Genetics ECA

Directions: Read through required information. Look for *** and address or answer the prompts.

College Board Learning Objectives

Natural selection acts on phenotypic variations in populations.

a. Variations are not directed by the environment but occur through random changes in the DNA and through new gene combinations

b. Changes in DNA occur during essential cellular processes, in particular, DNA replication, repair, and recombination. These changes may be silent with no observable phenotypic effects; or these changes can significantly alter the phenotype of the organism to increase or decrease fitness.

Students should be able to demonstrate understanding of the above concept by using an illustrative example such as:

Sickle cell

Yellow mice

In most eukaryotes, heritable information is passed to the next generation through mitosis or meiosis plus fertilization.

a. Processes pass genome from parent cell(s) to progeny.

b. Mitosis passes complete genome from parent cell to progeny.

1. Mitosis occurs after chromosome replication.

2. Mitosis produces genetically identical daughter cells.

3. Mitosis plays a role in asexual reproduction, growth, and repair.

c. Meiosis followed by fertilization ensures genetic diversity in sexually reproducing organisms.

1. Meiosis is a reduction process that reduces the chromosome number by one-half to produce haploid gametes.

2. Fertilization increases genetic variation in populations by providing for new combinations of genetic information in the zygote and restoring the diploid number of chromosomes.

3. One set of genetic information is retained in each of the gametes due to paring of homologous chromosomes. During meiosis homologous chromosomes are paired, with one homologue originating from the maternal parent, the other from the paternal parent. 4. During meiosis, homologous chromatids exchange genetic material, a phenomenon called crossing-over, which increases genetic variation in the resultant gametes. ***Learning Objective: The student is able to construct an explanation using representations with annotations how DNA in the forms of chromosomes is transmitted to the next generation via mitosis and meiosis followed by fertilization.

Learning Objective: The student is able to represent the connection between meiosis and increased genetic diversity necessary for evolution.

Learning Objective: The student is able to construct an explanation using diagrams with annotations how DNA in the form of chromosomes is transmitted to the next generation via mitosis and meiosis plus fertilization.

Learning Objective: The student is able to evaluate sources of data to support the claim that heritable information is passed from one generation to another generation through mitosis or meiosis followed by fertilization.

Mendelian genetics provides a basic understanding of the underlying causes of the pattern traits from parent to offspring.

a. Rules of probability can be applied to analyze passage of traits from parent to offspring.

****b. Segregation and independent assortment of chromosomes result in genetic variation.

***1. Mendelís laws of segregation and independent assortment can be applied to genes that are on different chromosomes.

***2. Genes that are adjacent and close to each other tend to move as a unit; the probability that they will segregate as a unit is a function of the distance between them. The mode of inheritance (monohybrid, dihybrid, sex-linked on the X chromosome, and genes linked on the same homologous chromosome) and probability of offspring phenotype or genotype can be predicted from data that gives the parent genotype and/or the offspring phenotypes or genotypes.

***c. Some human genetic disorders can be attributed to the inheritance of single gene traits (dominant or recessive, autosomal or sex-linked) or non-disjunction.

 

***Students should be able to demonstrate understanding of the above concept by using an illustrative example of each (single gene traits or non-disjunction):

 

Sickle Cell

Tay-Sachs

Huntingtonís Chorea

SCIDs

Color Blindness

Trisomy 21

Klinfelterís Syndrome

 

d. Ethical, social, and medical issues surround human genetic disorders.

 

Learning Objective: The student is able to construct a representation (punnett square or mathematically) that connects the passage of traits from parent to offspring to the process of meiosis.

***Learning Objective: The student is able to articulate reasons for the revisions to Mendelís model of inheritance.

***Learning Objective: The student is able to construct an explanation of an ethical, social, or medical issue surrounding a human genetic disorder.

Learning Objective: The student is able to evaluate evidence provided by data of Mendelís model of inheritance of traits.

 

The inheritance pattern of many traits cannot be explained by simple Mendelian genetics.

***a. Many traits are polygenic or multifactorial.

1. Patterns and modes of inheritance are usually not as simple as predicted by Mendelís laws and can be tested by quantitative analysis, whereby the calculated phenotypic ratios differ from the predicted ratios.

2. Mendelís law of independent assortment does not apply when the genes are located close together on the same chromosomes. These linked genes are inherited together unless crossing-over occurs during the formation of gametes.

***b. Traits can result from non-nuclear inheritance.

1. In animals mitochondrial DNA is inherited via the egg.

2. In plants, chloroplasts and mitochondria are randomly assorted to the daughter cells; in fungi, mitochondria are randomly assorted

***c. In mammals traits are located both on autosomal chromosomes and the sex chromosomes (X and Y).

1. Sex-linked genes are genes that reside on the sex chromosome (X). Few genes reside on the Y chromosome, and some traits are more easily seen in males (XY) than females (XX).

2. Some traits are sex limited, and expression depends on the sex of the individual, e.g., milk production in female mammals.

Learning Objective: The student is able to evaluate alternative explanations for the inheritance of traits that cannot be explained by simple Mendelian genetics.

Learning Objective: The student is able to describe representations of an appropriate example of inheritance patterns that cannot be explained by simple Mendalian genetics.