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Chapter 3
part 1
Heredity and Genetics
Section 3-1
 Turn to page 64 in your book.
 At the top of the page, look for the blue box that says Investigate.
 Work with the students in your table row.
 Kyle and Isaac work with the students to your right
 Jazlyn and Brian work with the students to your left
 On a piece of paper, list the 5 characteristics that describe your
appearance.
 Ex.) hair color, eye color, and height.
 Compare your list with others in your group
 Think about it - Does anyone in your group have the same exact
characteristics as you? Are any of them common?
Section 3-1What is heredity?
 Key terms
 Trait- characteristic
 Inherited trait – a trait that is passed from parents to
their offspring
 Heredity- passing of traits from parents to offspring
 Genetics- study of heredity
Traits
 You can make a list of characteristics about yourself.
 This list includes things about yourself such as
 Eye color
 Height
 Hair color
 It is very unlikely another student in the class or school will have
the same traits that you have.
 This is because the combination of traits that you have are very
unique. There is only one you.
 These characteristics are called traits.
Traits
Identifying Traits
 Have you ever noticed that you look like your parents? Siblings?
 Children often look like their parents or even grandparents.
 There is a reason for this:
 During fertilization (the making of you) male and female sex cells
join.
 Each cell contains a unique set of material that affects the
development of their offspring (children)
 Traits are passed from parents to children.
 These traits are called inherited traits.
 Ex.) eye color
Heredity
 The passing of traits from parents to offspring is called
heredity.
 The field of biology that studies heredity is called genetics.
 Why might we study genetics?
 1.)
 2.)
 3.)
Heredity
 Gregor Mendel was an Austrian monk who was one
of the first people to study genetics.
 He used pea plants for this studies.
 He is also often referred to as the “Father of
Genetics”.
The Heredity of Twins
 Twins are siblings that are born at the same time.
 There are 2 types of twins
 1.) Identical
 develop from 1 egg fertilized by 1 sperm cell, that splits in 2.
 These 2 cells become 2 individuals
 They are genetically the same; they have the same exact traits, which makes them
hard to tell apart.
 They are ALWAYS the same sex (either both boys or both girls)
 2.) Fraternal
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Develop from 2 eggs fertilized by 2 sperm cells at the same time.
These twins are genetically different from each other, just like regular siblings.
They CAN be 1 boy, and 1 girl, or both boys or both girls.
They are more common
What you need to do now…
 For Homework: On Pg. 65, Answer questions #1-12 on a piece of
paper.
 DUE TOMORROW!!!
 Take your time, make your answers and work NEAT!!!
 If you are struggling, READ the section over again.
 If you are still struggling come see me during HOMEROOM
TOMORROW.
 Tomorrow bring with you…
 Your homework, and turn it in the bin at the beginning of class.
 Also bring your Chapter 3 note packet
 A sharpened pencil
What you should be doing…
 Turning in your COMPLETED homework from
yesterday.
 Pg. 65, #1-12
 Get out your CHAPTER 3 note packet and a pencil
 Place everything else on the floor!
3-2 What is meiosis?
 Key Terms
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sperm cells – male reproductive cell
Egg cells- female reproductive cell
Gamete- reproductive cell
Meiosis- type of cell division that produces gametes
Gametes
 Every body cell of an animal has the same number of
chromosomes.
 However, there are special cells in an animals body that only
have ½ the number that the other cells have.
 These cells are called gametes
 They are used only in reproduction.
 Egg- female reproductive cell
 Sperm – male reproductive cell
 These develop from special cells in the body.
 When they are formed, the number of chromosomes is cut in ½.
 This process is called Meiosis.
Gametes contain half the number of
chromosomes as body cells.
Not all organisms have the same number of chromosomes.
Number of Chromosomes in various organisms
Organism
Body Cells
Gametes
Fruit Fly
8
4
Bull Frog
26
13
Human
46
23
Meiosis
 Type of cell division that produces gametes.
 It occurs in two parts
 Meiosis I
 Meiosis II
 These phases are similar to mitosis (cell division).
 At the end of meiosis II there are 4 daughter cells,
which contain half the number of chromosomes as
the original cell.
The steps of
Meiosis
What you should do now…
 Answer Questions 1-9 on page 67 in your book for
homework. It is due tomorrow.
 Take your time and make sure that your answers are neat
and correct.
 Begin your Meiosis II drawing with the time remaining in
class. I will assign you a due day, and you will have only 1
day in class to work on this assignment.
 You will be graded on NEATNESS!! If you need someone to
help you write out the labels I will help you!
What you should be doing…
 Get out your Chapter 3 Guided Note packet and a
pencil or pen
 Put everything else on the floor.
3-3 What is DNA?
 Key terms
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DNA – large molecule contained in chromosomes
Replication- process by which DNA is duplicated
Protein Synthesis- process by which proteins are made
RNA- molecule used in the making of proteins
Discovery of DNA
 After the discovery of
chromosomes, scientists began to
question what they were made of.
 They discovered that chromosomes
are made up of a large molecule
called DNA, which stands for
deoxyribonucleic acid.
 James Watson and Francis Crick are
credited with the discovery of
DNA’s structure in 1953.
Structure of DNA
 The model used to describe
the structure of DNA is called
a double helix and looks like a
twisted ladder.
 The sides of the ladder are
made up of sugars and
phosphates.
 The steps of the ladder are
made up of 4 different
nitrogen bases.
 Each base pairs with only 1
other base.
 Adenine (A) can only bond
with Thymine (T)
 Guanine (G) can only bond
with (C)
Let’s try a couple stands…
 Write the complimentary strand (or the one that each base
would pair with) for the strands below. REMEMBER! A=T
and G=C
 1.) GGTACATCGAT
 2.) TGATCGATCAG
Replication
 During Mitosis, the chromosomes replicate so that
each new daughter cell get’s a copy.
 For this to happen, DNA must also replicate. This
process is called replication.
 The DNA ladder breaks itself in half, like unzipping a
zipper.
 Then new bases are added to each half of the zipper.
 The new DNA is an exact copy of the old DNA
The role of DNA
 A single strand of DNA can have THOUSANDS of steps
or base pairs.
 The arrangement of these pairs will code for a specific
code, with determine what gene will be formed.
 Different genes determine the different kinds of
inherited traits of an organism.
How long is an actual gene?
Protein Synthesis
 DNA controls organism’s traits by producing certain
proteins at certain times.
 This is called protein synthesis.
 Proteins are made of molecules called amino acids, which
are made by the ribosomes in a cell.
 DNA is found inside the nucleus, which is where protein
synthesis begins.
 DNA is too big to fit through the nuclear membrane, so a
special molecule is needed to take the code from the
nucleus to the ribosome. This molecule is called RNA
(ribonucleic acid).
 RNA is a little different than DNA
 It is single stranded (one side of the ladder)
 Instead of Thymine (T) it has Uracil (U)
 It copies the code from DNA then carries it to the
ribosome.
 There it acts like a pattern where proteins can be built
from.
 Ribosome reads the RNA and attaches the correct
amino acids, which link together forming a protein.
Protein synthesis summary…
What you should do now…
 Complete Worksheet 3-3 for homework and turn it in
tomorrow.
What you should be doing…
 Get out your Chapter 3 Guided Note packet and a
pencil or pen
 Put everything else on the floor.
3-4 What are Chromosomes?
 Key Terms
 Karyotype – organized display of an organism’s
chromosomes
 Centromere – point of a chromosome where two
parts meet
 Gene- parts of a chromosome that control inherited
traits
 Allele- one of two or more forms of a particular
gene
Chromosomes
 The fine, threadlike structures
called chromosomes are found
in the cell’s nucleus.
 They control heredity
 Scientists study chromosomes
using something called a
karyotype.
 Karyotype – is a display of an
organism’s chromosomes
 It is organized by shape and
size
 The chromosomes are often
numbered.
Chromosome Structure
 Chromatin is a long thin strand of DNA that makes up
chromosomes
 When a cell is getting ready to divide, the chromatin
condenses and wraps around special proteins to give
it an X shape.
 Each side of a chromosome is called a chromatid, and
two chromatids are exact copies of each other. They
are held together by a centromere.
Genes
 Gene- a special part of the chromosome that controls
inherited traits.
 It is found on a specific part of the chromosome.
 Gene determine hair color, eye color, ear shape, etc.
 They also control processes in your cells.
Chromosome Pairs
 For organisms that carry out life through sexual
reproduction (2 parents), chromosomes exist as pairs.
 An organisms gets 1 set from mom, and 1 set from
dad.
 Ex.) 23 from mom, 23 from dad, give us our full 46.
 Chromosome pairs are often very similar in size and
shape.
Alleles
 Alleles are different versions of the same trait.
 Ex.) Trait – hair color
 Allele – brown hair vs. blonde hair
 Alleles for the same trait are ALWAYS found at the
same place on the same chromosome
What you should do now…
What you should be doing…
 Get out your Chapter 3 Notes, and something to write
with.
 Put everything else on the floor
3-5 Why can offspring differ from
their parents?
 Key terms
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Homozygous – having 2 like genes for the same trait
Heterozygous- having 2 unlike genes for the same trait
Dominate gene- gene whose trait always shows itself
Recessive gene- gene whose trait is hidden when the
dominate trait is present
Genes and Traits
 Gregor Mendel, the “Father of genetics” studied pea
plants
 During his study he noticed that there must be a
factor that affected how a plant was going to look.
These factors are now called, “genes”.
 For example, he noticed that some of his plants were
tall, and some where short.
 He then decided that there must be a gene for height.
 The height of a pea plant must be determined by 2
genes, one from each parent.
 Each trait of an organism must be determined by at
least one gene from each parent.
Homozygous Plants
 Mendel noticed that one kind of
tall pea plant always had tall
offspring.
 These plants have 2 tall genes,
one from each parent.
 He also noticed that one kind of
short pea plant always had
short offspring.
 These plants have 2 short
genes, one form each parent.
 These plants were
homozygous.
Heterozygous plants
 Mendel then tested to see what
the offspring of a homozygous
tall and a homozygous short
would look like.
 They were also all tall.
 He called them heterozygous
because he knew that had 2
unlike genes for a trait.
Dominate Genes
 When you cross 2 different organisms, one trait
always shows itself, and one is always hidden.
 Mendel then coined the terms:
 Dominate gene- a gene that always shows itself
 Recessive gene – a gene that is hidden when the
dominate gene is present.
What you should do now…
What you should be doing…
 Get out your Chapter 3 Notes, a calculator and
something to write with.
 Put everything else on the floor
3-6 How do genes combine in
offspring?
 Key terms
 Punnett square – chart that shows possible gene
combinations.
Gene Symbols
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Organisms have at least 2 genes for most traits
They receive at least one kind from each parent.
Letters are used to represent combinations of genes.
The dominate is always capital
The recessive is always lower case
Ex.) If we say that brown hair color is dominate over
blonde hair color, it would look like this:
 B – brown
 b- blonde
Let’s try a couple
 If brown eyes are dominate over green eyes
 If attached ear lobs are dominate over unattached
Predicting Traits
 Suppose you have a father that is homozygous
dominate for black hair (BB), and a mother who is
homozygous recessive for brown hair (bb).
 How could you predict what color hair their children will
have?
 A tool that is used to predict traits is called a Punnett
square.
 It is a chart used to show possible combinations for
offspring.
Constructing a Punnett Square
 Step 1 – draw a square with 4 boxes in it.
 Step 2 – put the parents on the sides of the Punnett
square
 Step 3 – fill in each square with the dominate gene
 Step 4- fill in each box with the recessive gene
 Your finished Punnett square should look like this:
B
b
b
B
Bb
Bb
Bb
Bb
So what will the offspring look like?
 Every box of that Punnett square was Bb, so:
 It was 4/4 Bb, which is the same as 100%
 So all of the children will have black hair.
 They will all be heterozygous dominate, because they
have both kinds of genes.
Combining heterozygous genes
 When both parents are heterozygous (Bb) for a gene,
the Punnett square will always show the same results:
 It looks like this:
B
b
B
BB
Bb
b
Bb
bb
BB - ¼ = 25%
Bb - 2/4 = 50%
Bb – ¼ = 25%
Let’s practice
 If you have a purple flowering plant that is
homozygous dominate for it’s flower color is crossed
with a homozygous recessive yellow flowering plant,
what will the resulting offspring look like?
 If you cross 2 heterozygous purple flower plants,
what will the resulting generations be?
What you should do now…
What you should be doing…
 Get out your Chapter 3 Notes, a calculator and
something to write with.
 Put everything else on the floor
3-7 What are incomplete dominance
and co-dominance?
 Key terms
 Incomplete dominance – pattern of inheritance in which
alleles from both parents are blended
 Codominance - pattern of inheritance in which both
alleles of a gene are expressed
Incomplete Dominance
 Usually if an allele is
dominant over another
allele, the dominate one is
the only that shows up in an
offspring
 This type of inheritance is
called incomplete
dominance.
 In this case the offspring will
show a blending of traits
from each parent.