Genetics What is genetics?

study of inherited traits What is heredity?

passing of traits from parents to offspring

What is a trait? feature an organism can pass on to offspring ex) hair color, eye color, etc

What are Your Traits?

Genes! Genes-segments of

DNA on chromosomesthat code for a protein which produces a trait.

There are 1000’s of genes on each chromosome. Chromosomegeneproteintrait

Genes

Some traits are coded for by one gene which codes for one protein. i.e. freckles, earlobe attachment, etc

Polygenic Inheritance – When a Single Trait is Influenced by Many Genes

Height is a polygenic trait

Other traits are coded for by two or more genes together- polygenic

More than one gene=more than one protein that causes the trait so more complex traits are shownHand span, height, eye color, etc.

Genes Homologous

chromosomes–two chromosomes that have the same number and types of genes.

Each HUMAN somatic cell has 23prs of homologous chromosomes

Other species have different numbers.

Homologous Chromosomes

Mom contributes one and Dad contributes other of each pair

This means each somatic cell has two copies of each chromosome, and therefore, each gene.

Alleles Alleles - forms of genes

Allele for round peas--R

Allele for wrinked peas--r

Position on chromosomes where pea shape gene is located

Genotype vs. Phenotype Genotype: the genetic

makeup of an organism RR, Rr, or rr 2 letters-one copy from

each parent Phenotype: the physical traits

the organism shows round or wrinkled peas

***Phenotype = Genotype + Environment

Genotypes The 2 alleles on homologous chromosomes can

be the same or different Homozygous (purebred)- having two identical

alleles for a particular trait. i.e. pea shape gene: Alleles: R=round and r=wrinkled RR or rr

Heterozygous (hybrid) – having different alleles for a particular trait on homologous chromosomes ????

Genotype Example Phenotype

Homozygous Dominant

RR Round

Homozygous Recessive

rr Wrinkled

Heterozygous

Rr Round

Early Ideas - Heredity Gregor Mendel decided

to test this idea Father of genetics It was originally believed

a child’s traits were result of “blending” between parent’s traits

He knew nothing about DNA!

Mendel’s Pea Plants

Why did Mendeluse pea plants?1. Peas had several contrasting traits he

could observe easily2. He understood their method of reproduction3. They reproduced

quicklyCharacters investigated by Mendel

Reproduction in Plants

Plant cells undergo meiosis, just like animals, to create gametes: pollen and ovules!

Pollination Anther releases pollen

(“plant sperm”) Stigma receives the pollen

which the fertilizes the ovules (“plant eggs”)

Similar to fertilization in animals.

Mendel could control how plants were fertilized because he understood this process

Mendel’s Experiments con’t

Parental generation (P) “original group”

First filial generation(F1) offspring of the parental cross

Second filial generation (F2) offspring of crossing two F1 plants

Mendel’s First Experiment

Wanted to know what would happen if cross 2 plants with different forms of a trait.

The 1st thing Mendel did was cross 2 purebred (homozygous) plants.

?

Results?

In F1 generation NO blending resulted. Round allele (R) dominated over wrinkled form of the gene (r)

Dominant allele - hides other allele; RRecessive allele- form NOT expressed

in presence of dominant form, “hidden”; r

Genetics Rule #1: Principle of Dominance- one allele dominates so trait coded by other allele hidden. R dominates over r when both present

ALL ROUND F1

Mendel’s 2nd Experiment

The next question: If all the seeds were round in the F1 generation, had the wrinkled allele disappeared?

Mendel extended his experiment and cross two of his F1 plants…

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Results?

F2 (Second filial generation)- offspring of F1 cross

Some offspring showed recessive trait, some the dominant trait

3:1 ratio (round: wrinkled) Do a Punnett square to

show his results for the F2.

Mendel’s Conclusion The dominant allele hides

the recessive allele in the F1 Since the recessive allele

(wrinkled) reappeared in the F2, it must have “separated” from the dominant allele

Law of Segregation- during meiosis when gametes form, alleles for a trait are separated (each parent gives only one allele in egg or sperm to offspring)

Passing of One Gene

Figure out the possible gamete genotypes these parents could make:

Parent 1: Parent 2: RR Rr

? Gametes ? ? Gametes ?

Passing of One Gene Remember that when considering only

ONE gene, the gametes that form only have ONE copy of every gene because the gametes only get ONE copy of every chromosome.

Parent 1: Parent 2:

RR RrR or R R or r

DIPLOID BODY CELL FROM WHICH EGG AND SPERM COME FROM—2 COPIES OF EVERY CHROMOSOME AND THEREFORE, EVERY GENE

HAPLOID GAMETES ARE FORMED--1 COPY OF EVERY CHROMOSOME AND, THEREFORE, EVERY GENE.

MEIOSIS-FORMATION OF GAMETES IN WHICH GENETIC MATERIAL IS CUT IN HALF

R r

R r

Consider TWO Genes! Try to figure out the possible

gamete genotypes a parent could make:**Remember there must be ONE copy of every gene in each gamete!

Parent 1: Parent 2: RrYy RrYy

? Gametes ? ? Gametes ?

R r Y y X R r Y y

1. 1. RYRY

2. 2. RyRy

3. 3. rYrY

4. 4. ryry

FOILFOIL – – FFIRST, IRST, OOUTER, UTER, IINNER, NNER, LLASTAST

BOTH PARENTS ARE BOTH PARENTS ARE THE SAME, SO THEIR THE SAME, SO THEIR GAMETE GENOTYPE GAMETE GENOTYPE POSSIBILITIES FOR POSSIBILITIES FOR BOTH PARENTSBOTH PARENTS ARE, ARE, TOO! TOO!

BODY CELL FROM WHICH EGG AND SPERM COME FROM—DIPLOID2 COPIES OF EVERY CHROMOSOME AND THEREFORE, EVERY GENE

MEIOSIS

R r

Yy

RY Ry r Y ry

4 gametes each with ONE copy of each gene!!!

Show the Punnett Square!

R r Y y X R r Y yRYRY RyRy rYrY ryry

RYRY

RyRy

rYrY

ryry

RRYYRRYY RRYyRRYy RrYYRrYY RrYyRrYy

RRYyRRYy RRyyRRyy RrYyRrYy RryyRryy

RrYYRrYY RrYyRrYy rrYYrrYY rrYyrrYy

RrYyRrYy RryyRryy rrYyrrYy rryyrryy

Round, Round, yellow: 9yellow: 9

Round, Round, green: 3green: 3

Wrinkled, Wrinkled, yellow: 3yellow: 3

Wrinkled, Wrinkled, green: 1green: 1

Each gamete MUST have one copy of EVERY gene so the children will have complete pairs!

Law of Independent Assortment

Does everyone with brown hair have blue eyes?

Does everyone with a big nose have freckles?

NO! Mendel’s Law of Independent Assortment-

inheritance of one trait will not affect inheritance of another. They are not “tied” together!

Peas could be green and wrinkled or green and round. The pea shape gene and the pea color gene assort independently into the gametes.