WHAT IS GENETICS? • Heredity: study of traits being passed from parent to offspring. • Genetics: the study of how these traits get passed on.
Mendel noticed that there were some “factors” that passed from parent to offspring Now we call these factors GENES Gene: section of DNA that contains a single recipe for a protein
Character: feature that can be passed to offspring from parents Trait – variation of a characteristic Example: Character: Height - traits: short, tall
Characters are controlled by GENES Traits are controlled by ALLELES Remember an allele is a variation of a gene.
CHROMOSOME = a string of genes wrapped around protein We have two of each chromosome • One from our mom, one from our dad • They both have the same type of information, but they might be different versions
For Example: Both have a hair color gene from Dad from Mom
For Example: And Dad’s has brown allele But Mom’s has blonde allele from Dad from Mom
If the alleles you inherit from your parents are: • Both the same you are called HOMOZYGOUS or PURE • Both different you are called HETEROZYGOUS or HYBRID
How does it happen? Each parent starts with two of each chromosome Mom Dad
Eggs Sperm During meiosis one of each chromo. Enters each egg/ sperm cell
Then during fertilization, one sperm will fuse with one egg BUT there are 4 possible combinations! Four Possible Zygotes
Mendel’s Law #1: • Law of Segregation: only one allele for each gene gets passed on from each parent • So… even though you might have a blonde allele and a brown allele, you only pass on one to each child.
Mendel’s Law #2: LAW OF INDEPENDENT ASSORTMENT: Alleles for different traits will be passed on independently from each other. This will allow new combinations of traits to appear in offspring
Mendel’s Law #3: LAW OF COMPLETE DOMINANCE – Some alleles over power other alleles when they are in the same cell. - Dominant allele: the one that wins - recessive allele: the one masked by the dominant allele
Phenotype: physical characteristic; what trait do you actually have Examples: brown hair, widows peak, purple flowers
Genotype: Gene formula that identifies which alleles you have. Alleles are abbreviated as a single letter. - Usually first letter of one of the traits; - Dominant allele gets a capital letter, recessive gets a lower case
Genotype: remember each person has two alleles for each gene so a genotype will have two letters for each characteristic
Example 1: In pea plants, Purple flowers are DOMINANT to white flowers. - Purple allele? - white allele? - Homozygous purple? - homozygous white?
Example 1: - Heterozygous? What color is this plant?
PARENTS: “P” GENERATIONS OFFSPRING/PROGENY: “F” GENERATIONS; RESULTS OF THE CROSS F1 – 1ST GENERATION, F2 – 2ND GENERATION
Monohybrid Cross: - examines what the outcome might be if two parents crossed. - looks at only one trait!
Uses a punnett square to map out the possible gametes and the possible zygotes GAMETE – EGG1 GAMETE – EGG2 GAMETE – SPERM1 ZYGOTE ZYGOTE ZYGOTE ZYGOTE GAMETE – SPERM2
Cross Number 1: Brown hair (B) is dom. to Blonde (b). Cross a Homozygous Brown haired Woman and a Homozygous Blonde Man. Step 1: What is Mom’s Genotype? What is Dad’s Genotype? BB bb
Cross Number 1: Step 2: What eggs can mom make? What sperm can dad make? B B b b
B B b B b B b b B b B b Cross Number 1: Offspring genotypes: Offspring phenotypes:
Cross Number 2: Purple flowers (P) are dom. to white (p). Cross a Heterozygous Purple Female and a Heterozygous Purple male. Step 1: What is Mom’s Genotype? What is Dad’s Genotype? Pp Pp
Cross Number 1: Step 2: What eggs can mom make? What sperm can dad make? P p P p
P P P p p p P p Cross Number 2: Offspring genotypes: Offspring phenotypes: P p P p
BUT only certain genes show complete dominance: • Other genes have different inheritance patterns where the two alleles behave differently when together.
Inheritance pattern II: Incomplete dominance • Neither allele “wins”. Instead the effects of both allele blend together. • Ex. R = red r = White Rr = ???
Inheritance pattern III: Co dominance • When two co-dominant alleles are present BOTH phenotypes are seen equally. • Ex. B = black W = white BW = ???
Fill in the chart for a gene in which B = black and b=white So…. Which genotype gives away the inheritance pattern? (which genotype tells you if the gene is complete, incomplete, or co-dominant?)
TEST CROSS: A cross to test whether a parent with a dominant trait is Heterozygous or Homozygous. - Rule: Cross the parent with the dominant trait with a recessive and examine the offspring.
Multiple alleles • Some genes have more than two alleles that exist. • Each person still only inherits two, BUT there are three possible variations in the population • Example: human blood type • A, B and O are the three alleles.
Multiple alleles • Which alleles you inherit will determine your blood type (more on this in your lab) • If you inherit AA or AO you have type A blood • (what does this say about A’s inheritance pattern with O??)
Multiple alleles • If you inherit BB or BO you have type B blood • (what does this say about B’s inheritance pattern with O??) • If you inherit AB you have type AB blood • (what does this say about A’s inheritance pattern with B??) • Finally how do we get type O blood?
TEST CROSS RESULTS: If 100% of the test cross offspring are dominant then the parent was homozygous If only 50% are dominant, then parent was heterozygous