Chapter 20 Flashcards
Gene
segment of DNA that codes for specific trait
Locus
location on a chromosome
Allele
variation of a gene
Homozygous
having 2 identical alleles at a certain loci
Heterozygous
having two different alleles at a certain loci
Genotype
description of genes carried by a person
phenotype
description of the appearance of an individual, or function of a protein
somatic cell
body cell; divides by mitosis
germ cell
reproductive cell; divides by meiosis
diploid
cells with 2 copies of each chromosome (2N)
haploid
cell with only one copy of each chr (N)
asexual reproduction
uses mitosis and results in identical offspring
3 examples of asexual reproduction
mitotic division of unicellular organisms,
budding of multicellular organisms,
regeneration of pieces of organisms
Sexual Reproduction
uses meiosis
germ cells become haploid
interphase of meiosis
same as mitosis. DNA still replicates in S phase
results of meiosis
4 haploid cells
Meiosis I
Reduction division,
separation of homologous chr,
results in 2 haploid cells
Homologous chromosomes
matching chrs from each parent
reduction division
from diploid to haploid
separation division
separation of sister chromatids
Prophase I
condensation of chromatin, nucleoli disappear, spindle formation, nuclear envelope breaks down, paring of homologous chrs and crossing over
Metaphase I
bivalents align at spindle equator,
spindle fibers attach to 1 kinetochore from each chr,
chr alignment is random
Bivalent
paired homologous chrs
Anaphase I
homologous chrs separated,
move to opposite poles,
still made of sister chromatids
Telophase I
chrs arrive at poles,
nuclear envelope forms,
cytokinesis makes 2 haploid cells
Meiosis II
separation division,
may be separated from Meiosis I by short interphase,
results in 4 haploid cells,
similar to mitosis
what’s the interphase between meiosis I and II like
needed to make some proteins and stuff for the next step but there is no replication of DNA
Prophase II
chromosomes condense, nuclear envelope breaks down, spindle apparatus forms
Metaphase II
chromosomes align on metaphase plate (only half as many this time)
Anaphase II
sister chromatids seperated
Telophase II
chrs reach poles, decondense, and nuclear envelope forms
followed by cytokinesis
results in 4 haploid cells with variable allele combos
Gametogenesis results in males
4 haploid sperm
Gametogenesis results in females
1 haploid egg cell and 3 polar bodies
Diplotene
the arrested egg cells that require a growth phase during prophase I
why do polar bodies form
unequal division of cytoplasm; because the egg needs to contain all of the protein, RNA, and nutrition needed for embryonic development
Genetic variability is the result of
crossing over during prophase I,
random assortment of chrs during metaphase I,
random combo of gametes at fertilization
why is sexual reproduction an advantage
genetic variability
results of mendel’s experiments
breeding 2 F1 plants created an appearance of both phenotypes in a 3:1 ratio in the F2 gen
what happened to the F1 gen after breeding two different P1 parents
F1 showed only the dominant traits
mendel’s law of independent assortment
the alleles of one gene segregate independently of the alleles of other genes (if located far away)
mendel’s law of segregation
2 alleles of a gene are distinct entities that separate from one another during formation of gametes
Chromosomal Theory of Inheritance (5 parts)
Nuclei of all cells (except gametes) have 2 sets of chrs;
Homologous chrs segregate independently;
homologous chrs synapse and segregate into 2 diff cells during meiosis;
each chr set carries a similar set of genes;
chrs retain their individuality
Crossing over
genetic recombination between homologous chrs which results in an exchange of genetic material between maternal and paternal chrs
non-independent assortment
linked genes are located close together on the same chr so they are often inherited together
Genetic mapping
more tightly linked genes are located closer together so they have less of a chance of crossing over to happen between them
genetic mapping measurements
centimorgans or map units;
corresponds to frequency of recombination
Mendelian inheritance
trait controlled by a single gene, only two alleles for that gene, 1 allele is completely dominant
what are the 5 exceptions to mendelian inheritance
linked genes, codominance, incomplete dominance, pleiotropy, polygenic inheritance
codominance
the effect of both alleles are present (red cow + white cow = red and white splotches)
incomplete dominance
blending of 2 phenotypes (red flower + white flower = pink flower)
pleiotropy
when single gene results in multiple effects (marfan affects heart, muscle, etc)
polygenic inheritance
continuous variation observed in phenotype (skin color or height); many different loci involved; (greater number of genes involved the more continuous the variation)
nondisjunction
failure of homologous or sister chromatids to separate during meiosis
aneuploidy
result of nondisjunction
one cell with missing copies of chrs; one cell with extra copies of chrs
typical cause of nondisjunction
failure of spindle fibers
“best” place for nondisjunction to occur
meiosis II because half of the gametes will be normal
down syndrome
Trisomy 21- 3 copies of chr 21
Turner Syndrome X0
nondisjunction in father; most spontaneously aborted; survivors are short
XXX syndrome
fertile females, slight learning disabilities
Klinefelter Syndrome XXY
usually nondisjunction in mother; tall men, often sterile
XYY condition
taller than average males, some mentally impaired, nondisjunction in father
