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MENDEL, GENETICS & MEIOSIS
Project in Biology
Gregor Mendel’s Discussions
Meiosis
Genetics
Credits
DNA
10.1 MENDEL’S LAWS OF HEREDITY
I. WHY MENDEL SUCCEEDED Gregor Mendol – father of genetics 1st studies of heredity – the passing of
characteristics to offspring Genetics – study of heredity The characteristics passed on called
traits
1. MENDEL CHOSE HIS SUBJECT CAREFULLY
Used garden peas to study Have male & female gametes (sex
cells) Male & female same flower Know what pollination & fertilization
mean He could control the fertilization
process Not many traits to keep track of
2. MENDEL WAS A CAREFUL RESEARCHER
USED CAREFULLY CONTROLLED EXPERIMENTS
STUDIED ONE TRAIT AT A TIME KEPT DETAILED DATA
II. MENDEL’S MONOHYBRID CROSSES
MENDEL STUDIED 7 TRAITS CAREFULLY Pg. 262 – figure 10.3
Mendel crossed plants w/ diff. traits to see what traits the offspring would have
These offspring are called hybrids – offspring of parents w/ different traits
A monohybrid cross is one that looks at only one trait (let’s look at plant height – tall or short)
A. THE 1ST GENERATION Mendel crossed two plants – 1 tall &
1 short (they came from tall & short populations)
These plants are called the parental generation (P generation)
The offspring were all called the 1st filial generation (F1 generation)
All the offspring were tall (the short plants were totally excluded)
B. THE 2ND GENERATION Next, Mendel crossed two plants
from the F1 generation The offspring from this cross are
called the 2nd filial generation (F2 GENERATION)
Mendel found that ¾ of the offspring were tall & ¼ were short (the short plants reappeared!!!!!!)
TO GO ANY FURTHER, WE MUST UNDERSTAND ALLELES,
DOMINANCE, & SEGREGATION Genes – a section of DNA that codes
for one protein These genes are what control & produce
traits The genes Mendel studied came in
two forms (tall/short - round/wrinkled - yellow/green…….etc.)
Alternate forms of a gene are called alleles
Alleles are represented by a one or two letter symbol (e.g. T for tall, t for short)
ALLELES CONT’D THESE 2 ALLELS ARE NOW KNOWN
TO BE FOUND ON COPIES OF CHROMOSOMES – ONE FROM EACH PARENT
THE RULE OF DOMINANCE A dominant trait is the trait that will
always be expressed if at least one dominant allele is present
The dominant allele is always represented by a capital letter
A recessive trait will only be expressed if both alleles are recessive
Recessive traits are represented by a lower case letter
DOMINANCE CONT’D LET’S USE TALL & SHORT PEA
PLANTS FOR AN EXAMPLE WHICH OF THESE WILL SHOW THE
DOMINANT & RECESSIVE TRAIT?TT Tt tt
DOMINANT TRAIT RECESSIVE TRAIT
THE LAW OF SEGREGATION MENDEL ASKED HIMSELF……..”HOW
DID THE RECESSIVE SHORT PLANTS REAPPEAR IN THE F2 GENERATION?”
HE CONCLUDED THAT EACH TALL PLANT FROM THE F1 GENERATION CARRIED TWO ALLELES, 1 DOMINANT TALL ALLELE & ONE RECESSIVE SHORT ALLELE
SO ALL WERE Tt
SEGREGATION CONT’D HE ALSO CONCLUDED THAT ONLY
ONE ALLELE FROM EACH PARENT WENT TO EACH OFFSPRING
HIS CORRECT HYPOTHESIS WAS THAT SOMEHOW DURING FERTILIZATION, THE ALLELES SEPARATED (SEGREGATED) & COMBINED WITH ANOTHER ALLELE FROM THE OTHER PARENT
The law of segregation states that during gamete formation, the alleles separate to different gametes
F1 GENERATIONFATHER MOTHERT t T t
T T T t t tF2 GENERATION
- the law of dominance explained the heredity of the offspring of the f1 generation - the law of segregation explained the heredity of the f2 generation
PHENOTYPES & GENOTYPESPG. 264
PHENOTYPE – THE WAY AN ORGANISM LOOKS AND BEHAVES – ITS PHYSICAL CHARACTERISTICS (i.e. – TALL, GREEN, BROWN HAIR, BLUE EYES, ETC.)
GENOTYPE – THE GENE COMBONATION (ALLELIC COMBINATION) OF AN ORGANISM – (i.e. – TT, Tt, tt, ETC.) HOMOZYGOUS – 2 ALLELES ARE THE
SAME HETEROZYGOUS – 2 ALLELES DIFFERENT
MENDEL’S DIHYBRID CROSSES
MONOHYBRID – MENDEL LOOKED AT ONE TRAIT
IN HIS DIHYBRID CROSSES – HE LOOKED AT 2 TRAITS
WANTED TO SEE IF TRAITS ARE INHERITED TOGETHER OR INDEPENDENTLY
DIHYBRID CROSS TOOK TWO TRUE BREEDING PLANTS
FOR 2 DIFFERENT TRAITS (ROUND/WRINKLED SEEDS ------- YELLOW/GREEN SEEDS)
1ST GENERATION WHAT WOULD HAPPEN IF HE CROSSED
JUST TRUE BREEDING ROUND W/ TRUE BREEDING WRINKLED (ROUND IS DOMINANT)ALL THE OFFSPRING ARE
ROUND
DIHYBRID CROSS – 1ST GENERATION CONT’D
SO WHAT DO YOU THINK HAPPENED WHEN HE CROSSED TRUE BREEDING ROUND/YELLOW SEEDS WITH TRUE BREEDING WRINKLED/GREEN SEEDS
ALL THE F1 WERE ROUND AND YELLOW
DIHYBRID CROSS – 2ND GENERATION
TOOK THE F1 PLANTS AND BRED THEM TOGETHER (PHENOTYPE WAS ROUND/YELLOW X ROUND/YELLOW)
2ND GENERATION FOUND ROUND/YELLOW - 9 FOUND ROUND/GREEN - 3 FOUND WRINKLED/YELLOW - 3 FOUND WRINKLED/GREEN - 1 ( 9 : 3 : 3 : 1 RATIO)
EXPLANATION OF 2ND GENERATION
MENDEL CAME UP W/ 2ND LAW – THE LAW OF INDEPENDENT ASSORTMENT GENES FOR DIFFERENT TRAITS ARE
INHERITED INDEPENDENTLY FROM EACH OTHER
THIS IS WHY MENDEL FOUND ALL THE DIFFERNENT COMBONATIONS OF TRAITS
PUNNETT SQUARES A QUICK WAY TO FIND THE
GENOTYPES IN UPCOMING GENERATIONS
1ST DRAW A BIG SQUARE AND DIVIDE IT IN 4’S
PUNNETT SQUARE
CROSS T T X Tt
CONT’D
T T X T tT T
T
t
T T T T
T t T t
DIHYBRID CROSSES A LITTLE DIFFERENT H h G g X H h G g MUST FIND OUT ALL THE POSSIBLE
ALLELIC COMBONATIONS USE THE FOIL METHOD LIKE IN MATH
H h G g X H h G g1. HG2. Hg
3. hG4. hg
FOIL – FIRST, OUTSIDE, INSIDE, LAST
BOTH PARENTS ARE THE SAME
NOW LET’S DO A DIHYBRID CROSS
H h G g X H h G gHG Hg hG hg
HGHg
hG
hg
HHGG HHGg HhGG HhGg
HHGg HHgg HhGg Hhgg
HhGG HhGg hhGG hhGg
HhGg Hhgg hhGg hhgg
WHAT ARE THE PHENOTYPIC RATIO’S?
H h G g X H h G gHG Hg hG hg
HGHg
hG
hg
HHGG HHGg HhGG HhGg
HHGg HHgg HhGg Hhgg
HhGG HhGg hhGG hhGg
HhGg Hhgg hhGg hhgg
DD:Dr:rD:rr:
9331
PROBABILITY WILL REAL LIFE FOLLOW THE
RESULTS FROM A PUNNETT SQUARE? NO!!!!!! – A PUNNETT SQUARE ONLY
SHOWS WHAT WILL PROBABLY OCCUR
IT’S A LOT LIKE FLIPPING A COIN – YOU CAN ESTIMATE YOUR CHANCES OF GETTING HEADS, BUT REALITY DOESN’T ALWAYS FOLLOW PROBABILITY
10.2 MEIOSIS GENES, CHROMOSOMES, AND
NUMBERS CHROMOSOMES HAVE 100’S OR 1000’S
OF GENES GENES FOUND ON CHROMOSOMES
DIPLOID & HAPLOID CELLS ALL BODY CELLS
(SOMATIC CELLS) HAVE CHROMOSOMES IN PAIRS
BODY CELLS ARE CALLED DIPLOID CELLS (2n)
HUMANS HAVE THE 2n # OF CHROMOSOMES
DIPLOID AND HAPLOID CELLS CONT’D
HAPLOID CELLS ONLY HAVE 1 OF EACH TYPE OF
CHROMOSOME (DIPLOID CELLS HAVE 2 OF EACH TYPE)
SYMBOL IS (n) SEX CELLS HAVE THE n # OF
CHROMOSOMES
HOMOLOGOUS CHROMOSOMES
HOMOLOGOUS CHROMOSOMES ARE THE PAIRED CHROMOSOMES THAT CONTAIN THE SAME TYPE OF GENTIC INFORMATION, SAME BANDING PATTERNS, SAME CENTROMERE LOCATION, ETC.
THEY MAY HAVE DIFFERENT ALLELES, SO NOT PERFECTLY IDENTICAL
WHY DO THEY HAVE DIFFERENT ALLELES?CAME FROM DIFFERENT
PARENTS
WHY MEIOSIS? MITOSIS – RESULTS IN GENETICALLY
IDENTICAL OFFSPRING – INCLUDING THE # CHROMOSOMES
WHAT WOULD HAPPEN IF THE EGG AND SPERM HAD THE SAME # OF CHROMOSOMES AS THE BODY CELLS?EGG = 46 CHROMOSOMES SPERM = 46 CHROM.
ZYGOTE = 46 + 46 = 92 CHROMOSOMES =
NOT HUMAN
MEIOSIS A TYPE OF CELL DIVISION WHICH
PRODUCES GAMETES CONTAING HALF THE NUMBER OF CHROMOSOMES AS THE BODY CELLS
2 STAGES – MEIOSIS I & MEIOSIS II START W/ 1 DIPLOID CELL, END UP W/
4 HAPLOID CELLS (GAMETES) 4 DAUGHTER CELLS ARE
GENETICALLY DIFFERENT FROM EACH OTHER AND MOTHER CELL
INTRO TO MEIOSIS CONT’D SPERM – MALE GAMETE (n) EGG – FEMALE GAMETE (n) FERTILIZATION PRODUCES A ZYGOTE
(2n) THIS TYPE OF REPRODUCTION IS
CALLED SEXUAL REPRODUCTION
STAGES OF MEIOSIS MEIOSIS I
PROPHASE I, METAPHASE I, ANAPHASE I, TELOPHASE I (PMAT)
MEIOSIS II PROPHASE II, METAPHASE II, ANAPHASE
II, TELOPHASE II (PMAT)
Cell Division (Meiosis)
1. A process of cell division where the number of chromasomes is cut in half2. Occurs in gonads (testes, ovaries, stamens, etc)
3. Makes gametes (sperm, ova, pollen, etc)
IMPORTANT THINGS TO KNOW
CROSSING OVER – OCCURS DURING PROPHASE I CREATES GENETIC VARIABILITY
(RECOMBINATION OF GENES) IN MEIOSIS I, HOMOLOGOUS
CHROMOSOMES SEPARATE (ANAPHASE I) IN MEIOSIS II, SISTER CHROMATIDS
SEPARATE TETRAD – WHAT THE HOMOLOGOUS
CHROMOSOMES ARE CALLED WHEN THEY PAIR UP DURING PROPHASE I
GeneticsSmall sections of DNA are
responsible for a “trait”. These small sections are called “Genes”. Gene - A segment of DNA that
codes for a specific trait Trait - A characteristic an organism
can pass on to it’s offspring through DNA
Gene
Genetics The study of heredity, how traits are
passed from parent to offspring
x =or
or
Genetic TraitsEarlobes: Free ear lobes (dominant trait) vs. Attached ear lobes (recessive trait) Free earlobes are those that hang below the point of attachment to the head. Attached ear lobes are attached directly to the side of the head.
Forelock: White forelock (dominant trait) vs. No white forelock (recessive trait) A white forelock is a patch of white hair, usually located at the hairline. Widow's Peak (below) is dominant over no widow's peak hairline.
Dimples: Dimples (dominant trait) vs. No dimples (recessive trait) Dimples are natural dents in the face to the right or left of the mouth. If a person has only one dimple, they should be counted as having dimples.Cleft chin is dominant over no cleft.
Thumbs: Straight thumb (dominant trait) vs. Curved thumb (recessive trait) When viewed from the side as in the illustration below, curved thumbs can be seen as part of a circle.Pinky: Straight pinky
(recessive trait) vs. Bent pinky (dominant trait)
Mid-digit hair: Mid-digit hair (dominant trait) vs. No mid-digit hair (recessive trait)Longer 2nd toe is dominant over 2nd toe shorter than big toe.
Tongue-Rolling: Rolling up edges (dominant trait) vs not rolling (recessive)
DNAD.N.A. - Deoxyribonucleic Acid Molecule made of:
1. Deoxy Sugar2. Combination of four nitrogen bases
Either: a. Guanineb. Cytocinec. Thymined. Adenine
The sum total of combinations that these four bases are capable of creating are greater than all the stars visible in the night time sky.
DNA Nitrogen bases pair up
Cytosine & Guanine Thymine & Adenine
Pairing creates a ladder shape Angle of bonds creates a twist
Ladder and Twist produces the famous
“Double Helix”
DNA
DNA resides in all cells Inside the nucleus
Each strand forms a chromosome
Cell
NucleusDNA
DNA
DNA is found in all living cells It controls all functions
inside a cell It stores all the genetic
information for an entire living organism
Single cell like an amoeba Multi cell like a human
Mery ’ Ant Bondad
Justin
Tan
Rein Emmie Dela Cruz
Mary Rose Hagupit
Mary Bridgette De Veyra
Thanks For Watching
=))