This document provides information about genetics and inheritance for a dragon genetics lab. It defines key terms like heredity, traits, alleles, and dominant and recessive genes. It summarizes Gregor Mendel's pioneering work in genetics, including his laws of segregation and independent assortment. The document discusses inheritance patterns for autosomal and sex-linked genes, as well as complex inheritance like incomplete dominance and environmental influences. The goal is for students to understand basic genetics concepts and how they are demonstrated in a model organism.

1. Lab 6 - Inheritance of Traits:
the Dragon Genetics Lab
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2. Students will be able to:
• Define the terms heredity, traits, karyotype,
autosome, Punnett square, alleles
• Determine the difference between dominant
and recessive genes.
• Compare homozygous and heterozygous
traits.
• Demonstrate how alleles affect the
inheritance of traits in a model organism.
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3. • The passing of characteristics from
parent to offspring is called heredity.
• Before DNA and chromosomes were
discovered, the mechanism of heredity
was
one of the greatest mysteries of
science.
• It was once believed (in the 16th
century) that a sperm contained a fully
formed, miniature human being (called
preformationism).
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4. Terminology to know
• DNA - deoxyribonucleic acid, a self-replicating material
present in nearly all living organisms as the main constituent
of chromosomes. It is the carrier of genetic information.
• Chromosomes - a threadlike structure of nucleic acids and
protein found in the nucleus of most living cells, carrying
genetic information in the form of genes.
• Genes - a distinct sequence of nucleotides forming part of a
chromosome, and determines some characteristics of
offspring
• Allele - one of two or more alternative forms of a gene
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5. • Autosomal Chromosome – pairs 1 – 22 in
humans, contain all the instructions for the
body’s anatomy and function
• Sex Chromosome – 23rd pair in humans,
contain the sex instructions, xx or xy
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6. Gregor Mendel
• An Austrian monk
named Gregor Mendel,
who is known as the
Father of Genetics,
pioneered the study of
heredity in the late
1800’s.
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7. Mendel’s Hypotheses
• For each inherited
character, an individual
has two copies of the
gene -one from each
parent.
• These are called alleles
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8. Mendel’s Hypotheses
1. There are alternative
versions of the gene -
for example, the
alleles (big) Y and
(little) y, (big) T and
(little) t
– The combination of
these alleles is the
organism’s genotype
for that gene
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9. Mendel’s Hypotheses
• Of the two alleles, one
of them may be
completely expressed
(dominant), while the
other one may have no
observable effect
(recessive) on the
organism’s phenotype
(appearance).
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10. Mendel’s Hypotheses
• When gametes are
formed, the alleles for
each gene in an
individual separate
independently of one
another. Thus gametes
carry only one allele for
each inherited trait.
• Gametes are the sex
cells – the egg or sperm
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11. Two Laws of Heredity
• The law of segregation states that the two alleles
for a character segregate (separate) when the
gametes are formed.
• The law of independent assortment states that
the alleles of different genes separate
independently of one another during gamete
formation. For example, the alleles for the height
of a plant separate independently of the alleles for
its flower color.
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12. The Human Karyotype
22 pairs of
autosomes
1 pair of sex
chromosomes
Female = XX
Male = XY
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13. For autosomal genes:
• If an individual’s genotype is homozygous
dominant or heterozygous, their phenotype
will show the dominant allele. Ie. HH, Hh
• If an individual’s genotype is homozygous
recessive, their phenotype will show the
recessive allele. Ie. hh
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15. Autosomal or Sex Linked?
• If a gene is autosomal (found on the autosomes), it
will appear in both sexes equally.
• A sex-linked gene’s allele is located on the X or Y
(sex) chromosome.
• Most sex-linked traits are carried on the X
chromosome and are recessive.
• If a trait is sex-linked, its effects are usually seen
only in males.
– Color-blindness
– Male-pattern baldness
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16. Sex-Influenced Traits
• A sex-influenced trait is a phenotype that is expressed differently
in males and females.
• While sex-linked genes are only found on the sex chromosomes,
sex-influenced genes can be autosomal
• Example:
– Male pattern baldness (due to high testosterone; males have
more testosterone than females, so baldness is much more
common in males)
• Also called a sex-limited trait (trait is found in only one sex)
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17. Complex Patterns of Heredity
• Not all traits that are inherited are controlled by one set
of genes.
• When several genes influence a character, this is called
polygenic inheritance
– eye color, weight, height, skin color (this is why we have so
many different eye colors, weights, skin colors, etc)
• In Mendel’s crosses there was either a dominant or a
recessive trait. In some organisms, an individual displays
a phenotype that is intermediate between the two
parents, a condition known as incomplete dominance
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18. Examples of Incomplete Dominance
• When a snapdragon with
red flowers is crossed with a
snapdragon with white
flowers, a snapdragon with
pink flowers is produced.
Neither the red nor the
white allele is dominant
over the other.
• In humans, the child of a
straight haired parent and a
curly-haired parent will
have wavy hair.
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19. Incomplete Dominance v. Codominance
Incomplete dominance: one allele is only partially dominant to
the other; the heterozygote exhibits a phenotype that is
intermediate relative to the dominant and recessive phenotypes
• Example: flower color in Carnations
– Homozygous dominant (AA) = RED phenotype
– Homozygous recessive (aa) =
– Heterozygous (Aa) = PINK
• Codominance: both alleles are equally
dominant and both alleles are visible in
the hybrid genotype
• Example: feather color in chickens
– Homozygote 1 (F1F1) = BLACK feathers
– Homozygote 2 (F2F2) =
– Heterozygote (F1F2) = Black and
pattern
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20. Characters Influenced by the Environment
• Some phenotypes depend on environmental conditions
• Hydrangea flowers of the same genotype can exhibit
different phenotypes based on the environment (soil pH)
• Plants in acidic soil have blue flowers, while
plants in neutral or basic soil have pink flowers
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21. Temperature-dependent Sex
Determination
• This is the condition where the
sex of the offspring is
influenced by the prevailing
temperatures during embryonic
development. In sea turtles,
warmer temperatures produce
more or all females, cool
temperatures produce more or
all males, and the pivotal
temperature is the constant
incubation temperature that
produces equal numbers of
males and females.
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22. Example from lab
F f Long neck
G G No back hump
h h Back spikes
i i Short tail
J J Flat feet
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