BIOL239 Chapter Notes -Gamete, Dwarfism, Zygote

3 views3 pages
Published on 17 Apr 2013
School
University of Waterloo
Department
Biology
Course
BIOL239
Mendel's Experimental Organism: The Garden Pea
Mendel's success attributed to choice of experimental test subjects.
Garden peas easily grown in gardens or green houses.
Pea flowers contain both male and female organs. The male sex organ, anthers, produce sperm
containing pollen, and the female organ, the ovary, produces eggs.
Flower petals close down, preventing pollen from entering or leaving the flower.
This causes self fertilization, pollen and eggs from the same flower fertilize to produce seeds.
Pea strains are highly inbred, displaying little genetic variation from generation to generation:
called true-breeding.
Each true-breeding pea strain was distinguished by one specific characteristic, such as size or
color.
Focusing on single differences allowed him to study 1 trait at a time.
Mendel succeeded where other biologists failed because they studied multiple traits at once.
Mono-hybrid Crosses: The Principles of Dominance and Segregation
Mendel cross fertilized tall and dwarf pea plants to see how the height trait was inherited.
He removed the anthers of one variety, and pollinated that variety with anthers of the other
variety.
The seeds of the cross fertilization were sown,he revealing hybrid plants that were all tall.
The same results were obtained regardless of which trait came from either male or female.
However, when all the tall plants were allowed to self fertilize, the yield was a 3:1 ratio of tall
to dwarf plants.
Mendel inferred that the hybrids contained a latent, recessive genetic factor for dwarfism, and a
dominant expressed factor for tallness.
He also inferred that the factors split when the hybrids self fertilized, explaining the re-
appearance of the dwarfed plants.
Each cross fertilization involving a single trait is called a mono-hybrid cross.
Multiple experiments revealed only one of the contrasting traits appeared in the hybrid
generation, but both appeared in the self fertilized generation, always in a 3:1 ratio.
Mendel's conclusion was that each trait was controlled by heritable genetic factor (now called a
gene) that existed in two alternative forms, one recessive and one dominant (now called alleles).
Mendel's other conclusion was that the genes came in pairs. Each of the parental strains in the
cross carried two identical versions of the gene, therefore diploid and homozygous. However,
during gamete production, only one version of the gene is obtained, therefore haploid.
The diploid gene number would be restored when the pollen and egg fertilized. The resulting
zygote would be diploid, and heterozygous as it would receive an allele from each parent,
assuming the plants were genetically different in the cross.
When the heterozygous hybrid reproduces, any gamete has an equal chance of obtaining either
the dominant or recessive allele.
The re-appearance of the dwarf plants would be explained by the fact that some zygotes from
the progeny of the hybrid plants would inherit both recessive alleles.
Both the true breeding parental varieties are homozygous for alleles controlling height.
Lowercase d represents the allele for dwarf, and uppercase D represents the allele for tall. The
letter denoting the alleles for a gene comes from the word corresponding the recessive trait (d
for dwarf).
Tall will be symbolized by DD, and dwarf by dd.
The allelic constitution of the genes of the strain is called the genotype. The physical
Unlock document

This preview shows page 1 of the document.
Unlock all 3 pages and 3 million more documents.

Already have an account? Log in

Document Summary

Mendel"s experimental organism: the garden pea: mendel"s success attributed to choice of experimental test subjects, garden peas easily grown in gardens or green houses. Pea flowers contain both male and female organs. The male sex organ, anthers, produce sperm containing pollen, and the female organ, the ovary, produces eggs. Flower petals close down, preventing pollen from entering or leaving the flower: this causes self fertilization, pollen and eggs from the same flower fertilize to produce seeds. Pea strains are highly inbred, displaying little genetic variation from generation to generation: called true-breeding: each true-breeding pea strain was distinguished by one specific characteristic, such as size or color. Focusing on single differences allowed him to study 1 trait at a time: mendel succeeded where other biologists failed because they studied multiple traits at once. Each of the parental strains in the cross carried two identical versions of the gene, therefore diploid and homozygous.

Get OneClass Grade+

Unlimited access to all notes and study guides.

YearlyMost Popular
75% OFF
$9.98/m
Monthly
$39.98/m
Single doc
$39.98

or

You will be charged $119.76 upfront and auto renewed at the end of each cycle. You may cancel anytime under Payment Settings. For more information, see our Terms and Privacy.
Payments are encrypted using 256-bit SSL. Powered by Stripe.