Transcript Genetics and Heredity

Genetics
and
Heredity
Deoxyribonucleic Acid (DNA)
• DNA is an
organism’s genetic
material.
• Large molecule
with a shape
similar to a twisted
ladder (double
helix).
• Chromosomes –
made of coiled DNA.
• Gene – a section
(pair) of a
chromosome that
has genetic
information for 1
trait.
• Allele – 1 copy of a
gene. Each
characteristic (trait)
has two alleles, one
from each parent.
Traits are controlled by genes
• Genes are located on your chromosomes
• Individuals inherit genes from their parents
• Your cells contain 23 chromosome pairs
What is a trait?
• Trait – a physical characteristic that can be seen.
• Example of traits – eye color, freckles, number
of legs, thumb on top, rolling tongue.
• Each trait is represented by two letters (ex: Tt).
Heredity and Genetics
• Heredity – passing
of traits from parents
to offspring.
• Genetics – the study
of how traits are
passed from parent to
offspring.
The Father of Genetics
•Gregor Mendel
•Austrian Monk
•Gardener, bee
keeper, scientist
•Experimented on
plants, especially
known for his
work on pea plants.
Mendel studied 30,000 common pea plants over 8
years and many generations. Mendel found that
traits show up without any blending.
Dominant vs. Recessive
• Dominant trait – the allele that masks the
appearance of another allele. Represented by a
capital letter.
• Recessive trait – the allele that is blocked by a
Dominant allele. Represented by a lower case
letter.
Dominant Traits
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Broad lips
Hazel or green eyes
Second toe longest
Widow’s peak hairline
Crossing thumbs – left on top
Unattached earlobe
Rolling tongue
Dimples
Freckles
Straight thumb when
extended
• Curly hair
Recessive Traits
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Thin lips
Blue or grey eyes
Big toe longest
Straight hairline
Crossing thumbs – right on
top
Attached earlobe
Non-rolling tongue
No dimples
No freckles
Bent thumb when extended
Straight hair
The Punnett Square
• Reginald Punnett
created the
Punnett Square
• A tool used by
scientists to
predict the
genotypes of
offspring.
Genotype & Phenotype
• Genotype – The two specific two alleles
inherited for a particular gene (example TT,
Ss, oo, Gg, etc.)
• Phenotype – The observable characteristic
that appears such as blue eyes, two legs,
tallness, etc.
Using the Punnett Square
• Draw the square
Using the Punnett Square
Write the genotypes of the parents on the outside
of the box.
T
t
T
t
Using the Punnett Square
• Fill in the boxes with the alleles down and
across
T
t
T
TT
Tt
t
tT
tt
Using the Punnett Square
Each box represents 1 offspring.
In the above Punnett Square, how many different
genotypes are there? How many different
phenotypes are there? How can you represent those
number in a percent (%)
Answers
•The genotypes are 1 or 25% BB , 2 or
50% Bb, and or 25% bb
•The phenotypes are 3 or 75% purple
and or 25% white
Different types of Genotypes
• Heterozygous genotype – a genotype in which
the two alleles are different. (example Tt)
• Homozygous genotype – a genotype in which the
two alleles are the same. (example TT or tt)
Different types of Genotypes
• Hybrid – a heterozygous genotype and is the
result of 2 genetically different parents.
▫ Example: TT + tt = Tt
• Pure Bred – a homozygous genotype and is the
result of 2 genetically same parents
▫ Example: TT + TT = TT or tt + tt = tt
What is a pedigree?
• A pedigree is a chart of the genetic history of
family over several generations.
• Show the phenotypes of genetically related
family members.
• http://www.schooltube.com/video/c188ce8266b54a18992b/tions
Symbols in a Pedigree Chart
Examples of Pedigrees