Part 4: MendelCHAPTER 14

DATE: 11/17/16

AP Bio Vocabulary of the Day(Stems, Prefixes, and Suffixes…Oh my!)

dors- back

Example: dorsal fin (a fin located on the back)

Fabulous FactShrimp's hearts are in their heads.

What You Need to Know:To understand Mendelian genetics.

Terms associated with genetics problems: P, F1, F2, dominant, recessive, homozygous, heterozygous, phenotype, genotype.

How to derive the proper gametes when working a genetics problem.

The difference between an allele and a gene.

AP Biology Standards addressed: Big Idea 3

People to Ponder

Gregor MendelBorn in 1822 in the Austrian Empire (Czech Republic)

Mendel did well in school and had a strong interest in science

In 1843 he entered an Augustinian monastery and was ordained in 1847- this order was known for scholarly study

Mendel worked briefly was a math sub- he failed the teaching exam with his lowest mark in biology

In 1851 he was sent to study science and math at school and returned to teach natural science at a local high school- he never passed the teaching exam

There was a strong scholastic attitude at the monastery and school- a group founded the Natural Science Society Mendel played an active role in

While walking in 1856 he noticed an atypical plant and decided to test whether environment influenced plant

Mendel took the plant and moved it next to a typical one- the offspring of both resembled their parents so environment wasn’t the key

Gregor MendelMendel started using the monastery greenhouse to experiment with green peas- he spent 7 years doing this

Mendel’s work was unique because it focused on single traits and he kept accurate counts

Mendel took another year to do the same tests on corn and flowers

He concluded that parent plants carried “factors” they passed on to offspring and some factors were dominant

In 1865 Mendel presented his findings to 40 polite listeners at the Natural Science Society

Mendel’s work was published, and he had copies sent to 40 prominent scientists- only one responded and he was critical

Mendel’s work may have been ignored because he was very shy and not good at being forceful about his findings

In 1868 Mendel was appointed abbot and had little time for science research

He was discouraged by the failure to recognize his work but in 1883 said he was convinced it would have to be acknowledged soon

Gregor MendelMendel developed kidney failure and died in 1884 at age 61

The next abbot had all of his papers burned to settle taxation disputes

In 1900 three scientists obtained results similar to Mendel’s and when searching through records rediscovered Mendel’s work and gave him credit

Mendel’s work and research methods led to more study and understanding of inheritance at the molecular level

Today he is considered the Father of Genetics

Gregor Mendel

Austrian monk

Brought experimental and quantitative approach to genetics

Bred pea plants to study inhertance

Why peas?◦ Control mating (self- vs. cross-pollination)

◦ Many varieties available

◦ Short generation time

P (parental) generation = true breeding plants

F1 (first filial) generation = offspring

F2 (second filial) generation = F1 offspring

Allele

Alternate versions of a gene found at a particular locus on a chromosome

Dominant vs. RecessiveDominant- an allele that is always expressed when it’s present (capital letter)

Recessive- an allele that is only expressed when the dominant allele is absent (lowercase letter)

Homozygous Vs. Heterozygous

Homozygous: having two identical pairs of alleles for a trait (true breeding, purebred)

Heterozygous: having two different alleles for a trait (hybrid)

Genotype Vs. Phenotype

Genotype: alleles possessed; actual genetic makeup

Phenotype: observable traits; physical appearance

Monohybrid Vs. Dihybrid Cross

Monohybrid Cross: cross between two heterozygotes for a single trait

Dihybrid Cross: cross between two heterozygotes for two traits

Mendelian Genetics

Law of Segregation

Tenants behind the law:

A gene can exist in more than one form (alleles)

Organisms inherit two alleles for each trait- one from mom and one from dad

When alleles are different in a pair, one is dominant and one is recessive

Law of Segregation: The two alleles segregate from each other in meiosis and reside in different gametes

Punnett Squares: Showing the Law of Segregation

Since alleles divide in meiosis, there are two possible gametes formed for each parent

At fertilization there are four equally likely combinations of sperm and egg

Law of Independent AssortmentAllele pairs separate independently from other pairs during the formation of gametes

SO traits are transmitted independently of each other

Only applies to genes on different chromosomes or very far apart on the same chromosome

Dihybrid Cross: Showing the Law of Independent Assortment

Shows the probable inheritance of two alleles at once assuming they are not linked

Genetics and Probability Two basic probability rules are applied- independently for simple problems and together for complex

The probability of all outcomes must add up to 1 (100%)

For independent events, the outcome is unaffected by previous trials

The laws of probability govern Mendelian inheritance

Rule of Multiplication:◦ probability that 2+ independent events will occur together in a

specific combination multiply probabilities of each event

Ex. 1: probability of throwing 2 sixes◦ 1/6 x 1/6 = 1/36

Ex. 2: probability of having 5 boys in a row◦ ½ x ½ x ½ x ½ x ½ = 1/32

Ex. 3: If cross AABbCc x AaBbCc, probability of offspring with AaBbcc is:

◦ Answer: ½ x ½ x ¼ = 1/16

Multiplication RuleProbability of bb: ½ b x ½ b = ¼ chance bb (aka 25%)

The laws of probability govern Mendelian inheritance

Rule of Addition:◦Probability that 2+ mutually exclusive events will occur add together individual probabilities

Ex. 1: chances of throwing a die that will land on 4 or 5?◦1/6 + 1/6 = 1/3

Addition RuleProbability of Bb: ¼ Bb + ¼ Bb = 1/2