Download Introduction to Mendelian Genetics

Introduction to Mendelian
Genetics
• Genetics:
– The study of heredity
• Heredity:
– How traits are passed down generation to
generation
• History:
– Gregor Mendel is known as the father of
genetics
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• Gregor Mendel/1850’s:
– Austrian monk
– Study mathematics and botany at the
University of Vienna
– Use both of these areas of study to analyze
genetic crosses using pea plants.
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Mendel worked with 7 pea
plant traits:
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Mendel’s experiments:
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Important terms to know:
• Gene:
– A segment of DNA that codes for a specific
protein/trait.
• Allele:
– A specific form of a gene
• Dominant:
– The overpowering form of a gene
– Occurs most often in a population
– Represented by a capital letter
• Recessive:
– The weaker form of a gene
– Occurs less often in a population
– Represented by a lower case letter
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Important terms to know:
• Phenotype:
– A physical trait that you can see
– Examples in peas: tall, short, wrinkled,
smooth
• Genotype:
– The genetic make up /gene combination
– Three types of genotypes:
• RR…..Homozygous dominant
• Rr……Heterozygous
• rr……. Homozygous recessive
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The law of dominance
• Simply stated:
– Anytime a dominant allele is present the
dominant trait will be seen, it overpowers the
recessive allele.
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• The ability to roll your tongue is dominant
over the inability to roll your tongue.
– Tongue roller …. T
– Non tongue roller…t
– Homozygous Dominant:
• TT
• Tongue roller
-Heterozygous
•Tt
•Tongue roller
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-Homozygous Recessive
•tt
•Nontongue roller
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Karyotype
- A diagram created from a picture of a
person’s actual chromosomes.
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Use of the karyotype:
• Used to determine if a person inherited a
certain gene or genetic disorder
• Used to determine the chance of passing
a gene or genetic disorder on to their child
• Used to determine the sex of a child.
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It’s a male:
Why?
XY
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It’s a female:
Why?
XX
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Down Syndrome
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Edward’s Syndrome
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Creating a karyotype:
-Look at the length of the chromosome
-Look for the position of the centromere
-Look at the repeating pattern of light and dark
bands representing genes
-Look at the specific genes which have been
identified and mapped/labeled through the
Human Genome Project.
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Punnett Squares
A mathematical method to determine the
chance of producing an offspring with a
specific trait.
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1 Trait Crosses
Purple pea blossoms are
dominant over white
blossoms
Heterozygous purple flower
crossed with another
Heterozygous purple flower
Phenotypic ratio:
Results:
Genotypic ratio:
-75% purple
-25% white
- 25% BB
- 50% Bb
- 25% bb
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In rabbits black fur is dominant over
tan fur.
Cross a Homozygous dominant black
fur male with a Homozygous
recessive tan fur female.
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2 trait crosses
Yellow peas (Y) are dominant
over green peas (y). Green
pea pods (G) are dominant
over yellow pods (g).
Cross a Heterozygous green
pea pod, Heterozygous yellow
pea with another Heterozygous
green pea pod, Heterozygous
yellow pea
GgYy x GgYy
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2 trait cross
In guinea pigs black fur is
dominant over white fur and
smooth fur is dominant over
rough fur.
Cross a Homozygous
recessive white,
Heterozygous smooth fur
female with a Heterozygous
black fur, Homozygous
dominant smooth fur male.
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