Honors Biology Unit 5 / Chapter 11 Powerpoint #1.
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Transcript of Honors Biology Unit 5 / Chapter 11 Powerpoint #1.
INTRODUCTION TO GENETICS: THE WORK OF GREGOR MENDEL
Honors BiologyUnit 5 / Chapter 11Powerpoint #1
•Gregor Mendel was born in 1822 in the Czech Republic
•Studied Science and Mathematics at the University of Vienna
•Spent the next 14 years teaching high school and working at a monastery in the garden
Mendel noticed that the SAME type of plant could have VARIATIONS, or differences, these are the
variations he noticed:
Seed Shape Seed Color Seed Coat Color
Round Yellow Gray
Wrinkled Green White
Pod Shape Pod Color Flower Position Plant Height
Smooth Green Axial Tall
Constricted Yellow Terminal Short
AFTER MENDEL NOTICED THESE VARIATIONS HE DECIDED TO DO AN EXPERIMENT OF HIS OWN. Mendel wanted to breed the pea
plants together in different combinations to see what the offspring (seedlings) would look like.
TECHNIQUES OF MENDEL
Describe how Mendel prevented self-pollination and controlled cross-pollination in pea plants: He cut off the male parts of one flower, then dusted the stigma with pollen from a second flower.
Why did he want to do this? He wanted plants with specific traits to breed with one another.
TERMINOLOGY
Genetics: study of heredity (how traits pass from one generation to the next)
True-breeding: if allowed to self-pollinate, produce offspring identical to self
Self-pollination: pollen from one flower fertilizes egg cells in same flower
Cross-pollination: pollen from one flower fertilizes egg cells in a different flower
TERMINOLOGY
Trait: specific characteristic that varies from one individual to another
Example: Hair color, Eye color, height
P generation: parental generation
TERMINOLOGY
F1 generation: first generation of offspring (first filial generation) (AKA kids of parents)
F2 generation: second generation of offspring (offspring of F1 plants) (AKA grandkids of parents)
Hybrid: offspring of crosses between parents with different traits. Example: Cross pollinate a red flower and a white flower. Seedlings=hybrid
X =
HYBRID CARS
Gas + Electric
TERMINOLOGY
Gene: segment of DNA that determines a trait
Alleles: different forms of a gene
(ex: Height: tall gene, or short gene)
Allele
PRINCIPLE OF DOMINANCE:
dominant trait always seen when dominant allele is present; recessive trait only seen when no dominant allele is present
TERMINOLOGY
Recessive allele: allele that is masked (hidden) when dominant allele is present
Allele for blue eyes
Dominant allele: allele that is always expressed when it is present
Allele for brown eyes
NOTATION
A capital letter represents the dominant allele.
A lower case letter represents the recessive allele.
Example: Pea plant height –
Tall: TShort: t
MECHANICS
Segregation of alleles: separation of alleles during gamete production (meiosis)
Gametes: sex cells (egg, sperm)
Note: all body cells contain two copies of each chromosome (and therefore two copies of each gene) – one copy is from the male parent and one copy is from the female parent
During meiosis, each gamete (egg or sperm cell) receives only one copy of each chromosome (and gene (allele)), thus the two copies of each gene are separated.
PEA PLANT TRAITS
Seed Shape
Flower Position
Seed CoatColor
Seed Color
Pod Color
Plant HeightPodShape
Round
Wrinkled
Round
Yellow
Green
Gray
White
Smooth
Constricted
Green
Yellow
Axial
Terminal
Tall
Short
Yellow Gray Smooth GreenAxial Tall
MENDEL’S OBSERVATIONS
• 1. In the first generation of each experiment, how do the characteristics of the offspring compare to the parents’ characteristics?
• 2. How do the characteristics of the second generation compare to the characteristics of the first generation?
Parents
Long stems short stems
Purple flowers white flowers
Green pods yellow pods
Round seeds wrinkled seeds
Yellow seeds green seeds
First Generation
All long
All purple
All green
All round
All yellow
Second Generation
787 long: 277 short
705 purple: 224 white
428 green: 152 yellow
5474 round: 1850 wrinkled
6022 yellow: 2001 green
P Generation F1 Generation F2 Generation
Tall Short Tall TallTall Tall Tall Short
Mendel’s Experiment
TT Tt Tttt TT Tt Tt tt
MECHANICS
Why are there no white flowers in the F1 generation? The purple parent has 2 purple alleles and the white parent has 2 white alleles. The F1 plants each have one purple and one white allele – the purple allele is dominant so it masks the white allele.
Why are there no light purple flowers in the F1 generation? Traits do not blend.
Explain why the offspring of a true-breeding pea plant with white flowers and a true-breeding pea plant with purple flowers are all purple
MENDEL’S EXPERIMENT
How did Mendel show that the recessive allele had not disappeared in the F1 generation? When he cross-pollinated plants from the F1 generation, the recessive trait showed up again in the F2 generation.
This showed Mendel that there must be two factors (genes) controlling each trait – one is dominant and masks the other (which is recessive).
MENDEL DID HIS WORK BEFORE DNA!
Pea Plant DNA (Electron
Microscope)