heredity chapter 4. standard: s7l3 students will recognize how biological traits are passed on to...
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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 flowersBUT, 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 dominantr 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
R
R
R
r
Eggs
Sperm
RR Rr
RrRR
R
R
R
r
Eggs
Sperm
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=Heterozygous- Have two different alleles for a gene: Rr
Purebreds=Homozygous- Have the same allele for a gene: RR or rr
Let’s Do Another One!
The Big Nose Allele is N.
Big Nose is NLittle 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!
NN Nn
nnNn
N
N
n
n
Eggs
Sperm
What is the genotype?25% NN- Homozygous Dominant
50% Nn- Heterozygous25% nn- Homozygous Recessive
What is the phenotype?
75% Big Nose25% little nose
Incomplete Dominance
When the offspring of two homozygous parents show an “in-between” phenotype.
ExamplePurebred white flowersPurebred red flowersMakes “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.
DDD D_
D_DDD
DD
D
D
?
Eggs
SpermDown’s Syndrome
Fetus Dies
Non-disjunctionWhen 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 carriers- They carry the defective allele, but don’t have the disease.
CC Cc
ccCc
C
C
c
c
Eggs
Sperm
Cystic Fibrosis
Sex Determination
Females have XX chromosomes.
Males have XY chromosomes.
XX XY
XYXX
X
X
X
Y
Eggs
SpermGirls
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
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