9a Flashcards
Zygote?
A fertilized egg cell; it is the first cell of a diploid organism
Nondisjunction
Failure of chromosomes to separate resulting in extra or missing chromosomes.
homologous chromosomes (5)
chromosome pairs, one from each parent, that are similar in length and centromere location and have the same sequence and location of genes
autosome
chromosomes that are the same for both sexes, nonsex chromosome
sex chromosome
chromosome that carries genes that determine sex
Allele
Alternate version of the same gene
gametes
A haploid sex cell: sperm or egg cell.
fertilization
Union of two gametes resulting in a diploid zygote
germ cell
Diploid cells that can produce gametes and occur only in testes and ovaries)
somatic cells
body cell that does not give rise to gametes.
crossing over
exchange of genetic material between homologous chromosomes during prophase I of meiosis
monozygotic
Identical twins, one zygote splits in half
dizygotic
Nonidentical twins, two zygotes (two sperm fertilize two different eggs)
Polyploid cell
Cell with extra chromosome sets
Meiosis
Division of genetic material that halves the chromosome number and yields genetically variable gametes.
mitosis
Division of genetic material that yields two genetically identical cells
Haploid cell vs. diploid cell
A diploid cell (2n) has two full sets of chromosomes, one set coming from each parent (mitosis). A haploid cell (n) has only one set of chromosomes. (Meiosis)
Compare and contrast sexual and asexual reproduction.
Asexual reproduction requires only one parent and produces offspring that are identical, except for mutations. (mitosis) Sexual reproduction requires two parents and produces genetically variable offspring. (meiosis/gamete formation/fertilization)
Polyploidy
Polyploidy is an organism or cell having more than twice the haploid number of chromosomes. Polyploidy arises as the result of total nondisjunction of chromosomes during mitosis or meiosis. Common in plants.
Aneuploidy
Aneuploidy is any deviation from the exact multiple of the of haploid number of chromosomes. Most aneuploids arise by nondisjunction, a failure of homologous chromosomes to separate at meiosis.
Chromosomes may be present in multiple copies (Trisomy) or one of a homologous pair may be missing in a diploid cell (monosomy).
How can deletions, duplications, inversions and translocations cause illnesses?
Deletions, duplications, inversions, and translocations can delete, duplicate, or damage genes, which may affect the normal production of proteins. Affected individuals may lack proteins, produce harmful proteins, or have fertility problems.
- Compare and contrast gamete formation in a man and a woman.
Spermatogenesis results in four equally-sized, very small spermatids that mature into sperm cells. Oogenesis results in one very large egg and three polar bodies. The processes are similar in that they involve an initial mitotic division and then two meiotic divisions to produce haploid gametes.
Chromosomal deletions
Results in the loss of one or more genes, may mean that an individual cannot make some proteins
Chromosomal duplication
Produces multiple copies of part of a chromosome
Chromosomal inversion
Part of a chromosome flips and reinserts changing the gene sequence. Inversion produces symptoms because chromosomes may not align properly during meiosis, causing fertility problems, miscarriage, or birth defects.
Chromosomal translocation
Nonhomolygous chromosomes exchange parts. In translocation, chromosomes may be missing parts, or genes can be broken
Meiosis/Mitosis - similarities
both divide the chromosomes of a eukaryotic cell and overall, the processes have a similar progression of stages, and similar mechanisms move chromosomes.
Meiosis/Mitosis - differences
Stage of life vs. anytime, 1 cell division/2 divisions, 2 daughter cells/4, 1 cytokineis/2, homologous alignment and crossing over only in meiosis, identical vs. genetically variable, growth and repair vs sexual reproduction.
Explain how crossing over generates variability among offspring.
In crossing over, homologous chromosomes align and swap segments with each other. After crossing over is complete, the chromosomes have new allele combinations. Crossing over occurs at random so the gametes produced in one round of meiosis are not identical to those produced in a subsequent round of meiosis. (prophase I)
Explain how independent assortment generates variability among offspring.
Homologous chromosomes can be attached to either spindle pole in Metaphase I, so each homologue can be packaged into either one of the two new nuclei. (Humans 223 possible combinations of homologous chromosomes)
Explain how fertilization generates variability among offspring.
Chance combinations of maternal and paternal chromosomes through fertilization produce a unique combination of genetic information.
- Explain the role of meiosis in sexual reproduction.
In meiosis, a diploid cell divides twice to produce four haploid nuclei, reducing the chromosome number by half. Meiosis also creates new allele combinations in the haploid nuclei.
- Explain the role of gamete formation in sexual reproduction.
Gamete formation packages the haploid chromosomes into reproductive cells (sperm and egg cells).
- Explain the role of fertilization in sexual reproduction.
Fertilization merges haploid gametes from two parents, producing a new diploid cell with half its chromosomes coming from each parent.
- Describe the role of homologous chromosomes in sexual reproduction.
Homologous chromosomes pair up during sexual reproduction and shuffle genetic information in a process called crossing over.
- Explain the roles of somatic cells and germ cells in sexual reproduction.
Germ cells are specialized diploid cells that make gametes and are found only in the ovaries and testes. Somatic cells are found in the rest of the body, and do not participate directly in reproduction.
- Distinguish between autosomes and sex chromosomes.
Autosomes are chromosomes that are the same regardless of sex, whereas the sex chromosomes determine whether an individual is male or female.
