Transcript Genetics PPT - West Essex High School

Genetics
Chapter 11
Gregor Mendel
Austrian monk that had an interest in science
Worked with pea plants at the monastery
Had a background in math and science
Proved valuable research in heredity
Gregor Mendel
Taught high school science
Kept a garden plot of pea plants
Observed 7 characteristics of pea plants
Each trait had 2 possible outcomes
Gregor Mendel
Recorded plant seeds and planted
them
Noticed purple plants all came
from purple seeds
White plants also grew from these
seeds
Noticed a pattern in height
Began his study on controlling
pollination
Pollination
•
When pollen grains produced by male part of a
flower are transferred to female part of the
flower
Self-Pollination
•
When pollen is transferred from anthers to
stigma of same plant or another flower on
same plant
Cross Pollination
•
When pollen is transferred between two plants
Gregor Mendel
•
To control the pollination, Mendel removed the
anther of the pea plants
•
Used pollen from anthers to cross pollinate
and control traits passed to next generation
Mendel’s Experiments
•
True-breeding plants
•
Plants that only produce offspring with same
characteristics every time
•
•
Ex: true-breeding yellow pod plants only
produced yellow pods in next generation
Mendel used true-breeding plants to test for
passed on traits
P Generation
•
Mendel himself cross-pollinated pairs of
plants that were true-breeding parents
•
Known as P generation
F1 Generation
•
Mendel recorded next generation of pea
plants characteristics
•
Known as F1 generation
F2 Generation
•
The F1 generation were able to self-pollinate
to make a new generation
•
Known as F2 generation
Mendel’s Results
•
Recessive and Dominant Traits
• Dominant traits were seen more often
• These traits mask or dominate other
traits
• Ex: Brown eyes are dominant over
blue
• Recessive traits are seen less often
https://www.youtube.com/watch?v=mnSkz8s-b44
Mendel’s Results
•
Law of Segregation
•
Law states that pair of
factors is separated
during formation of
gametes (meiosis)
•
Making gametes
(sperm and egg)
produces haploid
cells with only one
half the amount of
chromosomes
Mendel’s Results
•
Law of Independent Assortment
•
Traits do not necessarily appear together
•
The trait for pod seed color is not associated
with the flower color
•
They are independent traits
•
Random separation during meiosis
Mendel’s Conclusions
•
Molecular genetics
•
Study of heredity on the chromosomal level
•
Factors that Mendel was testing are known
as alleles on a chromosome
•
Area of a chromosome that determines a
specific trait
https://www.youtube.com/watch?v=Mehz7tCxjSE
Alleles
•
Alleles are represented with letters
•
Ex: Dominant (P) recessive (p)
Genotype/Phenotype
Genotype: bb
•
Genotype: BB, Bb
Genotype
•
Genetic makeup of an organism
•
Consists of 2 allele letters
•
Can determine phenotype from genotype
•
Ex: Brown eyes (BB or Bb), blue eyes (bb)
Genotype/Phenotype
Phenotype: blue eyes
•
Phenotype: brown eyes
Phenotype
•
Physical appearance that is seen
•
Phenotypes cannot always tell you the
genotype
•
Ex: brown or blue eyes
Genotype/Phenotype
•
•
Homozygous
•
When the two alleles are
the same
•
Ex genotype: BB or bb
Heterozygous
•
When the two alleles are
different
•
Ex genotype: Bb
Probability
Punnett Squares
•
Monohybrid Cross
•
Cross of one characteristic from two
organisms
•
Ex: eye color
Mom: BB (brown) Dad: bb (blue)
Example 1
•
Homozygous x Homozygous
•
Ex: Homozygous purple plants x homozygous
white plants
•
Genotypes:
P = purple
p = white
Example 2
•
Homozygous x Heterozygous
•
Ex: Homozygous black guinea pigs x
heterozygous black guinea pig
•
Genotypes:
B = black
b = white
Example 3
•
Heterozygous x Heterozygous
•
Ex: Heterozygous black coat rabbit x
Heterozygous black coat rabbit
•
Genotypes:
B = black
b = white
Testcross
•
To test for unknown
genotype
•
Unknown individual is
crossed with a
homozygous recessive individual
•
If the results are only phenotype dominant,
unknown individual is homozygous dominant
•
If the results show some phenotype recessive,
unknown individual is heterozygous
Dihybrid Crossing
•
Dihybrid Cross
•
Cross of 2 characteristics
•
Harder to predict because more possible
results
Example 1
•
Homozygous x Homozygous
Ex: Homozygous wrinkled, green peas x
homozygous round, yellow
Genotypes:
Example 2
•
Heterozygous x Heterozygous
Ex: Heterozygous round, yellow peas x
Heterozygous round, yellow peas
Genotypes:
Example 5
•
Incomplete dominance
•
When the phenotype of a heterozygous
individual is an in between of the two parents
•
Ex: four o’clock flowers
RR
RW
WW
Example 6
•
Codominance
• When both alleles are expressed at the same
time
• Three possible phenotypes
• Both alleles are dominant
• Ex: Red & white flowers
Codominance
•
Blood Typing
•
There are 4 possible blood
types
•
A, B, AB, & O
•
A and B are both dominant
•
O is recessive
•
Use letter I to show
genotype
Polygenic Inheritance
•
A trait that is influenced by many genes
•
Poly = many
•
Genic = genes
•
Usually show degrees of variation
•
Ex: skin color, height
http://www.tate.org.uk/context-comment/video/tateshots-roman-ondak-measuring-universe
Multiple Alleles
•
Genes with 3 or more alleles
•
•
Ex: Blood types (IAIB,IAIA, IBIB, IAi, IBi, ii)
This shows both codominance and multiple
alleles
Chromosomes
•
Thomas Hunt Morgan
•
Worked with fruit flies (Drosophila) and
noticed they have 4 pairs of chromosomes
•
Males and females have one pair of different
sized chromosomes (X and Y chromosomes)
Meiosis
•
•
•
Process of making
gametes
• Males = sperm
• Females = eggs
Gametes are haploid
cells
• 23 chromosomes (no
pairs!)
End result is 4 nonidentical daughter cells
Meiosis I
•
Prophase I
• DNA condenses to chromosomes
• Spindle fibers from centrioles appear
• Homologous chromosomes pair up called a
synapse
• Pair of homologous chromosomes is called
a tetrad
Meiosis I
•
Prophase I
• Tetrads exchange genetic info to mix up
possible genes
• Called crossing over
• When tetrads cross over, they create
recombinant DNA
• This is the reason why daughter cells are
non-identical
Meiosis I
•
Metaphase I
•
Tetrads line up randomly along middle of cell
Meiosis I
•
Anaphase I
•
Tetrads separate to opposite poles of the
cell
•
This is a RANDOM process
•
Random assortment of genes
Meiosis I
•
Telophase I & Cytokinesis I
•
Chromosomes reach opposite side of the cell
and cytokinesis begins
•
Creates 2 non-identical daughter cells
Meiosis II
•
Prophase II
• Nucleus disappears
• Chromosomes begin to move
• Spindle fibers form
• NO DUPLICATION OF CHROMOSOMES!
Meiosis II
•
Metaphase II
• Chromosomes line
up in the middle of
the cell
•
Anaphase II
• Chromosomes split
apart to sister
chromatids
Meiosis II
•
Telophase II & Cytokinesis II
• Nuclear membrane forms
• Chromosomes break down to chromatin
• Creates 4 non-identical daughter cells that are
haploid
• Only one sister chromatid of each
chromosome
Sexual Reproduction
•
Production of offspring through meiosis and the
union of a sperm and egg
•
After fertilization, the egg is called a zygote
•
The zygote undergoes division and becomes a new
organism
Mitosis vs. Meiosis