Download Intro to Genetics

Genetics & The
Modern Theory of
Evolution
What is Genetics?
• Genetics – The study of how heredity
information is passed from parents to
offspring
• The Modern Theory of Evolution =
• Genetics + Darwin’s Theory of Natural Selection
Gregor Mendel (1857-1865)
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Studied inheritance of
traits in pea plants
Published research
shortly after Darwin’s
book (but it was in an
obscure journal)
He received credit for
his work in 1900 (15 yrs
after his death)
The pea traits he
studied later became
known as GENES
He became the Father
of Genetics
Law of Dominance: (see below)
What is a Gene?
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Each cell in your body
contains a nucleus
Each nucleus contains
pairs of chromosomes
How many
chromosomes do
humans have?
What cell type in your
body only has ½ as
many chromosomes?
Chromosomes contain
your DNA sequence
A segment of DNA is
called a gene
A gene codes for a
specific trait
Cells > nucleus > chromosomes > genes (traits) > DNA segment
What is DNA?
•DNA stores information
•DNA = Deoxyribonucleic acid
•Subunit = nucleotides
•Nucleotides contain a nitrogen base
•4 different nitrogen bases
•adenine (A)
•guanine (G)
•thymine (T)
•cytosine (C)
•Complimentary Strands (A-T) (G-C)
•3,000,000,000 nitrogen base pairs make
you who you are
James Watson & Francis Crick (1953)
Discovered the structure of a
DNA molecule (double helix)
which provided details on
genes & how they work
Name the DNA structure and
draw an example
What is an Allele?
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Most organisms have TWO copies of every gene and chromosome (one from
each parent) – see picture below
Alleles are the different forms of a gene for a specific trait
– Ex: flower color gene in pea plants contain a white allele and a purple allele
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Remember genes exist as pairs so often one allele is considered the dominant
allele and the other the recessive allele
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Which is the purple allele?
Dominant & Recessive Alleles
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Dominant alleles are given a capital letter symbol
– Ex. Purple Flower = P
Recessive alleles are given a lower case letter symbol
– Ex. White Flower = p
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Since genes are found in pairs, a pea plant could have the following
combinations of alleles for flower color
– PP = purple
Pp = purple
pp = white
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The genetic make-up is called the genotype (PP, Pp, or pp)
– PP and pp is considered homozygous (all one allele type)
– Pp is considered heterozygous (two different allele types)
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The outward physical appearance for a gene is called the phenotype
(purple or white), which is based on its genotype
Punnett Square
B = purple
b = white
What are the chances of having
the white phenotype?
What are the chances of carrying
the white allele?
What is the chance of having a
heterozygous genotype?
Try some examples on the board: BB x bb and Bb x bb
How is it possible my two boys have blue eyes if my eyes are brown?
DNA Code and Mutations
• The DNA Sequence shows
how a species changes over time
• If a mutation (typo) occurs
within the DNA sequence, genes
can change causing alleles and
traits to change
• Over time as more mutations
accumulate the species changes
Human Genome (2001)
• All living things are made of genetic
information
• We have similarities in our DNA to all
animals including dogs and fruit flies.
• The more closely related two species
are to each other the more similar their
DNA code (genome)
• Find out your genetic code
• 23andMe (was $999, now $199)
• Visit: www.23andMe.com
• Other: deCODE; Navigenics