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Genetics
What is Genetics?

The study of heredity

Genetics does not just relate to people, but also
includes animals, plants, insects, etc.
Heredity: the passing of traits from parents to
offspring
Offspring: children (next generation)
Trait: a characteristic
What is Genetic Information?

There are several words we use to
describe where this information is found…
 DNA
 Chromosomes
 Genes
Where is the genetic
information?
Genetic Information
Found inside
every cell
 Located in the
nucleus

(main organelle in the
center of the cell)
Structure inside the nucleus
chromosomes carry the
genetic code (blueprints)
 chromosomes are made of
many sections of blueprints
called genes
 genes are made of DNA

Chromosomes
Package of genes
 Humans have 46
chromosomes
 They come in pairs…so 23
pairs
 Different organisms have
different # of chromosomes

Some plants: hundreds
Some bacteria: one
Mouse: 20
DNA
DeoxyriboNucleic Acid
 Double stranded
 Twisted ladder
 Structure discovered by
Watson and Crick
Rosiland Franklin
 Made of nitrogen bases,
sugars, phosphate
Gene
A section of DNA
 Contains specific information for a
particular trait
 Different traits are controlled by different
genes

Label the picture with
each of the following
terms:
– Chromosome
– DNA
– Gene
Analogy…
Spool of thread
 DNA…thread
 Gene…colored sections of thread
 Chromosome…thread on spool
How is this information
passed on?
It is passed on when new cells are
created…
2 PROCESSES
1. Mitosis
2. Meiosis
Mitosis
 Creates identical cells
 For growth and repair
 For asexual reproduction
Meiosis
 Creates sperm/egg
 For sexual reproduction
Steps in Mitosis
1.
DNA is replicated
Replication: making a copy of
DNA
Chromosome pairs
split and go to each
side
3. Cell divides
2.
Steps in Meiosis
DNA is replicated
2. DNA is recombined
(mixed)
3. Cells divide
4. Cells divide again
1.
Compare and Contrast…
Similarities
Differences

Mitosis

Meiosis
So…
How many chromosomes do
human cells have?
Then how come you don’t have 92
(46 + 46) chromosomes when
you combine an egg with sperm?
Important points about Meiosis
1.
2.
Creates sperm and egg cells
Reduces the number of chromosomes

3.
4.
cuts the number in ½
Produces 4 cells
Chromosomes have recombined (mixed)

creates variety
Karyotype
Karyotype
A picture of the chromosomes
 Identifies an error in meiosis that results
in a different # of chromosomes
 Used to identify some genetic disorders
 An incorrect number of chromosome is
ONE type of genetic disorder

Sex Chromosomes
X Chromosome



Larger chromosome
Contains over 2,000
genes
Contains info NOT
related to gender
Y Chromosome



Smaller chromosome
Contains 330 genes
Only one of its genes
determines the male
gender
Sex Determination…
Sex is determined by the Y chromosome
 XX = female
 XY = male

Twins
Two Types of Twins…
Identical Twins





One egg is released
Egg is fertilized by
one sperm
One fertilized egg
splits into two
Twins have identical
chromosomes
Twins are like
“clones”
Fraternal Twins
Two eggs are
released
 Each egg is fertilized
by a different sperm
(2 sperm total)
 Twins have different
chromosomes
 Twins are like siblings

Common Questions
Twins:
fraternal twins are generational
How long can sperm survive? Depends on environment, but ~5 days
Genetic Vocabulary
Genetic Vocabulary
P Parent
F1 First filial
1st generation
F2 Second filial
2nd Generation
Genetic Vocabulary
Allele
Letter representation of a
gene
 Consist of two letters (same
letter)
 Represents two forms of the
trait
 Ex) Tt

Genetic Vocabulary
dominant

The stronger trait
 Represented by a big letter
 Does the hiding…hides the
recessive trait
recessive

The weaker trait
 Represented by a small letter
 Gets hidden
 Only seen when there is no
big (dominant) letter
Genetic Vocabulary
heterozygous

Hetero=different
 Two different alleles
 Ex) Tt
homozygous

Homo=same
 Two same alleles
 Ex) TT or tt
Genetic Vocabulary
hybrid

An organism that is “mixed”
(heterozygous) for a trait
purebred

An organism that is “pure”
(homozygous) for a trait
Genetic Vocabulary
phenotype

Physical description of the
trait
 What does it look like?
 Uses words
 Ex) tall
genotype

Allele description of the trait
 What are the letters?
 Uses letters
 Ex) Tt
The Mating Game Article
You need the following:
 2 different colored highlighters

– You can share colors with a neighbor
Pencil or Pen
 Copy of the article

The Mating Game Article
1. Read the
2. How does
article.
the article define hybrid? Write the
word “definition” in the margin next to the
sentence in the article.
3. Circle all examples of hybrids .
4. Underline reasons for why different species
rarely mate in nature. Write a number for each
reason in the margin of the article.
5. Highlight the sentences that describe
disadvantages to the formation of hybrids.
6. Highlight in another color the sentences that
describe how creating hybrids can be beneficial.
Your Assignment

Using your annotated article, answer the
article questions.

Write in complete sentences.