chapter 10 mendel

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

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