Transcript File - Science with Snyder

Mendelian Genetics
Meiosis I & Meiosis II
Meiosis – Notes B-4.5

The process of meiosis and its importance to sexual
reproduction just as mitosis is to asexual reproduction.

In order for the offspring produced from sexual
reproduction to have cells that are diploid (containing
two sets of chromosomes, one set each parent), the
egg and sperm cells must be haploid (contain only one
of each type of chromosome). The division resulting in
a reduction in chromosome number is called meiosis.

Meiosis occurs in two steps:
 Meiosis I
 Meiosis II
Meiosis I and Meiosis II
Meiosis I, in which the chromosome pairs
replicate, results in two haploid daughter
cells with duplicated chromosomes
different from the sets in the original
diploid cell.
 Meiosis II, in which the haploid daughter
cells from Meiosis I divide, results in four
haploid daughter cells called gametes,
or sex cells (egg and sperm), with
undoubled chromosomes.

Meiosis

Production haploid cells that are different
 N-represents
chromosome number
 Sperm
or egg
 Reduction of chromosomes
Somatic cells – regular body cells
 Germ cells – sex cells

spermatogenesis
46 Duplicated Chromosomes
92 Chromosomes
Oogenesis
Results?
Spermatogenesis
- 4 functioning sperm
 Oogenesis
 – 1 egg, 3 polar bodies

Meiosis I- Homologous Chromosomes Separate


Meiosis I begins with interphase, like in mitosis, in which cells:
(1) increase in size, (2) produce RNA, (3) synthesize proteins,
and (4) replicate DNA
Prophase I
 The nuclear membrane breaks down; centrioles separate
from each other and take up positions on the opposite sides
of the nucleus and begin to produce spindle fibers.
 Chromosomes pair up and become visible as a cluster of
four chromatids called a tetrad.
 A homologous chromosome pair consists of two
chromosomes containing the same type of genes.


the paternal chromosome in the pair contributed by the organism’s
male parent
the maternal chromosome in the pair contributed by the organism’s
female parent
Meiosis I- Prophase I
 Each
chromosome consists
of two sister chromatids
attached at a point called
the centromere.
 Because
the homologous
chromosome pairs are in
close proximity, an
exchange of chromosome
genetic material between
pairs often occurs in a
process called “Crossing
over.”

Meiosis I
I – homologous chromosomes
come together, form tetrad (4 chromo)
 Prophase
Crossing over – exchange portion of chromosome
 Synapsis
 Independent assortment

 Meta
I, Ana I, Telo I, Cyto I
Meiosis I- Other Phases
Metaphase I
 Anaphase I
 Telophase I
 Cytokinesis
Product: 2 Haploid
Daughter Cells


Each of the two daughter cells from
meiosis I contains only one
chromosome (consisting of two sister
chromatids) from each parental pair.
Each daughter cell from meiosis I
proceeds to undergo meiosis II.
Meiosis II- Sister Chromatids Seperate
Meiosis II- Sister Chromatids Separate
NO INTERPHASE PHASE! Why?
 Prophase II
 Metaphase II
 Anaphase II- sister chromatids pulled apart
 Telophase II
 Cytokinesis

Product- 4 Genetically Diverse Haploid
Daughter Cells
Turn & Talk
Mitosis vs. Meiosis

Similarities?

Differences?
End Product of Mitosis?
 End Product of Meiosis?
 What does this tell us about Genetic
Diversity?

Let’s Make a Foldable
Meiosis I & II
 Turn
to page 174 and 175 in book and/or get
iPad
 Materials : Two Sheets of 8’x11” Paper, Colored
Pencils, Markers, Book, iPad
 Rubric
 Must have ALL (8) the Phases of Meiosis I and
Meiosis II (PMAT I & PMAT II)
 Must have a correct descriptions and drawings
 Must include why there is no interphase
between Meiosis I and Meiosis II
 Must copy and answer the Essential Questions
Essential Questions
Answer on Foldable
1.
2.
3.
4.
Does Mitosis or Meiosis occur more frequently
in your body? Explain.
List two differences AND two similarities
between Mitosis and Meiosis.
Are homologous chromosomes identical to
each other? Explain.
Why is it important that gametes are haploid
cells?
The Work of Gregor Mendel
Video
 http://www.cleanvideosearch.com/media/action/
yt/watch?videoId=2UuSLDvPZnU

Work of Mendel


Studied 7 traits of pea plants (pg 179)
 Pea Shape, Pea Color, Flower
Color, Pod Shape, Pod Color,
Flower Position, Plant Height
His Process
 Since most plants are selfpollinating, he wanted to
manipulate the fertilization.
 Mendel controlled fertilization of
pea plants by removing the male
parts of stamens, then fertilizing
the female part (pistil) with pollen
from a different plant
Mendel came to 2 conclusions after
the breeding
1.
2.
Genes, segment of DNA, occurs in pairs,
controll heredity. Visual form called
alleles. (noted as “factors”)
Found that some of the alleles are
dominant and some are recessive.
Dominant trait always uppercase (TT, Tt)
2. Recessive always lowercase (tt)
1.
Notes B-4.6





Genetics is the study of patterns of inheritance and
variations in organisms. Genes control each trait of a
living thing by controlling the formation of an organism’s
proteins.
Since in all cells (except gametes) chromosomes are
diploid (exist as a pair of chromosomes), each cell
contains two genes for each trait, one on the maternal
chromosome and one on the paternal chromosome.
The two genes may be of the same form or they may be
of different forms.
The different forms of a gene are called alleles. These
are the Letters!!! TT, Tt
The two alleles are segregated during the process of
gamete formation (Law of Segregation)
Law of Dominance
States that some alleles are dominant
whereas others are recessive.
 When an organism has two identical
alleles for a particular trait that organism is
said to be homozygous for that trait.
 When an organism has two different
alleles for a particular trait that organism is
said to be heterozygous for that trait.

Question: What are alleles?
Genotype vs. Phenotype

Study Tip! What does the word
“genotype” look like? What does the word
“phenotype” look like?
Genotype
Phenotype
The genotype (genetic makeup) of
an organism reveals the type of
alleles that an organism has
inherited for a particular trait.
• TT represents a homozygous
dominant genotype.
• tt represents a homozygous
recessive genotype.
• Tt represents a heterozygous
genotype.
The phenotype (physical
characteristics) of an organism is a
description of the way that a trait is
expressed in the organism.
• Organisms with genotypes of TT
or Tt would have a phenotype of
tall.
• Organisms with a genotype of Tt
would have a phenotype of short.
Project Time!
Bunny Genetics (25 mins)



Obtain a paper bag and a handout for Bunny Genetics.
Design your Bunny. Use markers and colored pencils.
Fill out the chart with the correct Phenotypes &
Genotypes
Law of Segregation



The law (principle) of segregation explains how
alleles are separated during meiosis.
Each gamete receives one of the two alleles that
the parent carries for each trait. Each gamete
has the same chance of receiving either one of
the alleles for each trait.
During fertilization (when egg and sperm unite),
each parent organism donates one copy of each
gene to the offspring producing a diploid zygote.
Law of Independent Assortment




Dihybrid Cross
The law of independent assortment states that the
segregation of the alleles of one trait does not
affect the segregation of the alleles of another trait.
Genes on separate chromosomes separate
independently during meiosis.
This law holds true for all genes unless the genes
are linked. In this case, the genes that do not
independently segregate during gamete formation,
usually because they are in close proximity on the
same chromosome.
The F1 Cross

F1 =First Filial (parent cross  produce the
F1 then cross the F1 making an F2)
 Law
of segregation: Segregation of alleles
occurs during the formation of gametes, sex
cells.
 Law of Independent Assortment – factors for
individual characteristics are not connected.
Assort independently of each other.
Punnett Squares
A Punnett square can be used to predict
the probable genetic combinations in the
offspring that result from different parental
allele combinations that are independently
assorted.
 • A monohybrid cross examines the
inheritance of one trait. The cross could be
homozygous-homozygous, heterozygousheterozygous, or heterozygoushomozygous.

Punnett Squares

Punnett square – table representation of
crossing alleles
 REMEMBER….
or tt – homozygous – same alleles
 Tt – heterozygous – different alleles
 Phenotype – physical look, all tall (TT, Tt) have
same phenotype.
 Genotype – based on alleles. (TT, and Tt) are
different now.
 TT




















Dominant
Curled Up Nose
Clockwise Hair Whorl
Can Roll Tongue
Widow's Peak
Facial Dimples
Able to taste PTC
Earlobe hangs
Middigital hair (fingers)
No hitchhiker's thumb
Tip of pinkie bends in
Oval face
Cleft chin
Broad eyebrow
Separated eyebrows
Long eyelashes
Almond eyes
Freckles
Wet-type earwax
Left thumb on top of
interlocking fingers
Recessive
Roman Nose
Counter-clockwise Hair Whorl
Can't Roll Tongue
No Widow's Peak
No Facial Dimples
Unable to taste PTC
Earlobe attaches at base
No middigital hair
Hitchhiker's thumb
Pinkie straight
Square face
no cleft chin
Slender eyebrow
Joined eyebrows
Short eyelashes
Round eyes
No freckles
Dry-type earwax
Right thumb on top of
interlocking fingers
Probability
Penny = ½ = .50
 A cross results in 787 pink flowers and
277 white flowers. If we cross the same P
generation, the probability will be the
same)

Homozygous x Homozygous (YY x yy)
Homozygous x Heterozygous (AA x Aa)
a
AA x Aa
A

A
Aa
A
Aa
AA
AA
Heterozygous x Heterozygous
(Bb x Bb)
Dihybrid cross – two traits
Lets Practice Punnett Squares!!
We can do some together as practice, then
work independently on Bunny Project with a
partner.
B-4.7 Notes

Chromosome theory of inheritance is a basic principle in
biology that states genes are located on chromosomes
and that the behavior of chromosomes during meiosis
accounts for inheritance patterns, which closely parallels
predicted Mendelian patterns.

Gene linkage simply means that genes that are located
on the same chromosome will be inherited together.
These genes travel together during gamete formation.

This is an exception to the Mendelian principle of independent
assortment because linked genes do not segregate
independently.

Crossing-over is a process in which alleles in
close proximity to each other on homologous
chromosomes are exchanged. This results in
new combinations of alleles.
 When
chromosomes pair up during meiosis I,
sometimes sections of the two chromosomes become
crossed. The two crossed sections break off and
usually reattach.
Question: What phase of Meiosis does
crossing over occur?




Incomplete dominance is a condition in which one allele
is not completely dominant over another. The phenotype
expressed is somewhere between the two possible
parent phenotypes.
Red x white = pink
Codominance occurs when both alleles for a gene are
expressed completely. The phenotype expressed shows
evidence of both alleles being present.
Red x White = both red and white
What’s this?
What’s this?

Multiple alleles can exist for a particular trait
even though only two alleles are inherited. For
example, three alleles exist for blood type (A, B,
and O), which result in four different blood
groups.

Polygenic traits are traits that are controlled by
two or more genes. These traits often show a
great variety of phenotypes, e.g. skin color