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GENETICS
Nature’s Solar Panel
ASEXUAL REPRODUCTION

Reproduction without sex

Genetically identical

Cloning

Propagating
SEXUAL REPRODUCTION

Fertilization between male and
female plants

Gametes


Sexual cells

Sperm

Egg
Gametes form a single offspring
cell

Zygote

First cell of a new individual
SEXUAL REPRODUCTION

Gamete cells have 1 set of chromosomes


Haploid cells

Sperm (1n)

Egg (1n)
Sperm and egg combine to create a zygote cell
with 2 sets of chromosomes (2n)

Diploid cell


One set from each parent
Meiosis is the cell division that creates gametes

Similar to mitosis
SEXUAL REPRODUCTION

Sperm and egg merge to form zygote

Complete set of chromosomes
SEXUAL REPRODUCTION

Genetic recombination can
spontaneously occur during meiosis

Crossing over of DNA

Variability
SEXUAL REPRODUCTION

Zygote is a diploid cell


2 sets of chromosomes (2n)
Three sets can occur (3n)


Triploid
Sterile organism
STRUCTURE OF DNA

Chromosomes composed of 2 types
of large molecules

DNA

Protein
STRUCTURE OF DNA

DNA is a long double helix chain


Resides in nucleus
Composed of nucleotides

Adenine (A)

Guanine (G)

Cytosine (C)

Thymine (T)
STRUCTURE OF DNA

Nucleotides form only two “rungs” on the
double helix ladder



A—T

C—G
The sequence of pairs is the code or
instructions on growth, color, function, etc.


Base pairs
Morse code or Braille
A typical plant cell contains billions of pairs
GENETIC INFORMATION

A segment of the DNA strand

Gene


Determine plant height, flower color, drought
tolerance…
Direct the production of enzymes (protein)

Proteins function as enzymes

Facilitate chemical reactions
GENETIC INFORMATION

The total sum of DNA in an organism’s
chromosomes


Single cell bacterium


Genome
Several thousand genomes
Complex organisms

50,000 genomes
DUPLICATION OF DNA

Duplication of DNA needed to divide cells

The base pairs are disconnected




Rungs broken apart
The double helix strands unzipped
New pairs can be reestablished on each strand

A—T

C—G
Two double helices are completed
DUPLICATION OF DNA

Mismatch error occurs about once every
million pairs


Mutation
Corn contains 4 billion base pairs

4000 mutations possible
MUTATION


Causes of mismatching errors are mutagens

Genetic recombination

UV light

Radiation

Carcinogens
Mismatching errors change sequence of base
pairs

Repair enzymes fix mutations

Do not catch all of them
MUTATION

Most mutations are silent


No visible consequence
Mutations that occur in cell and passed on
through mitosis

Somatic mutation


Not through seeds
Branch that looks different than rest of plant


Sport
Can be propagated

Naval oranges

Red delicious apples
MUTATION

Mutations that occur in gametes


Germ-line
Genetic changes passed on to offspring

Flower color

Fragrance

Taste
MUTATION

Mutation essential for evolution

Organisms adapt to changing
environment
MENDELIAN GENETICS

Cross breeding different characteristics

Removed stamens on one parent plant

Manually fertilized with pollen from other parent
plant

Tall pea plant x short pea plant = intermediate
plant?
MENDELIAN GENETICS

Parent plants (P)


P tall x P dwarf
Offspring between parent plants (F1)

P tall plant x P dwarf plant = ALL TALL PLANTS (F1)
MENDELIAN GENETICS

Offspring between F1 plants gives rise to F2

F1 tall plant x F1 tall plant = 3 TALL PLANTS (F2) and 1 DWARF (F2)

For every 3 tall plants, there will be one dwarf
MENDELIAN GENETICS

Every cell has one set of chromosomes


One from each parent
Alternative forms of gene expression

Alleles

Height

Seed color

Flower color
MENDELIAN GENETICS

One allele is considered dominant

G = green-pod dominant

g = yellow-pod recessive

Green-pod allele dominant over yellow-pod allele

If both parent plants had G allele

F1 offspring will have GG


Green-pod
If one parent plant has G allele, the other parent
plant had g allele

F1 offspring will have Gg

Green-pod
MENDELIAN GENETICS

If both parent plants have g allele

F1 offspring will have gg

Yellow-pod
MENDELIAN GENETICS

Genetic make up of an organism

Genotype
MENDELIAN GENETICS

Physical appearance of an organism

Phenotype
MENDELIAN GENETICS

Both alleles are identical


Homozygous

GG = green-pod

gg = yellow-pod
Alleles are different

Heterozygous

Gg = green-pod
MENDELIAN GENETICS

Single trait is studied

Monohybrid cross
MENDELIAN GENETICS

Multiple traits are linked

Dihybrid cross
MENDELIAN GENETICS

Neither allele is completely dominant


Incomplete dominance
Snapdragon flower color

RR = red

rr = white

Rr = pink
MENDELIAN GENETICS

Recessive allele the result of a mutation

Not fully functional allele

Smooth peas (SS) versus wrinkled peas (ss)

s allele due to malfunction in converting
glucose into starch


Water loss higher during drying period
S will produce adequate starch
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