Introduction to Introduction to GeneticsGenetics

Gregor MendelGregor Mendel

Gregor Mendel is Gregor Mendel is the “father of the “father of modern genetics”modern genetics”

Austrian monk Austrian monk who did genetic who did genetic experiments with experiments with pea plants pea plants

Defined basic Defined basic units of heredityunits of heredity

1822-1844

Mendel used pea plants to conduct experiments. He concentrated on petal color and shape of peas.

Experiments led to basic genetic understandings such as:

•What happens when two different plants breed?

•How traits are passed from parents to offspring?

•Basic understandings of dominant and recessive traits?

Different traits Mendel observed:

Why Peas?Why Peas? Mendel could do two Mendel could do two

experiments a yearexperiments a year Lacked modern Lacked modern

technologytechnology Today scientists use Today scientists use

organisms that reproduce organisms that reproduce quickly such as quickly such as drosophila (fruit fly) drosophila (fruit fly) which reproduces in 2 which reproduces in 2 weeks or bacteria such weeks or bacteria such as E. coli which as E. coli which reproduces within hours.reproduces within hours.

GeneticsGenetics DNA are the blue-DNA are the blue-

prints of all of your prints of all of your genetic information.genetic information.

DNA is tightly DNA is tightly wound into wound into chromosomeschromosomes

Your genetic Your genetic information is on information is on genesgenes

Genes are located Genes are located on chromosomeson chromosomes

Your Genes and DNAYour Genes and DNA

You are a combination of your You are a combination of your parents.parents.

You have ½ of your mom’s and ½ You have ½ of your mom’s and ½ of your dad’s DNAof your dad’s DNA

Remember Meiosis?Remember Meiosis? You have 23 pairs (one from each You have 23 pairs (one from each

parent) to make a total of 46 parent) to make a total of 46 chromosomes.chromosomes.

Human ChromosomesHuman Chromosomes

Genetic TraitsGenetic Traits

Genes you get from your dad are Genes you get from your dad are “paternal” and genes you get from your “paternal” and genes you get from your mom are “maternal”mom are “maternal”

These make up your traits.These make up your traits.

Trait: characteristic determined by Trait: characteristic determined by genesgenes

Example: I have the trait for blue eyesExample: I have the trait for blue eyes

AllelesAlleles

Each trait is carried on a Each trait is carried on a chromosome stripe.chromosome stripe.

These stripes are called alleles.These stripes are called alleles. Allele: form of a gene on a specific Allele: form of a gene on a specific

region of a chromosomeregion of a chromosome

Alleles for flower colorAlleles for flower color

Maternal

Chromosome

Paternal

Chromosome

Which of Your Parents Traits Which of Your Parents Traits Will You Get?Will You Get?

Based on probabilityBased on probability For example, eggs have X For example, eggs have X

chromosomes and sperm have chromosomes and sperm have either X or Y chromosomes.either X or Y chromosomes.

XX= girlXX= girl XY= boyXY= boy What is the probability offspring What is the probability offspring

will be a girl?will be a girl?

Boy or GirlBoy or Girl

50% chance or 1 out of 250% chance or 1 out of 2 Only two different combinations!Only two different combinations! XX or XYXX or XY Determining the sex of a baby is Determining the sex of a baby is

one example of probability.one example of probability. But…it doesn’t always work that But…it doesn’t always work that

way…way…

Dominant Alleles vs. Dominant Alleles vs. Recessive AllelesRecessive Alleles

Certain traits are stronger then Certain traits are stronger then others. This means that they will others. This means that they will more likely be expressed.more likely be expressed.

For example: If I mix black paint For example: If I mix black paint with white paint, what color will with white paint, what color will paint most likely be?paint most likely be?

Black! It is a “stronger color”.Black! It is a “stronger color”. Dominant allele: one that is Dominant allele: one that is

expressed physically expressed physically (what organism looks (what organism looks like)like)

Dominant Alleles vs. Dominant Alleles vs. Recessive AllelesRecessive Alleles

What about the white paint?What about the white paint?

Recessive allele: one that is Recessive allele: one that is

masked or hidden by the dominant masked or hidden by the dominant allele.allele.

White paint would be an example White paint would be an example of the “recessive color”. There is of the “recessive color”. There is still white paint in the mixture, but still white paint in the mixture, but it looks black.it looks black.

Terms To KnowTerms To Know

Genotype: combination of two Genotype: combination of two allelesalleles

Homozygous: When the genes areHomozygous: When the genes are

identicalidentical Heterozygous: When the genes areHeterozygous: When the genes are

differentdifferent Phenotype: The observable trait Phenotype: The observable trait

(the trait you see)(the trait you see)

Boy: XY Girl: XXBoy: XY Girl: XX

What is the genotype for girl?What is the genotype for girl? XXXX

Is boy homo or heterozygous?Is boy homo or heterozygous? Heterozygous XY (different letters)Heterozygous XY (different letters) Homozygous XX (same letters)Homozygous XX (same letters)

What is the dominant allele (X or What is the dominant allele (X or Y?)Y?) YY

How do you know?How do you know? Wherever Y is means a boy will formWherever Y is means a boy will form

If an organism carries any If an organism carries any combination of dominant genes, it combination of dominant genes, it will be expressed in an organism.will be expressed in an organism.

Recessive genes are only Recessive genes are only expressed when there are two expressed when there are two recessive genesrecessive genes Example XX in girlsExample XX in girls

How genes are expressedHow genes are expressed