particular sex
–Ex: Baldness
Disorders by
Mutations of
Chromosomes
• Sickle Cell Anemia
– Occurs among people of African descent
– Red Blood Cells are sickle shaped rather than
circular
– Causes anemia, clogged blood vessels, and
restricted blood flow
• Cystic Fibrosis
– One in 20 males are carriers
– Causes respiratory infections due to fluid in the
lungs.
Continued…
• Huntington’s Disease
– Lethal disease which does not occur
until age 40
– Breakdown of areas of the brain,
caused by dominant allele
– Causes loss of muscle control
Disorders by Non-Disjunction
• Chromosomes fail to separate
during meiosis
• Down Syndrome: non-disjunction
st
of the 21 chromosome (extra
chromosome)
• Multiple traits are effected
• Klinefelters Syndrome
–Non-disjunction of the sex
chromosome
–Extra X chromosome, XXY instead
of XY
–Male is sterile
• Turners Syndrome
–Female’s X Chromosome is missing
–Female is sterile
Twins
• Identical Twins
–Produced from a single zygote that
splits after fertilization
–Babies will have exact same
genotypes
• Fraternal Twins
–Two eggs are fertilized by different
sperm cells
–Genotypes are not exactly the same