Monday, April 1, 2013
Name: ____________________________________ Period: ____
Describe heredity as the passage of instructions from one generation
Competency
to another and recognize that heredity information is contained in
3d – DOK 2
genes, located in the chromosomes of each cell.
I can define recessive and dominant alleles. I can determine if an
8th Grade –
organism is homozygous dominant, homozygous recessive, or
Lesson 5.3
heterozygous.
Page
3
Unit 5 – Heredity and Genetics: Dominance of Alleles
Quick Review
1.
2.
3.
4.
5.
Chemicals that make up DNA backbone = deoxyribose sugar and phosphate
Four different nitrogenous bases = adenine, thymine, cytosine, and guanine
Section of DNA that determines a specific trait = gene
Long strand of DNA that is tightly coiled, contains many genes = chromosome
A female has an allele of the BRCA1 gene that causes her to have a high risk of
developing breast cancer. Her daughter has the same allele of the BRCA1 gene. This
scenario illustrates the idea of heredity.
Key Points on Dominance of Alleles:
1. Most traits are determined by several genes that act together.
2. Some traits such as the ability to taste certain substances and the presence or absence of
dimples are controlled by a single gene.
3. Organisms have two alleles for each gene; one allele comes from each parent.
a. There are two different types of alleles, dominant and recessive alleles.
i. The dominant allele is usually indicated with a capital letter.
ii. The recessive allele is usually indicated with a lower-case letter.
b. If either of an organism’s alleles is the dominant allele, the trait given by this allele
will be seen in the organism’s phenotype.
c. The trait given by the recessive allele will only be seen in the organism’s phenotype
if the other allele is also the recessive allele.
4. We can describe the genotype of an organism based on the alleles that it has.
a. If the organism has two dominant alleles, it is called homozygous dominant.
i. Remember, “homo” means same. It has two of the same alleles and they
are dominant.
ii. Its genotype would be given with two capital letters.
b. If the organism has two recessive alleles, it is called homozygous recessive.
i. Remember, “homo” means same. It has two of the same alleles and they
are recessive.
ii. Its genotype would be given with two lower-case letters.
c. If the organism has one dominant allele and one recessive allele, it is called
heterozygous.
i. Remember, “hetero” means different. It has two different alleles.
ii. Its genotype would be given with a capital and a lower-case letter.
iii. Heterozygotes are carriers for the recessive allele though it has the dominant
phenotype.
Monday, April 1, 2013
Competency
3d – DOK 2
8th Grade –
Lesson 5.3
Name: ____________________________________ Period: ____
Describe heredity as the passage of instructions from one generation to
another and recognize that heredity information is contained in genes,
located in the chromosomes of each cell.
I can define recessive and dominant alleles. I can determine if an organism
is homozygous dominant, homozygous recessive, or heterozygous.
Page
3
Unit 5 – Heredity and Genetics: Dominance of Alleles
Quick Review
1.
2.
3.
4.
5.
Chemicals that make up DNA backbone =
and
Four different nitrogenous bases =
,
,
, and
Section of DNA that determines a specific trait =
Long strand of DNA that is tightly coiled, contains many genes =
A female has an allele of the BRCA1 gene that causes her to have a high risk of
developing breast cancer. Her daughter has the same allele of the BRCA1 gene. This
scenario illustrates the idea of
.
Key Points on Dominance of Alleles:
1. Most traits are determined by
that act together.
2. Some traits such as the ability to
certain substances and the presence or
absence of
are controlled by a
.
3. Organisms have
alleles for each gene; one allele comes from
.
a. There are two different types of alleles,
and
alleles.
i. The
allele is usually indicated with a
.
ii. The
allele is usually indicated with a
.
b. If either of an organism’s alleles is the
allele, the trait given by this
allele will be seen in the organism’s
.
c. The trait given by the recessive allele will only be seen in the organism’s phenotype
if the other allele is also the
.
4. We can describe the genotype of an organism based on the alleles that it has.
a. If the organism has
alleles, it is called
.
i. Remember, “
” means
. It has two of the
alleles and they are
.
ii. Its genotype would be given with two
letters.
b. If the organism has
alleles, it is called
.
i. Remember, “
” means
. It has two of the
alleles and they are
.
ii. Its genotype would be given with two
letters.
c. If the organism has one
allele and one
allele, it is
called
.
i. Remember, “
” means different. It has two
alleles.
ii. Its genotype would be given with a
and a
letter.
iii. Heterozygotes are
for the
allele though it has
the
.
Dominance of Alleles: Guided Practice
Monday, April 1, 2013
tt
Name: ____________________________________ Period: ____
Tt
Homozygous dominant
The allele for dimples in humans is dominant. If an individual has the dominant allele, they
will have dimples. If the both alleles are recessive, the individual will not have dimples. For
the given genotypes below, give the phenotype.
2. Homozygous
1. DD
recessive
3. Dd
4. dd
5. Homozygous
dominant
6. Heterozygous
Dominance of Alleles: Independent Practice
Directions: Answer the following questions in complete sentences.
1. KP1: How many genes control most traits in humans?
2. KP3a: What are the two different types of alleles and how can they be represented with
symbols?
3. KP4b: For an organism to show a recessive phenotype, what must be true about its
genotype?
4. KP4b/Guided Practice: An organism’s genotype is described as being homozygous
recessive. If the letter “T” is used to represent this gene, show this genotype.
5. KP4b (Challenge): An organism’s genotype is tt. What is another way to describe this
organism’s genotype?