genetics origin and theory gregor mendel. pea plant characters and traits wrinkled short character...
TRANSCRIPT
Mendel’s Experiments
Began with monohybrid crosses Crosses that involve organisms
that are different in only one trait Ex- tall pea plant with a short
plant (P1)
1st step…
• Allow self-pollination for several generations
• Result: true-breeding P generation (parent generation)• Purple flowers plants
will only produce purple flowered offspring
2nd step….
• Cross-pollination of P generation
• Result: F1 generation (first filial generation)
• All same trait
…3rd step
• Self-pollination of F1 generation
• Result: F2 generation (second filial generation)
• Some purple, • Some white
Mendel’s Hypotheses1. For each inherited character, an individual has two
copies of the gene-one from each parent.
2. There are alternative versions of genes: alleles
3. When two different alleles occur together, one of them may be completely expressed (dominant )
while the other may have no observable effect on the organism’s appearance (recessive)
4. When gametes are formed, the alleles for each gene separate independently of the other (law of independent assortment
Monohybrid cross- plant height
• Two traits (alleles) tall and short
• Dominant trait: tall• Recessive trait: short
In genetics problems we generally assign a letter to each trait with the upper case being the dominant and lower being the recessive allele.
Ex. Height T = Tall & t = short
Monohybrid cross
Example of a Monohybrid Cross with seed shape
Create a visual of Mendel’s Experiment with plant height.
F2 Generation
From this cross his 2nd generation were. 2nd generation 75% tall and 25% short
(F2) Why was the short gene apparent in the
2nd and not in the 1st Generation of offspring?
Back to his hypotheses
From this experiment Mendel concluded that for each gene we carry there are two factors called Alleles.
One allele from each homologous chromosome One from Mom and one from Dad
Mendel Cont.
This brought up the terms recessive and dominant For a recessive trait to show both alleles must
be recessive. For a dominant trait to show only one
dominant allele needs to be present Can be a carrier if you have one
dominant and one recessive (carrier for recessive) – The recessive trait does not show.
Passing on the Trait
When gametes (sex cells) are formed only one of the alleles is passed on from each parent
The allele combination that the child receives is called the genotype. (Tt)
Genotype= genomic composition The genotype may be homozygous or
heterozygous homozygous have the same alleles (TT, tt) Heterozygous have different alleles (Tt)
The trait that physically appears is the phenotype (tall or short)
Write out the genotype for pea height ex for….
Homozygous dominant, homozygous recessive, and heterozygous
Punnett squares
The Punnett square is a diagram that is used to predict an outcome of a particular cross or breeding experiment.
Named after Regi Punnett Is a summary of every possible combination
Draw the punnett squares for the height example
Mendel’s Laws
Law of Segregation: Gene pairs separate when gametes form.
Alleles separate during meiosis Alleles are found on the homologous
chromosomes so when they separate the Gene Pairs separate.
Mendel’s Law
Law of Independent Assortment: Gene pairs segregate into gametes randomly and independently of each other regardless of how they are connected in the organism. Note: they have to be on different
chromosomes. These allele pairs are then randomly
united at fertilization.