GENETICSBiology
Chapter 10-12
Gregor Mendel- the Father of GeneticsAustrian monkworked in gardens in monastery
studied pea plants
studied heredity- passing on of traits or characteristics from parents to offspring
genetics – the branch of biology that studies heredity
traits- characteristics that are inherited
gametes- sex cells; sperm and egg cells
fertilization- when sperm unites with egg cell forming a 1 celled structure called a zygote
in plants, achieved thru pollination
2 types of reproduction:1. Asexual reproduction- when there is
NO exchange of genetic information between organismsex: mitosis in paramecium
2. sexual reproduction- where there is an exchange of genetic info between orgex: meiosis
in unicellular organisms, MITOSIS is form of asexual reproductionwon’t go thru MEIOSIS
in multicellular organisms, (plants, animals, us, etc) MITOSIS is how more cells are formedMEIOSIS is how sperm & egg cells
are formed
on chromosomes, there are segments that code for specific traits; segments are called GENES
genes are the factors that offspring have received from mom & dad
chromatid
SISTER CHROMATIDS
chromosome
child receives one chromosome from mom and one fromdad for each DNAmolecule in species
genes code for traitstraits are characteristics
that are inherited alleles- alternate forms
of genes
receive 1 allele from mom & 1 allele from dad for each trait
represent alleles by using LETTERS
dominant allele is represented by a CAPITAL LETTER
represents the trait that is stronger or dominant
(usually will use the 1st letter of the dominant trait)
for ex: rolling tongue is a dominant trait in humans
usually use R to represent ability to roll tongue
recessive alleles are represented by a small letter
represents the weaker or hidden trait
for example, not being able to roll your tongue is a recessive trait
represented by r
terms we have to learn:
phenotype- physical appearance of the trait in the organism
genotype- gene or allele combination of an organism for that traitex: RR or Rr or rr
got 1 from mom; 1 from daduse the combo of letters to represent genotype
more terms to learn: homozygous dominant-
means 2 capital letters (dominant trait)
homo= same aka: pure dominant for ex: RR= can roll tongue
homozygous recessive- 2 little letters ( 2 recessive alleles)
aka: pure recessive for ex: rr = can’t roll tongue
heterozygous- have 1 capital letter (dominant trait) & 1 little letter (recessive trait)
hetero= different (means size here or trait)
aka: hybrid
for ex: Rr What does this genotype mean?
can roll tongue Why?
Dominant: L k e M r O d S E Recessive: Mp Q t r D K n s Homozygous Dominant: BB Hh gg TT Rr Homozygous Recessive: ff Aa Cc tt KK Ll mm
Offspring combinations in which dominant trait must show:BB Dd ee Jj Rr ii
Offspring combinations in which recessive phenotype must show:Ee ff Hh ii Ll nn Oo
Dominant: L k e M r O d S E Recessive: M p Q t r D K n
s Homozygous Dominant: BB Hh gg TT Rr Homozygous Recessive: ff Aa Cc tt KK Ll mm
Offspring combinations in which dominant trait must show:BB Dd ee Jj Rr ii
Offspring combinations in which recessive phenotype must show:Ee ff Hh ii Ll nn Oo
to figure out traits organisms inherit:
use a Punnett square perform monohybrid crosses use a 4 box square
Karotype
Meiosis in multicellular org, there are 2 types of
cells:1. body cells (somatic) stomach, bone,
nervous, etc2. sex cells (gametes)- sperm, egg
inside somatic cells, you’ll find 2 of each kind of chromosome= DIPLOID (2n)
inside sex cells, you’ll find only 1 of each kind of chromosome= HAPLOID (n)
chromosomes occur in pairs called homologous chromosomeshave genes for the same traits located in the same positions
they are not genetically identical (we got 1 from mom, 1 from dad)
we have 23 pairs of these homologous chromosomes
somatic cells (body) have 46 chromosomes in them
in sex cells (sperm or egg) we have just 23 chromosomesthis is IMPORTANT WHY?
different organisms have different numbers of chromosomes in their cells
look p. 265
chromosome # does NOT indicate complexity
if an org has 24 chromosomes in its body cells, how many chromosomes will be in the sex cells?
What would happen in humans if the sperm and egg cells each contained 46 chromosomes?
the resulting zygote would have 92
SOMETHING has to occur to prevent too many chromosomes
Meiosis- process of nuclear division that reduces chromosome # by half
meiosis is involved in sexual reproduction
results in haploid cells – makes sperm & egg cells
in order to happen, there has to be 2 nuclear divisions
similar to mitosis, but divides twice
divided into Meiosis I & Meiosis IIsame names as mitosis (easier)
Interphase-chromosomes are replicated, but aren’t visible yet
Prophase I chromosomes
become visible nucleus/ nucleolus
disapppears UNIQUE to meiosis:
homologous chromosomes form TETRAD
chromatids are paired tightly; genetic material is exchanged= CROSSING OVER
Metaphase I tetrads line
up at equator (middle)
UNIQUE:homo chromos are lined up as PAIRS
Anaphase I homo chromos
separate & move to opposite ends of cell
UNIQUE: centromeres do NOT split- this ensures that each new cell only receives ONE chromosome from each parent
Telophase I spindles break down
chromosomes uncoil cytoplasm divides to 2
cells each new cell has ½
genetic info of parent cell
another division must occur because chromosomes were copied
Prophase II new spindle
fibers form chromosom
es are visible again
Metaphase II chromosom
es line up individually at middle of cell
Anaphase II centromeres
split sister
chromatids separate & move to opposite ends of cell
Telophase II
spindles break down
nuclei reforms
cytoplasm divides
Results of meiosis 4 haploid cells formed from
original diploid cell
they become gametes- sperm and egg cells