Transcript Day 10 GHSGT Geneticsx

Genetics
Observable Patterns
of Inheritance
Gregor Mendel
•
Mendel’s
Insight Into
Patterns of
Inheritance
Gregor Mendel
Monk in Brunn, Austria
Attended University of
Vienna (Math Major)
Child of a Farmer
Experimented with
the Pea Plant
Pisum sativum
• The pea plant has seven major traits
that Mendel studied that are true
dominant and recessive
characteristics.
• The pea was an excellent plant to
study because…
– 1. it is self-fertilizing
– 2. many samples can be grown at one
time
– 3. the traits were easy to see
Seven Major Traits of the Pea
Trait Dominant Recessive
Seed Shape
Round
Wrinkled
Seed Color
Yellow
Green
Pod Shape
Inflated
deflated
Pod Color
Green
Yellow
Flower Color
Purple
White
Flower
Position
Stem Length
Along stem
At the tip
Tall
Dwarf
Genetic
Terminology
•Genes
–Units of information about specific
traits. These are passed from
parent to offspring.
–Each gene has a specific location
(GENE LOCUS) on a chromosome.
• Diploid Cells (2N) ~ have a pair
of genes on a pair of homologous
chromosomes.
(human diploid cells have 46 chromosomes)
• Haploid Cells (N) ~ have ½ the
number of chromosomes as a
diploid cell with no homologous
pairs.
(human haploid cells only have 23 chromosomes)
• Alleles ~ the different forms of
a gene.
Ex. “T” is used for tall and “t” is
used for short (T and t are alleles)
• Homozygous alleles ~ 2 alleles
in a pair are the same. Ex. TT or tt
• Heterozygous alleles ~ 2 alleles
in a pair are different. Ex. Tt
Genotype ~ refers to the
actual genes present in the
individual.
Phenotype ~ refers to the
individual’s observable
traits, “physical appearance”
Eyes are blue. Blue is
the phenotype and
the alleles that make
them blue (bb) is the
genotype.
• Parental Generation (P)~
represents the parents in the first
cross
• F1 Generation ~ first generation
offspring (the babies of the P
generation)
• F2 Generation ~ second
generation offspring (the babies of
the F1 generation)
Mendel’s Theory
of Segregation
• Mendel believed
that a plant
inherited 2 genes of
information for a
trait, one from each
parent. To test this
idea, he performed
thousands of
monohybrid
crossings.
Monohybrid cross
a cross between
2 individuals
where only
one trait is
being studied
Probability
• Being a mathematics major, Mendel
was fascinated with the idea of
probability (the chance of each
outcome occurring is proportional to
the number of ways that it can be
reached). Mendel created a visual
solution to the probable outcome for
each of his monohybrid crossings.
This was called the “Punnett-Square
Method”
Punnett~Square Method
Setting up a Punnett square
• 1. Set up a 2 x 2 Punnett square.
• 2. Write the alleles for parent 1 on the
left side of the Punnett square.
Each gamete will have one of the two alleles of the
parent. In this particular cross, half of the gametes
will have the dominant (S) allele, and half will have the
recessive (s) allele. We will use blue and brown to
keep track of the alleles of each parent.
S
s
• 3. Write the alleles from parent 2 above
the Punnett square.
For this heterozygous parent (Ss), half of the
gametes will have the dominant (S) allele, and
half will have the recessive (s) allele.
S
S
s
s
4. Fill
the squares
for parent 1.
Fill each square with
the allele from
S
Parent 1 that lines
up with the row.
Capital letters go in
s
the first position,
lower case go in the
second position.
s
S
S
S
s
s
S
S
S S
s
S s
s
S
s
s s
• 5. Fill the
squares for
parent 2.
Fill each
square with
the allele from
Parent 2 that
lines up with
the column.
Mendel’s Theory of
Segregation
Theory of Segregation was the first in Mendel’s research.
It states…
~
Diploid cells have pairs of
genes that segregate during
meiosis and as a result, each
half ends up segregated in
different gametes.
Dihybrid
Crosses
• Experimental
crosses where
two pairs of
genes are
observed
instead of
one.
Theory of Independent
Assortment
• From his work with dihybrid crosses,
Mendel created his theory of independent
assortment which states…
–At meiosis, gene pairs on
homologous
chromosomes are sorted
randomly of each other.
Human Traits
• Most traits in humans are controlled
by multiple alleles.
– That means that more than one type
of letter could be received from a
parent.
• Example… Blood Type you could
inherit an A, B or o allelle from a parent.
This creates many different varieties in
one trait (A blood, B blood, AB blood
and o blood)
Sex-Linked Traits
• Some traits in humans are
linked to an X or a Y
Chromosome
–These are called Sex-Linked
Traits
• Examples of sex linked traits are…
–COLOR BLINDNESS and
HEMOPHILIA
• How might a biologist
determine whether a
mutation has occurred
and, if so, what type of
a mutation it is?
• Frameshift mutation
• A frameshift mutation changes the amino
acid sequence from the site of the
mutation.
•
In this example, one nucleotide (adenine)
is added in the DNA code, changing the
amino acid sequence that follows.
In this example, one nucleotide (adenine) is
deleted from the DNA code, changing the
amino acid sequence that follows.
Tranlocation/Inversion
• Translocation ~ switch the genes from one
chromosome to another
• Inversion ~ flip the genes upsidedown!
A section of
DNA is
accidentally
duplicated
when a
chromosome
is copied.
Pair Share
• A’s tell B’s how a
mutation affects proteins
• B’s tell A’s three different
ways mutations can
occur.
Point Mutations
• An alteration in DNA sequence
caused by a single nucleotide
base change, insertion, or
deletion.
The Operon Model of gene regulation was proposed by
Francois Jacob and Jacques Monod. Groups of genes
coding for related proteins are in units known as operons.
An operon consists of an operator, promoter, regulator, and
structural genes. The regulator gene codes for a repressor
protein that binds to the operator, obstructing the promoter
(thus, transcription) of the structural genes.
Now its your turn!
What kind of mutations
occurred?
1. DNA ~ ATTCGGATAACG
RNA ~ UAAGCCAUUGC
2. DNA ~ ATTCGGATAACG
RNA ~ UAAGCCGCCUAUUGC
3. DNA ~ ATTCGGATAACG
RNA ~ UAACCGUAUUGC
4. DNA ~ ATTCGGATAACG
RNA ~ CUAAGCCUAUUG
Do you really get this?
• Try it with your partner.
How else can your
genes mutate?
• What if your whole chromosome is
deleted?
• What if you ended up with an extra
one?
• How does this happen?
Nondisjunction
• Occurs when homologous chromosomes
do not separate during meiosis.
There are two possible results from
nondisjunction in chromosomes
1.Monosomy – resulting when one
chromosome is missing (often lethal)
2. Trisomy – resulting when there is one
EXTRA chromosome.
Individuals that receive nondisjunctive
gametes are often sterile
Disorders caused by
Nondisjunction
• Down Syndrome – the
most common
chromosomal disorder.
– Called trisomy 21
because of the extra
chromosome on the 21st
pair.
– Mental retardation,
abnormal eyelids, thick
lips deformed hearts,
short stature
Klinefelter’s Syndrome
• Caused by nondisjunction of the sex
chromosome and results in a man with an
extra X chromosome.
• Appearance Enlarged breasts, high
pitched voice
• Abnormally long arms
• Bad skin condition on feet and legs
Turner’s Syndrome
• Due to nondisjunction of
the sex chromosomes
resulting in monosomy.
• Appearance: short,
stocky girl, immature sex
organs and breasts as
an adult.