Transcript Chapter 5 Heredity & Genetics
Heredity & Genetics PART ONE
I: Mendel and Genetics :
A. What are dominant & Recessive traits?
B. What is a Punnett Square? C. What is incomplete dominance?
A- Genetics:
Similarities and differences among parents and offspring. It studies how offspring inherit characteristics from their parents and how DNA is involved.
B- Mendel: in 1866, this Austrian monk studied traits of pea plants.
1. Mendel studied 7 traits one at a time. Each trait had two forms.
Height Tall Vs. Short.
2. Mendel grew short and tall pea plants.
3. Mendel let these plants self-pollinate for several generations to get pure breed seeds.
Self-pollinate = Pollination within one plant
4. Mendel cross-pollinates the pure tall with the pure short pea plants.
Cross-pollination = Take pollen from one plant and put it on another plant. 5. The seeds Mendel collects are Hybrids.
Hybrid = combination of two varieties of organisms.
6. Mendel plants the hybrid seeds to see if they will grow tall, short, or medium.
They all grow tall.
7.
Mendel self-pollinates the hybrid for several generations, and plants the seeds from the hybrids. 3:1 ratio some grew tall some grew short.
8. Conclusion the trait for tallness was visible and the trait for shortness was hidden.
Visible trait = dominant, prevents the expression of recessive trait in organism.
Hidden trait = recessive.
C-What we learned from Mendel.
1.Traits (characteristics) are
determined by Genes.
2.Genes = a section of chromosomes
that determines a trait. { eye color, hair color, etc..}
3. Two genes for every trait. Example tallness in pea plants if pure tall two tall genes, if short two short genes, if a hybrid one tall gene and one short gene.
4. The different forms of a gene are ALLELES {recessive & dominant}
D- Punnett Squares.
1. Genotype = the genetic make-up of an organism.
Homozygous: alleles of a gene are the same.
Heterozygous: alleles of a gene are different; one allele for tall one for short.
Hybrids are heterozygous
.
2. Phenotype = What the organism looks like.
3.Punnett Squares: predict the genotypes & phenotypes of offspring.
Symbols for different alleles of a gene. Dominant is capital and recessive is lower case letter.
Height = T for dominant & t for recessive.
TT or tt= homozygous Tt = heterozygous or hybrid.
4. Offspring receive one allele for each trait from each parent.
5. Heterozygous pass on either T or t.
D- Incomplete Dominance: Condition in which the two alleles of a gene are both dominant.
1-It produces a blended phenotype.
Blended phenotype = hybrid.
Example: cross a pure red snapdragon with a pure white snapdragon, and you get a pink snapdragon. RW is the hybrid note both are dominant.
Part Two Genes and Traits:
A.In the nuclei of a human cell you find two sets of
chromosomes
23 pairs. This is a
diploid
number of chromosomes.
1. One pair of the chromosomes comes from the
father
the other set comes from the
mother
.
2. Genes are sections of
DNA
, each human chromosome may contain
1,000’s
of genes.
3. The way chromosomes
pair
up results in different genetic
make-ups
in the offspring.
B. Meiosis : is the formation of sex cells or gametes .
1. Eggs are produced in the female sex organ the
ovaries
, sperm is produced in the male sex organ the
testes
.
2. Meiosis produces sex cells with only
one
set of
chromosomes
these cells are
monoploid
.
3. In meiosis the chromosomes separate
twice
as do the cells.
4. Steps of Meiosis
:
a.
1 st
everything that occurs in
Mitosis
happens with Meiosis. Except the
2 nd
time the chromosomes
DO NOT DOUBLE.
b. Sometimes the twin chromosomes that are similar pair with each other. If they
exchange
DNA this is known as
crossing
over this increases the
differences
in the offspring compared to the parent.
3. At the end of meiosis we have
4
cells with a
monoploid
number of chromosomes. {
HALF
THAT OF PARENT CELL} 4. When the egg and sperm cells unite the two
monoploid
cells combine their DNA forming a diploid
zygote
.
2n Diploid 4n 2n Diploid n Monoploid
PART THREE
I. How Sex is Inherited
: Sex of an offspring is determined by a pair of
chromosomes
.
A. The
male
body cell has
XY
The
female
body cell has
XX
B. Twins: 1. IDENTICAL TWINS: ONE
EGG IS FERTILIZED BY
ONE
SPERM. THE
ZYGOTE
SPLITS. ALWAYS THE SAME
SEX
.
Sperm
Egg
Zygote
Same Sex
Always
2. FRATERNAL TWINS: TWO
EGGS AND
TWO
SPERM CELLS. THEY
DO NOT
CONTAIN THE SAME
DNA
. CAN BE DIFFERENT SEX.
2 Sperms 2 Egg 2 Zygote
C.
X-
Linked
determined
Traits: are traits by genes on the x-chromosome.
1. Several diseases are
more
common in males then in females.
• Women may
not
be
affected
by the disease, but pass it on to their sons. These
women
are known as
carriers
. • X-chromosomes are
larger
so they carry more
genes
. The ability to see
color x-chromosome
.
is on the
2) X-chromosomes
have genes that tell whether or not you see
color
. (
Red
,
Green
) • Women are
seldom
color-blind because the gene is a
recessive
gene on the X-chromosome and they have
two x-chromosomes .
X ’ =
recessive gene for
color blindness
3)Hemophilia
: is another x-linked
disease
it is a blood disorder that prevents the blood from
clotting
properly.
X’
= recessive trait for
hemophilia
IV.Source of Gene Variations:
When cells divide each DNA molecule in the cell makes the cell makes a
mistake exact
copies of itself. But sometimes ; bases may pair up
incorrectly
. The
codon
are changed the
altered
gene is passed on to the new cell.
A Mutation permanent DNA
is any change in the of a cell.
1.Mutation
increases
exposure of
DNA
with the to some
chemicals damage
ands radiation that the DNA molecule.
B.Chromosome Mutation:
When a
piece
of chromosome
breaks
and are
rearranged lost
. During meiosis chromosomes
mutation
separate
evenly
.
or may occur when chromosomes do not
1.Muscular Dystrophy
= Weak muscles.
2.Down Syndrome or Trisomy 21=
is caused as a result of a sex cell having too many
chromosomes
contains
three 21st
. The fertilized egg, 21st
chromosomes
instead of two.
3.Importance of Mutations= are a source of
new
traits or new
forms
of traits.