Chapter 11: Genetics!!!!!!! 11.1 ****************************************************** Genetics : the study of heredity – how traits get passed from one

Chapter 11: Genetics!!!!!!!

11.1 ******************************************************Genetics : the study of heredity – how traits get passed

from one generation to the next: example: eye color, blood type, skin color

Gregor Mendel – An Austrian monk (mid 1800’s )who was a gardener. Pioneer in studying genetic inheritance….a huge component if biology!

A. Mendel’s Experiments: * self-pollintation: pollen (sperm) from a pea plant

fertilizes its own eggs. The resulting seeds are all

identical to themselves.

* cross-pollination: pollen from one pea plant is used

to fertilize the eggs of another pea plant. 2 parents.

* He studied 7 traits that had two versions of the trait

round vs. wrinkly seeds

yellow vs. green seeds

tall vs. short pea plants

* He cross-pollinated plants with different traits and

observed the appearance of the offspring plants

Mendel pea plant traits

Mendel called:

P = original parent generation (your parents)

F1 = 1st generation offspring (you)

The offspring in the F1 between parents with

different traits are called hybrids

F2 = 2nd generation offspring (your kids)

When Mendel crossed his plants he found that the F1

looked like only 1 parent….not a blend of the 2 traits!!!!P generation F1 generation F2 generation

Notice the F1 are not medium

They are all tall like one of the parents.

B. Mendel’s Conclusions:1. Inheritance is determined by

factors that are passedfrom one generation to the next.

Genes small portions of DNA that code for proteins. The proteins then control one trait. Each trait Mendel studied was controlled by two genes that come in contrasting forms. Example: The gene for “plant height” comes in 2 forms a. Tall plants b. Short plants The 2 forms of a gene are called alleles

2. Principle of Dominance (later called this)

* Some alleles are dominant and some are recessive (some forms of genes are dom etc………..) * An organism that has a dominant allele for a trait will always show the dominant form of the trait. * An organisms that has a recessive allele for a trait will only show the recessive form of the trait when the dominant allele is not present. * A dominant allele can mask or hide a recessive allele ….more later ………………

Mendel noticed that the recessive form of the trait (short), seemed to disappear in the F1 generationand reappear in the next generation.

Mendel wanted to figure out why….leading to ………..

P F1 F2

3. Law of Segregation When Mendel crossed his F1 plants…..the recessive

form of the trait showed up. Why?

Law of Segregation : the pair of genes for a trait separate from one another in meiosis. Example: a parent plant who is Tt can pass an T or t to the offspring via the egg.

The result of this process is an F2 generation with new

combinations of alleles. More later……….

11.2 A lot of genetics is about trying to figure out the

likelihood that a trait will appear. This is called

probability.

Punnett Squares can be used to figure out the

probability of genetic combinations occcuring in a

cross between 2 parents.

A punnett square does not tell what will actually

happen in a cross, just the LIKELINESS of an event

happening….or that a result CAN happen. (a family of 6 kids SHOULD have 3 boys and 3 girls)

think of families with 6 girls or 6 boys!!!!!!!

Some key terms:

Example: trait = plant height T= tall t=short

Phenotype : the physical observable form of a trait.

Genotype : the 2 genes that make-up of a trait.

*phenotype : tall or short plant

*genotype : TT, Tt, tt

Using this….we can look at all the gene

combinations in forming offspring.

For most traits, an organisms has 2 genes, one from

each parent, so the allele combinations would be:

TT = tall plant Tt= tall plant tt= short plant

Homozygous Dominant = 2 dom alleles TT

Heterozygous Dominant – 1 dom & 1 rec allele Tt

Homozygous recessive – 2 recessive alleles tt

Time for a quiz!!!!!!!!!!1. A piece of DNA that codes for a trait is called

a _______________ .


a gene.


a gene.

2. The different forms of genes are called_____


a gene

2. The different forms of genes are called alleles


a gene


3. The 2 alleles an organisms has for a trait

_________________


a gene



genotype


a gene



genotype

4. The physical appearance of a trait________


a gene



genotype

4. The physical appearance of a trait phenotype

The trait is nose shape. Flat nose is dominant

over pointy nose. Use letters F, f to show:

4. Dominant allele_______



4. Dominant allele F




5. Recessive allele________




5. Recessive allele f





6. Homozygous flat nose genotype________





6. Homozygous flat nose genotype FF






7. Heterozygous flat nose genotype________






7. Heterozygous flat nose genotype Ft






7. Heterozygous flat nose genotype Ft

8. Pointy nose genotype_______________






7. Heterozygous flat nose genotype Ff

8. Pointy nose genotype ff


a _______________ .

2. The different forms of genes are called_____


_________________

4. The physical appearance of a trait________



4. Dominant allele_______

5. Recessive allele________

6. Homozygous flat nose genotype________

7. Heterozygous flat nose genotype________

8. Pointy nose genotype_______________

How to use punnett squares!!1. We can predict alleles(forms of a gene) that

will be passed on by using a Punnett Square.

R = can roll tongue R r

r = cannot roll tongue R

r

* parents are Rr and Rr

The type of gametes

possible by each parent

are placed on the sides of the square

RR Rr

Rr rr

2. we can predict possible outcomes of the traits that then show up in the F1 generation.

R = can roll tongue R r r = cannot roll tongue R

parents are Rr and Rr r

genotype ratio 1RR: 2 Rr: 1rr 25% 50% 25% phenotype ratio 3 can roll : 1 can’t roll

75% roller 25 % non-roller

A test-cross is used to determine if an organism is homozygous or heterozygous dominant for a particular trait. “cross” the organism with a recessive individual. If any of the offspring reveal the recessive trait, then you know that the dominant individual is heterozygous.

rRR

Rr

Rr

rr

11.3 More Genetic Ideas….1. Law of Independent Assortment:

Each gene/chromosome pair lines up along the equator

for metaphase, independently of the next homologous

pair. Alleles, therefore could be sorted into gametes

In different combinations.

Ex: siblings with similar

facial features but totally

different hair color

Diagram of independent assortment

Homologous pairs can line up 2 different ways increasing the gamete combinations

Gametes are all a little different………………

A little Dihybrid Review…………..

parent: Tt Gg what are the possible gamete combos?

________

________

________

________



TG

Tg

tG

tg



TG

Tg

tG

tg

Now try these two!!!

parent: tt Gg parent: Ttgg



TG

Tg

tG

tg



tG Tg

tg tg



________

________

________

________



A. Dihybrid Cross – 2 trait cross Use a punnett square to show all the new offspring phenotypes

Gg Yy 2 traits seed & pod color

GY

Gy

gY

gy

G=green pods Y=yellow seeds…dominant

4 kinds of gametes

4 phenotypes now!

9 green pods yellow seeds

3 green pods green seeds

3 yellow pods yellow seeds

1 yellow pod green seed

New phenotype ratio

9:3:3:1

Remember a cross with only 1 trait (monohybrid)had a phenotype ratio of 3:1

B. Incomplete Dominance The dominant allele isn’t completely dominant over the

recessive allele, so the phenotypes are a blend of the 2 alleles.

Ex: 4 o’clock flower R= red r=white

RR = Red flower

WW = white flower

RW = PINK flower

Hint:

Heterozygous will have a 3rd phenotype that is a blend of other.

Incomplete Dominance ProblemCross 2 pink 4 o’clock flowers

RW x RW

R W

R RR RW

W RW WW

What are the phenotype ratios?

Sooooo pretty

C. Codominance Both alleles for a trait are dominant and are both

expressed!

Ex: cattle: red and white alleles for hair are codom.

RR = reddish hair – reddish cow color

WW= white hair – white cow

RW = red & white hairs on cow – looks pinkish

HRHR = Red HRHW = roan HWHW = white

Hint:

3rd phenotype will be a combination of the other

2 phenotypes show at the same time.

Codominance (together dominant)A roan cow has both red and white hairs,

not pink ones:

D. Multiple Alleles

Genes that are controlled by more than two alleles are said to have multiple alleles.

An individual still has 2 alleles for the trait. However, more than two possible alleles exist.

This causes increased number of phenotypes because there are more allele choices

Labs can be yellow, black, chocolate or white!!!

Examples of multiple allele traits

Humans show multiple alleles in their blood type:

A, B, o

A rabbit's coat color is determined by a single pair of genes that has at least four different allele choices.

Different combinations of alleles result in the colors shown here.

Full color: CC, Ccch, Cch, or CcChinchilla: cchch, cchcch, or cchcHimalayan: chc, or chchAIbino: cc

KEY

C = full color; dominant to all other alleles

cch = chinchilla; partial defect in pigmentation; dominant to ch and c alleles

ch = Himalayan; color in certain parts of the body; dominant to c allele

c = albino; no color; recessive to all other alleles

E. Multigene Traits

Many traits are controlled by more than 1 gene harder to predict and have many phenotypes

* Height, weight, hair color, eye color in humans

* Many of these are also affected by the envir

like temperature.

F.Pedigree Fun!! used to observe patterns of inheritance within generations.

= males = females shaded = recessive trait or

widow’s peak = dominant trait (W)

what is the genotype of dad #1 what is the genotype of mom

#2

1 2 what is the genotype of kid # 3

what is the genotype of kid #4

3 4 5

Pedigree Fun!! used to observe patterns of inheritance within generations.

= males = females shaded = recessive trait or

ww Ww widow’s peak = dominant trait (W) what is the genotype of dad #1

what is the genotype of mom #2

1 2 what is the genotype of kid # 3

what is the genotype of kid #4

3 4 5

ww Ww ww

13.6 Sex Determination

Chromosomes come in matching or homologous pairs except for the sex chromosomes.

1. Sex in humans is determined by the 23rd pair

Come in X or Y

2. X is a full size chromosome that contains

many genes on it.

3. Y is a very very small chromosome that contains

basically no genes

4. Non-sex chromosomes are called autosomes

Get one sex chrom from each parent XX=woman XY=man * the male can pass on an X or a Y the male determines the sex of the offspring * A woman can only pass on an X or X X X X XX XX Y XY XY

Sometimes problems arise with sex chrom andusually results in being sterile (nondisjunction) will discuss later

3. Multiple alleles* In multiple allele traits, there are 2 or more

alleles possible for a trait. an individual will still only have 2 alleles for that trait.

Ex: blood type IA = type A

IB = type B

i = type O

blood type genotypes:

IA IA = A

IA i = A

IB IB = B

IB i = B

IA IB = AB (also codominance)

i i = O

Will have more than 2 phenotypes for a trait

And there are more than 3 genotypes

13.8 Linked Genes Genes on the same chromosome are said to be linked

because when chromosomes are passed on all of their genes are passed on too.

But crossing over can occur during which the chromosomes become tangled and swap sections in the process of being sorted during meiosis. This leads to new allele combinations and so more variation of phenotypes expressed together

The further apart the genes are, the more likely the crossing over.

13.9 X-Linked (or sex-linked) TraitsThe X chromosomes have many genes on

them, which are called X-linked traits. There is no gene for them on the Y chromosome, therefore these traits are connected to the sex of the individual. (remember the Y is shorter)

* Tend to be passed from Mom to son

* Ex: Color-blindness, male pattern baldness,

Duchenne’s muscular dystrophy,hemophilia

Example: Color Blindness

C = see color Mom is XCXc - normal

c = color blind Dad is XcY- colorblind

XC Xc

Xc XCXc XcXc XCXc = normal female

Y XCY XcY XcXc = color blind female

XCY = normal male

XcY = color blind male Recessive trait tends to show more in boys because

they only need one recessive allele to show trait

13.10 Nondisjunction

Failure for the homologous chromosomes to separate properly in the production of sperm/egg so the offspring has an extra or missing chromosome. Affects can be severe or deadly.

* Extra 21st chromosome = Downs syndrome

* Extra 23rd chromosome (XXY) = Klinefelter

syndrome

* Extra or missing 23rd (X) or (XXX) = Turners

syndrome

16.1 – 16.5 : population geneticsPopulation genetics – a study of the genetic

compositions of a populations. * looks at the change of a species in time, not the overall development of new species. microevolution vs macroevolution * gene pool - all the genes of a specific population of organisms. example: in flowers purple = dominant. 100 homoz. purple flowers in a pop.- allele frequencies are 100% P & 0%p 200 P

Hardy-Weinberg Principle/Equation

a mathematical tool used to measures allele frequencies and changes in a population of organisms.

Principle:

the distribution of dom and rec alleles in a pop remain constant from one generation to the next if:

1. no mutation 2. no migration

3. random mating 4. large population

5. no natural selection

Equation: p2 + 2pq + q2 = 1

50 people = 100 alleles either T, t

p= frequency of T in a pop - decimal

q=frequency of t in a pop. Decimal

p+q = 1 this represents all the alleles in

the pop for this trait

if there are 50 people = 100 alleles (T, t)

40 T alleles = 40 % = .4 = p

60 t alleles = 60% = .6 = q

p2 + 2pq + q2 = 1

this equation shows the possible gamete combinations using the dom/rec alleles.

Plug in the values for p and q to get the

homozygous dominant TT = p2

heterozygous dominant Tt = 2 pq

recessive tt = q2

p = .4 q = .6 homo dom = .42 16%

hetero dom = 2(.4)(.6) 48%

recessive = .62 36%

lutionIf the p & q values change, indicates that

the gene pool is changing. …..evolution! What causes a gene pool shift in a population?

1. Natural selection – environment forces organisms in a pop with adaptations less suited for survival to die out. Peppered moth & sickle cell

2. Gene Flow - the effect of migration of organisms between gene pools.

3. Mutations – spontaneous change in DNA. Most are bad or neither. Good ones can be selected for, and increase in the gene pool over time.

4. Genetic Drift. Random change in allele frequencies. A substantial effect in small population. A change in 10 vs a change in 1000 organisms shows larger shift.

Genetic Drift can lead to :

1. Founder effect: genetic drift that influences new populations. The new population may have allele frequencies that are different from the source…by chance. New pop is small so changes will be more dramatic

2. Bottleneck effect – large populations change because the population numbers were reduced and they then inbreed. Decreases the variation in the population…….gene pool change.

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Chapter 11: Genetics!!!!!!! 11.1 ****************************************************** Genetics : the study of heredity – how traits get passed from one