GENETICSChapter 11

1. EXPLAIN WHY MENDEL’S EXPERIMENTS WERE AN IMPORTANT DISCOVERY IN SCIENCE.

Inheritance… What is that?

Something that gets passed on from one generation to the next In science, it is going to be our DNA

Every living thing has a set of characteristics it inherited from their parents

Genetics: The study of heredity

GREGOR MENDEL (1822-1884)

The Father of Genetics

Worked on Pea Plants

In 1866, his papers were 1st published but weren’t found until the 1900’s.

WHY PEA PLANTS?

Male and female parts are on one flower. Fertilization: When the sperm combines with

the egg

Pea plants are self-pollinating Sperm and egg come from same flower, meaning

identical kids These are called true-breeding: offspring are

identical to parents

Contained a wide variety of variation (7 traits)

HIS EXPERIMENT

Had plants self-pollinate to get true-bred parents This is known as the parent generation(P)

He then mated two plants that had opposite traits (Ex: Short plant with a tall plant) This is known as the filial generation (F1)

He then let the offspring created self-pollinate This is the F2 generation Counted the number of each trait that is

produced

HIS EXPERIMENTS

Parent generation (purebreds)

F1 generation (hybrids)

F2 generation

(3 dominant:

1 recessive)

EXAMPLE:

Parents: 1 yellow pea plant, 1 green pea plant

F1: All yellow

F2: 3 yellow:1 green

HIS RESULTS

What would you expect to happen when we cross a pure short plant with a pure tall plant?

His results: All of the offspring of F1 had the characteristic of one parent His experiment showed they all had the tall

characteristics.

1st Conclusion of his experiment Inheritance is passed from one generation

to another through genes

2. DESCRIBE THE FOLLOWING TERMS AND HOW THEY RELATED TO GENETICS

Trait: a specific characteristic that varies from one individual to another

Crosses: Mating between parents

Hybrid: Offspring of crosses between parents with different traits

Genes: Chemical factors that determine traits

Alleles: Different forms of the gene

3. SUMMARIZE THE PRINCIPLES OF DOMINANCE AND SEGREGATION.

Principle of Dominance: Some alleles are dominant while others are recessive

Dominant allele: Always is the trait that is shown We show this as having a capital letter

Recessive allele: Will only show the trait if the dominant is not present We show this as having a lowercase letter

DOMINANCE AND RECESSIVE

Homozygous: Organisms that have two identical alleles for a particular trait Can be dominant or recessive Also known as true-breeds Example: TT or tt

Heterozygous: Organisms that have two different alleles Know as hybrids Example: Tt

DID THE RECESSIVE ALLELE DISAPPEAR?

To answer, Mendel allowed the F1 generation to self-pollinate

Results: Discovered that the recessive allele reappeared!

He then said that the alleles must separate at some point during reproduction, this is known as Segregation

THE RETURN OF GAMETES!

As in meiosis, only 1 set of chromosomes ends in the final gamete

So each parent produces a gamete that has only one allele for a trait.

The gametes then combine in fertilization so that 2 alleles are now found in the offspring and a full trait is expressed!

T Tt t

TT

Tt Tt tt

4. SOLVE GENETIC PROBLEMS BY USING PUNNETT SQUARES, MONOHYBRID CROSSES, AND PROBABILITY.

When Mendel crossed the F1 parents, he always got the same results ¾ of them were tall plants and ¼ were short

plants

This can be explained by probability: likelihood that a particular event will occur

To understand this lets look at a brief activity.

This applies to genetics b/c the segregation of alleles is random like a coin flip.

PUNNETT SQUARES

In order to determine the genetics of an organism we can draw a diagram called a Punnett square.

It is used to show the possible genetic variations in the offspring between two parents

F1 Parent

F1

Pare

nt

Alleles of parents segregated

F2

O

ffsp

ring

T T

t Tt Tt

t Tt Tttt

TTExample

T t

T t

5. ANALYZE PUNNETT SQUARES TO DETERMINE THE OUTCOME OF PARENTAL CROSSES.

In our example, all of the tall plants have the same phenotype

Phenotype: Physical characteristics (Uses Traits) Ex: Tall, Short, Purple, White

However, they do not all have the same genotype

Genotype: Genetic makeup (Uses the “letters”) 1/3 of the tall plants are TT 2/3 of the tall plants are Tt

EXAMPLE: (3 GENOTYPES): YY Yy

yy Yellow yellow

green

(only 2 phenotypes)

6. CALCULATE GENOTYPE AND PHENOTYPE RATIOS WITH MONOHYBRID.

Overall, there are 3 tall plants for every 1 short plant This is because of the law of dominance: Even though

½ the plants have a recessive allele (Tt), it expresses tallness

We can write all of these as a ratio

The ratio is set up as dominant trait:recessive trait So the ratio would be 3:1

This verifies Mendel’s thoughts that alleles segregate because all traits produced a 3:1 ratio

WHAT ABOUT GENOTYPE?

Genotypes are a little bit different How many combinations do we have? 3 Different genotypes

The order they are going to appear in are Homozygous Dominant: Heterozygous: Homozygous Recessive

For the genotypes it would be GG: Gg: gg So the ratio for pea plants would be 1:2:1

7. EXPLAIN THE PRINCIPLE OF INDEPENDENT ASSORTMENT AND ANALYZE DIHYBRID CROSSES.

Mendel wondered the same thing so he took a purebred yellow, round seed plant (RRYY) and mated it with a green, wrinkled seed plant (rryy).

Every gamete produced has one shape gene and one color gene

The Punnett square for the following problem looked like this…

This generation was all heterozygous for round, yellow seeds (RrYy).

SO WHAT HAPPENS WHEN WE MATE TWO RRYY TOGETHER?

Two possible ways exist on how the alleles could sort out in order to make the gametes.

1.Do the two dominant alleles/recessive alleles always stay together?

2.Do they segregate independently, which means is it completely random.

HIS RESULTS AND WHAT THEY MEAN

The F2 plants produced 556 seeds Out of the 556, 315 seeds were dominant for both

traits Out of the 556, 32 were recessive for both traits There was an unanswered 209 seeds that had

phenotypes not previously seen… Round green seeds & Yellow wrinkled seeds

This lead to the law of independent assortment

Law of independent assortment: genes do not influence each other’s inheritance

You inherit one gene and then the other.

THURSDAY START HERE!!!!

BIG IDEA: Every GENE has 2 alleles.

The most common type of hat, gene, anything is considered DOMINANT

Our example: Baseball Hat (Symbolized by H)

The least common or not seen often, is considered RECESSIVE Our example: Floppy Hat (Symbolized by h)

If we pair up the alleles, how many different combinations can we get? 3 What would they be: HH, Hh, hh

First combination will be HH, which is called Homozygous Homo- SameZygous- Zygote is a certain type

A zygote is a Fertilized Egg

It is a DIPLOID cell which means it has 46 chromosomes

We have 2 chromosomes in a pair and 2 alleles in a gene

Second combination will be Hh, which is called Heterozygous Hetero- Different Zygous- Zygote is a certain

type

Third combination will be hh, which is called Homozygous

How could we tell them apart? By Dominant and Recessive

HH: Homozygous Dominant hh: Homozygous Recessive

The actual combination of letters that makes up the gene is called a GENOTYPE Geno: Gene Type: Symbol

A word used to represent our characteristics in science is called a PHENOTYPE Pheno: Showing, Display Type: Symbol

Independent Assortment: one Gene does not affect another Gene

SEGREGATION: HOW ALLELES SPLIT APART DURING MEIOSIS

Genes

Parental:

Parental Gametes:

Generation 1:

Chromosomes

RR rr

Only R only r

Rr

8. DEMONSTRATE THE PRINCIPLE OF SEGREGATION AND INDEPENDENT ASSORTMENT IN TERMS OF CHROMOSOMES AND MEIOSIS.

CHROMOSOME THEORY OF HEREDITY

material of inheritance is carried by genes on chromosomes.

1903—Sutton (American)

9. EXPLAIN THE OTHER PATTERNS OF DOMINANCE: INCOMPLETE, CO-DOMINANCE, POLYGENIC, MULTIPLE ALLELES, SEX-LINKED.

Incomplete Dominance: Heterozygote has a phenotype intermediate to the two homozygote types.

Ex: Snapdragon color RR= Red Rr= Pink rr= White

Phenotype ratio is similar to genotype 1:2:1

CO-DOMINANCE

Both alleles of a Heterozygote are expressed

Ex: Cows

RR= Brown Rr= Roan (Brown with White spots) rr= White

MULTIPLE ALLELES

More than 2 alleles exist for some gene Means more phenotypes and genotypes to deal

with.

Ex: Coat color in rabbits

C+- agouti Cch- chinchilla Ch- Himalayan C- albino

C+ > Cch > Ch > C

MULTIPLE ALLELES

Ex: Blood Types IA – A Antigen IB- B Antigen i= no Antigen

Antigen- Proteins that mark you as being you.

Phenotypes GenotypesA IAIA, IAiB IBIB, IBiAB IAIB

O ii

POLYGENIC TRAITS

Traits that are controlled by two or more genes

Polygenic traits produce a lot of phenotypes

One example of this is with skin, eye, and hair color

More than four different genes control this trait and that is why we have all the different ranges of color of human skin

ROLE OF THE X AND Y CHROMOSOMES

Females – XX Males – XY

Sperm determines sex Only true of Fruit flies and Humans Region on Y chromosome that determines sex=

SRY

Other organisms have different rules that apply

SEX-LINKED

Gene expressed usually in one sex

1. Hemophilia – failure of blood to clot

2. Color blindness- Can’t see certain colors

3. Muscular Dystrophy – wasting away muscles

10. EXPLAIN WHAT A PEDIGREE IS AND WHY ONE WOULD USE IT.

Pedigree: A CHART THAT SHOWS HOW A TRAIT AND

THE GENES THAT CONTROL IT ARE INHERITED.

PEDIGREES: STEPS ON HOW TO READ THEM

1. Sex-Linked? Usually seen only in males because they have 1

X If not, should be = distribution between sexes

2. Dominant or Recessive? Dom- every offspring that has it should have

parent Rec- parent is a hetero, normal but a carrier

PEDIGREES

SYMBOLS FOR THE SEXES:

PARENTS – CONNECTED BY A HORIZONTAL LINE…

A VERTICAL LINE DOWN FROM THE PARENTS = CHILDREN

CHILDREN ARE SHADED… IF THEY ARE HOMOZYGOUS RECESSIVE

CARRIERS (TRAIT NOT EXPRESSED) ARE HALF SHADEDHETEROZYGOUS

GENERATIONS GET ROMAN NUMERALS, INDIVIDUALS GET NUMBERS

11. ANALYZE A PEDIGREE FOR GENETIC TRAITS.

http://www.zerobio.com/drag_gr11/pedigree/pedigree_overview.htm