Introduction: This Worksheet Discusses Material Covered in the Nineteenth Lecture(02/27/2017)

Introduction: This worksheet discusses material covered in the nineteenth lecture(02/27/2017). Chapter 4 examines these topics.

Concepts

1. Sex-influenced inheritance.
2. Cytoplasmic inheritance.
3. Maternal effect.
4. Imprinting.

Material

1. Sex-influenced inheritance.

In this section, we’ll discuss sex-influenced inheritance of traits.

1. Are sex-influenced traits autosomal or sex-linked?

1. Fruit flies have two alleles for body color, A and a. The A allele codes for normal body color while the a allele codes for albinism. In females, heterozygous individuals exhibit an intermediate phenotype between normal and albino body color. Males do not exhibit this unique heterozygous phenotype.
2. Perform the following cross and give the expected phenotypic ratio.

Aa x aa

1. Perform the following cross and give the expected phenotypic ratio.

Aa x Aa

1. You perform a testcross with a male fly. What is the expected phenotypic ratio of the offspring if the male is homozygous AA?

1. Cytoplasmic inheritance.

This section will discuss cytoplasmic inheritance.

1. Describe the mechanism by which cytoplasmic inheritance occurs. Why doesn’t the male gamete affect cytoplasmic inheritance?

1. A novel mutation in a male organism’s mitochondria causes the ATPases produced to become CTPases. This means that the affected mitochondria will produce CTP instead of ATP (this is a non-lethal mutation). If the male organism is heterozygous for ATP-producing and CTP-producing mitochondria and mates with a wild-type female, what type of offspring can be produced?

1. Follow the above scenario, but as a reciprocal cross. Can you determine the offspring ratio?

1. Maternal effect.

1. Describe the mechanism by which maternal genetic inheritance occurs.

1. Again in fruit flies, a mutation to a certain gene can result in no formation of legs in a maternal affect manner. The allele that results in legless development (w) is recessive. The wild-type allele is dominant (W).

1. Perform the following cross (female listed first) and list the phenotypic and genotypic ratios of the offspring.

Ww x ww

1. Perform the reciprocal cross of the cross listed above. Again describe the expected phenotypic and genotypic ratios of the offspring.

1. Genomic imprinting.

1. Describe genomic imprinting. Is the imprinted allele silenced, expressed, or overexpressed?

1. In a certain breed of plant, a dominant allele F results in the formation of two cotyledons prior to the flower while the recessive allele f results in the formation of four cotyledons.
2. Bearing imprinting in mind, you cross an FF female with an Ff male and observe the following offspring phenotypes. How did this happen?

1. Given the above method of imprinting, what will be the expected phenotypic and genotypic ratios in the offspring of the following cross?

Ff x Ff

Things to do next

• Focus your review on things that were difficult from this worksheet. If it was really challenging, don’t worry; these are meant to be tough and push your understanding of the topics we covered.
• Practice makes perfect here. The exact mechanisms how these arise aren’t all that important (with the exception of cytoplasmic inheritance) so long as you understand the outcomes. Test questions will be most likely to follow the format, “Considering this cross [XY x WZ] is governed by sex-influenced / maternal effect / genomic imprinting inheritance, what are the expected phenotypes?” So make sure you feel comfortable working through this.
• If you have any questions, ask me in session, in class, or by email. I’m more than happy to help.
• Next session (Thursday03/02/17) will be from 5:10 to 6:00 PM in Gilman 1051. We’ll be discussing material from Wednesday’s lecture.