Chapter 13 Flashcards
Heredity
The transmission of traits from one generation to the next
Variation
Demonstrated by the differences in appearance that offspring show from parents and siblings
Genetics
the scientific study of heredity
Genes
the units of heredity and are made up of segments of DNA
Gametes
sperm and egg; the reproductive cells that pass genes to the next generation
Somatic cells
All the cells of the body except gametes and their precursors; these have 46 chromosomes in humans
Locus
A gene’s specific position along a chromosome
Asexual reproduction
a single individual passes all of its genes to its offspring without the fusion of gametes
Clone
a group of genetically identical individuals from the same parent
Sexual reproduction
two parents give rise to offspring that have unique combinations of gene inherited from the two parents
Life Cycle
the generation-to-generation sequence of states in the reproductive history of an organism; Develop -> survive -> reproduce
homologous chromosomes
or homologs; the two chromosomes in each pair
Sex chromosomes
These determine the sex of the individual and are called X and Y; females have a homologous pair of X (XX) and males have an X and a Y (XY)
Autosomes
the remaining 22 pairs of chromosomes that are not sex chromosomes
Diploid cell
(2n) has two sets of chromosomes
Karyotype
a visual representation of an organism’s complete set of chromosomes, including their number, size, and shape
Haploid cell
A gamete (sperm or egg) that contains a single set of chromosomes (n)
Maternal
from the mother
Paternal
from the father
The human life cycle
Meiosis -> gametes ->fertilization -> mitosis
Three types of sexual life cycles
1) Animals
2) Plants and some algae
3) Most fungi and some protists
Animal sexual life cycle
Gametes are the only haploid cells; gametes are produced by meiosis and undergo no further cell division before fertilization; gametes fuse to form a diploid zygote
Plants and some algae sexual life cycle
Each spore grows by mitosis into a haploid organism called a gametophyte; a gametophyte makes haploid gametes by mitosis; fertilization of gametes results in a diploid sporophyte
Most fungi and some protists sexual life cycle
The only diploid stage is the single-celled zygote - there is non multicellular diploid stage; the zygote produces haploid cells by meiosis; each haploid cell grows by mitosis into a haploid multicellular organism; the haploid adulate produces gametes by mitosis
Only a ________ cell can undergo meiosis
diploid
Meiosis I
The first stage of meiosis; When homologous chromosomes separate (One cell that splits into two with sister chromatids still together)
Meiosis II
second stage of meiosis; When the sister chromatids of the two cells split, forming four cells
Prophase I
In early prophase I, each chromosome pairs with its homolog and crossing over occurs; X-shaped regions called chiasmata are crossover sites
Metaphase I
pairs of homologs line up at the metaphase plate, with one chromosome facing each pole; microtubules connect to the kinetochore of each chromosome
Anaphase I
Pairs of homologous chromosomes separate; one chromosome of each pair moves toward opposite poles, guided by the spindle apparatus
Telophase I and Cytokinesis
Each half of the cell has a haploid set of chromosomes; each chromosome consists of two sister chromatids; cytokinesis usually occurs simultaneously, forming two haploid daughter cells
Prophase II
A spindle apparatus forms; Chromosomes move toward the metaphase plate
Metaphase II
Sister chromatids are arranged at the metaphase plate (because of crossing over, each chromosome are no longer genetically identical); kinetochores of sister chromatid attach to microtubules extending from opposite poles
Anaphase II
Sister chromatids separate; Sister chromatids now move as two newly individual chromosomes towards opposite poles
Telophase II and Cytokinesis
The chromosomes arrive at opposite poles; Nuclei form and the chromosomes begin decondensing; cytokinesis the cytoplasm
synaptonemal complex
A zipper-like structure that holds one homolog tightly to the other during crossing over
synapsis
the fusion of chromosome parts during crossing over
random fertilization
adds to genetic variation because any sperm can fuse with any egg
