Download Unit 8: Genetics Summary Sheet

Unit 8: Genetics Summary Sheet
COMPARISON OF MITOSIS AND MEIOSIS
MITOSIS-all cells divide to make two cells just like themselves
MEIOSIS-Sex Cells are formed with half the chromosomes
Consists
of two cell divisions, but only one chromosome replication
Cell cycle consists of interphase, mitosis, and cytokinesis
(sometimes
called reduction division)
Interphase – longest part of cell cycle
Each
cell
division
consists of prophase, metaphase, anaphase, and
Growth, metabolism, and preparation for division occurs
telophase
Duplicates chromosomes (DNA Replication)
Occurs only in sex cells (diploid) – to produce more sex cells (haploid)
Mitosis – division of nucleus of the cell
Prophase - duplicated chromosomes and spindle fibers First Meiosis Division
Produces cells containing ½ # of double stranded chromosomes (haploid)
appear
Metaphase – duplicated chromosomes line up randomly Second Meiosis Division
Results in formation of four cells
in center of cell between spindle fibers
Anaphase – duplicated chromosomes pulled to opposite Each cell w/ ½ # of single-stranded chromosomes (haploid)
Produces four sperm or one egg and three polar bodies (gametes)
ends of cell
Results in genetically different cells – increases genetic diversity
Telophase – nuclear membrane forms around
-----------------------------------------------------------------------------------chromosomes at each end of cell; spindle fibers disappear;
Sperm
chromosomes disperse
Each primary sperm cell develops into four haploid cells of equal size. As
Cytokinesis – division of plasma membrane; two daughter cells
cells mature, the cells lose most of their cytoplasm and develop a long
result with exact genetic information
(in plant cells a “cell plate” forms along the center of the cell and cuts whip-like tail for movement.
Egg
the cell in half; cell plate forms new cell walls once the plasma
Each primary egg cell develops into one large haploid cell and three
membrane divides)
smaller haploid cells called polar bodies. The first meiosis division
RESULTS:
produces one large cell and one polar body. The second meiosis causes
Two daughter cells (body cells)
the large cell to produce one egg cell and a polar body; the original smaller
Same number of chromosomes as original cell (humans = 46)
polar body divides into two polar bodies. The polar bodies eventually
Cells are diploid (human diploid # = 46 or 23 homologous pairs)
disintegrate. The final egg cell is provided with the larger supply of stored
nutrients
RESULTS:
Four daughter cells (sex cells)
½ # of chromosomes (haploid) with genetic variation (n = 23)
Sex cells combine during sexual reproduction to produce a diploid
individual
Genetics: The scientific study of heredity is called genetics. Heredity is the study of how traits are passed from parent to offspring.
A genotype is what we call the genetic make-up of organism.
A person’s phenotype is a physical description of their genotype.
For example: A genotype that reads BB for hair color probably means that a person’s phenotype for hair color is black
An individual that has two different alleles for the same trait is said to be heterozygous (Bb).
An individual that has two identical alleles for one trait is said to be homozygous (bb or BB).
Mendel:
A scientist named Gregor Mendel used
purebred
pea plants in order to understand how traits are inherited. In his experiments, Mendel discovered that each
trait is controlled by one gene that occurs in two different forms. These different forms are referred to as
alleles.
Mendel’s Theories:
Theory of Dominance: Mendel concluded that some alleles are dominant & some are recessive.When an organism inherits a dominant
allele that trait is visible and the effects of a recessive allele cannot be seen. Example: Brown eyes are usually dominant over blue eyes.
This doesn’t mean that a recessive allele just disappears only that it is masked by the dominant one, making it invisible.
Theory of Segregation: Mendel concluded that alleles separate when sex cells (egg & sperm) are formed. Each sex cell carries only one
copy of each gene.
Law of Independent Assortment: Mendel found that genes that control one trait (like hair color) do not affect genes that control another
trait (like hair texture). Each gene sorts independent of all others during the formation of sex cells.
Some alleles are neither dominant nor recessive, and many traits are controlled by multiple alleles or multiple genes. Here are some
exceptions to Mendel’s principles:
Incomplete dominance: Occurs when one allele is not completely dominant over another. For example, a cross between a red-flowered
plant and a white-flowered plant that results in pink-flowered offspring.
Codominance: Occurs when both alleles contribute to a one’s physical characteristics (phenotype). For example, in some species of chicken
black feathers and white feathers are codominant, therefore chickens that have these genes display speckled black and white feathers
Sex-Linked: occurs when trait is carried on the X sex chromosome, usually recessive. Males, XY, and Females, XX.
Monohybrid Crosses
 A cross that provides data about one set of traits. (mono = one, hybrid = cross)
 Each box is filled with two letters: one from the left side of the square and one from the top of the square; note that the dominant
trait is always written first.
 The letters indicate the possible genotypes of the offspring.
 For example: A cross between homozygous dominant (TT) and homozygous recessive (tt) plant:
Tt x tt
T
T
Tt
Tt
Tt
Tt
In this cross, all resulting offspring
are heterozygous for the tall trait.
t
t
For example: A cross between two heterozygous plants (Tt x Tt).
T
t
TT
Tt
Tt
tt
T
t
Dihybrid Crosses

A cross that involves two pairs of contrasting traits
(di = two, hybrid = cross).


In these crosses, alleles must be independently sorted and then listed for the cross.
For example: A cross between two heterozygous guinea pigs (SsBb x SsBb):
In this cross, the
resulting
offspring ratio is
1:2:1 with one
being
homozygous
dominant, two
being
heterozygous and
one being
homozygous
recessive.
SsBb x SsBb
SB
Sb
sB
sb
SSBB
SSBb
SsBB
SbBb
s = long
SSBb
SSbb
SbBb
Ssbb
B = black
sB
SsBB
Ssbb
ssBB
ssBb
sb
SSBb
SSbb
ssBb
Ssbb
SB
The offspring that result from the cross of these
two heterozygous guinea pigs have four
different phenotypes:
9/16 = short, black hair
3/16 = long, black hair
Sb
3/16 = short, black hair
1/16 = long, brown hair
S= short
b = brown
9:3:3:1 ratio
ENETIC ENGINEERING (GENOMICS):
sometimes called biotechnology
process of transferring a gene (DNA) from one organism to another
- Organisms with transferred gene now produce “recombined” genetic code ( called “recombinant DNA”)
- Ex: insulin produced through bacteria
- Ex: oil-eating bacteria
- Has application in medicine, environment, industry, agriculture, selective breeding
- Human Genome Project
- DNA Fingerprinting
KARYOTYPE: to identify gender or chromosomal abnormalities
-
PEDIGREE: used to trace disorders
through generations
GEL ELECTROPHORESIS/ DNA FINGERPRINTING:
Samples A and D are most alike because the bands of
DNA are in the same location