SciRev. wk 14 Mendel latest update 2025 with accurate solutions

Continuous Variations

-darwin

-evolution resulted from many tiny variations

-Biometricians (like Galton and Pearson) studied heredity by quantitative methods

-they believed in blending inheritance

blending inheritance

parental traits blend such that their offspring have intermediate traits

biometricians

-followers of Darwin

-continuous variation is inherited/evolves

-evolution/speciation happens gradually by natural selection

-studied hereditary patterns by quantitative methods of characters w/in a population

-showed "normal" distributions which led to the conclusion of continuous variation

Two difficulties of continuous variation

1. there was no clear-cut evidence that existed to indicate such variations were indeed inherited

2. examination of populations in nature showed that from one locality to another, variations seemed to be discontinuous

Discontinuous Variations

-occurred in discreet forms w/ no intermediate ones

-Bateson

-explored Asian lakes w/ different degrees of salinity

William Bateson

-discontinuous variation

-studied a wide range of plants and animals

-looked at the relationship btw variation in the environment and variability w/in populations of organisms

-explored different Asian lakes

What did Bateson find when exploring the Asian lakes?

-continuous changes in salinity among many lakes accompanied with discontinuous variations in the crayfish population

-in other words, the environment showed a continuous graduation of physical characteristics while organisms were discontinuous

-concluded that variations that were hereditary were discontinuous

Bateson's influence

-allowed the Mendelian theory to be heard and considered viable

-won a major victory for the concept of discontinuous variation (against biometricians who were in support of continuous variation)

Galton

-accepted a blending theory of inheritance

-argued that no matter how pronounced initial variations may be, eventually they will weaken by cross-breeding (regression to the mean or mediocrity)

-"bean machines" or "Galton box"

-coined the term eugenics

bean machines/Galton box

-illustrates his views

-that eventually pronounced initial variations will weaken by cross-breeding

-if balls are dropped in a galton box, each ball bounces left or right as it hits a pin until it falls into a bin at the bottom

-when several balls have been dropped, their distribution privileges the middle boxes (mean)

eugenics

-coined by Galton

- = well born

-study of factors that influence the hereditary qualities of the human race and ways to improve those qualities by selection

-first laws introduced in Indiana in 1907

first eugenics laws were meant to combat what?

-criminality and mental illness

-allowed the forced sterilizations of people who were deemed a public threat

-after Indiana, most other states adopted similar laws (where about 20,000 people were then sterilized)

-eugenics legislation was much harsher in Germany

Gregor Mendel

-a teacher and monk

-he started an extensive experimental program on peas

-work was published in 1866 but was ignored

why did Mendel start an extensive experimental program on peas?

to study the transmission of hereditary characters in successive generations

Mendel's monastery

-in Brno

-was 20x100 feet

-for some characters, offspring were not a "blended" average of their parents

-mendel knew that peas had some characters like this

-if one parents had yellow and the other had green seeds, the offspring would all have yellow seeds NOT yellowish-green

What was Mendel's reason for the peas being yellow and not yellowish green?

-argued that this was because one factor was dominant and the other recessive

-each parent contributed one factor to the offspring plant

-so while the offspring plant does have both factors, only the dominant one is expressed

Mendel's pea plant traits

-height

-seed shape

-seed color

-seed coat color

-pod shape

-pod color

-flower position

Mendel's Law of Segregation

-In the formation of germ cells, the two factors for any characteristic are always separated from each other and ended up in a different egg of sperm

-offspring acquire one factor from each parent

-F1 and F2 mean first and second generation

-When F1 plants plants are crossed with each other, even though all of them have purple flowers, some of their offspring F2 are white again (1 in 4 or 25%) a 3:1 ratio of purple to white

-relevant to Darwin's problem of blending inheritance

law of independent assortment

the law that states that genes separate independently of one another in meiosis

How does Mendel's law of inheritance relevant to Darwin's problem of blending inheritance

-the parent's traits can be passed down unchanged, without being blended and diluted w/ each generation

-if having green seeds is a rare but advantageous trait, a green-seeded plant producing offspring w/ a yellow-seeded plant does not lose its genetic factor that made it green, but passes it on unchanged (even though all of the Hybrid F1 offspring are yellow)

Mendel's work

-was mathematical

-didn't receive much attention until it was separately rediscovered about 1900 by three scholars

the chromosome

-became clear in the last quarter of the 19th century it played a role in the process of cell division

-they could be observed because they stained dark under the microscope

-while their chemical composition was investigated, it was unclear what role they had in cell division and how exactly they accomplished that role

was the role of the chromosome known in the last quarter of the 19th century?

-no

-it was unclear what role they had in cell division and how exactly they accomplished that role