Download Introduction to Genetics

Introduction
to Genetics
Gregor Mendel
Gregor Mendel is
the “father of
modern genetics”
 Austrian monk who
did genetic
experiments with
pea plants
 Defined basic units
of heredity

1822-1844
Mendel used pea plants to
conduct experiments. He
concentrated on petal
color and shape of peas.
Experiments led to basic
genetic understandings
such as:
•What happens when two
different plants breed?
•How traits are passed
from parents to
offspring?
•Basic understandings of
dominant and recessive
traits?
Different traits Mendel observed:
Why Peas?
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Mendel could do two
experiments a year
Lacked modern technology
Today scientists use
organisms that reproduce
quickly such as drosophila
(fruit fly) which
reproduces in 2 weeks or
bacteria such as E. coli
which reproduces within
hours.
Genetics
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DNA are the blueprints of all of your
genetic information.
DNA is tightly wound
into chromosomes
Your genetic
information is on
genes
Genes are located on
chromosomes
Your Genes and DNA
You are a combination of your
parents.
 You have ½ of your mom’s and ½ of
your dad’s DNA
 Remember Meiosis?
 You have 23 pairs (one from each
parent) to make a total of 46
chromosomes.

Human Chromosomes
Genetic Traits

Genes you get from your dad are
“paternal” and genes you get from your
mom are “maternal”

These make up your traits.
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Trait: characteristic determined by genes
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Example: I have the trait for blue eyes
Alleles
Each trait is carried on a chromosome
stripe.
 These stripes are called alleles.
 Allele: form of a gene on a specific
region of a chromosome

Alleles for flower color
Maternal
Chromosome
Paternal
Chromosome
Which of Your Parents Traits
Will You Get?
Based on probability
 For example, eggs have X
chromosomes and sperm have either
X or Y chromosomes.
 XX= girl
 XY= boy
 What is the probability offspring will
be a girl?

Boy or Girl
50% chance or 1 out of 2
 Only two different combinations!
 XX or XY
 Determining the sex of a baby is one
example of probability.
 But…it doesn’t always work that way…

Dominant Alleles vs.
Recessive Alleles
Certain traits are stronger then
others. This means that they will
more likely be expressed.
 For example: If I mix black paint with
white paint, what color will paint most
likely be?
 Black! It is a “stronger color”.
 Dominant allele: one that is expressed
physically (what organism looks like)

Dominant Alleles vs.
Recessive Alleles

What about the white paint?
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Recessive allele: one that is masked
or hidden by the dominant allele.

White paint would be an example of
the “recessive color”. There is still
white paint in the mixture, but it
looks black.
Terms To Know
Genotype: combination of two alleles
 Homozygous: When the genes are
identical
 Heterozygous: When the genes are
different
 Phenotype: The observable trait

(the trait you see)
Boy: XY Girl: XX

What is the genotype for girl?
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XX
Is boy homo or heterozygous?
Heterozygous XY (different letters)
 Homozygous XX (same letters)
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What is the dominant allele (X or Y?)
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Y
How do you know?
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Wherever Y is means a boy will form
How genes are expressed
If an organism carries any
combination of dominant genes, it will
be expressed in an organism.
 Recessive genes are only expressed
when there are two recessive genes
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Example XX in girls