Transcript Chapter 5 - SchoolRack

Heredity
Chapter 4
Standard: S7L3
Students will recognize how biological traits
are passed on to successive
generations.
 a. Explain the role of genes and chromosomes
in the process of inheriting a specific trait.
Heredity
The passing of traits
from parents to
offspring.
Traits- The
characteristics of an
organism.
Alleles
A different form of a
gene.
One allele may code for
dimples, and the other
for no dimples.
Parents
You get one allele from
mom, and one from
dad.
Genetics
The study of how traits
are inherited through
the interactions of
alleles.
Gregor Mendel
The first to
study how traits
were passed
from one
generation to the
next.
He studied pea
plants.
Mendel’s Experiments
Mendel crossed a pure breeding white
flowered plant with a pure breeding purple
flowered plant
He got all purple flowers
BUT, then he crossed two of the second
generation purples and he got ¾ purple
and ¼ white!
What does that mean?
Mendel decided that meant that one
alleles was dominant and the other allele
was recessive
Dominant vs. Recessive
Dominant Alleles- An
allele that covers, or
dominates another allele.
Recessive Allele- An
allele that is covered, or
hidden by another allele.
Punnett Squares
A tool to predict the
probability of certain
traits in offspring.
Punnett squares show
the different ways
alleles can combine.
Representing Alleles
Letters!
Upper case= dominant
alleles. (R)
Lower case =recessive
alleles. (r)
Homozygous
If the two alleles that you get
from mom & dad are the
same, it is homozygous(RR,
rr)
Heterozygous
An organism that has two
different alleles for a trait
is called heterozygous.
(Rr)
Genotype vs. Phenotype
Genotype- An organism’s
genetic makeup.
Phenotype- Outward
appearance, or behavior of
an organism.
Example
The tongue
rolling allele is R.
R is dominant
r is recessive
Your mom is
homozygous dominant
for the tongue rolling
gene.
Her genotype is RR
Your dad is
heterozygous for the
tongue rolling gene.
His genotype is Rr
Probability
What is the probability
that you will be able to
roll your tongue?
Do a Punnett Square!
Making a Punnett Square
To set up a Punnett
Square, draw a large
square, and then divide
it into four equal
sections.
Dad’s Alleles go on top
Mom’s
Alleles
go on
the
side
Sperm
R
R
Eggs
Sperm
R
RR
Rr
R
RR
Rr
Eggs
Your genotype could be:
•50% RR- Homozygous
Dominant
•50% Rr- Heterozygous
Your phenotype would be:
•100% Tongue Roller
•0% No Tongue Roller
Hybrid vs. Purebred
Hybrids=HeterozygousHave two different alleles for
a gene: Rr
Purebreds=HomozygousHave the same allele for a
gene: RR or rr
Let’s Do Another One!
The Big Nose
Allele is N.
Big Nose is N
Little nose is n
Mom is Heterozygous for
Big Nose: Nn
Dad is Heterozygous for
Big Nose: Nn
What is the chance you’ll
have a big nose?
Do the cross!
Sperm
N
NN
Nn
n
Nn
nn
Eggs
What is the genotype?
25% NN- Homozygous
Dominant
50% Nn- Heterozygous
25% nn- Homozygous
Recessive
What is the
phenotype?
75% Big Nose
25% little nose
Incomplete Dominance
When the offspring of two
homozygous parents show
an “in-between”
phenotype.
Example
Purebred white flowers
Purebred red flowers
Makes “in-between” color
pink flowers
Multiple Alleles
Any trait that is
controlled by many
alleles.
Blood type is an
example.
Polygenic Inheritance
When many genes act
to control a trait.
Examples include hair,
eye and skin color
Chromosome Disorders
If a sperm or egg cell gets
fewer or more
chromosomes than normal,
this can cause genetic
disease.
Down’s Syndrome
These persons have three
copies of chromosome #21.
They can be shorter, have
learning disabilities and heart
problems.
Down’s
Syndrome
Sperm
D
DDD D_
D
DDD D_
Eggs
Fetus
Dies
Non-disjunction
When chromosomes fail
to separate.
One sex cell gets an extra
chromosome.
One sex cell doesn’t get a
chromosome.
Recessive Genetic Disorders
Offspring only gets the
disease if he/she inherits
the recessive alleles from
mom and dad.
Cystic Fibrosis
Causes a thick fluid to build
up in the lungs, making it
difficult to breathe.
Cystic Fibrosis is a
Recessive Genetic Disorder.
Carriers
Mom and dad are carriersThey carry the defective
allele, but don’t have the
disease.
Sperm
C
CC
Cc
c
Cc
cc
Eggs
Cystic
Fibrosis
Sex Determination
Females have XX
chromosomes.
Males have XY
chromosomes.
Sperm
Girls
X
XX
XY
X
XX
XY
Eggs
Boys
Sex-Linked Disorders
An allele inherited on a
sex chromosome.
Color blindness is an
example.
Selective Breeding
Selecting plants or
animals with the most
desirable traits to breed for
the next generation.
Genetic Engineering
Finding desirable genes in
one plant, and inserting them
into another plant.
This can make vegetables
bigger, heartier and more
resistant to insects and fungi.
Genetic Anomalies