Download Intro to Genetics Notes

Introduction to Genetics
“the study of heredity”
• Gregor Mendel
• The Father of Genetics
• carried out important studies of
heredity, used pea plants
• Heredity—the passing on of traits from
parents to offspring
• Trait- a specific characteristic that is
controlled by genes
• Exp. Eye color, hair color,
height
All of our “traits” are
coded into the DNA
that makes up our
chromosomes.
• Chromosomes
• Tightly coiled
DNA where your
genes are carried
• Genes
• Sections of DNA
that control your
traits
Homologous Chromosomes
Chromosomes that are the same size and
shape and carry the same
genes. You
P
get one from your mother and one from
Short pea plant
Tall pea plant
your father that match up.
1
F1
F2
3 tall: 1 short
Karyotype
• A picture of all the chromosomes
contained within a single cell.
• Contains 22 pairs of autosomes and one
pair of allosomes (sex chromosomes)
• Alleles
• The different forms a gene can take. (Letters)
• 2 Types of Alleles:
• 1. Dominant - Represented by a capital letter
(Exp. A)
• 2. Recessive - Represented by a lower-case
letter (Exp. a)
• Genotype
• The combination of two alleles (letters)
that represent the genetic make-up of
an individual. (AA, Aa, aa)
• Phenotype
• The observable physical characteristic of
an individual that are the result of its
genotype.
(Long eyelashes, Blue or Brown eyes)
3 Types of Genotypes:
• 1. Homozygous Dominant (purebred)
• 2 identical alleles that are capitalized
(AA, TT)
• 2. Heterozygous (hybrid)
• 2 different alleles (Aa, Tt)
• 3. Homozygous Recessive
• 2 identical alleles that are lower-case
(aa, tt)
Principle of Dominance
• If a dominant allele is present that
phenotype is visible
• An organism that is recessive for a
particular trait will exhibit that form only
when the dominant allele is not present.
• Organisms with a heterozygous genotype
(Aa) will never exhibit the recessive trait
because it is hidden (masked) by the
dominant allele.
Mendel’s Principles
• Law of Segregation -• the two alleles for a characteristic are
packaged into separate gametes
• Law of Independent Assortment -• each pair of alleles segregates into
gametes independently
The Tall (T) allele in
snapdragons is
dominant to the
short (t) allele.
If two heterozygous
tall (Tt)
snapdragons are
crossed, what will
be the ratio of short
to tall plants?
• You try this one:
A
A
a
A
Question 1
The passing on of characteristics
from parents to offspring is
__________.
A. genetics
B. heredity
C. pollination
D. allelic frequency
The answer is B.
Genetics is the branch of biology that
studies heredity.
Question 2
What are traits?
Answer
A specific characteristic that is controlled
by genes. Height, hair color and eye color
are examples of traits in humans.
Question 3
Gametes are __________.
A. male sex cells
B. female sex cells
C. both male and female sex cells
D. fertilized cells that develop into
adult organisms
The answer is C.
Organisms that reproduce sexually produce
male and female sex cells, called gametes.
Question 4
Which of the following genotypes
represents a animal that is
homozygous dominant for a trait?
a. KK
b. Kk
c. kk
Question 5
Which of the following genotypes
represents a plant that is homozygous
recessive for height?
A. TT
B. Tt
C. tt