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Genetics
The study of heredity
Vocabulary
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Heredity—the passing of traits from parent to offspring.
Traits—a trait is a characteristic; hair color, height, ear lobes…
Probability—the mathematical chance that an event will occur.
Polygenic Inheritance: when more than one gene controls the trait. When this
happens you get a variety of sizes or colors.
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Types of traits
DOMINANT
• Dominant traits—the trait
observed when at least one
dominant allele for a trait is
inherited.
• Examples: brown eyes,
curly hair, dimples, freckles.
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TYPES OF TRAITS
RECESSIVE
Recessive traits are traits that show up only
when two recessive alleles for the same
trait are inherited. Examples are green
eyes, red hair and nearsightedness.
Comparing Genes and alleles
gene
Alleles
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Segments of DNA found on chromosomes
Alleles are different forms of a single gene
Genotype and phenotype
• Genotype -- the inherited
combination of alleles.
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AA
Aa
aa
• Phenotype – the physical
appearance of an individual.
Homozygous (purebred) heterozygous (hybrid)
ALLELE COMBINATIONS
Homozygous
• Homozygous is when there are two identical
alleles of a particular gene present.
homozygous
• Homozygous is when there are two identical alleles of
a particular gene present.
• If the letter T represents height, then a capital T =
tall and t = short.
• A homozygous trait would be either
• TT (homozygous tall)
• or tt (homozygous short).
• PUREBRED is another word for homozygous. It is
the result of all dominant or all recessive genes.
heterozygous
• A heterozygous trait is when two different
alleles of a particular gene show up.
heterozygous
• A heterozygous trait is when two different alleles of a
particular gene show up.
• If T = tall and t = short, then a heterozygous trait could only
be
• Tt = (heterozygous tall)
• Whenever a capital letter shows up, that trait is
DOMINANT, and the recessive trait will not show up in the
individual.
• HYBRID is another word for heterozygous. It is the result of
a dominant gene and a recessive gene.
Incomplete dominance
• Incomplete dominance refers to a situation where one
allele does not completely dominate another allele,
and it results in a new phenotype. There is a blending
of color.
• Examples:
• 1. A red snapdragon flower breeds with a white
snapdragon flower and their offspring will be a pink
snapdragon. (RR red + WW white= RW pink)
2. Two mousies breed, one black and one white and their
offspring is a gray mouse.
(BB black + W W white = BW gray)
CoDominance
• Codominance is when both alleles for a gene
are expressed and both alleles show up in
some form.
codominance
• Codominance is when both alleles for a gene are
expressed and both alleles show up in some form.
• Examples:
1. When cattle with red hair and cattle of white hair
breed, the resulting offspring will have a coat color of
roan, a combination of the red hair and the white hair.
2. In a certain fish, blue scales and red scales are
codominant. When a fish has the genotype BR, it has a
patchwork of blue and red scales.
Multiple gene (allele) inheritance
• Multiple gene inheritance is when more than one gene
controls the trait. When this happens you get a variety of
sizes or colors. It is also known as ‘polygenic’ inheritance.
• Examples
1. More than one gene controls eye color, so humans have a
variety of eye colors from bright blue to hazel and green to
dark brown, almost black.
2. Skin color, height and hand spans are also polygenic.
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Betty and Barney Rubble
Pedigree—the recorded ancestry of an organism
Hemophilia and queen victoria’s family
Period 1
Period 3
Period 4
Period 5
Period 6
Period 7
All classes 157 students
50:50 LAB
50:50 LAB
COMPARING GRAPHS
50:50 LAB
HAND SPAN LAB
Hand span and 50:50 lab follow up questions
Write down the sentence starter and fill in the blank.
1. There were differences in the curves because
_________________________________________.
2. The sample size was ___________________ in the
_________________________lab.
3. The Hand span lab was an example of
________________inheritance
4. The 50:50 lab simulated the p__________________
of families having boys or girls.
Punnett Square: a model used to show the possible ways
genes can combine during fertilization.
T= tall t = short (representing alleles)
Capital letters are dominant, lower case are recessive.
Two alleles from each parent are passed on to offspring
T
T
TT
t
T
t
Heredity Sentence Frame Review
1. ___________________________ is the same as hybrid.
2. TT is an example of a(n) _________________________ genotype.
3. A(n) _______________ is a different form of a single gene.
4. An example of a ______________________ is hair color.
5. The genetic combination of alleles is called a _____________________.
6. Recessive traits are represented by ____________________ letters.
7. The _______________________ trait is the one that always shows
through.
8. Homozygous is also know as ______________________.
9. In a Punnett square, the alleles of the ___________________ are on the
outside of the square.
10. The four squares of the Punnett Square represent the probable
_______________ of the parents.