Transcript ii. history of genetics

Unit 7:Introduction to Genetics
Test on:
Intro
Although the resemblance between
generations of organisms had been noted for
thousands of years, it wasn’t until the 1800s
that scientific studies were carried out to
develop an explanation for this. Today we
know that we resemble our parents because of
heredity which is the set of characteristics we
_______,
our parents
receive from __________.
The study of
genetics
heredity is known as ________.
I.
SEXUAL REPRODUCTION &
MEIOSIS
(pp. 275-278)
In sexual reproduction, an egg and
sperm cell fuse together to create a
zygote
fertilized egg or ________.
Egg and
gametes
sperm cells are known as _________.
Gametes are the only cells in the
body that are not produced by
mitosis
________.
I.
SEXUAL REPRODUCTION &
MEIOSIS
(pp. 275-278)
Instead gametes are created
through a special process
of cell division called
meiosis
__________
which
halves the chromosome
_______
number. Meiosis only
ovaries
occurs in the _________
of females and the
testes of males.
________
A. Chromosome Number
1. Human _______
somatic
cells, or body cells,
contain ___
46 chromosomes. Somatic cells
2n because these cells
are ________
or ___
diploid
double set of chromosomes –
contain a ______
half (___)
and half (___)
23 from ______
mom
23
from ____.
These “matching”
dad
chromosomes are known as
_______________.
A homologous pair
homologous pairs
is a pair of chromosomes – one from each
type of traits
parent, with the same ___________
or
_______.
genes
A. Chromosome Number
egg and ______)
sperm
2. Human gametes (____
23 chromosomes. They are
contain ____
haploid or __.
______
n These cells contain ___
1/2 the
single
total number of chromosomes, a _______
set of chromosomes. When the gametes
fuse together in ___________,
fertilization
the
zygote has _______
46
resulting ________
chromosomes.
B. Formation of Gametes: Meiosis
Gametes are formed in meiosis – a special
type of cell division that only occurs in the
_______
ovaries of females and ______
testes of males.
In meiosis, DNA is replicated once in
___________________,
S
phase of the cell cycle but the cell goes
through two cell divisions, resulting in ___
4
1/2
cells with _______
the original
chromosome number.
Meiosis occurs in two stages:
1. Meiosis I
Prior to meiosis I, the DNA is replicated in
S____________________________.
phase of the cell cycle (or interphase)
When the chromosomes, each consisting
of 2 _______________
sister chromatids line up in the
middle of the cell in __________
metaphase I, they
homologous pairs. In anaphase
line up in ___________
I and telophase I, the homologous pairs
__________,
but the sister chromatids and
separate
centromeres are still intact.
_____________
Meiosis occurs in two stages:
1. Meiosis I
Two cells are formed, each with
23 pairs of _______________
___
sister chromatids
making up ___
23 chromosomes, but
there are no longer any
________________
homologous pairs present, so
the two cells are ____________.
haploid or n
Meiosis occurs in two stages:
2. Meiosis II
The process continues with the two
cells formed moving directly into
prophase II without any further
________________.
replication of DNA After the
chromosomes align in the middle of
the cell in __________
metaphase II, this time the
sister chromatids are pulled apart in
anaphase II.
_________
Meiosis occurs in two stages:
2. Meiosis II
Two new cells are formed from
each of the two cells formed in
Meiosis I, resulting in a total of
4 new cells, each with ___the
___
1/2
original number of chromosomes.
The cells produced are called
gametes
_______. Therefore, meiosis results in
4 haploid gametes
C. Crossing Over
Crossing over occurs during
prophase I
homologous
___________
when ___________
pairs of chromosomes come together.
sister chromatid
A portion of one ______________
may be broken off and exchanged
with the corresponding portion of a
sister chromatid of the homologous
chromosome. Crossing over is very
increases the genetic
common and __________
variability in offspring.
II. HISTORY OF GENETICS (pp. 263-270)
A. Gregor Mendel
Genetics Mendel
Known as the “Father of ________”,
pea
is famous for his experiments with ____
plants. He used true-breeding pea plants,
purebred, pureline and
which means _______________
characteristics always show. This
generation of true-breeding plants is known
P generation. Mendel studied seven
as __
traits
____, including plant height, seed color,
flower color, etc.
II. HISTORY OF GENETICS (pp. 263-270)
A. Gregor Mendel
A trait is an _______________.
inherited characteristic
Pea plants cross-pollinate,
meaning pollen from one plant
fertilizes an egg from another,
but they can also self-pollinate,
meaning pollen can fertilize egg
same plant. Mendel
from _____
controlled the fertilization
process of the pea plants by
self-pollination
preventing ______________
and controlling cross-pollination
II. HISTORY OF GENETICS (pp. 263-270)
B. Mendels’ Results
• 1. P generation – Crossed
pureline plants with one trait
_________
pureline plants with the
with ________
other. For example,
tall plants X short plants
_____________________
II. HISTORY OF GENETICS (pp. 263-270)
B. Mendels’ Results
2. F1 generation – Offspring produced
from _____.
P x P In F1, one trait seemed to
disappear
________.
For example, tall plants X
short plants = ___________.
all tall plants
3. F2 generation – Offspring produced
F1 x F1
from _______.
In F2, trait that
disappeared in F1 reappeared in ____
1/4 of
the offspring; the other ¾ showed
trait seen in F1
______________.
II. HISTORY OF GENETICS (pp. 263-270)
C. Mendel’s Principles
After analyzing his results carefully, Mendel
formed conclusions that increased
understanding of inheritance and opened
the door for the study of genetics.
genes determine
1. Individual units called _______
inheritable characteristics. A gene is a
DNA that codes for a specific
portion of _____
trait
______.
II. HISTORY OF GENETICS (pp. 263-270)
C. Mendel’s Principles
2. For each gene, an
organism inherits two
alleles, one from each
parent Alleles are
_______.
different forms or
gene
_____________
possibilities of a ______.
a. If the two alleles are the
same, the organism is said to
homozygous for that
be ____________
trait and the allele will be
expressed.
II. HISTORY OF GENETICS (pp. 263-270)
C. Mendel’s Principles
b. If the two alleles differ, the organism is
said to be __________
heterozygous for that trait and
only one allele will be expressed. The
expressed allele is the ________
dominant allele,
designated by an _____-case
letter. The
upper
allele that is not expressed in a
recessive
heterozygous trait is ________,
designated by a _____-case
letter. A
lower
recessive allele is only expressed when an
homozygous for that allele
organism is ___________________.
II. HISTORY OF GENETICS (pp. 263-270)
C. Mendel’s Principles
3. In meiosis, the two alleles for a
separate Each
trait segregate (_______).
egg or sperm cell receives a copy of
one of the two alleles present in the
somatic cells of the organism. Due
to the random separation of
chromosomes in meiosis, there is a
50% chance that a copy of that
____
allele will end up in the gamete
produced. This is known as the
principle of segregation.
II. HISTORY OF GENETICS (pp. 263-270)
D. Genetics Terminology
Physical description of trait; for
1. Phenotype - ________
example, ______________
tall, short
2. Genotype – Genetic make-up of an organism
TT, Tt, tt
or set of alleles; for example, ____________
3. Application of Terminology - If round pea
seeds are dominant to wrinkled pea seeds,
R and wrinkled is
round is designated __
designated __.
r
II. HISTORY OF GENETICS (pp. 263-270)
D. Genetics Terminology
a. Homozygous dominant for pea seed shape is
RR Seed shape? ______
round
written ____.
RR Phenotype = ______
round
Genotype = ___;
b. Heterozygous for pea seed shape is written
____.
Seed shape? _______
round
Rr
Rr Phenotype = ______
round
Genotype = ___;
c. Homozygous recessive for pea seed shape is
written __.
rr Seed shape? _________
wrinkled
Genotype = ___;
rr Phenotype = _________
wrinkled
III. ANALYZING INHERITANCE
(pp.135-137)
A. Probability
Due to the law of segregation, if you know
the genotype of the parents, you can
predict the likelihood of a trait occurring in
the offspring. Probability can be written 3
ways. The probability of a coin coming up
heads after being flipped is (fraction)
1/2 (ratio) ________,
1:2
_____,
or (percent)
_______.
50%
III. ANALYZING INHERITANCE
(pp.135-137)
B. Punnett Squares
A Punnett square is a tool used to predict
meiosis and
the possible outcomes of ________
fertilization in other words, a Punnett
___________;
square is used to determine the probability
of certain traits appearing in offspring.