11 Q/A

Seite 1

11.1 Q/A

1) How is Mendel's work connected to what we learned in previous chapters on Mitosis and Meiosis?

Genes are passed down from parent to child and have a chance of reappearing in the 3rd generation if inbreeding occurs.

Genes are passed down by crossing over, and some are more dominant than others and they are the ones used.

2) What is the Principle of Segregation?

Each parent can only give their offspring one copy of each gene. When fertilization occurs the offspring should have one copy of each gene from each parent giving them two copies of each gene.

3) What type of cross did Mendel perform to show support for the Principle of Segregation?

Hybridization of True-breeding plants. /Dihybrid cross.

4) How does the setup of a Punnett square rely on the Principle of Segregation?

Because it relies on the fact that 2 or more genes on top and side of the square in order to predict the children's genes.

5) What is the Principle of Independent Assortment?

Traits move independently of each other. Ex. Hair color cannot affect Eye color, gender, etc.

6) Describe how the Principle of Independent Assortment can be explained by the behavior of chromosomes during meiosis.

The principle of Independent Assortment can be explained by the behavior of chromosomes during meiosis since the genes cross over and recross over during prophase 1 independent of each other. Alleles are unique to each parent which is why they can't be the same as each other

Seite 2

11.2

1) Use a Punnett square to predict the results of a monohybrid cross, stating the phenotypic and genotypic ratios of the F2 generation.

phenotypic ratio: 3 dominant to 1 recessive

genotypic ratio: 2 Heterozygous Dominant to 1 Homozygous dominant to 1 homozygous recessive.

2) Explain how a test cross can be used to determine if an individual with the dominant phenotype is homozygous or heterozygous.

A test cross shows the possible gene combinations. This will show if the two alleles inherited from the parents are the same (homozygous) or different (Heterozygous).

3) Use a Punnett square to predict the results of a dihybrid cross and state the phenotypic ratio of the F2 generation.

genotype ratio: 1 (Ho Dom, Ho Dom) to 2 (Ho Dom, He Dom) to 2 (He Dom, Ho Dom) to 4 (He Dom, He Dom) to 1 (Ho Dom, Ho Rec) to 2 (He Dom, Ho Rec), to 1 (Ho Rec, Ho Dom) to 2 (Ho Rec, He Dom).

the phenotypic ratio: 9 (Dom, Dom) to 3 (Dom, Rec) to 3 (rec, dom) to 1 (Rec, Rec) ratio

4) Use the multiplication rule to calculate the probability that a particular F2 individual will be homozygous recessive or homozygous dominant.

50 percent for monohybrid cross, 5 out of 8 in a dihybrid cross.

5) Given a Mendelian cross, use the addition rule to calculate the probability that a particular F2 individual will be heterozygous.

50 percent chance of a heterozygous result.

6) Use the laws of probability to determine the probability of rolling a die (one dice) four times and getting two 3's and two 6's?

1/1296

7) Use the laws of probability to predict, from a dihybrid cross between two individuals that are heterozygous for both traits, the expected proportion of the offspring that would be:

a. homozygous dominant for the two traits 1/16

b. heterozygous for both traits 1/4

c. homozygous recessive for both traits 1/16

Seite 3

11.3

1) Give an example of incomplete dominance and answer the following question. In guinea pigs, hair texture exhibits incomplete dominance. The gene for curly hair (C) is incompletely dominant to the gene for straight hair (c). Individuals that are heterozygous (Cc) have wavy hair. Two heterozygous parents have a child. What is the chance that the child will have wavy hair?

Incomplete dominance would be when instead of it being one or the other, both genes express themselves and you get a mixture instead. 50% chance for wavy hair.

2) In some chickens, feather color is controlled by codominance. When a black chicken mates with a white chicken, all of the offspring are covered in both black and white feathers. A farmer mates a black chicken (BB) with a black-and-white (BW) chicken. What are the predicted phenotypes of their offspring?

50% Black, 50% Black and white

3) Explain how phenotypic expression in the heterozygote differs with complete dominance, incomplete dominance, and codominance.

Complete dominance- Only the Dominant allele is visible.

Incomplete Dominance - The two alleles blend together.

Co-dominance - Both alleles are visible but don't blend.

4) Describe the inheritance of the ABO blood system and explain why the IA and IB alleles are said to be codominant.

Because both A and B alleles can be manifested.

5) A mother of known blood type A has a child whose blood turns out to be B. Based on this information, what is the mother's genotype?

AIAi?

6) Define and give examples of pleiotropy and epistasis.

Epistasis- "To stand upon" The first gene determines whether or not the second gene will be expressed in the phenotype.

Pleiotropy - the ability of a gene to have effects on more than one organ system in the body.

7) Describe a simple model for polygenic inheritance.

Lots of genes code for one trait. (Ex. Height) Person A might have AABbcc, whereas person B might have aaBBCc.

8) Describe how environmental conditions can influence the phenotypic expression of a character. Explain what is meant by “a norm of reaction.”

The environment and nutrition play a large part in what genes are expressed as without certain stressors, certain genes do not get expressed.

A norm of reaction is a curve that relates for a given genotype the contribution of environmental variation to observed phenotypic variation.

Seite 4

11.4

1) Given a simple family pedigree, deduce the genotypes for specific family members. For example, determine the genotypes of the individuals labeled 1, 2, & 3 in the pedigree for Alkaptonuria.

Can't see the pictures, but usually, those with the trait are marked in a color and men are squares whereas women are circles. Two lines connecting two people horizontally means they reproduced. A vertical line connection between the reproduction line means that they are parent/child. Autosomal is non-sexual genes. Half-shaded means that the person is a carrier.

2) Explain why dominantly inherited genes are much rarer than recessive genes.

No clue. It must come down to heterozygous Dominance, sex-linked traits, and chance.