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GENETICSGENETICS
Heredity – how traits are passed from parents to offspring
GREGOR MENDELGREGOR MENDEL (1822- (1822- 1884)1884)
- Father of Genetics - Austrian Monk from 1822- 1884 - Job was to take care of the
garden- Worked with pea plants ( lots of pea soup)
- Noticed that traits were passed from parent peas to their offspring
- Before him people believed in the blending hypothesis
Why are pea plants good to study?
- Reproduce quickly, easy traits to view, many offspring - Pea plants have DNA just like we do
Self FertilizationOffspring= Purebred
Sperm and egg from the same plant produce offspring
Cross Fertilization Offspring = Hybrid
process by which sperm from one flower's pollen fertilizes the eggs in a flower of a different
plant, heterozygous
CROSS POLLINATIONCROSS POLLINATION
HYBRID HYBRID
COCKAPOCOCKAPOOO
COCKER SPANIEL
+POODLE
HYBRIDHYBRIDPUG
+BEAGLE
PUGGLE
HYBRIDHYBRID
DOG DOG ANDAND WOLFWOLF
male lion and
a female tiger
Liger
Peas!
GENETIC GENETIC TERMINOLOGYTERMINOLOGY
•DominantDominant•RecessiveRecessive•HomozygousHomozygous•HeterozygouHeterozygouss
•GenotypeGenotype•PhenotypPhenotypee
•TraitTrait•AlleleAllele
• Dominant allele- trait is always expressed if present
- Written as capital letter
- Ex. Tall= T
• Recessive allele- only expressed if no dominant allele is present (Dominant allele masks this one)
- For a particular trait written as the same letter but lower case
- Ex. Short= t
Dominant and Recessive Alleles
• Homozygous - the same alleles for a gene
– TT, tt
• Heterozygous - having different alleles for a gene
– Tt
• Genotype- the genes you get from your parents– Two letters represent the two alleles– One from mom one from dad – TT, Tt, tt
• Phenotype- the physical trait, what you look like – Tall short, yellow or green – TT, tt what is the phenotype?
Trait = CharacteristicTrait = CharacteristicEx: HeightEx: Height
TALL SHORT alleles
Flower Color Trait
• Gene- unit of inherited information in DNA • Allele- alternative form of a gene (white purple)
Reginald PunnettReginald Punnett
Introduction to Monohybrid Crosses
• Punnett Square- chart to predict offspring
• Monohybrid- looks ONE trait• Ex: Looking at just plant color,
or just height, or just seed color
In Starfish In Starfish being being redred is is
dominant over dominant over being being pinkpink.. What would What would
PatrickPatrick’’s s phenotypephenotype be? What be? What would his would his
genotypegenotype be? be?
Because Patrick is pink… his
phenotype is PINKPINK
And since pink is
recessive – his
genotype
would be “rrrr ”
RedRed is dominant over
pinkpinkSuppose we
had a HETEROZYGO
US redred starfish what
would the genotype be?
Rr
LetLet’’s do some… s do some… MONOHYBRID MONOHYBRID
CROSSES!CROSSES!
MonohybridMonohybrid means means we are only using we are only using
ONE TRAITONE TRAIT
STEP by STEPSTEP by STEP1.1. Select a Select a ““goodgood”” letter to use letter to use
2.2. Write down your Write down your ““givensgivens””
3.3. Determine parents and recordDetermine parents and record
4.4. Set up Punnett SquareSet up Punnett Square
5.5. Determine genotypes & Determine genotypes & phenotypes of offspring phenotypes of offspring
(use percentages or fractions)(use percentages or fractions)
In pea plants, In pea plants, Tall is dominant to shortTall is dominant to short
Cross a Cross a Heterozygous Tall plant Heterozygous Tall plant
with a with a Homozygous Tall plantHomozygous Tall plant
Tt x TT
Geno = 50% T T50% T t
Pheno =100% Tall
A
A
A
T
t
T T
T T T T
T t T t
In sponges, In sponges, beingbeing blueblue
is dominant is dominant over beingover being
yellow.yellow.Cross a Cross a
heterozygouheterozygous blue s blue
sponge with sponge with a yellow a yellow
one.one.
HeterozygoHeterozygous us BlueBlue = = BbBbRecessive Recessive YellowYellow = bb = bb so we so we cross…cross…
Bb x Bb x bbbb
Time for someTime for some
LOONEY Monohybrid Monohybrid Crosses onCrosses on your own! your own!
MENDELS LAWSMENDELS LAWS
1. Dominance & Recessiveness
2.Segregation3. Independent
Assortment
1. Dominance & Recessiveness
• one gene( dominant) can mask the other ( recessive)
2. Segregation• genes are separated or segregated during
the formation of sex cells. • Only one gene from one parent.
3. Independent Assortment
• genes for traits separate independent of each other
• In dihybrid crosses, gives you several possibilities– Ex: In Nemo- short fin can be inherited with a
red body or an orange body- separate chromosomes
Independent Assortment
TTEESSTT CCRROOSSSS
Test Cross- mate an unknown genotype ( TT or Tt) with homozygous recessive (tt)
PEDIGREEPEDIGREEmale female