Download Slide 1

Genetics
and
Heredity
Learned Behavior
Inherited Trait
• Look at he list below and decide if each
is a learned behavior or an inherited
trait
•
•
•
•
•
•
•
using tools
curly hair
bright feathers
where to hunt for food
what food tastes good
blue eyes
building a shelter
Prokaryotes and Eukaryotes
• Prokaryotes and eukaryotes both have DNA
Prokaryotes
Eukaryotes
archaebacteria
bacteria
protists
fungi
plants
animals
Goals
• We will focus on genetic material and how it is
passed from one generation to the next.
• All living organisms reproduce and pass traits to
their offspring
Heredity
• The process in which traits pass from
parents to offspring
Genetics
• Scientific study of heredity
Traits
• Traits
–characteristics controlled by
genetic material found in the
chromosomes
• Phenotype – what you can see
• Genotype – genetic code for a trait
Traits
• Where do traits come from?
–parents
Chromosomes
• Chromosomes are
found in the
nucleus
• Chromosomes are
made of DNA
Chromosomes
• The piece of yarn on your desk is a
model of the amount of genetic material
inside each one of your cells.
• Human cells have 46 chromosomes
(except the sperm and egg) and if they
were connected and stretched out, they
would be about 2 meters long
• Other organisms have different
numbers of chromosomes
Chromosomes
Chromosomes
• This is a karyotype of human
chromosomes
DNA
• DNA is an organic compound called
deoxyribonucleic acid
DNA
• DNA is made up of four nitrogenous
bases
– Adenine (A)
– Guanine (G)
– Cytosine (C)
– Thymine (T)
• When linked properly, these connected
bases create a shape called a double
helix (spiral staircase)
DNA
• Guanine (G) always pairs with Cytosine
(C)
• Thymine (T) always pairs with Adenine
(A)
A G T C C A G T A A
T C A G G T C A T T
Genes
• Segment of a DNA molecule that
contains information for a specific trait
– hair color
– eye color
– height
– chin shape
– ear lobes
Alleles
• An allele is a different form of a gene
• Genes come in pairs
• One member of the pair is called an
allele
• You have 2 or more alleles
for each trait you have
Chromosome
gene
alleles
smallest to largest
gene→ DNA→ chromosome→ nucleus
DNA
Dominant and Recessive Alleles
• Even though you get at least 2 alleles
for each trait, only one shows
• The dominant allele will be the one that
you see
• The recessive allele will be hidden
Dominant Allele
• If the dominant allele is present in the gene pair,
the organism shows the dominant phenotype
• represented with a capital letter
rolling tongue
RR or Rr
free ear lobe
FF or Ff
curved pinkies
PP or Pp
cleft chin
CC or Cc
widow’s peak
WW or Ww
straight thumb
SS or Ss
dimples
DD or Dd
Recessive Allele
• Allele that is hidden if the dominant allele is
present
• Both alleles in the gene have to be recessive to
see the recessive phenotype
• Represented with a lower case letter
non -rolling tongue
rr
attached ear lobe
ff
straight pinkies
pp
smooth chin
cc
no widow’s peak
ww
curved thumb
ss
no dimples
dd
summary
• Within the nucleus, genes occur in
pairs.
• A gene is a segment of DNA located on
each chromosome
• Each gene has a particular form called
an allele
summary
• An allele can be either dominant or
recessive
• If a dominant allele of a gene is present,
the dominant trait will appear in an
organism
• In order for a recessive trait to appear,
both alleles of a gene must be
recessive
Gregor Mendel
(1822 – 1884)
•
•
•
•
Father of genetics
Lived in Austria
Became a monk
studied genetics
using pea plants
Mendelian Genetics
• Mendel looked at
several traits in
pea plants
– pod shape
– flower color
– plant height
Mendelian Genetics
• Mendel termed traits as
dominant or recessive
• Punnett square – a chart used
to predict what traits the
offspring of two parents would
have
Punnett Square
• To set up a Punnett Square, decide
which trait is dominant
• dominant trait = capital letter
• recessive trait = lower case letter
• homozygous = two capital or two
lowercase (PP or pp)
• heterozygous = one capital and one
lower (Pp)
Punnett Square
• Use P for
purple
flower
color
• Use p for
white
flower
color
homozygous
P P
homozygous
p Pp Pp
p Pp Pp
Punnett Square
• Cross two
heterozygous
plants
heterozygous
P p
P PP Pp
heterozygous
p Pp pp
Results of the Punnett Square
• Each individual from the
Punnett Square will have a
genotype and a phenotype
–Genotype – what the genes
are
–Phenotype – what it looks like
Results of the Punnett Square
Punnett
Results
Genotype
Phenotype
PP
Homozygous dominant
Purple Flowers
PP
Purple Flowers
Pp
Pp
Heterozygous
Purple Flowers
Pp
Pp
Heterozygous
White Flowers
pp
pp
Homozygous recessive
Punnett Square Practice
1. A dog breeder is mating a brown
heterozygous lab to a black homozygous
lab. Brown is dominant. Set up a Punnett
Square and decide what percent of the
offspring will be black and brown.
X
=
?
B = brown
b = black
One parent is heterozygous brown Bb
One parent is homozygous black bb
B
b
b
Bb
bb
b
Bb
bb
Results of
Cross
Genotype
Phenotype
Bb
Bb
brown
bb
Bb
Bb
bb
brown
bb
bb
black
black
50% are brown, 50% are black
Punnett Square Practice
2. A cattle breeder wants to get rid of horns in
his cattle herd. Polled (no horns) is a
dominant trait. Horned is recessive. If he
bred a heterozygous bull to heterozygous
cows would he get all polled calves? Set up
an Punnett Square and answer the question.
X
=
?
H = polled
h = horns
One parent is heterozygous horned
One parent is heterozygous horned
H
h
H
HH
Hh
h
Hh
hh
Hh
Hh
Results of
Cross
Genotype
Phenotype
HH
Hh
polled
Hh
HH
Hh
Hh
polled
hh
hh
horned
polled
75% are polled, 25% are horned
Incomplete Dominance
• Some traits are not dominant or recessive
• These traits will blend when heterozygous
• You can use a Punnett square and will have
3 genotypes instead of two
X
=
Punnett Square Practice
3. In purple people eaters one eye is
homozygous dominant, two eyes is
homozygous recessive, and three eyes is
heterozygous. The number of eyes in an
incomplete dominant trait. What would the
offspring look like from a homozygous
recessive purple people eater and a
homozygous dominant purple people
eater? Set up a Punnett Square and find the
genotypes and phenotypes of the offspring.
EE = one eye
ee = two eyes
Ee = three eyes
One parent is homozygous dominant
One parent is homozygous recessive
E
E
e
Ee
Ee
e
Ee
Ee
EE
ee
Results of
Cross
Genotype
Phenotype
Ee
Ee
3 eyes
3 eyes
Ee
Ee
Ee
Ee
Ee
Ee
3 eyes
3 eyes
100% three eyed
Polygenic Inheritance
• Some traits are controlled by more than
one gene
• There are more than 2 phenotypes
– eye color
– blood type
– skin color
– height
Genetic Mutations
• Gene undergoes a change
• An error in the copying of the
DNA
• Some mutation are beneficial
• Some mutation are harmful
Chromosome Disorders
• Sometimes the incorrect number of
chromosomes occur
• This is produced by mistakes during
meiosis
• A change in the total number of human
chromosomes (46) usually leads to
death before the baby is born
• However, some additions and
subtraction in the chromosome number
do survive
Down’s Syndrome
• Extra chromosome at pair 21
Environmental Factors
• The environment can effect
how your genes are expressed
–Genes for height but not
enough food
–Genes for thin but too much
food