Chapter 9 Flashcards
Define fertilization
When male and female reproductive cells join to produce a new cell
What made pea plant flowers good for Mendel’s research?
They can self-pollinate, so they’ll produce genetically identical offspring
Through what process was Mendel able to produce seeds that had 2 different parents?
Through cross-pollination
Define a trait
A characteristic that varies from one individual to another
How many pea plant traits did Mendel study?
7, each with 2 contrasting characteristics
What did Mendel do with each of the 7 plants with contrasting characteristics?
He cross bred them with the plant with the opposite characteristic
What is the original pair of plants called?
The P generation
What is the first generation of offspring (from the P generation) called?
The F1 generation
What is the second generation of offspring called?
F2
What did Mendel know before conducting his research?
That:
- The male part of each flower produces pollen (containing sperm)
- The female part of the flower produces egg cells
Define hybrid
The offspring of 2 organisms with contrasting characteristics
What was Mendel’s first conclusion?
That biological inheritance is determined by factors that are passed from one generation to the next
What are the “factors” mentioned in Mendel’s first conclusion?
Genes
What are the different forms of a gene called?
Alleles
What does the principle of dominance state?
The principle of dominance states that some alleles are dominant and others are recessive
The trait controlled by the recessive allele appeared in how many of the F2 generation in Mendel’s experiment?
25% (1/4)
What does the reappearance of the trait controlled by the recessive allele indicate?
That at some point the recessive allele had been separated, or segregated, from the dominant allele
When did Mendel suggest that the 2 alleles for tallness and shortness segregate?
Mendel suggested that the alleles for tallness and shortness in the F1 plants segregated from each other during the formation of the sex cells, or gametes
What organisms are said to be homozygous?
Organisms that have two identical alleles for a particular trait
What organisms are considered to be heterozygous?
Organisms that have two different alleles for a particular trait
Heterozygous organisms can also be referred to as what for a particular trait?
They can be referred to as hybrid for a specific trait
All plants that are tall (dominant over short) have the same what?
Phenotype
Plants that are tall (dominant over short) can have a different what?
Genotype
What do probabilities predict?
Probabilities predict the average outcome of a large number of events
What can’t probabilities predict?
Probabilities cannot predict the precise outcome of an individual event
How does probability relate to genetics?
-In genetics, the larger the number of offspring, the closer the resulting numbers will get to the expected values (frequency of the occurrence of a trait)
What is a 2 factor cross?
Crossing 2 plants that have 2 contrasting characteristics **
The punnet square predicts what ratio for the F2 generation of Mendel’s 2-factor cross?
9:3:3:1
What does the principle of independent assortment state?
It states that genes for different traits can segregate independently during the formation of gametes
What does independent assortment account for?
It helps account for the many genetic variations observed in plants, animals, and other organisms
Define incomplete dominance
When one allele is not completely dominant over another
What do the genotypes of a trait with incomplete dominance look like in the parents and offspring
The heterozygous (new) phenotype of the offspring is a mix between the two homozygous phenotypes of its parents
Give an example of incomplete dominance
A cross between red (RR) and white (WW) plants produces pink-colored flowers (RW). No different shades of pink, just one shade for all of the offspring
Define codominance
When both alleles contribute to the phenotype
Give an example of codominance
In certain varieties of chicken, the allele for black feathers is codominant with the allele for white feathers
Heterozygous chickens are speckled with both black and white feathers. The black and white colors do not blend to form a new color but appear separately
Define multiple alleles
A gene that is controlled by multiple alleles. Note that an individual can’t have more than 2 alleles for a trait but more than 2 exist.
Give an example of a gene/ trait with multiple alleles
A rabbit’s coat color is determined by a single gene that has at least four different alleles
Define a polygenic trait
Traits controlled by two or more genes (not alleles, genes)
Give an example of a polygenic trait
Skin color in humans is a polygenic trait controlled by more than four different genes. This results in different shades of skin tones.
Who used fruit flies to advance the study of genetics?
Thomas Hunt Morgan
What did T. Morgan learn during his studies of fruit flies?
Morgan and others tested Mendel’s principles (on fruit flies and other organisms) and learned that they applied to other organisms as well as plants
Describe Mendel’s first law in detail. (Principle of dominance)
The two members of a gene pair (alleles) segregate from each other in the formation of gametes. Half the gametes carry one alleles, and the other half carries the other allele. Alleles, not genes.
What is Mendel’s first law?
The Principle of Dominance
What is Mendel’s second law?
The Principle of Independent Assortment
Describe Mendel’s second law in detail (Principle of Independent Assortment)
Genes (NOT alleles, genes) for alleles assort independently of one another during the formation of gametes
