Meiosis

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14 Δεκ 2012 (πριν από 4 χρόνια και 10 μήνες)

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DNA STRUCTURE

Blueprint of Life


Standard 5a
-
c

5a. DNA & RNA


DNA is a double helix made of a sugar
-
phosphate backbone with complimentary
bases paired in middle



Nucleotide (sugar, phosphate, & base)


A pairs with T


C pairs with G



RNA vs. DNA


Difference

DNA

RNA

#

of Strands

Double

Single

Bases

thymine

uracil

Sugar

Deoxyribose

Ribose

Questions


1. The monomers that are put together to make
nucleic acids are called:


A) Nucleotide


B) Phosphate


C) Base


D) Sugar

A. Nucleotides

C. Nucleic Acids

2. DNA & RNA are made up of which type of macromolecule?

A) Carbohydrate

B) Lipids

C) Nucleic Acids

D) Proteins



DNA




RNA

-
________ stranded



-

______ stranded

-

____________ (sugar)





-

_______ (sugar)

-

thymine (nitrogenous base)


-

_____ (nitrogenous base)

1. DNA or RNA?

2. Identify
the bases in strand B

GTGACC

5b. DNA Replication


DNA Replication makes a copy
of DNA
before cell division
(mitosis or meiosis)



DNA replication is semi
-
conservative


Each parent strand is a template
for new daughter strand.



DNA has
anti
-
parallel strands


They run in opposite directions


Enzymes carry out replication


1)
Helicase



unzips DNA


2)
Primase



starts replication


3) Polymerase


matches A
-
T, C
-
G
to make new strands


4)
Ligase



glues lagging strand


fragments together


Question


What does semi
-
conservative mean?


A) Strands are anti
-
parallel.


B) The old strands serve as templates for the new DNA.


C) The old strands are lost.


What enzyme matches DNA base pairs (A
-
T, C
-
G)?

A)
Helicase

B)
Primase

C) Polymerase

D)
Ligase


B. Old strand is conserved

C. Polymerase

5c. Genetic Engineering


Recombinant DNA contains DNA from 2+
organisms.



Restriction enzymes cut out gene from
DNA



Vectors (bacteria & viruses) can be used
to insert new gene into cell.



Uses:



1)
Make medicines


Ex: insulin, human growth hormone


2)
Food Crops


Ex: pest
-
resistant, larger fruits/veggies


PROTEIN SYNTHESIS

DNA > mRNA > ribosome > protein


Standard 4a &
b

4a. Protein Synthesis

Protein Synthesis = making proteins


1.
Transcription

= DNA > mRNA



DNA is
transcribed

(copied) into
messenger RNA (mRNA)
to leave
the nucleus


DNA is too big, it does not leave
the nucleus


mRNA carries the info in DNA out
of the nucleus to the
ribosomes

in
the cytoplasm



4a. Protein Synthesis


2.

Translation

= mRNA > protein


mRNA is translated into a protein by
a
ribosome



Codon

= 3 letter “words” on mRNA


Ex. U G G U C A A U C



Transfer RNA

(
tRNA
) matches each
codon

and transfers the correct
amino acids



Amino acids
add together to make
a polypeptide chain
, which becomes
a
protein


4b. Build a Protein


1. Transcription DNA > mRNA


Base Pairing Rules


DNA: A
-
T C
-
G


mRNA: A
-
U C
-
G



Transcribe the DNA template strand into mRNA

DNA :


C T G T A C G G A


template strand

mRNA:

G A C A U G C C U




A base sequence of DNA is shown below.

ACAGTGC

How would the base sequence be coded on mRNA?

A)
TGTCACG

B)
GUGACAU

C)
UGUCACG

D)
CACUGUA


4b. Build a Protein


2. Translation:
mRNA > protein


Use the
codon

table

Codon

Amino Acid

AUG

UGU

ACG

GAC

UAA, UAG,
UGA

MUTATIONS &
PROTEINS

Making Sex Cells



std. 2a
-
d, 2g

4c. Mutations


Mutation = permanent change in the DNA
base sequence


Mutations can be good, neutral, or bad


1.Single base change


may or may not have an
effect
(ex: A


C)


What would happen if GGG changed to GGC?


both=
Gly

so nothing…


What would happen if UAC changed to UAG?


stops protein production so effect could be major…



2. An insertion or deletion changes the reading “frame”


The fat cat ate the rat


The
atc

ata

tet

her at


Major effects!



Mutations occurs in sperm or egg


passed to offspring
= disease


Tay

Sachs disease, sickle
-
cell anemia, muscular dystrophy



Mutations occurs in regular body cells they may cause
cancer


4d. Cell Specialization


All cells in your body have the
SAME

DNA



Only genes needed by that cell are
expressed.



Each cell only expresses the portion of the
DNA containing the genetic information
for the proteins required by that cell at
that time.


The remainder of the DNA is not
expressed



Example:


The cells of in your skin have the DNA that
codes for your eye color protein. They just
don’t use it

4e. Proteins


20 amino acids make up all proteins.


Your body creates
many different proteins
by changing
the
number

and
sequence

of
amino acids



Proteins vary from about 50 to 3,000 amino acids in
length.



The types, sequences, and numbers of amino acids used
determine the type of protein produced.





Hemoglobin


574
aa


Insulin


51aa


One human disease is caused by a change in one

codon

in a gene from GAA to GUA. This disease

is the result of:

A a mutation.

B a meiosis error.

C crossing
-
over.

D polyploidy.


Although there are a limited number of amino acids, many different
types of proteins exist because the

A. size of a given amino acid can vary.

B. chemical composition of a given amino acid can vary.

C. sequence and number of amino acids is different.

D. same amino acid can have many different properties.



Mutations within a DNA sequence are:

A. natural processes that produce genetic diversity.

B. natural processes that always affect the
phenotype.

C. unnatural processes that always affect the
phenotype.

D. unnatural processes that are harmful to genetic
diversity.


CHROMOSOMES

Wound up DNA



Standard 2e
-
f

2e. Chromosomes


Chromosome
-

wound
-
up
DNA containing genes



Sister
chromatids

are
identical copies
held
together by a
centromere


Draw & label a chromosome
on the right margin.

2e. Homologous Chromosomes


Homologous chromosomes


have the SAME genes
at the SAME locations


One from mom, one from dad



2f. Sex
-
determination


Karyotype



chart shows all the homologous pairs


Autosomes

-

pairs 1
-
22


Sex chromosomes
-

23
rd

pair determines sex


XX = girl


XY = boy


Questions


True or False:


1) Humans have 46 chromosomes


2) Humans have 23 pairs of chromosomes


3) Pairs 1
-
23 are
autosomes


4) XX is male


5) XY is male


6) Sister
chromatids

are copies of each other.


7) Homologous chromosomes are identical.

MEIOSIS

Making Sex Cells



std. 2a
-
d, 2g

2a. Chromosome Number

1. Chromosome Number


Diploid (2n)



somatic (body) cells with
2 sets of homologous chromosomes


Humans =
46 chromosomes (23 pairs)



Haploid (
n
)



gamete sex cells that
have
1 set of chromosomes


Humans =
23 single chromosomes


Divide Box 2a into 2 columns (5 concepts to write, 2 in left column, 3 in right)


Questions

1) A bug has a haploid number
n
=5. What is the
diploid number (2n)?

2) A crocodile has a diploid number 2n=50. What is
the haploid number (
n
)?


meiosis

meiosis

Haploid gamete

Diploid

Haploid gamete

2n

n

n

2a. Meiosis Overview

2. Meiosis vs. Mitosis


Meiosis



cell division specific to
sexual reproduction
that results in
4, genetically different, haploid
gamete (sex) cells






Mitosis



asexual

cell division that results in
2,
genetically identical, diploid cells

Zygote

46

23

23

First cell of a new
organism


Questions


A = Mitosis B = Meiosis C = Both


1) Type of cell division.


2) Produces 2 cells


3) Produces 4 cells


4) Sexual reproduction


5) Asexual reproduction


6) Resulting cells are genetically different


7) Diploid to haploid


8) Resulting cells are genetically identical


9) Diploid to Diploid

1)
C

2)
A

3)
B

4)
B

5)
A

6)
B

7)
B

8)
A

9)
B

2a. Steps of Meiosis

3. Steps of Meiosis


Steps are mostly the same as Mitosis, but
diploid cell
divides twice


Meiosis I

separates the homologous pairs


Meiosis II

separates sister chromatids


Steps of Meiosis

2a. Crossing Over

4. Crossing Over


Homologous chromosomes
pair up
and
randomly trade pieces of
DNA

during Prophase I



This
creates genetic variation
(new
gene combinations that never
existed before)



Draw Crossing Over (middle step
in diagram)

2a. Independent Assortment

5. Independent Assortment


Genes for different traits sort independently into
gametes


Genes on different chromosomes are not connected

Ex: The gene for eye
color is not connected
to the gene for hair
color.


Questions


What accounts for so many possible combinations of
genes in gametes?


A) Crossing
-
over


B) Independent Assortment


C) Both of these

C. Both


True or False:


Meiosis 1 separates
homologous pairs
, while Meiosis
II separates
sister
chromatids
.

True!

2b. Meiosis in Humans


Only gonads undergo meiosis


MALES = the testis produce 4 sperm (gametes)


FEMALES = the ovaries produce 1 large egg (gamete)
and 3 polar bodies


2c. Random Segregation

Law of Segregation


It is random whether the gamete gets the maternal
or paternal version of each trait


Each gamete only gets one allele

Draw the diagram:

Ex: If a pea plant is tall (
Tt
), half the gametes
will have T and the other half will have
t
.


After fertilization, the offspring will have 2
alleles, one from mom & one from dad


If a corn plant has a genotype of
Ttyy
, what are
the possible genetic combinations that could be
present in a single grain of pollen from this plant?



A. Ty,
ty


B. TY,
ty


C. TY, Ty,
ty


D. Ty,
ty
,
tY
, TY

2d. Fertilization


Fertilization:


Sperm + egg = zygote



(23) (23) (46)


haploid + haploid = diploid



n

+
n

= 2n

2g. Predicting Offspring


Alleles
-

different versions
of a trait


Ex: Blue or brown eyes


Knowing the alleles of the
parents allows you to
predict the possible traits of
the offspring.


Use a Punnett Square

Questions


True or False?


1) Segregation occurs when genes separate into
gametes.


2) Females produce 4 eggs.


3) Males produce 4 sperm.


4) Fertilization occurs when diploid eggs and sperm
make a zygote.


5) Human zygotes have 23 chromosomes.


6) Alleles are different versions of a trait.

PUNNETT SQUARES

Predicting Inheritance



Standard 3a &
b

3a. Punnett Squares


Vocabulary to know:


Genotype = genes (TT,
Tt
,
tt
)


Phenotype = appearance (Tall or short)


Homozygous/Purebred = 2 of the same allele (TT or
tt
)


Heterozygous/Hybrid = 2 different alleles (
Tt
)

Types of Inheritance

1. Autosomal


genes on regular
body chromosomes (#1
-
22)


Dominant covers up recessive


ex: Bb


The protein created by the
dominant gene functions better
or is darker/stronger than the
recessive protein




2. Incomplete & Codominance


Incomplete dominance = show
mix/blend between two alleles


Ex: Red + White = pink




Codominance = show both
traits at once


Ex: Red + White = red & white
stripes




3. Sex
-
linked


genes on
X
-
chromosome


Because men have only 1
X (XY) they don’t have a
“backup” X like women
(XX) to hide the trait


If the X is bad, men have
the disease


Colorblindness, hemophilia

3b. Mendel’s Laws (see 2a &
c
)


Divide the box into 3 columns:


Title each column:


Autosomal

dominant/recessive


Incomplete Dominance/
Codominance


Sex
-
linked

Normal thumbs (T) is an
autosomal

dominant trait and
hitchiker’s

thumbs (
t
) is an
autosomal

recessive trait. A
man with
hitchiker’s

thumb marries a women that is
heterozygous for a normal thumb.





t




t




T


t

% of Normal thumbs?
%
Hitchiker’s

thumbs?

Ratio?

Tt

Tt

tt

tt

50 % Normal

50%
Hitchiker’s


1: 1

Flowers can be white, pink, or red. Does this show Incomplete Dominance
or
Codominance
?

Genotypes:

white
-



red





pink
-


Show a cross between a white and red flower





W




W




R


R

% White=


%Red=

%Pink=

RW

RW

RW

RW

0%


0%


100%



Sex
-
linked


Hemophilia (
X
h
) is a recessive sex
-
linked disease.
A normal man marries a carrier woman.