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Genetics: Vocabulary
Nucleus
DNA
Chromosome
Allele
Gene
Traits
Dominant
Recessive
Genotype
Phenotype
Homozygous
Heterozygous
Nucleus
Our cells are controlled by the nucleus.
The nucleus also contains our
genetic information
(DNA- DeoxyriboNucleic Acid)
on structures called
Chromosomes.
Chromosomes
Humans have 46 chromosomes in
each body cells or 23 pairs.
Pea Plants have 14 chromosomes in
each cell or 7pairs.
Made of thousands of genes (over
60,000 in humans).
Each parent contributes half of each
chromosome pair to their offspring.
Usually there is one pair of sex
chromosomes
Genes
The genes on chromosomes have
control for different traits. For example
a gene may control for eye color. All
genes come in pairs.
Half of the pair coming from mother, the
other half coming from father
Humans: 23 genes from mother
23 genes from father
Pea Plants 7 genes from mother
7 genes from father
(XX)
(XY)
(XX)
(XY)
Alleles
There are different forms of genes called
alleles.
For example: eye color (gene) brown
eyes, blue eyes, and green eyes (allele)
Dominant Allele vs Recessive Allele
Individual C is
the only one
who will have
blue eyes
(recessive
allele)
Because the
allele for brown
eyes is present,
individual B and
individual A will
have brown
eyes
Dominant Allele vs Recessive Allele
• Dominant allele – a trait that always
shows up when the allele is present
– Symbol – Capital letter (T)
• Recessive allele – a trait that is covered
up or masked when a dominant allele is
present
– Symbol – lower case letter (t)
For example brown eyes (B) are dominant
over blue (b), and appear more often.
Allele: Eye Color
B represents the dominant trait brown
b represents the recessive trait of blue.
–
the child could have B from one parent and B from
the other = child with brown eyes
GENOTYPE: BB PHENOTYPE: Brown Eyes
– the child could have B from one parent and b from
the other = child with brown eyes
GENOTYPE: Bb
PHENOTYPE: Brown Eyes
– the child could have b from one parent and b from
the other = child with blue eyes
GENOTYPE: bb
PHENOTYPE: Blue Eyes
Any time the dominant gene appears, the
offspring will have the dominant trait.
Gregor Mendel’s Pea Plant
Experiment
Let’s Review: Beach Ball
Activity
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8.
What is the phenotype for Bb when b= blue eye
color and B= brown color?
What is a phenotype and a genotype?
When does a phenotype for a recessive trait show
up in an organism?
How many pairs of chromosomes do humans have?
T = tall and t= short, what is the phenotype for Tt?
T = tall and t= short, what is the phenotype for tt?
T = tall and t= short, what is the phenotype for TT?
Sex chromosomes for males is?