GENETICS

GENETICS

Gregor Mendel considered the father of genetics

Studied Pea Plants to learn about the transmission of traits from parents to offspring

Trait = Genetically determined characteristic

Characteristic = a heritable feature ( fur/hair color, eye color, height ect..)

Mendelian Genetics Mendel started with plants that were

True-Bred (when self pollinate) True-bred =all offspring of same

variety Hybridization – Cross-Pollinated

(crossing of 2 different true-breds) P generation (parents) F1 generation (first filial generation)

Leading to the Law of Segregation Alleles: Alternative versions of genes that

account for variations in inherited characteristics For each character, an organism

inherits 2 alleles, one from each parent Dominant – the allele that is fully

expressed when carried by only one of a pair of homologous chromosomes

( designated by a capital letter P)

Recessive- an allele that is expressed only when two recessive alleles for the same characteristic are inherited

Designated by a lower case p

The alleles for each character segregate (separate) during gamete production (meiosis).

Genetic vocabulary……. Punnett square: predicts the

results of a genetic cross between individuals of known genotype

Homozygous: pair of identical alleles for a character

Heterozygous: two different alleles for a gene

Phenotype: an organism’s traits, what is physically shown

Genotype: an organism’s genetic makeup

Testcross: breeding of a recessive homozygote X dominate phenotype (but unknown genotype)

Codominance-both alleles for a gene are expressed in a heterozygous offspring; neither allele is dominant or recessive and there is no blending; Ex. Blood Types

Monohybrid cross-a genetic cross in which only one characteristic is trackedEx; Fur Color in guinea pigs

Di hybrid cross- a genetic cross in which two different characteristics are trackedEx. Fur color and length of fur in guinea pigs

Probability is the likelihood that a particular event will occur

It can be written as a:

Fraction 1/4

Percent 25%

Ratio 1:3

If we flip a coin we have a two outcomes Heads or tails

We can express this as50%½1:1

Alleles segregate randomly just like a coin flip. . . So can use probability to predict outcomes of genetic crosses.

Used to predict the probability of offspring.

Show how both parents’ alleles might combine in their offspring.

Punnett Squares

Start by drawing your punnett square.Place the genotype of the parents alleles above and beside the boxFill in the box by carrying the letters

down and across

B b

B

B

rabbit heterozygous forBlack fur (dominant B)Bb

Rabbit homozygous forBlack fur - BB

Did you get it?

B b

B

B

BB

BB

Bb

Bb

Now Practice with Bikini Bottom Genetics Page One!

Agenda

Go over Genetic Cross Worksheet Introduce:Incomplete Dominance and Dihybrid

Crosses Complete Genetic Cross Worksheet #2 and go

over Notes: Dihybrid Cross Worksheet

How is the phenotypic outcome in a incomplete dominance cross different than a dominant cross?What process must you complete to determine what gametes a parent will produce in a dihybrid genetic cross?

Dihybrid-Two Factor Crosses A dihybrid cross involves two alleles per trait for

two traits, for a total of four alleles. Due to independent assortment an allele for a

particular trait has an equal chance of being in the gamete.For example, a guinea pig's alleles for a dihybrid cross

are BbSs. Using foiling the possible allele combinations in the

guinea pig's gametes are: BS, Bs, bS, bs,

P- parent F1- first generation

F2-second generation

Incomplete dominance-phenotype of a heterozygote is intermediate between the phenotypes determined by the dominant and recessive traits – Ex. Red flowers crossed with white flowers produce pink flowers

Red – AA

White – aa

Pink - Aa

Review

How is the phenotypic outcome in a incomplete dominance cross different than a dominant cross?

What process must you complete to determine what gametes a parent will produce in a dihybrid genetic cross?

Complete Dihybrid Cross Worksheet

Agenda

Notes: Sex-linked crosses Guided Practice Worksheet Genetic Disorder Project

Why are more sex linked traits expressed in males?What is a woman called if she carries a sex-linked trait on only one of her chromosomes?

Sex-linked Traits

X and Y chromosomes not only carry the genes that determine male and female traits but also those for some other characteristics as well.  Genes that are carried by either sex chromosome are said to be sex linked.

 

XBX XBY

XX XY

X Y

XB

X

Baldness is a sex-linked trait carried on the x chromosome•Expressed more often in males because they only have one x chromosome•Females with the gene present on one chromosome called “carriers” for the trait.

http://www.ksu.edu/biology/pob/genetics/xlinked.htm

Review

Why are more sex linked traits expressed in males?

What is a woman called if she carries a sex-linked trait on only one of her chromosomes?

Complete Sex-linked Cross Worksheet and hand in

Work on Genetic Disorder Research Project

Agenda

Notes: Multiple Alleles or Codominance

Multiple Alleles or Codominance

Two alleles in a gene pair are each as sociated with different substances.

When both substances appear together in heterozygotes, codominance occurs.

The two alleles of a pair at a specific locus are not identical but the expression of both is observed.

An example is blood types

Cross a heterozygous B with an heterozygous A

IAIB IAi

IBi ii

I B i

IA

i

Agenda

Genetics Quiz Notes: Pedigrees Worksheet: Pedigree Problems & Family

Tree Project Sheets

What are two ways we may use the information provided on a pedigree?

A pedigree chart is a diagram of family relationships that include two or more generations.

Example of Pedigree Charts

The Shaded means that person has that trait

Interpreting a Pedigree Chart2. Determine whether the trait is dominant or

recessive. (remember: the dominant traits shows if there is one or two, the recessive shows only if there are two)

If the trait is dominant, one of the parents must have the trait.

If the trait is recessive, neither parent has to have the trait because they can be heterozygous.

Circle= female

Square=male

Solid or colored in= express the trait

Dot or line inside= carrier of trait

ee EE

Ee Ee

eeEe Ee

ee

Below is a pedigree for an inherited lung disease, which is recessive.  Provide the genotypes of each of the individuals marked with lower case letters.

aaAA

Aa Aa Aa

aa Aa

aa aaAa Aa

Aa Aa

Aa, AA Aa, AA aa

Lung cancer is a recessive disease. what are the genotypes of a, b, c, d.

Pedigrees can be drawn up to trace any trait through a family tree.

They are used to trace genetic traits through several generations and determine the probability that a trait will be passed from one set of parents to their parents.

The applications of Mendel’s Laws provide opportunities for treatment and prevention of genetic disorders.

Review

What are two ways we may use the information provided on a pedigree?

Worksheet: Pedigree Problems & Family Tree Project Sheets