Download Self-fertilization

Wednesday 4/9/14
• AIM: Why is Gregor Mendel the father of
genetics?
• DO NOW: How many chromosomes do you
have and where do they come from?
• What would happen if you had an extra
chromosome and why?
• HOMEWORK: Text read pages 267-70.
Reading check pages 267 and 268, q 1 and 2
pages 270
What is genetics?
Genetics
•
•
•
•
The study of inherited traits
Chromosomes are the units of inheritance
Chromosomes carry genes
Genes are the specific direction or code for
your physical trait
• Genes: code for proteins
• Proteins cause chemical reactions
• Chemical reactions lead to physical traits
Where do your inherited traits
come from?
Your dads sperm and your moms egg
Homologous chromosome
• Similar in size shape and
genetic content
• Homologous
chromosomes pair up at
fertilization
•
n+n=2n
Remember
• Zygote gets one complete set of chromosomes
from the egg
• And one complete set of chromosomes from
the sperm
• Bringing together homologous chromosomes
Haploid + haploid = diploid
Human Chromosomes
• Total we have 23 pairs
• 2(23)=46
• 22 of those pairs are
called autosomes
• The 23 pair is the sex
chromosomes
Sex Chromosomes
• XX female
• XY male
Y chromsome
• Carries the SRY gene
• SRY: sex determining
region
• If the SRY gene is
turned on, then gonads
develop into testis and
fetus becomes male
• If not then gonads
become ovaries
• AIM: How does the structure of DNA relate to its
function?
• DO NOW: How many chromosomes do each of your
cells have?
• How many genes does each of your cells have?
• How many nuclei does each of your cells have?
• Homework: text read pages 293,296,297 and 299.
Answer Reading questions 293,296,297
• Somatic or body cells have 46 chromosomes
– Examples of somatic cells
• Cardiac cells
lung cells
brain cells
• Skin cells
muscle cells gall bladder cells
• Tracheal cells
esophagal cells liver cells
• Gametes or sex cells have 23 chromosomes
– Male-sperm
– Female-ova or egg
• There are thousands of genes in each cell
• There is one nucleus in each cell that houses the
chromosomes which carry genes on them
• Each cell expresses specific genes to make them
specialized
So how do we know anything about
genetics and homologous
chromosomes?
Gregor Mendel
• Father of genetics
• Looked at the pea plant
• Specifically 7 visible
traits
• Followed their
inheritance over many
generations
• HE KNEW NOTHING
ABOUT GENES!!!!!
Mendel was lucky
• Each of the 7 traits Mendel observed was only
present in 1 of 2 possible forms
– Ex: Plant color was either purple or white
• Pea shape was either round or wrinkled
• Mendel used this when performing his
experiments.
Thursday 4/10/14
• AIM: How did Gregor Mendel develop his
basic laws of heredity?
• DO NOW: What is genetics? How do we know
anything about genetics?
• HOMEWORK: Textbook read pages 276-277.
do the reading check on page 277
Genetics
•
•
•
•
The study of inherited traits
Chromosomes are the units of inheritance
Chromosomes carry genes
Genes are the specific direction or code for
your physical trait
• Genes: code for proteins
• Proteins cause chemical reactions
• Chemical reactions lead to physical traits
• AIM: How did Mendel develop his basic laws of
heredity?
• DO NOW: What is the difference between self
fertilization and cross fertilization?
• HOMEWORK: textbook read pages 267-270. 1Explain the difference between true breeding and
hybrid.
• 2- Define P generation, first filial generation and
second filial generation.’
• 3- Explain why Mendel studied pea plants
Gregor Mendel’s experiments:
Fertilization
• Self-fertilization: egg in
the flower is fertilized
by the sperm of the
same flower
• Cross-fertilization:
sperm from a foreign
plant fertilizes an egg
Gregor Mendel
• Used both the processes of self fertilization
and cross fertilization to experiment on pea
plants
• This helped him develop his basic laws of
heredity
Definitions
• True breed or pure breed: plants with a trait
such as purple flowers that is always inherited
by all offspring
– Can only produce one type of gamete
• HYBRID:
– The offspring of a cross fertilization
– 2 parents similar to sexual reproduction
– Can produce different types of gametes
Definitions continued
• Monohybrid cross: tracks one trait at a time
– Ex: flower color
• Dihybrid cross:
Mendel’s work
• Self fertilized true breed
parents for many
generations
– All offspring gave the
same results
• Cross fertilized true
breeds to get an F1
generation
• Self fertilized the F1 and
observed the F2
generation
•
Mendel’s Experiment
Parent Generation (P1):
Purple true breed X White true breed
First Filial (F1)
100% Purple flowers
Second Filial (F2)
75% Purple: 25% White
3:1 ratio
Self fertilize
Why were all the F1 generation
flowers purple?
Purple Trait is obviously dominant over
the white trait
The white trait was hidden but not gone
Why were some of the F2 generation
part purple and part white?
The F1 parent was carrying the white trait
but it was masked or hidden.
White is recessive to purple
Just from looking at these results,
what can Mendel conclude?
Mendel’s Conclusions from a monohybrid
cross
1- Copies of inherited traits must be separated
when gametes are formed
2- When present in 2 forms one form is
dominant over the other
3- the recessive trait will show itself when
present in two copies
Tuesday 4/22/14
From these experiments, Mendel
concluded:
• Traits are determined by physical unit that come in
pairs (he did not know these would later be called
alleles)
• Gametes separate and carry only 1 allele(copy) for
each gene
• The particular allele that ends up in a gamete is
caused by chance
• One allele is dominant and one recessive
• True-breeding organisms have the 2 copies of the
same allele (homozygous)
• AIM: How can we predict the possible genotypes and
phenotypes of offspring?
• DO NOW: 2- if I cross fertilized a true breed green
seed pea plant by a true breed yellow seed pea
plant, what phenotypes do I expect to get?
• HOMEWORK: Textbook read pages 272-273. answer
questions 1,2,3 on page 275
Create a list
• 7 traits observed by Gregor Mendel
1- Flower color
2- Plant size
3- Flower position
4-Seed color
5- shape of pod
6- Pod color
7- Seed shape
Each of these traits has a dominant and a recessive
phenotype
•
Seed color
• Dominant phenotype: green
• Recessive phenotype: yellow
• Genotype
Phenotype
– GG
– Gg
– gg
Mendel had no idea about the following
• We know we get 2 copies of genes
– 1 from sperm
– 1 from egg
• Allele: is a copy of a gene
• Homologous chromosomes carry alleles
Monohybrid Cross
• Tracked one (mono) trait at a time
Mendel’s work
• Cross fertilized two
true breed parents that
displayed opposite
traits.(P or Parental
generation)
• All First filial or F1
offspring were purple
What happened to the white color?
Self-fertilized F1
• Second filial or F2
generation yielded
about ¼ white and ¾
purple
• So the white flower
color was not lost just
masked
Self-fertilized F2
• Saw that all white flowered F2 yielded all
white F3 but the purple still yielded 3:1 ratio
of purple to white
• Therefore the white allele was not lost but
rather hidden or masked by the purple allele
From these experiments, Mendel
concluded:
• Traits are determined by physical unit that come in
pairs (he did not know these would later be called
alleles)
• Gametes separate and carry only 1 allele for each
gene
• The particular allele that ends up in a gamete is
caused by chance
• One allele is dominant and one recessive
• True-breeding organisms have the 2 copies of the
same allele
Thursday 4/24/14
AIM: why did Mendel
decide to perform a
dihybrid cross?
DO NOW: Let A
AA
represent the allele
coding for terminal
flowers and a axial
Aa
flowers. Complete the
following table:
HOMEWORK: text read aa
pages 274-275. answer
questions 3 and 4 page
275
Genotype
Phenotype
Homozygous
dominant
terminal
Heterogygous
terminal
Homozygous
recessive
axial
Mendel’s Law of dominance
• When two different alleles are present, the dominant
alleles gives the resulting phenotype and masks the
trait of the recessive allele
• However the recessive allele is still present
• Homozygous Dominant and heterozygous organisms
display the same phenotype
• Recessive alleles are only displayed when present in
2 copies
– Homozygous recessive
Mendel’s Law of segregation
• Pairs of alleles on homologous chromosomes
separate from each other during gamete
formation
• Gametes receive only one allele from a
homologous pair.
• Fertilization produces offspring with a copy of
one allele from mom and one from dad
•
•
•
Mendel’s Hypothesis were consistent
with his results
• 2 plants that look alike may actually carry different
combinations of alleles
• Genotype: the combination of alleles carried by an organism
– Homozygous Dominant: AA
– Heterozygous: Aa
– Homozygous recessive: aa
• Phenotype: The physically observable feature
• So a homozygous dominant individual and a heterozygous
individual will display the same phenotype but have different
genotypes
• The only way for the recessive phenotype is observed is if the
individual is homozygous recessive
Mendel was not satisfied
• He wanted to see if alleles could be inherited
together
• He asked himself are all round seeds yellow?
• Are all green seeds wrinkled?
• He looked at two traits at the same time
• Dihybrid cross
• Ex: seed shape and seed color
• His results were inconclusive which means all
round seeds were not yellow all wrinkled
seeds were not green
In order to investigate, Mendel
performed a dihybrid cross
• Dihybrid cross: crossed
plants that differed in
more than one trait
• Specifically Mendel
looked at seed shape
and seed color
Cross Fertilization
Homozygous Dominant
Homozygous recessive
ALL heterozygous
Both Dominant traits
Dominant shape
Dominant color
Recessive color
Recessive shape
Both recessive traits
•
•
•
•
•
R-round
r-wrinkled
Y-Yellow
y-green
•
Friday 4/25/14
Mendel’s dihybrid cross
• P: true breed RRYY(Round Yellow) x rryy(wrinkled
green)
• All F1: RrYy (Round Yellow)
• Allowed F1 to self-fertilize which yielded the
following phenotypic ratio
• F2: 9:3:3:1 ratio of
Round Yellow: Round green: wr Yellow: wr,green
• F1: Self Fertilization
•
F1: self fertilization
•
•
Display of all possible genotypes
•
•
•
•
•
Law of independent assortment
• Multiple traits are inherited independently of
each other because alleles of genes are
distributed independently during gamete
formation
• Genes found on different chromosomes assort
independently of each other during gamete
formation
• Genes are inherited independently
What was the major question Mendel
was trying to answer when he
performed his dihybrid cross?
Mendel asked himself if two characteristics
were inherited together.
Specifically is seed color inherited with
seed shape?
Testcross
• Cross fertilize a dominant
phenotype plant with a
homozygote recessive plant
• WHY?
• Purpose is to analyze the
ratio of the offspring
• This will tell us the parents
genotype
(homozygous dominant or
heterozygous)
What do we call this type of cross ad
why would we perform it?
Test cross
• Determines the genotype of a dominant
displayed phenotype
Testcross
• The only way to display the recessive phenotype is to
have a homozygous recessive genotype
• After performing a testcross, If the f1 offspring
display ALL dominant phenotypes then I know the
Parent genotype is homozygous Dominant.
• If the offspring display 50% dominant phenotype and
50% recessive than the Parental genotype is
heterozygous