Transcript Mendel and His Peas - Middle School: BLRA

HEREDITY
AND
GENETICS
Gregor Mendel - Used pea plants for experiments
- Crossbred, testing ONE trait at a time
- Color, height, etc.
Heredity
- Passing of traits from parents to offspring
Offspring
- Product or child that is the result of reproduction
by the parents
Self- Pollinating
Plant
- Have male and female reproductive structures
- Can fertilize itself
True-Breeding
Plant
- Can self-pollinate
- Offspring is identical to parent
CrossPollination
- Involves two different plants
- One plant fertilizes another
- Offspring are not identical
3.
1.
2.
Characteristic - Feature we see on the outside
- Ex: Hair color, Eye color, Height
Trait
- Different forms of characteristics
Breed
- To mate or fertilize
with another organism
Mendel’s First
Experiments
- Crossed pea plants
- Focused on 7 characteristics
- One trait seemed to always disappear
- One trait seemed to always stay
Dominant Trait - The trait that stayed
Recessive
Trait
- The trait that disappeared
- Mendel studied one characteristic at a time
- Mendel only used true-breeding plants
(offspring identical to parents) so he would know
what to expect
Mendel’s
Second
Experiments
- Investigating recessive traits
- First generation offspring were bred
- Some recessive traits reappeared
- Recessive traits didn’t show up as much as the
dominant traits
- 3:1 ratio
- Realized two sets of instructions were needed
- Opened the doors to modern genetics
TRAITS AND INHERITANCE
Chapter 5: Section 2
Genes
- Provide instructions
- Control inherited traits
Alleles
- Different forms of genes
- Can be the same or different details
Phenotype
- An organism’s appearance
- Physical features
- Determined by genes
Genotype
- An organism’s genes
- Different combinations of alleles
Punnett
Squares
- Used to organize different combinations
- Possible genotypes of offspring
- Dominant traits  Capital Letters
- Recessive traits  lower case letters
- Two alleles per trait (two sets of instructions)
- Helps calculate probability
Probability
- Mathematical chance something will happen
- Expressed in a fraction or percentage
Homozygous
- Both alleles are the same, dominant or recessive
Heterozygous - Have one dominant and one recessive allele
Punnett
Squares
- Used to organize different combinations
- Possible genotypes of offspring
Incomplete
Dominance
- Both traits appear
- Neither trait is dominant nor recessive
Ex: Red flower + White flower = Pink flower
One gene –
Many traits
- One gene ONLY
- Can influence many traits
One trait –
Many genes
- Several genes involved
- ONLY one trait influenced
Ex: Skin color, Hair
- Environment can influence traits too
- Sometimes genes are not the only factor
Asexual
Reproduction
- Only one parent needed
- Offspring is identical to parent
Mitosis
- Method used for eukaryotic cells to divide
- Asexual reproduction is a type of mitosis
Sexual
Reproduction
- Involves two parents
- Needs sex cells
- Offspring are different from parents
Homologous - Pair of chromosomes
Chromosomes - Carry the same genes
- Sex cells only have one of the pair
Meiosis
- Making of sex cells
- Sex cells have half as many chromosomes as
non-sex cells
MEIOSIS
Walter Sutton
- Studied meiosis in grasshoppers
- Determined that genes are located on
chromosomes
Steps in Meiosis
- Two phases: Phase I and Phase II
- Chromosomes are copied only once
- Chromosomes divide twice
- New cells have half as many chromosomes
Meiosis Interphase
Meiosis is preceded
by interphase. The
chromosomes have
not yet condensed.
http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html
Meiosis Interphase
The chromosomes
have replicated, and
the chromatin begins
to condense.
http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html
Meiosis Prophase I
The chromosomes are
completely
condensed. In meiosis
(unlike mitosis), the
homologous
chromosomes pair
with one another
http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html
Meiosis Metaphase I
The nuclear membrane
dissolves and the
homologous
chromosomes attach to
the spindle fibers. They
are preparing to go to
opposite poles.
http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html
Meiosis Anaphase I
The chromosomes move to
opposite ends of the cell.
http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html
Meiosis Telophase I & Cytokinesis
The cell begins to divide
into two daughter cells. It
is important to understand
that each daughter cell
can get any combination
of maternal and paternal
chromosomes.
http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html
Meiosis Prophase II
The cell has divided into
two daughter cells.
http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html
Meiosis Metaphase II
As in Meiosis I, the
chromosomes line up on
the spindle fibers.
http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html
Meiosis Anaphase II
The two cells each begin to
divide. As in Meiosis I, the
chromosomes move to
opposite ends of each cell.
http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html
Telophase II & Cytokinesis
With the formation of four
cells, meiosis is over. Each
of these prospective germ
cells carries half the
number of chromosomes of
somatic cells.
http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html
- Carry genes
Sex
Chromosomes - Determine sex of organism (male or female)
- Females have 2 X chromosomes (XX)
- Males have 1 X and 1 Y (XY)
Sex-Linked
Disorders
- Sex chromosomes carry genes for certain
disorders
Ex: Color blindness is on the X chromosome
Pedigree
- Diagram used to trace traits
- Studies family history of traits
- Used by genetic counselors
Selective
Breeding
- Traits are selected or desired
- Organisms with those traits are bred