Genetics Terms You`ve Gotta Know
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Transcript Genetics Terms You`ve Gotta Know
BASIC GENETICS TERMS
Terms you’ve gotta know
GENE
Gene: a section of DNA
that codes for a trait
A chromosome is a
chunk of DNA and
genes are parts of
chromosomes
ALLELE
Allele: the different options for a gene
Example: attached or unattached earlobes are
the alleles for the gene for earlobe shape
DOMINANT/RECESSIVE
Dominant: an allele that blocks or hides a
recessive allele (UPPER CASE letter) A
Recessive: an allele that is blocked by or hidden
by a dominant allele (Lower case letter)a
HOMOZYGOUS/HETEROZYGOUS
Homozygous: When a person’s two alleles for a
gene are the same (AA or aa)
Heterozygous: When a person’s two alleles for a
gene are different (Aa)
You get one allele from your mom and one from
your dad.
If you get the same alleles from your mom and
dad, you are homozygous for that trait.
If your mom gave you a different allele than your
dad, you are heterozygous for that trait
GENOTYPE
Tt
Genotype: A person’s set of alleles (gene options)
Genotype is written in letters (Tt)
It is usually the first letter of the dominant allele
to make it easier
Choose a letter for each of these traits. Write
both the dominant and the recessive genotype
allele letters
Attached Earlobes
Freckles
Dimples
Tongue-roller
GENOTYPE
Now, using your letters from before write a
genotype for a person without freckles (Freckles
are dominant)
Write a genotype for a person with freckles
GENOTYPE-HETEROZYGOUS AND
HOMOZYGOUS
A Heterozygous genotype means an organism
has both the dominant and the recessive allele
(e.g. Aa)
Homozygous recessive means an organism has
2 recessive alleles (e.g. aa)
Homozygous dominant means an organism
has 2 dominant alleles (e.g. AA)
PHENOTYPE
Phenotype: A person’s physical features because
of their genotype
What you look like (your phenotype) is based on
what your genotype is (your genes)
What will the phenotype of these genotypes be:
WW, Ww, ww (Widow’s Peak dominant over straight hair
line)
HH, Hh, hh (Hitch hiker’s thumb is dominant over a
straight thumb)
CC, Cc, cc (Curly hair is dominant over straight hair)
PRACTICE PROBLEMS
One cat carries heterozygous, long-haired traits
(Ss), and its mate carries homozygous shorthaired traits (ss). Use a Punnett square to
determine the probability of one of their offspring
having long hair.
One cat carries heterozygous, long-haired traits
(Ss), and its mate carries homozygous shorthaired traits (ss). Use a Punnett square to
determine the probability of one of their offspring
having short hair.
PRACTICE!!
One flower is heterozygous red (Rr) and it is
crossed with a homozygous white (rr) plant. Use
a Punnett square to determine the probability of
one of their offspring having a white color.