Introduction to Genetics

• What does genetics mean?

• Branch of biology that studies heredity.

• What is heredity?

• Key to differences between species. Makes species unique. Something that is passed on from one generation to the next.

First Theory of Heredity

• Blending Inheritance– Get 50% from mom and 50% from dad

Is this TRUE or FALSE?

11.1 Gregor Mendel

• “Father of genetics”• Became a priest in a monestary, teacher at high

school. • In charge of the garden• Understood the sexual mechanism of pea plants

-pea plants have both male and female parts

-self pollination-true breeding (identical offspring)

Mendel’s Experiment

• He wanted to see if self pollination could be prevented or manipulated.– He cut the male part off all the flowers of one

plant (stamen) and dusted pollen on the female parts off another plant (pistil).

– Refer to page 264

What is this process called?

Cross Pollination

• Produces seeds that are offspring of two different plants.

• What did the stamen say to the pistil?– I like your style. Get it??

Terms

• Self pollination

• Cross pollination

• True breeding- produces purebreds

• Purebred- allowed to self pollinate; produce offspring identical to themselves.

• Traits/characteristics- size, shape, looks, texture, color, etc.

Genes and Dominance

• Genes-sequence of DNA that codes for a protein and thus determines a trait.

• Mendel crossed the seeds of tall plants with the short plants; crossed yellow seeds with green seeds.

• He produced HYBRIDS- organisms produced by crossing with different characteristics.

• The result was not a 50/50 mix of tall and short or yellow and green.

More terms

• Allele- different form of a gene. Given 2 letters to represent each trait.– Example for tall: TT or Tt– Example for short: tt

– Why are there always two alleles given?• One from mom and one from dad.

Principle of Dominance

• Some alleles are dominant and others are recessive.

• Dominance-when present, is the trait that will always show up

• Recessive-will not show up when dominant is present. Has to be two small alleles only.

Heterozygous & Homozygous

• Heterozygous (different-one of each) Tt

• Homozygous (same) TT or tt

• Heterozygous tall plant crossed with a homozygous tall plant.

• Tt x TT

• Purebred tall plant with a short plant

• TT x tt

Segregation

• Separation of alleles

• What happens to the recessive traits?

• P generation (parent generation)

• F1 first filial or first generation.

• F2 second generation –(offspring from the F1 generation)

11.2 Genetics and Probability

• Probability- likelihood that a particular even will occur

• Equation for probability= # of times event occurs# of times it could occur

Larger # of trials, the closer you get to the expected ratio.

Punnett Squares

• Diagram that shows the outcome of a particular cross.

Genotype

• The letters inside the boxes indicate probable genotypes (genetic makeup) of offspring resulting from the cross of these particular parents. There are 4 boxes, and the genotypic results can be written either as fractions or percents. In this case, all 4 boxes out of the 4 are showing the Tt genotype. Therefore, each of the offspring has a 4/4 or 100% chance of showing the Tt genotype.

Phenotype

• We have also written the phenotype (physical appearance) in each box under the genotype. Remember, T = tall and t = short (see step #1 above). Since a capital letter indicates a dominant gene, T (tall) is dominant over t (short). Therefore, each of the offspring has a 4/4 or 100% chance of being tall.

What are the possible genotype(s) of a tall plant? What are the possible genotype(s) of a short plant?

What would be the phenotype of TT? What would be the phenotype of tt?

Why is the phenotype of Tt tall and not medium/average?

One Factor Cross

• Using only one trait or set of alleles

• TTx tt One trait…Height

• How many boxes would you need in your punnett square?

• 2 x 2 = 4

Two factor cross

• Using two different traits and alleles

• Example would be height and color

• TT, Tt, tt would be alleles for height

• BB, Bb, bb would be for color

• T=tall t=short

• B=black b=white

Practice with Punnett squares

• A heterozygous tall white weasel crossed with a small heterozygous black weasel.

• Ttbb x ttBb

• How many squares would the Punnett Square have?

• 4 x 4= 16

FOIL

• F = First terms

• O= Outter terms

• I = Inner terms

• L = Last terms

• I know, I know…this isn’t math class, but the same concepts do apply…math and science go hand in hand…

Ttbb x ttBb

• First terms Tb first tB

• Outter Tb outter tb

• Inner tb inner tB

• Last tb last tb

Ttbb x ttBb

11.3

• Independnet Assortment- genes for different traits can segregate independently during the formation of gametes.

• Gametes- sex cells. – Males=sperm– Females=egg– Zygote is a fertilized egg

Summary of Mendel’s Principles

• 1. traits are determined by genes from parents to offspring.

• 2. when present a dominant trait will always show up. 2 recessive traits must exist together for recessive to show up.

• 3. each adult has two copies of a gene (one from each parent). These genes segregate (separate) from each other when gametes (sex cells) are formed.

• 4. Alleles for different genes usually segregate independently from on another.

Beyond dominant and recessive

• Incomplete dominance- one allele is not completely dominant over another. – RR x WW R=red W=white– Pink flowers

• Codominance- when both alleles contribute to the phenotype. – Example: cows with an allele for red hair and white

hair, are roan cows…they look pink but close up you can see the different hair colors.

– Example: speckled chickens have black and white feathers.

– Example: Blood type A=IA B=IB O=ii

• Multiple alleles- more than two forms of alleles, individuals cannot have more than two alleles.– C=full color (dominant)– cch=chinchilla (partial defect, dominant to ch

and c alleles)– ch=Himalayan (parts of body colored,

dominant to c allele)– c=albino, no color (recessive)

• Polygenic traits- traits formed by two or more traits.– Example: skin color…more than four different

genes control this trait

Meiosis

• Process by which the # of chromosomes per cell are cut in half through separation of homologous chromosomes of a diploid cell. (1/2 # of chrom. & different kinds)

• Homologous- two sets of chromosomes. A male chromosome has a corresponding female chromosome.

• Diploid-2N means two sets• Haploid- N means one set

Phases of Meiosis

• Interphase I= cells undergo replication and form duplicate chromosomes

Meiosis I

• Prophase I= chromosomes find homologous pair (tetrad-4 chromatids)

• Metaphase I= spindle fibers attach to the chromosome. Chromosomes line up at equator and crossover-exchange different alleles.

• Anaphase I= fibers pull homologs to opposite poles

• Telophase I and Cytokinesis= cell splits into two daughter cells with different # & kind of chromosomes.

Meiosis II

• Prophase II

• Metaphase II

• Anaphase II

• Telophase II and cytokinesis

Gene Map• Diagram showing the relative locations of

each known gene on a particular chromosome.