18 Questions
During which stage of meiosis do sister chromatids move to opposite poles?
Anaphase II
What is the result of crossing over between two non-sister chromatids of homologous pairs?
Individual chromosomes have both paternal and maternal genes
How many diploid combinations are possible due to independent assortment in humans?
70 trillion
What is the term for the process by which homologous pairs line up randomly during metaphase I?
Independent assortment
Which stage of meiosis follows Anaphase II?
Telophase II
What is the approximate number of possible gamete combinations due to independent assortment in humans?
8.4 million
What is the primary function of histone proteins in the organization of genetic material?
To act as spools for DNA wrapping
What is the term for the thread-like structures that form during cell division?
Chromatin
What is the term for the number of chromosomes present in a species?
Karyotype
What is the region known as, where chromosomes pinch in during cell division?
Centromere
What is the term for the study of the number and structure of chromosomes in a species?
Cytogenetics
What is the term for the genetic information stored in DNA?
Genome
What is the result of nondisjunction of sex chromosomes in females?
Turner Syndrome (XO)
What is the purpose of chorion villus sampling?
To detect chromosomal disorders
During which phase of meiosis is genetic variation introduced?
Prophase I and Metaphase I
What is the purpose of amniocentesis?
To detect chromosomal disorders
What is the result of nondisjunction of sex chromosomes in males?
Klinefelter Syndrome (XXY)
What is the incidence of XXX Females?
1:1000
Study Notes
Chromosomal Abnormalities
- Turner Syndrome (XO): underdeveloped female sex characteristics
- Klinefelter Syndrome (XXY Males): high levels of female sex hormones; more developed female sex characteristics; sterile
- Jacobs Syndrome (XYY Males): somewhat taller; below average intelligence
- XXX Females (1:1000 live births): healthy and fertile; karyotype determines
Prenatal Screening for Genetic Disorders
- Chorion Villus Sampling (Biopsy): cells from the outer membrane of the embryo are removed for karyotyping to detect chromosomal disorders; can be done as early as 8 weeks into pregnancy
- Amniocentesis: amniotic fluid containing cells from the fetus is drawn to prepare and analyze karyotypes for chromosomal abnormalities
Mitosis and Meiosis
- Genetic variation is introduced during Prophase I and Metaphase I
- Chromatin condenses into visible chromosomes during cell division
- Histones act as spool, wrapping DNA to fit in the nucleus
- Chromosome = DNA and associated proteins
- Centromere: the pinched region on a chromosome
Organization of Genetic Material
- Genetic information is stored in DNA (deoxyribonucleic acid)
- Chromosomes are found in the nucleus
- Histones wrap DNA, allowing it to fit in the nucleus
Chromosome Number
- Humans have 46 chromosomes: 22 pairs of homologous chromosomes (autosomes) and 2 sex chromosomes (XX or XY)
- Different species have different numbers of chromosomes
Alleles and Homologous Chromosomes
- Homologous chromosomes carry the same genes at the same location (locus)
- Alleles: different "flavors" of the same gene
- Each side's microtubules on a kinetochore of one replicated chromosome separate during Anaphase II
Meiosis
- Meiosis results in genetically distinct daughter cells
- Crossing over: occurs between two non-sister chromatids of homologous pairs
- Independent assortment: occurs in Metaphase I, where homologous pairs line up randomly
- Random fertilization: 2 gametes combine, resulting in 70 trillion diploid combinations with crossing over
Test your knowledge on cell division, chromatin, mitosis, and the organization of genetic material in cells. Learn about the history of these concepts and the structure and function of chromosomes and DNA.
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