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Introduction
to Genetics:
MeiosisCH. 11
ADAMS
11.1 The Work of Mendel
Heredity: basically just the passing on of genetic
traits from parents to offspring.
Gregor Mendel: demonstrated that inheritance
followed particular patterns
Every organism inherits a single copy of every gene
from each of its “parents.”
Offspring acquire genes from parents by inheriting
chromosomes
11.1 The Work of Mendel
Genes and Dominance Inheritance is possible because:
– Sperm and ova carrying each parent’s genes are combined in the
nucleus of the fertilized egg
– True Breeding: (sometimes also called a purebred), is an
organism that always passes down certain physically expressed
traits (purebred German Shepard)
Hybrids: also known as cross breed, is the result of mixing, through sexual reproduction, two animals or plants of different breeds, varieties, species (German shepherd basset hound)
http://media.gettyimages.com/photos/german-shepherd-picture-id128603647?s=170667a
True
Breed
http://www.nextdogbreed.com/b
hao/images/132.jpeg
Hybrid
11.1 The Work of Mendel
Genes and Dominance Simplifying Genetics:
So we've all got chromosomes, which are the form that our DNA takes in order to get passed on from parent to child.
Human cells have 23 pairs of chromosomes
Gene: a section of DNA in a specific location on a chromosome that contains information that determines a trait. (hair color)
Allele: specific gene, version of a gene (brown hair color)
Physical trait: a reflection of a bunch of different genes working together
Polygenic trait: are those traits that are controlled by more than one gene (hair color, eye color, height…)
Pleiotropic. : is single gene can influence how multiple traits are going to be expressed
gamete is the male or female reproductive cell that contains half the genetic material of the organism.
11.1 The Work of Mendel Mendel’s Two Conclusions:
1st Conclusion:
Biological inheritance is determined by factor that are passed down from one generation to the next
Factors are now called genes
Each trait he studied was controlled by one gene in two forms producing different contrasting forms
These different forms called alleles
2nd Conclusion:
Principle Of Dominance
Some alleles are dominant and some are recessive
Dominant traits will always show in offspring
Recessive only show when the dominant trait is not present
11.1 The Work of Mendel
http://www.slideshare.net/guest9476bb/ib-biology-genetics-3807192
11.1 Segregation
http://www.slideshare.net/guest9476bb/ib-biology-genetics-3807192
11.1 Segregation
What happens to the recessive alleles?
~25% the recessive genes reappeared in Mendel’s experiments
T-> dominant (TT; Tt) dominant trait will show (75%)
T-> recessive (tt) only recessive trait will show (25%)
Genotypes:
25% = TT
50% = Tt
25% = tt
11.2 Probability and
Punnett Squares
Mendel used the laws of probability
to help predict results in plant
succession
Probability: how likely something is
going to happen
Relate to Genetics:
Alleles segregation is random but the
laws of probability can be used to
predict outcomes
11.2 Punnett Squares Drawings used to help predict genetic outcomes
Below: Brown eyes are dominant (B); blue eyes are recessive
(b).
Both “parents” heterozygous for eye color
Meaning that they carry the allele for both brown and blue eyes
This cross shows that 75% of the time offspring will have brown
eyes but 25% they will have blue
http://study.com/cimages/multimages/16/Punnett_hetero_x_hetero.svg.png
Phenotype: Brown eyes or blue
eyes (phenotype is the physical
characteristics)
11.2 Punnett Squares
Drawings used to help predict genetic outcomes
Here we have one homologous recessive and one
heterozygous
W w
w
w
Ww ww
Ww ww
50%
homozygous
50%
heterozygous
50% dominant
50% recessive
Drawings used to help predict genetic outcomes
Below: Red flowers dominant(F); pink flowers
recessive(f).
Both “parents” homozygous for petal color
Meaning that they carry the allele for either red or white
only
This cross shows that 100% of the time offspring will have
red petals but will be carriers for both
http://dvbiology.org/biologyweb/pun2.gif
Genotype: the genotype for
this cross is Rr. The genetic
make up (it’s the letters)
The phenotype is red petals
11.2 Punnett Squares
Probability and segregation
25% of the time recessive genes that
were segregated will reappear
Probability and predict averages
Higher your population of study the
closer your averages are
Mendel’s Conclusions
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11.3 Exploring Mendelian
Genetics
Independent Assortment
Alleles can separate independently during the
formation of gametes
Any one pair can combine with any other pair
independently during construction
This gives different traits equal opportunities to be
expressed in offspring
11.3 Independent Assortment
http://www.slideshare.net/guest9476bb/ib-biology-genetics-3807192
11.3 Independent Assortment
http://68.media.tumblr.com/18ac04cb50bf98a2362a93e8b02c685e/tumblr_inline_n92ctxcO5a1qg4nwx.png
TWO-FACTOR CROSS
HOMOZYGOUS
HOMOZYGOUS
11.3 Summary Mendel1. Biological inheritance is determined by individual
genes
In organisms that reproduce sexually, genes are passed from
parent to offspring
2. In cases of two or more forms of the gene for a single
trait exist, some genes will exhibit over others
Dominance and recessive
3. In most sexually reproducing organisms each
offspring has two copies of a trait, one from each
parent
These traits can be segregated and reformed in new gametes
4. Alleles for different genes will mostly segregate
independently of one another
11.3 Beyond Dominant and
Recessive Mendel's Principles have two major
exceptions
Not all genes show simple patterns of
dominant or recessive
Many traits are controlled by one or more gene
Majority of genes have more than one allele
11.3 Incomplete Dominance
Incomplete Dominance:
intermediate inheritance where one allele for a
specific trait is not entirely expressed over its
paired allele.
Results: in a third phenotype in which the
expressed physical trait is a combination of the
phenotypes of both alleles.
http://www.biologia.arizona.edu/mendel/sets/mono/graphics/10TF1.gif
11.3 Codominance
Codominance:
Both alleles contribute to the phenotype.
This results in offspring with a phenotype that is neither
dominant nor recessive.
http://cdn.shopify.com/s/files/1/0267/4223/products/codominance-panda-t-shirt-teeturtle_800x.jpg?v=1480438537
11.3 Multiple Alleles
Multiple Alleles
Genes that have more than two alleles
More than two possible alleles can exist
https://ka-perseus-images.s3.amazonaws.com/d6049ca09dfc688504e47172cc9e692b04f3ca00.png
11.3 Polygenetic
http://www.slideshare.net/guest9476bb/ib-biology-genetics-3807192
Other
examples:
• Fingerprints
• Eye color
• height
11.3 Polygenetic
https://www.ontrack-media.net/biology/bm2l5rimage3.jpg
11.4 Meiosis
Key terms:
Homologous Chromosome pairs: similar relation
½ of chromosomes come from mom/other ½ from dad
Each of the chromosomes from dad have a corresponding
pair from mom
Diploid: meaning two sets of chromosomes (one
inherited from each parent)
Not identical
Haploid: meaning one set
11.4 Meiosis Chromosome
Number
The gametes (sex cells) haploid
Meiosis: Not exact copies of parent
Somatic cells (body cells) are
diploid
Mitosis: Clones of parents
Human Life Cycle
Each human somatic cell (body cell) has 46
chromosomes or 23 matching pairs (diploid)
Autosomes: non-sex chromosomes
Sex chromosomes:
determine gender (XX; XY)
Review Chromosome: location of genetic information in the form of
genes
Chromatid: Each strand of a chromosome that divides longwise
during cell division.
Centromere: What connects the chromatids
https://dr282zn36sxxg.cloudfront.net/datastreams/f-
d%3A0cfa6ca6bdccc9a09f3ffe60c5e3d777529c14771d85ab4cc4f712b1%2BIMAGE_THUMB_POSTCARD_TINY%2BIMAG
E_THUMB_POSTCARD_TINY.1
Phases of Meiosis
Phases of Meiosis
Mixture of chromosomes from both
parental chromosomes
Meiosis involves two divisions, meiosis I and
meiosis II.
By the end of meiosis II, the diploid cell
that entered meiosis has become 4
haploid cells.
Phases of Meiosis IMajor differences in Prophase I (meiosis) and Prophase (mitosis)
• Crossover
http://pumatrendbio.weebly.com/uploads/6/0/9/7/60977291/398998105.png
Interphase I
Cells undergo a round of DNA replication, forming duplicate
chromosomes.
Each chromosome pairs with its corresponding homologous
chromosome to form a tetrad
Tetrad is formed: structure of 4 chromatid
http://www.phschool.com/science/biology_place/labbench/lab3/images/interpha.gif
Like Mitosis: cells
undergo a round
of DNA
replication,
forming
duplicate
chromosomes.
Prophase I: Different from
Mitosis
http://pumatrendbio.weebly.com/uploads/6/0/9/7/60977291/398998105.png
• Pairs of homologous
chromosomes now will
intertwine
• Crossover occurs
• Chromosomes swap
genetic info
Cross Over When homologous chromosomes form tetrads in meiosis I, they
exchange portions of their chromatids in a process called crossing
over.
Crossing-over produces new combinations of alleles.
http://biologycellcycles.weebly.com/uploads/4/2/5/7/42572589/8819453_orig.jpg
Crossing-over occurs during
meiosis.
(1)Homologous
chromosomes form a
tetrad.
(2)Chromatids cross over
one another.
(3)The crossed sections of the chromatids are
exchanged.
Metaphase I: Like Mitosis Spindle fibers attach to the chromosomes.
Chromosomes line up in the middle (just like mitosis)
Anaphase I: Like Mitosis
The fibers pull the homologous chromosomes toward opposite ends
of the cell.
Telophase I
Nuclear membrane reforms,
Nucleoli form within
Chromosomes unwind into
chromatin
Crease forms
End of Round 1 We now have two haploid cells with 23 chromosomes each
with unique combinations
But we want to have 4 cells so we go for Round 2. Which is the same process but with different goal
Instead of duplicating chromosomes we want to pull them apart into separate single strand chromosomes
Unlike meiosis I, neither cell goes through chromosome replication.
Each of the cell’s chromosomes has 2 chromatids.
Meiosis II
During meiosis, the number of chromosomes per cell is cut in half through the
separation of the homologous chromosomes. The result of meiosis is 4 haploid
cells that are genetically different from one another and from the original cell.
Prophase II
Prophase II is where the nuclear membrane will again break
down and the spindle fibers are formed.
The chromosomes condense again after a interphase but this
time there is NO DNA replication
http://www.utm.utoronto.ca/~w3bio380/picts/supp/supp2/Meiosis_ProphaseII.jpg
Metaphase II The chromosomes line up in the center of cell.
http://images.slideplayer.com/15/4802798/slides/slide_9.jpg
Anaphase II The sister chromatids separate and move toward opposite ends
of the cell.
http://images.slideplayer.com/15/4802798/slides/slide_10.jpg
Telophase II Meiosis II results in four haploid (N) daughter cells.
Cytokinesis when they finally separate
http://keltonlesliealvarado.weebly.com/uploads/9/6/2/6/9626115/1652037.png
Comparing Mitosis and
MeiosisMitosis results in the production
of two genetically identical
diploid cells.
Meiosis produces four
genetically different haploid
cells.
Comparing Mitosis and
Meiosis
Mitosis
Cells produced by mitosis have the
same number of chromosomes
and alleles as the original cell.
Mitosis allows an organism to grow
and replace cells.
Some organisms reproduce
asexually by mitosis.
Comparing Mitosis and
Meiosis
Meiosis
Cells produced by meiosis have half the
number of chromosomes as the parent
cell.
These cells are genetically different from
the diploid cell and from each other.
Meiosis is how sexually-reproducing
organisms produce gametes.
