Transcript Genetics - Cloudfront.net

Standard 2: Genetics
Mutation and sexual reproduction
lead to genetic variation in a
population.
a. meiosis is an early step in sexual reproduction
in which the pairs of chromosomes separate
and segregate randomly during cell division to
produce games containing one chromosome of
each type
b. only certain cells in a multicellular organism
undergo meiosis
c. how random chromosomes segregation
explains that a particular allele will be in a
gamete
d. that new combinations of alleles may be
generated in a zygote through the fusion of
male and female gametes (fertilization)
e. why approximately half of an individual’s DNA
sequence comes from each parent
f. the role of chromosomes in determining an
individual’s sex
g. how to predict possible combinations of alleles
in a zygote from the make-up of the parents
Genetics
Have you ever wondered why
you have the same eye color as
your mother? Or the same hair
color as your father?
• Genetics is the study of heredity or
inheritance.
• Genetics helps to explain how traits
are passed from parents to their
young.
• Parents pass traits to their young
through gene transmission
Inheritance of Traits
Gregor Mendel discovered this idea over 100
years ago. The principle has three parts:
1. Hereditary traits are determined by
specific genes.
2. Individuals carry two genes for each trait,
one from the mother’s egg and one from
the father’s sperm.
3. When an individual reproduces, the two
genes split up (segregate) and end up in
separate gametes.
• Genes are located
on chromosomes
and consist of
DNA.
• They contain
specific
instructions for
protein synthesis
DNA- Deoxyribonucleic Acid
Genes on Chromosomes
Reproduction
• Asexual
– Many single-celled organisms reproduce
asexually by splitting or budding.
– Some multicellular organisms can
reproduce asexually, produce clones
(offspring genetically identical to parent).
Sexual Reproduction
• Fusion of two gametes (male and female)
to produce a single zygote.
• Introduces greater genetic variation,
allows genetic recombination.
• With exception of self-fertilizing organisms
(e.g. some plants), zygote has gametes
from two different parents.
Question
• Fertilization is the fusion of two
gametes (male and female) to
produce a
?????????????
Answer
• Fertilization is the fusion of two
gametes (male and female) to
produce a
ZYGOTE
Homologues
• Chromosomes exist in homologous
pairs in diploid cells.
Exception: Sex chromosomes (X, Y).
Other chromosomes are known as
autosomes (body cells).
In humans …
• 23 chromosomes donated by each
parent called haploid (means half) cells.
– haploid number “n” = 23 in humans.
• The total we have is 46 called diploid
• 23 from egg and 23 from sperm= the
complete number of chromosomes
for the child
In humans …
(continued)
• Gametes (sperm or ova):
– Contain 22 autosomes and 1 sex
chromosome.
– Are haploid (having a single set of
unpaired chromosomes)
Mitosis vs. Meiosis
Fertilization results in zygote with 2 haploid
sets of chromosomes - now diploid.
Diploid cell; 2n = 46. (n=23 in humans)
Most cells in the body produced by
mitosis. Ex: skin cells, tissue cells
Only sex cells are produced by meiosis.
Question
• If an organism has 60 chromosomes,
how many chromosomes would be in
their gametes produced?
Answer
• If an organism has 60 chromosomes,
how many chromosomes would be in
their gametes produced?
30
half the total number
Mitosis
Meiosis
Meiosis I and II
• Meiosis I and meiosis II are two separate
substages of meiosis.
• Meiosis 1 occurs by producing genetic
recombination in the daughter cells while
in meiosis 2 each of the four daughter
cells will contain half the amount of
chromosomes of the parent cell.
Phases of Meiosis I and II
• Meiosis has five phases including:
prophase, metaphase, anaphase,
telophase and interphase.
• It goes through each phase twice
– Prophase 1 through telophase 1 then
prophase 2 through telophase 2
Meiosis–key differences from mitosis
•
•
•
•
Meiosis reduces the number of chromosomes by half.
Daughter cells differ from parent, and each other.
Meiosis involves two divisions, Mitosis only one.
Meiosis I involves:
– Synapsis – homologous chromosomes pair up.
Chiasmata form (crossing over of non-sister
chromatids).
– In Metaphase I, homologous pairs line up at
metaphase plate.
– In Anaphase I, sister chromatids do NOT separate.
– In Telophase 2, Haploid cells are formed.
–.
Ticket Out
the Door
Mnemonic for PMAT
• P=Paco
Prophase
• M=Made
Metaphase
• A= a
Anaphase
• T=Taco
Telophase
Make Your Own!