The Scientific study of heredity

1850’s; 21 y.o. Scientist +

Mathematician Paper: 1865 “Father of Modern

Genetics”

Mendelian Genetics

Easy to grow Matures quickly Produces

generations quickly

Large # offspring Cross and self

pollination *Each trait on a

separate gene

Mendel’s crosses and results

The Perfect Flower

Self Pollination: has both male and female parts

Removal of Stamens Transfer of pollen from

a white flower to the purple stigma (P1- parents)

Carpel/peapod/seeds Plant the seeds (F1- First Generation)

First Filial

Controlled Cross-Pollination

F1 x F1

Mendell’s Experiments

Parent generation = P Offspring of P generation = F1 Offspring of F1 generation = F2

Cross a homozygous dominant Tall flowerwith a homozygous recessive short flower. Give the F1 genotype and phenotype

percents.

Tall = TT, short = tt

Generations

Phenotype – the physical appearance of an organism. Determined by it’s alleles (maternal/paternal) “Photo”

Genotype – the genetic makeup of an organism “Genes”

The many different alleles that an organism can possess: BB, Bb or bb

(Often use the 1st letter of the dominant trait)

Genetics Terminology

Homozygous – an individual who has the same alleles for a trait.

Ex. 2 genes for cystic fibrosis(CC = homozygous dominant or cc = homozygous recessive)

Heterozygous – an individual who has different alleles for a trait. Ex. One gene for cystic fibrosis, one for normal (Cc)

Results Statistics/Ratios

Conclusions◦ Dominant/Recessive

4 Principles Notesheet

Mendel’s crosses and results

A trait is controlled by factors (genes) that occur in pairs

1865 Paper Published by Gregor Mendel based on his research with garden peas

1. Principle of Unit Characters:

One gene in a pair can mask or hide the expression of the other gene(dominant vs recessive)

Dominant allele: When only ONE of the alleles affects the trait. (Use a CAPITAL letter)

Recessive allele: the allele that is NOT expressed if there is a dominant allele present. (Use a small letter).

2. Principle of Dominance:

A pair of genes (alleles) separate during the formation of sex cells (gametes)

(Later learned that gametes are formed during meiosis…come together later to supply the alleles that form a trait)

3. Principle of Segregation:

The inheritance of one gene does not affect or depend on the inheritance of another gene

*Mendel was looking at traits on different chromosomes….. *Modification: Linked genes are inherited together on a chromosome) **EXCEPTION: crossing over.

4. Principle of Independent Assortment:

Handout: DOMINANT vs RECESSIVE Dark Hair Nonred hair Dark Skin Skin Pigment Brown eyes Near or far sighted Astigmatism Normal Hearing

Inherited Traits in Humans

Cross … Punnett Square* (TT x tt) *Represents ONE offspring- 4 possible genetic outcomes…

Phenotype:

%

% Ratio:

Genotype:

% Hom. Dom.

% Het. Dom.

% Hom. Rec.

Ratio:

*HW: Key, Cross, Punnett, Answer

HW: #1-5,7

Genetics Online Practice Problems

More Online Genetics Problems

Neither gene dominates Blending of traits Notation: 2 different Capitol Letters

Example: White Flowers x Red Flowers produce PINK flowers

WW x RR = RW white red pink

Incomplete Dominance

(HW #8-9)

BOTH genes are expressedNotation: 2 different Capitol Letters

Example: “ROAN” cows/horsesWhite/Red hair dispersed evenly…looks pink

P176 L1 text… (HW #7)

Codominance

(HW #7)

Example of Codominance:

‘Pink’ Roan HorseRR= redWW =whiteRW= Roan

(RR, R’R’,R’R)

Genes on the X chromosome Usually recessive; different chances male/female Ex: Color-blindness, hemophilia

NOTATION:How males and females inherit:X Y = Normal vision maleXc Y = Color blind male*More in males-50/50

X X = Normal vision femaleX Xc = Female color blind carrier Xc Xc = Color blind female

(or written with hashmarks X ’ X ’)

Sex-linked inheritance (on X or Y)*We will look at only X-linked traits

Sex-Linked Recessive males get their X from their mother

fathers pass their X to daughters only

females express the trait only if they get a copy from both parents.

recessive in females; females can be ‘carriers’

ALWAYS expressed in males if present; can NEVER be carriers of X-linked traits

(#20-24)

Sex-Linked Inheritance Problem Sets

“X” linked Problem #20:

White eyed fruit flies are the result of an X-linked recessive gene. Show the results from a cross between a red-eyed male and a white-eyed female Drosophila.

Indicate the results of each sex separately for genotype and phenotype.

Key: Cross: XR Y x XrXr

or X Y x X’X’

Answer

*Phenotype:“Carrier Females” are considered “Unaffected/Normal”

Multiple Alleles

There are more than 2 alleles in the gene pool BUT an individual inherits only TWO (one allele from mom, and one from dad)

When there are 4 or more possible phenotypes for a particular trait.

Example: Blood Typing: Inherited A,B,O Six GENOTYPE possibilities ?? = FOUR different bloodtypes: ??

(#10-12)

Blood Typing

3 different possible alleles for the blood type gene:

Co-dominant A or B, or recessive O

4 possible Phenotypes: Genotypes: Type A IAIA, IAIi (AA,AO) Type B IBIB, IBIi (BB,BO) Type AB IAIB (AB) Type O IiIi (OO)

(#10-12)

Worksheet #11 If a type O person

marries a type AB person, what blood type could occur in their children? Remember, type O is recessive to both A and B

Key

Cross i i x IAIB

Answer

(#10-12)

The factors for different traits are sorted into the gametes independent of each other.

S = Smooth pea

Y = Yellow Color 1. Determine all possible combinations of alleles in the gametes for each parent.

DiHybrid Cross: Independent Assortment

(#13-19)

Dihybrid crosses

1. To set the Crosses: The FOIL Method:First Outer, First Inner, Last Inner, Last

Outer2. Fill in, matching the traits back up again

3. Typical Question: What is the Phenotypic Ratio? ie: Number that will be bothTall and Yellow, etcStart with the FIRST box and count (add up to 16)Marking boxes as you go, choose the NEXT Phenotype and add those that match, until all boxes accounted for; final ratio

(#13-19)

Involves TWO traits Ex: tall/short, green/yellow

Dihybrid Crosses

DiHybrid Crosses

Dihybrid Cross Problem Sets

Genetics Probability Mendelian Cross:

In Pea Plants, the flower color Purple is dominant to white.

If two heterozygous plants are crossed, what % of the offspring will be white?

PROBABILITY: Same set-up: what is the probability that the offspring will be homozygous recessive?

Probability that an egg from the F1 (Pp) will receive a p allele = 1/2.

Probability that a sperm from the F1 will receive a p allele = 1/2.

The overall probability that two recessive alleles will unite, one from the egg and  one from the sperm, simultaneously, at fertilization is: 1/2 X 1/2 = 1/4.

Rules of Multiplication n and Addition 10.35

Pedigree charts follow a genetic mutation/disease through several generations of a family.

You can determine what chance offspring has of having a disease based on family history and Punnett Square.

The main diseases that are tracked this way are:◦ Tay-sachs◦ Huntingtons ◦ Colorblindness◦ Hemophilia◦ Cystic fibrosis

Pedigree Charts

Basic Symbols

Pedigree:DominantInheritance

1.Every affected individual has at least one affected parent

3. Two affected MAY have unaffected children

Pedigree:recessivedisorder1. An individual who is affected may have parents who are unaffected.2. ALL children of 2 affected parents are affected

Sample Pedigree:Inheritance

1.Dominant (has the trait, one parent has the trait)or recessive trait?

If Dominant….Know the FIRST allele is a Large letter, so can fill that in….

If recessive, must be two small letters

*Back of Problems

Autosomal Recessive (nn) Dominant or recessive trait?

Autosomal Dominant (D_)

Dominant or recessive trait?

Test Cross

*Dominant =Gray, Normal wings=

Bb VvOr

b+bvg+vgWhere + is dominant

Two- PointTest Cross

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+

% Recombination

• Calculating the frequency of crossing-over reveals the linear order of linked genes on a chromosome.

• Total Recombinant/Total # Offspring X 100

• = 11% where 1% recombination = 1 map unit

So the loci are 11 map units apart on the same chromosome (11 centimorgans)

The closer two genes are to each other, the less likely crossing over will occur; genes are linked.