Transcript Patterns of Inheritance: Genetics Chapt. 10

Genetics
Genetics is the
science of inheritance.
It requires sexual
reproduction..
wherein a sperm
and egg combine
to form a zygote.
Patterns of Inheritance: Genetics
Chapt. 10
• Interest in genetics is
as old as humankind…
• Modern genetics
began in 1860’s
• Czech Monk- Gregor
Mendel
• Playing with peas in his
garden
Gregor Mendel
• Used peas to study how
physical traits passed
from parent to offspring
• Mendel measured 7
traits in peas, each trait
with 2 forms.
• How were these traits
passed on?
• Mendel came up with
rules….
• Text pg. 178
Examples of two Pea traits (Shape & Color)
that Mendel studied
Mendel’s
st
1
Rule
The Law of Segregation:
• For each trait (i.e. pod color or plant
height) an individual has 2 factors
• The 2 factors may be the same or different
• When making kids, each parent will
contribute only 1 factor
• The 2 factors a parent has will separate
when making a kid (plant or human)
The Law of Segregation
• Each parent will pass
on 1 factor during sex
(gamete production)
• Kids get 1 factor (for
each trait) from each
parent...
Text pg 181
The Factors
• Each individual has 2
factors for each trait…pod
color, height, eyes, hair...
• If both factors for a trait
are the same, you are
homozygous for that
trait…
• If you have 2 different
factors for a trait, you are
heterozygous for that trait
How to Label these factors?
• G for Green pods
• Y for yellow pods
• B for brown hair
• x for blond hair
But…we don’t do this!!
The Factors
• You have 2 factors, but only 1 factor for
each trait is typically used (expressed)..
• This is the dominant factor
• The other one is the recessive factor
So; How we do Label the
factors?
• Dominant factor is written in upper
case… i.e. “B”
• Recessive factor in lower case, using
the dominant abbreviation.. i.e. “b”
• B is for brown hair (which is dominant)
• b is for blond
Quiz
• If the you are heterozygous for brown hair,
what two factors will you have?
• If homozygous, what two factors?
How to Predict which factor
you’ll give your kids?
• Each parent has 2 factors for each trait
• But, each gamete you produce has only 1
factor for each trait
• Which factor goes to which kid?
• Best described by a Punnett Square
Punnett Square..
• Used to predict how offspring will get
their share of factors…
• Parents mate (x): BB X bb
• What possible offspring will each make?
B
b
Female
Gametes
b
B
Male Gametes
Possible Offspring….
Or, F1 Generation
B
b
b
B
Bb
Bb
Bb
Bb
Each F1 Offspring has the same traits for hair color… Bb
Another Example..
Trait for Seed Shape (S)
Text pg 181
Mendel’s 2nd Law
• Factors for each trait segregate into gametes
independently of each other
• The factor for hair color (B or b) will segregate
independently of the factor for height (T or t)
• Consider a dihybrid cross… Two traits at once
• Example: Say Parents are Bbtt x bbTT
Dihybrid Cross
• If a Bbtt male mates with a bbTT
female?
• What are the possible gametes for
each?
Male Bbtt
x
Female bbTT
Bt
bT
BbTt
bt
gametes
bbTt
New individuals
gametes
(with two factors
for each trait)
bT
BbTt
bbTt
So What?
• What does Mendel and his Peas have to
do with you?
• Chromosomes and Heredity…
Mendel’s Factors = Genes
• Every normal human has thousands of
genes
• Each gene describes the information for
one human trait.
• You have two genes for each trait
• Where are these genes located?
On Chromosomes
• We each have 46
chromosomes in each
cell
• 23 chromosomes came
from Mom, 23 from Dad
• Each chromosome
contains hundreds of
genes…
An example using the FISH technique
of identifying the location of one gene
on a chromosome.
Gene location on Chromosomes
Quiz
• If the human trait for Hairy knuckles is
located on 1 gene…how many copies of
this gene will you have?
• If Hairy knuckles is a dominant trait,
how would you characterize the
genotype?
• Use H for Hairy knuckles
• HH or Hh
Why should you care about
Chromosomes?…
Have a Baby!
• Karyotype…spread out a fetus’s
chromosomes to check for normalcy
• Amniocentesis (Text pg. 768-769)
…Enables us to karyotype a fetus
• What are they looking for?
Chromosomal Abnormalities:
Downs Syndrome
• An extra chromosome # 21
(3 copies)
• Also referred to as Trisomy 21
• Slow development, flat face,
slanted eyes, intelligence
varies greatly
• 50% of children die before
age 1
• Karyotype tests can predict
the disorder but not its
severity
Karyotyping reveals lots of
information
• Normal 23 pairs of
chromosomes
• Of the 23 pairs, 22 are
autosomal pairs and 1
pair are the sex
chromosomes
• Females have two
identical sex
chromosomes (XX),
• While males have one X
and one smaller
chromosome called Y
Sex Chromosomes
Male vs. Female
• Females are
determined by XX
chromosomes
• Males by XY
chromosomes
• Males get the X from
Mom, the Y from Dad
• Females get one X
from each parent
Sex Chromosomes
Male or Female?
Sex-linked Traits
• Each X chromosome carries ~1,000
genes, whereas Y contains very few
• So, if a male gets an X chromosome from
his Mom with a bad gene, he is going to
suffer from it
• A female has a second X copy to work
with…
Example: Hemophilia
• A sex-linked recessive
disorder in which
blood does not clot
effectively
• Therefore, cuts are
slow to heal
• Disease is carried on
the X chromosome
• Queen Victoria and
extended family
suffered from this
Female Carriers for Hemophilia
Genetic Defects:
Can be due to chromosomal disorders…
Genetic Defects:
Or, at the level of Genes
Sickle Cell anemia; autosomal recessive. 9 % of US
blacks are heterozygous, while 0.2% are homozygous
recessive. The recessive allele causes a single amino
acid substitution in the beta chains of hemoglobin. When
oxygen concentration is low, sickling of cells occurs.
Heterozygotes make enough good beta-chain
hemoglobin that they do not suffer as long as oxygen
concentrations remain high, such as at sea-level.
Genetic Defects:
at the level of Genes
Huntington’s Disease; (also referred to as Woody
Guthrie's disease) is an autosomal dominant resulting in
progressive destruction of brain cells. If a parent has the
disease, 50% (or more) of the children will have it. The
disease usually does not manifest until after age 30.
Cystic Fibrosis; CF is the most common genetic disease
in Caucasians. An individual must inherit a defective
copy of the CF gene from each parent to have cystic
fibrosis. CF causes the body to produce an abnormally
thick, sticky mucus, due to the faulty transport of sodium
and chloride (salt) within cells