Chapter 13 Flashcards
Living organisms are distinguished by their ability to …
reproducing offspring that resemble their parents but may look slightly different (demonstrating variation)
Variation
shows that offspring differ somewhat in appearance from parents and siblings
Genetics
the study of heredity and hereditary variation (uniqueness)
Offspring acquire genes from parents by…
inheriting gene on chromosomes
Genes
the units of heredity and are composed of segments of DNA
Each gene in an organism’s DNA has a …
specific locus (location) on a certain chromosome
In sexual reproduction,
in terms of genes
we inherit one set of chromosomes from our mother and one set from our father
In asexual reproduction,
one parent produces genetically identical or exact copy (clone) offspring by mitosis
- more simple process
i.e. the multicellular hydra reproduces by budding
In sexual reproduction,
2 parents (produce gametes) give rise to offspring that have unique combinations of genes inherited from the two parents
Fertilization and meiosis alternate in…
sexual life cycles
Life Cycle
is the generation-to-generation sequence of stages in the reproductive history of an organism
in humans, each somatic cell has…
46 chromosomes
made up of 2 sets, one from each parent
Karyotype
an ordered, arranged, visual representation of the chromosomes in a cell that can be used to determine their homology or similarity
Homologous chromosomes (autosomes)
a pair of chromosomes that have the same characteristics
humans have 22 autosome pairs
Heredity
the transmission of genes on chromosomes and their traits from one generation to the next
Sex Chromosomes
distinct from each other and are represented as X and Y
determine the “sex” of an individual
XX = female
XY = male
Diploid Cell
has 2 sets of each of its chromosomes and a human has 46 chromosomes (2n=46)
where n = the number of single set chromosomes
n =
the number of single set chromosomes
Haploid
sperm and ova (gametes)
have only one set of chromosomes
In a cell in which DNA synthesis has occurred…
the chromosomes are duplicated and consist of 2 identical sister chromatids
Gametes
unlike somatic cells, gametes only contain 1 set of chromosomes
Meiosis
variety and the production of new cells that are genetically distinct
cells produce non-identical daughter cells that are used in reproduction
cells contain genes
at sexual maturity, the ovaries and testes produce haploid gametes by this process
Forming a Diploid Zygote
during fertilization, the gametes, sperm, and ovum fuse forming a diploid zygote that develops into an adult organism
3 main types of sexual cycles differ in the …
timing of meiosis and fertilization
In animals,
meiosis occurs during gamete formation and the gametes are the only haploid cells
plants and some algae exhibit…
an alternation of generations where the life cycle includes both diploid (sporophyte) and haploid (gametophyte) multicellular stages
in most fungi and some protists, meiosis produces
haploid cells that gives rise to a haploid multicellular adult organism that carries out mitosis, producing cells that will become gametes
haploid multicellular organism
predominant phase in plants
diploid multicellular organism
predominant phase in animals/humans
Meiosis
resembles mitosis but reduces the number of chromosome sets from diploid to haploid
takes place in 2 sets of divisions
2 sets of meiosis division
1) Meiosis I
2) Meiosis II
Meiosis I
separates the chromosomes and makes the chromosomes haploid
Prophase I
Metaphase I: the tetrads line up on equator (Cross-over occurs here)
Anaphase I: homologous chromosomes pull apart sister chromatids
Telophase I and Cytokinesis
Meiosis II
separates the sister chromatids and makes 4 daughter cells containing 1/2 the chromosomes as the parent cell (different than parental)
Prophase II
Metaphase II
Anaphase II
Telophase II and Cytokinesis
Meiosis can be distinguished from mitosis by 3 events in Meiosis I
1) Synapsis and direct crossing over of homologous chromosomes through physical contact and exchange genetic information
2) Tetrads on the metaphase plate, during metaphase I of meiosis, paired homologous chromosomes (tetrads) are positioned on the metaphase plates
3) Separation of Homologous at anaphase I of meiosis, homologous pairs move toward opposite poles of the cell
=> in anaphase II of meiosis, the sister chromatids separate
Tetrads
paired homologous chromosomes
Genetic Variation
produced in sexual life cycles (meiosis) contributes to species diversity and the reshuffling of genetic material in each generation
provides the “raw material” for biological changes that are beneficial to the organism and its offspring
3 mechanisms contribute to genetic variation
1) Independent assortment
2) Crossing over
3) Random Fertilization
Independent assortment
of chromosomes
each pair of chromosomes sorts its maternal and paternal homologues into daughter cells independently of the other pairs
Crossing Over
produces recombinant chromosomes that carry genes derived from 2 different parents
during metaphase I
Random Fertilization
the fusion of gametes will produce a zygote with any of about 64 trillion diploid combinations
Mutations
a source of genetic variation
Sexual reproduction
produces new combinations of variant genes, adding more genetic diversity and variability
Chiasma
physical site where the two chromosome can exchange genetic material
