Advertisement Upgrade to remove ads

Snustad, D.P. & M.J. Simmons. (2009) Principles of Genetics, 5th ed. Chapter 2: Mendelism: The Basic Principles of Inheritance Lecture 2, Professor Michael Pierce

Theories of Inheritance through the ages

homunculus, inheritance of acquired characteristics; blending model of inheritance, particulate model of inheritance.

homunculus

spermists and ovists; preformation; idea of preformed human in the sex cell

inheritance of acquired characteristics

introduced in the 18th century by LaMarck; theory that characteristics were developed through use and disuse.

blending model of inheritance

developed in the 19th century; the idea that the genetic material of both parents were mixed, or blended.

problems with blending model

-parental contribution cannot be recovered
- populations will become homogenous
-characteristics can skip generations and blending cannot explain this.

particulate model of inheritance

the "gene idea" developed by Mendel in the 1860s; explains all the blending problems and introduces a discrete unit of inheritance in offspring, parental contributions coexist independently and retain their individual properties and can be recovered.

Why did Mendel pick the garden pea, or Pisum satirum?

- It's a dicot, a plant that sprouts 2 leaves or a cotyledon.
- The petals of the flower close down tightly, preventing pollen grains from entering or leaving, which enforces self-fertilization. Peas, as a result, are highly inbred, displaying minimal genetic variation, or true breeding.
- Had contrasting traits which helped him determine inheritance of characteristics of the peas.
- singular differences allowed him to study one trait at a time.
- easy to grow, control
- clearly distinct traits

7 traits identified and used by Mendel

height, texture, seed color, flower color, pod shape, pod color, flower position

cross-fertilization

sperm and egg from different individuals; male organs removed before matured; Mendel used tall and dwarf pea plants to investigate how height was inherited.

mono-hybrid crosses

a cross between parents differing in only one trait or in which only one trait is being considered.

monohybrid

an offspring of 2 homozygous parents that differ from one another by the alleles present at only one gene locus.

steps of a monohybrid cross

1) Tall (dominant) and dwarf varieties are cross-fertilized
2) all the hybrid progeny are tall.
3) the hybrid progeny are self-fertilized.
4) Tall and dwarf plants appear among the offspring of hybrids approximately in a ratio of 3 tall :1 dwarf.

ex:
parental (P): dwarf x tall (cross-pollinated) -->First filial (F1): tall = monohybrids (self-pollination) --> Second Filial (F2): 3Tall + 1Dwarf

reciprocal cross

crosses between different strains with the sexes reversed; for example: female A x male B and male A x female B.

genotype

genetic makeup or identity of the alleles.

phenotype

physical appearance

homozygous

2 alleles are identical

heterozygous

2 alleles are different

dominant & recessive alleles

dominant: expressed factor in a cross; recessive: latent factor

The Principle of Dominance

when one allele conceals the presence of the other allele; Mendel inferred that for all characteristics, there's 1 dominant and 1 recessive.

The principle of Segregation

In a heterozygote, two different alleles segregate from each other during the formation of gametes; reduces the number of alleles; Mendel predicts meiosis with this principle.

testcross

backcross to the recessive parental type or a cross between genetically unknown individuals with a fully recessive tester to determine whether an individual in question is heterozygous or homozygous for a certain allele.

dyhybrid

an individual that is heterozygous for two pairs of alleles; the progeny of a cross between homozygous parents differing in two respects.

dyhybrid cross

following the inheritance for two traits; Mendel used seed color and texture; uses the principle of independent assortment

ex:
P: yellow, round x green, wrinkled
F1: Yellow, round (self-fert.)
F2: 9:3:3:1 ratio of yellow, round:green, round:yellow, wrinkled: green wrinkled.

Please allow access to your computer’s microphone to use Voice Recording.

Having trouble? Click here for help.

We can’t access your microphone!

Click the icon above to update your browser permissions above and try again

Example:

Reload the page to try again!

Reload

Press Cmd-0 to reset your zoom

Press Ctrl-0 to reset your zoom

It looks like your browser might be zoomed in or out. Your browser needs to be zoomed to a normal size to record audio.

Please upgrade Flash or install Chrome
to use Voice Recording.

For more help, see our troubleshooting page.

Your microphone is muted

For help fixing this issue, see this FAQ.

Star this term

You can study starred terms together

NEW! Voice Recording

Create Set