What is Genetics

HeredityThe passing on of characteristics from parents to offspring

TraitsCharacteristics that are inherited

GeneticsThe branch of biology that studies heredity

Gregor Mendel

•Before Mendel what did people think about heredity?

•Blending hypothesis: offspring were a blend of traits from their parents. Ex. Tall mom + short mom = medium child

•Austrian monk that first developed the study of

genetics therefore, Mendel is the father of genetics•Experimented with pea plants to discover the general laws of genetics

Why Pea Plants???

Pea plants are: small, matures quickly, produces many offspring.

Male and female parts on same flower

Several characters exist in 2 clearly different forms

both male and female reproductive organsGametes: male and female sex

cellsPollination: transfer of pollen (male gametes) from a male reproductive organ to a female reproductive organ in a plant

Mendel allowed pollination to occur within the same flower or

between different flowers for his

experiments (cross-pollination)

Fertilization of gametes gives a

seed.

Mendel

Mendel’s Work

Mendel studied 7 different traits in pea plants.

A trait is a specific characteristic that varies from one individual to another.

Mendel used true-breeding plants which means if they were left to breed with themselves they would produce offspring identical to themselves.

•*Monohybrid crosses: study one trait at a time

P1 = Parental generationF1 = First filial generationF2 = Second filial generation

More on Mendel’s Work… The rule of unit factors

2 separate heritable factors One comes from _________, the other comes

from_________ When gamete forms it receives only 1

version During fertilization, the offspring gets both

copies of the trait from each gamete

A single gene can exist in different forms called alleles

Example: ________________________________are alleles for the eye color gene

Blue, brown, and green

momdad

Mendel’s law of segregation

Every organism has 2 alleles of each gene

When gametes are made, each gamete receives only one of these alleles

During fertilization, the offspring will receive one allele for each gene from each parent

The Rule of Dominance

•Dominant allele: “stronger” allele that always shows up when it is present

*Represented by a capital letter; ____ is for brown eyes

•Recessive trait: “weaker” trait that shows up only when the dominant allele is not present

*Represented by a lowercase letter; ___is for blue eyes

B

b

Laws of Inheritance

Phenotypes and genotypes Phenotype: the physical

appearance of an organism Ex. Brown eyes

Genotype: genetic makeup of an organism Ex. Alleles for brown eye color are

____________BB, Bb

Phenotype and genotype cont…

BB

bb

Bb

Heterozygous: 2 alleles for a trait are not the same

Ex. ____is heterozygous

Homozygous: 2 alleles for a trait are the same Ex. ______is homozygous dominant for

brown eyes, ______is homozygous recessive for blue

eyes

8.4 Pre-view Qs: Define phenotype and genotype What is another word for a trait Usually, 1 gene = ? Alleles What type of letter would you use if a character

is dominant , what type for a recessive

Trait:

Phenotype Dominant/recessive Genotype

Allele # 1

Allele # 2

Trait:

Phenotype Dominant/recessive

Genotype

Allele # 1

Allele # 2

Probability & Genetics

Probability is the likelihood that an event will happen.

The principle of probability can be used to predict the outcomes of genetic crosses.

Punnet Squares

:Shorthand way of determining the

probability of having a certain type of

offspring if you know the parents’

genotypes

Naked Punnett Square

How to use Punnett Squares1. Choose a letter to represent the

alleles in the cross.2. Write the genotypes of the parents.3. Determine the possible gametes

(reproductive cells) that the parent can produce.

4. Enter the possible gamete at the top and side of the Punnett square.

How to use punnet squares….5. Complete the Punnett square by

writing the alleles from the gametes in the appropriate boxes.

6. Determine the phenotypes of the offspring.

7. Using the results of step 5 and 6 write down the genotypic and phenotypic ratios.

Mendels’ experiment and punnet squares

T: tall pea plant __: short pea plant

Possible phenotypes:______tall______short

t

75 %

25 %

Mendels’ experiment and punnet squares cont…

Possible genotypes:

25% TT50% Tt25% tt

Test cross: figuring out unknown genotypes

http://www.castlefordschools.com/kent/07-08%20lessons/Lessons/Biology%20Lessons/chapter%208/video/60163.html

Bell work: 3/31/09 TUE

1. Some diseases are considered rare because they are recessive: if the child has this recessive disease and the parents are healthy, what are the genotypes of the parents.

2. Make a punnet square to show the probability of having a child with the rare recessive disease.

Inheritance of traits: Genes can be autosomal or sex-

linked. Autosomal- on regular chromosomes

Chromosome #s____________ trait will

1-22appear in both sexes equally.

Sex-linked-

Most of these genes are carried on X chromosome and are recessive.

Therefore,

affects mostly males Because they only need

Inheritance of traits:

located only on X or Y chromosome.

women need 2 copies to get the disease

1 copy of the gene

Example of conditions that are caused by a sex-linked trait:

Color blindness-

Hemophilia-

Both are carried on the x chromosome, therefore women are mostly carriers and men get the disease.

Can’t see certain colors well

Bleeding disease

Pedigree

: family tree that shows how a trait is passed on generation after generation

http://www.castlefordschools.com/kent/07-08%20lessons/Lessons/Biology%20Lessons/chapter%208/video/60210.html

1.The pedigree below is studying the incidence of blonde hair in a family. In humans, dark hair (B) is dominant to blonde hair (b). In this case, individuals who are shaded in are homozygous recessive. Individuals who have clear circles and squares have at least one dominant gene.

What are the genotypes of persons A

through F above?

Explanation: Person B is blonde, because they are shaded in.

They are thus homozygous recessive (hh). Persons C through F must have at least dominant

allele (H). Without more information, this would make them HH or Hh.

Person B can only provide the h alleles to its eggs, so persons C-F must be heterozygous (Hh).

Without more information, Person A who is dominant must be HH or Hh.

Mendel’s Principles

The inheritance of biological characteristics are determined by genes.

For two or more forms of a gene, dominance and recessive forms may exist.

Most sexually reproductive organisms have two sets of genes that separate during gamete formation.

Alleles segregate independently.

Blood Typing/ Multiple Alleles   A number of human traits are the result of

more than 2 types of alleles. Such traits are said to have multiple alleles for that trait.

Blood type is an example of a common multiple allele trait. There are 3 different alleles for blood type, (A, B, & O). A is dominant to O. B is also dominant to O. A and B are both codominant.

Beyond Dominant and RecessiveB. Incomplete

Dominance – One allele is not completely dominant over the other.

Ex. White flower crosses with a red = pink flower.

Other inheritance patterns:

Polygenic Multiple alleles Codominance Incomplete dominance

Chapter 11.3 Notes: Complex patterns of heredity

A. Polygenic traits – Several genes control the trait.

ex. Skin color or height in humans.

C. Multiple Alleles – More than two alleles control the phenotype.

Ex. 1: Coat color of rabbits.

Ex. 2: blood types

III. Characters influenced by the environment.

Skin color is influenced by genes and exposure to sun

Fur color of Siamese cats influenced by temperatureExtremities are darker

D. Codominance –

Both alleles contribute to the phenotype.

Ex.1: Red cow X White Cow = Roan Cow.

Ex. 2: blood types

II. Blood types are controlled by multiple alleles and co-dominance.

http://nobelprize.org/educational_games/medicine/landsteiner/readmore.html

Antibodies attach to stuff they recognize!!!

A is dominant to O. B is also dominant to O. A and B are both co-dominant.

There are 3 different alleles for blood type: (A, B, & O).

Possible genotypes of blood types:

How to make each blood type:

Type A

Type B

Type AB

Type O

With Rh:

w/out Rh:

With Rh:

w/out Rh:

With Rh:

w/out Rh:

With Rh:

w/out Rh:

Pre-lab: TESTING blood phenotypes

Clumps with A antibody

Clumps with B antibody

Clumps with Rh antibody

Blood type (A, B, AB, O) + / -

yes yes no

yes no yes

no no no

no yes yes

Blood type examples: Who is my Baby’s Father????

Genetic disorders: are caused by mutations, which are changes in our DNA (genes).

Sickle cell anemia

Autosomal Recessive disorder

Causes abnormal hemoglobin & results in poor blood circulation

Cystic Fibrosis

Cystic Fibrosis

Autosomal Recessive disorder

Defective ion channel that clogs major organs with mucus

Hemophilia

Hemophilia

Sex-linked recessive

Defective clotting factor that decreases bloods’ ability to clot.

Huntington’s disease

Huntington’s disease

Autosomal dominant

Brain cell death that causes brain illness and eventual early death

A. Treating genetic disorders

Gene therapy:Replacing bad genes with

copies of healthy ones.

Practice Qs incomplete dominance Sample Questions I

1. Predict the phenotypic ratios of offspring when a homozygous white cow is crossed with a roan bull. 2. What should the genotypes & phenotypes for parent cattle be if a farmer wanted only cattle with red fur?

3. A cross between a black cat & a tan cat produces a tabby pattern (black & tan fur spots together). a) What pattern of inheritence does this illustrate? b) What percent of kittens would have tan fur if a tan cat is crossed with a black cat?

Questions II1. A cross between a blue blahblah bird & a white blahblah bird produces offspring that are silver.  The color of blahblah birds is determined by just two alleles. a) What are the genotypes of the parent blahblah birds in the original cross? b) What is/are the genotype(s) of the silver offspring? c) What would be the phenotypic ratios of offspring produced by two silver blahblah birds?

2.  The color of fruit for plant "X" is determined by two alleles.  When two plants with orange fruits are crossed the following phenotypic ratios are present in the offspring: 25% red fruit, 50% orange fruit, 25% yellow fruit.  What are the genotypes of the parent

orange-fruited plants?

ABO blood groups:1. If 2 parents with blood types (homozygous for type B and heterozygous for type A) have children, what would be the phenotypic ratios of their possible children?

2. Can type A and a type B parents have a child that is type O? show punnet square.

IncOMpleTe & COdominANce In many ways Gregor Mendel was quite lucky in

discovering his genetic laws.  He happened to use pea plants, which happened to have a number of easily observable traits that were determined by just two alleles.  And for the traits he studied in his peas, one allele happened to be dominant for the trait & the other was a recessive form.  Things aren't always so clear-cut & "simple" in the world of genetics, but luckily for Mendel (& the science world) he happened to work with an organism whose genetic make-up was fairly clear-cut & simple. INCOMPLETE DOMINANCE

If Mendel were given a mommy black mouse & a daddy white mouse & asked what their offspring would look like, he would've said that a certain percent would be black & the others would be white.  He would never have even considered that a white mouse & a black mouse could produce a GREY mouse!  For Mendel, the phenotype of the offspring from parents with different phenotypes always resembled the phenotype of at least one of the parents.  In other words, Mendel was unaware of the phenomenon of INCOMPLETE DOMINANCE.   I remember Incomplete Dominance in the form of an example like so:

RED Flower x WHITE Flower ---> PINK Flower   With incomplete dominance, a cross between

organisms with two different phenotypes produces offspring with a third phenotype that is a blending of the parental traits. It's like mixing paints, red + white will make pink.  Red doesn't totally block (dominate) the pink, instead there is incomplete dominance, and we end up with something in-between.

We can still use the Punnett Square to solve problems involving incomplete dominance.  The only difference is that instead of using a capital letter for the dominant trait & a lowercase letter for the recessive trait, the letters we use are both going to be capital (because neither trait dominates the other).  So the cross I used up above would look like this:

 

R = allele for red flowers W = allele for white flowers

red x white ---> pink RR x WW ---> 100% RW

CODOMINANCE First let me point out that the meaning of the prefix "co-" is "together".

Cooperate = work together.  Coexist = exist together.  Cohabitat = habitat together. Have we got it together?

The genetic gist to codominance is pretty much the same as incomplete dominance.  A hybrid organism shows a third phenotype --- not the usual "dominant" one & not the "recessive" one ... but a third, different phenotype.  With incomplete dominance we get a blending of the dominant & recessive traits so that the third phenotype is something in the middle (red x white = pink).

In COdominance, the "recessive" & "dominant" traits appear together in the phenotype of hybrid organisms.   I remember codominance in the form of an example like so:

red x white ---> red & white spotted   With codominance, a cross between organisms with two different phenotypes

produces offspring with a third phenotype in which both of the parental traits appear together. When it comes to punnett squares & symbols, it's the same as incomplete dominance.  Use capital letters for the allele symbols.  My example cross from above would look like so:

I have seen some texts use letters & superscripts when dealing with codominance, which is nice, but not necessary.  Just in case your text uses it, it looks like this: We'll use "F" for the flower color allele. FR = allele for red flowers FW = allele for white flowers red x white -------> red & white spotted flowers FRFR  x FWFW ----> 100% FRFW

The symbols you choose to use don't matter, in the end you end up with hybrid organisms, and rather than one trait (allele) dominating the other, both traits appear together in the phenotype.  Wa-la, codominance.

A very very very very very common phenotype used in questions about codominance is roan fur in cattle.  Cattle can be red (RR = all red hairs), white (WW = all white hairs), or roan (RW = red & white hairs together).  A good example of codominance. Another example of codominance is human blood type AB, in which two types of protein ("A" & "B") appear together on the surface of blood cells.

Co-dominance and incomplete dominance practice Qs

Sample Questions I 1. Predict the phenotypic ratios of offspring when a homozygous white cow is crossed with a roan bull.

2. What should the genotypes & phenotypes for parent cattle be if a farmer wanted only cattle with red fur?

3. A cross between a black cat & a tan cat produces a tabby pattern (black & tan fur spots together). a) What pattern of inheritence does this illustrate? b) What percent of kittens would have tan fur if a tan cat is crossed with a black cat?

Questions II1. A cross between a black blahblah bird & a white blahblah bird produces offspring that are gray.  The color of blahblah birds is determined by just two alleles. a) What are the genotypes of the parent blahblah birds in the original cross? b) What is/are the genotype(s) of the gray offspring? c) What would be the phenotypic ratios of offspring produced by two gray blahblah birds?2.  The color of fruit for plant "X" is determined by two alleles.  When two plants with orange fruits are crossed the following phenotypic ratios are present in the offspring: 25% red fruit, 50% orange fruit, 25% yellow fruit.   What are the genotypes of the parent orange-fruited plants?

ABO blood groups:1. If 2 parents with blood types (type BB and A0) have children, what would be the phenotypic ratios of their possible children?

2. Can type A and a type B parents have a child that is type O? show punnet square.

A Red cow is crossed with a White cow and all the offspring turn out Roan. a. write the genotypes of the parents:_______________ b. Do a punnet square to show the cross between the Red and White cow. c. write the genotype(s) of the offspring along with a

probability:____________

. A cross between a Black blahblah bird & a White blahblah bird produces offspring that are Grey.  a) What are the genotypes of the parent blahblah birds in the original cross? __________ b.)b) What is/are the genotype(s) of the silver offspring? ____________________ c) What would be the phenotypic ratios of offspring produced by two grey blahblah birds?

Show punnet square

Joe has blood Type A and Diane has blood type B, they have a son who is blood type O. Did Diane cheat on Joe? Yes or No

a. Do a punnet square to show how Diane and Joes’ blood type might or might not result in a type O baby.

b. Write down the probability of having a type O baby.

Examples