BiologyB_4 Heredity PART 1 (Chapters 11 and 14)

(B-4.5-8) Demonstrate an understanding of the molecular basis of heredity.

Website with good review images http://www.personal.psu.edu/staff/d/r/drs18/bisciImages/index.html

B-4.5 Meiosis (sec 11-4)

• What is DIPLOID and HAPLOID? • What is the chromosome # in somatic cells & gametes?• What is the function of Meiosis?• What happens in interphase?• What happens in Meiosis I?

• List stages; Crossing over; Anaphase I

• What happens in Meiosis II?• How does gamete production differ in males &

females?

Explain Chromosome # in somatic cells & gametes

SOMATIC CELLS (body cells)• DIPLOID (2N) cells which Contains 2 sets

(N) of chromosomes (double);• TWO alleles (copies) of each gene

GAMETES (sex cells)• HAPLOID (N) Contains ONE set of

chromosomes (Half of body cells); • ONE allele (copy) of each gene• Egg (1 copy of mother’s DNA) • Sperm (1 copy of father’s DNA)

VOCABULARYGENE –section of DNA codes for trait. EX: HeightALLELE - different version of a gene (trait) EX: Tall or Short

Examples: Diploid vs HaploidFruit Flies

• Diploid (2N) = 8 (body cells)• Haploid (N) = 4 (gametes)

Humans• Diploid (2N) = 46 (body cells)

• Haploid (N) = 23 (gametes)

Mitosis division makes identical diploid cells– repair, growth, and development (begins shortly after fertilization and ongoing)

• BODY CELL (diploid) divides once to make more BODY CELLS (diploid)• ACTIVITY – All cells arise from pre-existing cells: http://dnaftb.org/7/

So how are gametes (egg/sperm) made if they have half the chromosomes of a body cell???

• ACTIVITY – Sex cells have one set of chromosomes; body cells have two: http://dnaftb.org/8/

N = set of chromosomes2N = 2 sets of chromosomes

What process produces gametes (egg/sperm)? ____MEIOSIS___

MEIOSIS: Cuts Chromosome # in HALF /(2N N) 46 23

• Interphase Interphase • DNA is replicated (46 doubled to 92)• Instead of 2 copies of every gene there are now 4 copies

• Meiosis IMeiosis I – begins w/ 1 diploid1 diploid cell(92) ends w/ 2 haploid cells• CROSSING OVER occurs genes swapped/causes variety in

gametes• HOMOLOGOUS pairs (similar chromosomes) are Separated

• Meiosis IIMeiosis II - begins w/ 2 haploid 2 haploid cells (46) ends w/ 4 haploid gametes (23)• Phases work the same as mitosis • Anaphase II - chromosomes separated at centromere

REVIEW:Chromosome Structure

ChromosomesDNA during cell divisionChromatids joined by centromereHumans cells have total (23 pairs)

http://avonapbio.pbworks.com/f/chromosome.bmp

http

://staff

.jccc.net/P

DE

CELL/ce

lldiv

ision

/chro

moso

me1

.gif

Homologous Chromosomes

http://staff.jccc.net/PDECELL/celldivision/chromoterm.html

http://theano5.blogspot.com/

course1.winona.edu

1st DIVISION - Meiosis I

Interphase I

Dna is doubledProphase I Metaphase I Anaphase I

Prophase I(92)

Chromosomes arrange in Homologous pairs; Crossing over occurs – pairs swap alleles making new combinations

Metaphase I Homologous pairs line up at middle

Anaphase I Homologous PAIRS are split apart

Telophase I(46)

2 nuclei with 46 chromosomes each followed by cytokinesis (2 cells)

Prophase II Metaphase II Anaphase II

Prophase II chromosomes prepare to divide

Metaphase II Chromosomes meet at middle

Anaphase II Sister chromatids are split apart

Telophase II 4 haploid gametes (23 chromosomes)Followed by cytokinesis

http://www.cix.co.uk/~argus/Dreambio/cell%20division/meiosis%20animation.gif

2nd DIVISION - Meiosis II (similar to mitosis)

Telophase II

Explain Crossing Over..• Increases genetic variation in gametes (causes variety in

offspring)Doubled

HOMOLOGOUS PAIR (tetrad)

Mom’s Dad’s Creates 4 different combinations

Chromatids trade alleles

Each chromatid willBe passed on to diff.

gamete

A,B-brown eyesC,D,E-brown hair

a,b-blue eyesc,d,e-blonde hair

Gamete Production• In malesIn males —

spermatogenesis produces 4 haploid sperm

• In femalesIn females — oogenesis produces

1 haploid egg (ovum), 3 polar bodies

•http://www.classzone.com/cz/books/bio_07/resources/htmls/animated_biology/unit3/bio_ch06_0175_ab_meiosis.html

46XY

46XX

23 Y23 X23 X

23 X

23 Y

MitosisMitosisGrowth/DevelopmentGrowth/Development

Asexual reproductionAsexual reproduction

MeiosisMeiosis

Egg and SpermEgg and Sperm

Sexual ReproductionSexual ReproductionStart: 1 Diploid Cell (2N) Start: 1 Diploid Cell (2N)

Cell Divides Once Cell Divides TwiceCrossing over makes new combination of alleles

End: 2 Diploid Cells (2N)Body cells – skin, muscle

End: 4 Haploid Cells (N)Gametes – egg, sperm

New cells are genetically IDENTICAL

New cells are genetically DIFFERENT from each other & parent

http

://use

rs.rcn.co

m/rp

ohlm

an/co

mpariso

n.g

if

B-4.6 Mendelian Genetics(sec 11-1,2,3)Use Mendel’s laws to predict inherited traitsSummarize Mendel’s experiment.

Hypothesis – Variables (IV & DV) - Conclusion

Law of Segregation states…Principle of Dominance states… How are dominant and recessive traits shown?Relationship between Genotype and Phenotype.

Practice Probability & Monohybrid Crosses

Law of independent assortment states… How does that differ from the law of segregation?

Practice Dihybrid Crosses

Intro to GENETICS…• GENETICS is the study of heredity…

• (passing of traits from one generation to the next)

• GREGOR MENDEL (an Austrian Monk) 1852• Performed experiments using pea plants and which where

the basis for understanding genetics.• Mendel’s LAW explains how GENES are passed from one

generation to the next• ACTIVITY – Children resemble their parents:

http://dnaftb.org/1/

• WALTER SUTTON 1902• Developed the Chromosome Theory of Heredity… states

that GENES are located on CHROMOSOMES

Mendel’s Experiment:• PROBLEM:

• How are traits passed from one generation to the next?

• HYPOTHESIS:• If then P generation had different traits, then the F1

generation would be a MIX of both parents.

• PROCEDURE: (pea plant experiments)• P (parents) = Tall plant X Short plant (cross pollination to

produce hybrids)• F1 = offspring; predicted to be all Medium Height

• F1 = 1st generation offspring & F2 = 2nd generation offspring) • TRIALS = He studied 7 traits (height, color, shape, etc…)

Cross-Pollination

Mendel’s RESULTS• P cross = Tall X Short

• F1 generation = All Tall• F1 cross = Tall X Tall

• F2 generation = 3 Tall, 1 Short (3:1)

P Generation F1 F2

Seed Shape

Flower Position

Seed CoatColor

Seed Color

Pod Color

Plant Height

PodShape

Round

Wrinkled

Round

Yellow

Green

Gray

White

Smooth

Constricted

Green

Yellow

Axial

Terminal

Tall

Short

Yellow Gray Smooth Green Axial Tall

Section 11-1 Mendel’s Seven F1 Crosses on Pea Plants

Go to Section:

Conclusions and Law of Segregation

• ACTIVITY – Genes come in pairs: http://dnaftb.org/2/• ACTIVITY – Some genes are dominant: http://dnaftb.org/4/• Traits are inherited as separate units (genes) which are not

blended.• Gene section of DNA, codes for trait…

• Ex: such as Height• Allele: different form (version) of a gene…

• Ex: such as Tall / Short• LAW OF SEGREGATION:

• Organisms inherit 2 copies of each gene; 1 from each parent.

• Organisms donate only 1 copy of each gene in their gametes (egg or sperm) during meiosis

Principle (law) of DOMINANCE

Alleles can be either…• DOMINANT… written in UPPER CASE • recessive… written in lower case (same letter)

• EX: Gene = Height• Alleles = T (tall), t (short)

• Organism inherit 2 alleles for each gene…• If organism has a Dominant allele, it will show Dominant

trait (TT or Tt = tall)• If dominant is not present then RECESSIVE trait is shown (tt

= short)

Relationship Between Genotype & Phenotype

• GENOTYPE – genetic make up (the alleles) of organism (EX: Tt, GG)• HOMOZYGOUS – has same alleles, purebred (EX: tt, TT, gg, GG)• HETEROZYGOUS – has different alleles, hybrid (EX: Tt, Gg)

• PHENOTYPE – physical make up (traits shown by alleles) of organism (EX: tall, yellow)

Law of Independent Assortment

• Review – Law of Segregation:• aka separation of genes

• Organisms donate 1 copy of each gene

Law of Independent Assortment:• During meiosis…Traits are inherited separately – causing

different combination of traits (Tall, yellow plants; Short, yellow plants)

• Traits do NOT influence the inheritance of other traits• Color of plant does not affect height• Attached earlobes does not affect freckles

Probability & Genetic Crosses• ACTIVITY – Genetic inheritance follows rules: http://dnaftb.org/5/• PROBABILTY is the likely hood that an event will occur

(prediction)• In reality you don’t get the EXACT ratio of results shown in the

square. This is because genetics is kind of like flipping a coin (each time you flip it you have a 50:50 chance of getting heads).

• PUNNETT SQUARES use probability to quickly predict possible outcomes of a genetic cross In 1905, Reginald Punnett, devised a shorthand way of finding the expected possible offspring genotypes.

• MONOHYBRID• Predict all possible outcomes of how 1 trait will be inherited

• DIHYBRID• Predict all possible outcomes of how 2 traits will be inherited

http://kmbiology.weebly.com/mendel-and-genetics---notes.html

Monohybrid Cross RATIOS:• Genotypic = TT :Tt: tt• Phenotypic = Tall : Short(always in this order)

T(sperm)

T(sperm)

t(egg)

t(egg)

TT (parent)

tt (parent)

Monohybrid Cross

• Uses Punnett Squares to see POSSIBLE result of how ONE GENE (trait) is passed on…

• TT X tt (Homozygous tall) X (Homozygous short)

RATIOS:• Genotypic = 0:4:0

• TT :Tt: tt

• Phenotypic = 4:0• Tall : Short

(always in this order)

T(sperm)

T(sperm)

t(egg)

Tt Tt

t(egg)

Tt Tt

TT (parent)

tt (parent)

G G

g

g

T t

T

t

ResultsResults• Genotypic Ratio =

______:_____:_____• Phenotypic Ratio =

_____:_____ResultsResults• Genotypic Ratio =

____:____:____• Phenotypic Ratio =

_____:____

G G

g Gg(green)

Gg(green)

g Gg(green)

Gg(green)

T t

T TT(tall)

Tt(tall)

t Tt(tall)

tt(short)

ResultsResults• Genotypic Ratio = 0:4:0

(GG:Gg:gg)• Phenotypic Ratio 4 :0• (green):0 (yellow)

ResultsResults• Genotypic Ratio =

1:2:1 (TT:Tt:tt)• Phenotypic Ratio 3 :1• (tall): 1 (short)

Test Cross• A test cross is a way

to determine the genotype of an organism with an unknown genotype.

• Cross unknown with known.

• http://kmbiology.weebly.com/test-cross---notes.html

Dihybrid CrossesPossible combination of how TWO Genes are inherited.

• Size of Punnett Square is 4 X 44 X 4• Each Gene is inherited Independent of other (law of

independent assortment)• EX: Height and Color

Tall yellow (TTYY) X short green (ttyy)

List the possible allele combination that could be in a gamete (egg or sperm)

TTYY 1. __TY___2. __TY____3. __TY____4. __TY____

ttyy1. __ty___2. __ty____3. __ty____4. __ty____

Gamete possibilities

TY TY TY TY

ty

ty

ty

ty

Try this TWO Factor Cross of P generation (TTYY) x (ttyy)

TY TY TY TY

ty

ty

ty

ty

What are the possible phenotypes? genotypes

TtYy

TtYy

TtYy

TtYy

TtYy

TtYy

TtYy

TtYy

TtYy

TtYy

TtYy

TtYy

TtYy

TtYy

TtYy

TtYy

List the possible allele combination that could be in a gamete (egg or sperm)

TtYy1. __TY___2. __Ty____3. __tY____4. __ty____

TtYy1. __TY___2. __Ty____3. __tY____4. __ty____

TY Ty tY ty

TY

Ty

tY

ty

What are the possible phenotypes? Genotypes?

TY Ty tY ty

TY TTYY (tall, yellow)

TTyY (tall, yellow)

tTYY (tall, yellow)

tTyY (tall, yellow)

Ty TTYy (tall, yellow)

TTyy (tall, green)

tTYy (tall, yellow)

tTyy (tall, green)

tY TtYY (tall, yellow)

TtyY (tall, yellow)

ttYY (short, yellow)

ttyY (short, yellow)

ty TtYy (tall, yellow)

Ttyy (tall, green)

ttYy (short, yellow)

ttyy (short, green)