Chapter 14: Mendel and the Gene Idea

Question 1

What were Mendel’s two hypotheses on inherited traits?

Answer 1

Blending hypothesis: Suggests that hereditary material from both parents mixes together in offspring and remains blended indefinitely

Particulate hypothesis: Offspring inherit a blend of traits from their parents, and over successive generations, the traits become increasingly diluted or blended together.

Question 2

Define true breeding.

Answer 2

True-breeding organisms are homozygous for a particular trait, meaning that they carry two identical alleles for that trait. When true-breeding organisms are crossed, all of their offspring will also exhibit the same trait, generation after generation, as long as they are bred with other true-breeding individuals for that trait.

Question 3

Define hybridization.

Question 4

What are alleles?

Answer 4

Different forms of a gene that can lead to variations in a particular trait.

Question 5

Distinguish between dominant and recessive alleles.

Answer 5

Dominant: Alleles that mask the effects of recessive alleles when they are present together in an individual’s genotype (uppercase letter, Aa or AA)

Recessive: Alleles that are only expressed when there are two copies of the recessive allele present in the genotype (homozygous recessive) (lowercase letter, aa)

Question 6

Explain Mendel’s Law of Segregation.

Answer 6

It describes the process by which pairs of alleles separate or segregate during the formation of gametes (sex cells) in the parents.

Question 7

What is the difference between genotypes and phenotypes?

Answer 7

Phenotype: Observable physical or biochemical characteristics of an organism, like its appearance, behavior, or other measurable traits (3:1)

Genotype: The genetic makeup of an organism, particularly with regard to a specific trait or set of traits

Question 8

Distinguish between heterozygous and homozygous.

Answer 8

Homozygous: Refers to a condition where an individual has two identical alleles for a particular gene, either both dominant or both recessive (TT or tt).

Heterozygous: Refers to a condition where an individual has two different alleles for a particular gene, one dominant and one recessive (Tt).

Question 9

Explain Mendel’s Law of Independent Assortment

Answer 9

The inheritance of one trait is not dependent on the inheritance of another trait. This law helps explain the diversity of traits observed in offspring and contributes to the variability of genetic combinations.

i.e. if an organism inherits an allele for tallness (T) from one parent and an allele for yellow seed color (Y) from the other parent, the inheritance of seed color is independent of the inheritance of plant height.

Question 10

Distinguish between an independent hypothesis and a dependent hypothesis.

Answer 10

Dependent hypothesis: two traits if passed on, they will depend on each other to be present. will be passed on as a package

Independent hypothesis: each trait will be assorted into the gametes independent of each other.

Question 11

What is a testcross and when is it used?

Answer 11

Testcross: A technique used to determine the genotype (the genetic makeup of an organism) of an individual with a dominant phenotype.

Question 12

Define a monohybrid cross.

Answer 12

A cross between two heterozygotes.

Question 13

Define a Dihybrid cross.

Answer 13

A cross between two pairs of alleles.

Question 14

What are mendelian traits vs non-mendelian traits?

Answer 14

Mendelian traits are traits that follow the principles of inheritence as described by Mendel that characters are either dominant OR recessive.

Nonmendelian traits are traits that dont follow classic patterns of inheritance described by mendel.

Question 15

Explain the three degrees of dominance.

Answer 15

Complete dominance: The phenotype of the dominant allele is going to hide the phenotype of the ressesive allele.

Incomplete dominance: The dominant allele is not completely expressed when the recessive allele is around, causing a third “in-between” non-parental phenotype. (phenotypic ratio = genotypic ratio)

Codominance: Both alleles are expressed and work together to share dominance. ex. chickens can be black (BB) or white (WW) or speckled b&w (BW)

Question 16

What are polygenic traits?

Answer 16

Multiple genes coding for one specific trait. Involved in skin color.

Question 17

Define epistasis.

Answer 17

When one gene depends on the presence of another gene for it to be expressed. Ex. rat can be black (BB or Bb) or brown (bb), or have no color (cc). (9:3:1)

Question 18

Is there an environmental impact on Phenotype?

Answer 18

Yes, for example hydrangea plants can be pink in pH of 6.5-7.0, or blue in pH of 5.0-5.5.

Question 19

What is pleiotropy?

Answer 19

the phenomenon where a single gene influences multiple, seemingly unrelated phenotypic traits. Ex. phenylketonuria (PKU), a genetic disorder caused by mutations in the gene encoding phenylalanine hydroxylase (PAH).

Question 20

Explain why lethal dominant genes are much rarer than lethal recessive genes.

Answer 20

individuals with a lethal dominant allele typically die before they can reproduce and pass on the allele to the next generation. Also, lethal recessive genes are often masked by the presence of a functional allele on the other chromosome (heterozygosity).