x and Y chromosome

Exam on Monday will cover various topics including details from the photosynthesis lab.
Photosynthesis worksheets will be available similar to previous workshops.
Review of material is encouraged as there may be questions that involve previous labs.

Details covered in the last exam but relevant due to the recent lab exercise.
Importance of understanding details may vary between students, but it is essential not to ignore the topic completely.
Worksheets available to practice knowledge from previous workshops.

Mitosis and Meiosis: Key lab topic where students will:
- Use microscopes to observe stages of mitosis in plant and animal cells.
- Use pipe cleaners as a hands-on activity to model mitosis and meiosis.
Exit Quiz: Prepare for an exit quiz on lab information. Review materials beforehand.

Schedule changes noted: Review sessions typically on Tuesday at 1 PM will move to 11 AM for better attendance.
Other sessions on Mondays are anticipated to be full. Attendance is encouraged but not mandatory.

Discusses that genes that express traits are located on chromosomes.
Example: Thomas Hunt Morgan's work on Drosophila (fruit flies) related to eye color.
- Red eye color (wild type allele) dominant over white eye color (mutant allele).
- Crosses between true breeding red-eyed female and white-eyed male demonstrate inheritance patterns.

F1 generation displays only red eyes indicating dominance of red over white.
Self-hybridization of F1 leads to typical 3:1 phenotypic ratio, but sex-based segregation observed.
Male fruit flies exhibited mixed phenotype ratios; highlights the X-linked nature of this trait.

Essential to understand mechanisms behind sex-linked inheritance.
Example traits discussed: color blindness, Duchenne muscular dystrophy, and hemophilia.
Caution in problem-solving noted; don't default to sex linkage without evidence in the question.

Various systems of sex determination:
- XY system: typical in mammals (XX for females, XY for males).
- XO system: found in some insects like grasshoppers (females have two X chromosomes, males have one).
- ZW system: seen in birds, where females are heterogametic (ZW) and males are homogametic (ZZ).
- Haploid-diploid system: observed in bees where males are haploid (n) and females are diploid (2n).

Female mammals randomly inactivate one of their X chromosomes (X inactivation) to equalize gene dosage with males.
- Resulting structure known as a Barr body.
- Random inactivation leads to females being genetic mosaics.
- Example: tortoiseshell cats have distinct fur patterns due to X-linked color gene expression.

Occurs early in development (16-64 cell stage).
Random X activation gives rise to cellular diversity in phenotype expression across the body.
- E.g., sweat gland activity in females showing varied sweat patterns due to different active alleles.

Misalignment/separation of chromosomes during meiosis can lead to aneuploidies (wrong chromosome number).
- Klinefelter syndrome (XXY): traits include underdeveloped testes, and infertility, often resultant from nondisjunction.
- Turner syndrome (XO): missing second sex chromosome leads to developmental issues in females.

Different types of structural chromosomal mutations:
- Deletion: loss of chromosome segments may lead to severe health issues depending on lost genes.
- Duplication: may not always cause issues but can depending on affected genes.
- Inversion: chromosome segments reversed; can disrupt gene regulation.
- Translocation: exchange of DNA segments between chromosomes; can lead to disorders (e.g., Philadelphia chromosome linked to chronic myelogenous leukemia).

Proper understanding of these biological concepts is crucial for the exam.
Engage in reviewing practice problems and concepts thoroughly to reinforce knowledge.
Identify and clarify any confusion during review sessions or office hours.