Transcript czech sex

Biology of the Human Body
NSCI352
Dr. Ekaterina (Kate) Vorotnikova
E-mail: [email protected]
Lecture 11.
Cell Reproduction
Chapter 18
(Page 354-360; 362-369)
Introduction to Genetics
Chapter 19
(Page 374-378)
Cell Reproduction
Chapter 18
(page 354-360; 362369)
Objectives
1. Be able to describe a chromosome and tell the
numbers found in sex and non-sex cells.
2. Understand the cell cycle and be able to visualize
where mitosis fits into the cell cycle.
3. Be able to describe each phase of mitosis.
4. Understand the effect that meiosis has on
chromosome number.
5. Describe the events that occur in each meiotic
phase.
6. Compare mitosis and meiosis; cite similarities and
differences.
• Reproduction
– Produces a new
generation of cells
– Produces a new
individual
– Part of the life cycle;
series of recurring
events in which
individuals:
•
•
•
•
Grow
Develop
Maintain themselves
Reproduce
• Mitosis
– Division of somatic cells
– Purpose
• Growth
• Replace worn out or dead
cells
• Repair tissue
• Meiosis
– Division of germ cells
– First stage in sexual
reproduction
• Chromosome
– Very long DNA
molecule in
association with
protein
• Gene
– Segment of DNA in a
chromosome
• Chromatin
– DNA and protein
combined
Eukaryotic chromosomes are composed
of chromatin
– Chromatin = DNA + proteins
– To prepare for division, the
chromatin becomes highly
compact, and the
chromosomes are visible with a
microscope
– Early in the division process,
chromosomes duplicate
– Each chromosome
appears as two sister
chromatids, containing
identical DNA molecules
– Sister chromatids are
joined at the centromere,
a narrow region
The large, complex chromosomes of eukaryotes duplicate with each cell
division
Animation: Chromosome structural
organization
Having Two Sets of Chromosomes Makes a Cell Diploid
• Chromosome number
– Sum of chromosomes in a
given type of cell
– Humans have 46; 23 from each
parent
– Diploid (2n): two sets of
chromosomes
– Autosomes: pairs 1–22
– Sex chromosomes
• XX in females
• XY in males
– Homologous chromosomes
• Paired corresponding
chromosomes
The Usual Chromosome Number for Humans Cells Is Forty-Six
The human sex
chromosomes X and Y
differ in size and genetic
composition
Mitosis Maintains Diploid Chromosome Number from One
Generation to Next
Having Only One Set of Chromosomes Makes a Cell Haploid
• Meiosis
– Reductional
division
– Reduces the
number of
chromosomes
to a haploid
number (n)
– Occurs in
spermatogonia
or oogonia
• Duplicated
chromosomes
– Attach to the spindle
• Two sets of
microtubules
extending from the
centrioles
• Overlap in the
“equator” region
• Sister chromatids
moved via the spindle
apparatus
Animation: Duplicating
chromosome
The Cell Cycle
• Every time a new cell comes into being, a multistep cell cycle begins anew
• Cell cycle
– “Lifetime” of a somatic cell
– Varies depending on cell type
• Interphase
– G1: cell growth
– S: DNA copied and its chromosomes are duplicated
– G2: Preparation for mitosis
• Mitosis: chromosomes sorted into two sets and the cytoplasm divides; four
phases
Animation: The cell cycle
The Four Stages of Mitosis
1. Prophase
3. Anaphase
2. Metaphase
4. Telophase
After Mitosis, Daughter Cells Have Same Chromosome Number as
Parent Cell
Fig. 18-7 (a-d), p. 358
Fig. 18-7 (e-h), p. 359
Animation: Mitosis step-by-step
Animation: Mitosis
Animation: Cytoplasmic division
Meiosis: The Beginnings of Eggs and Sperm
• Meiosis divides the nuclei of germ cells in a way that halves the
number of chromosomes in daughter cells
• Spermatogenesis
– Diploid germ cell increases in size
– This primary spermatocyte → four haploid
spermatids → change in form to become sperm
Animation: Sperm formation
Oogenesis Is the Process That Forms Eggs
Animation: Egg formation
Animation: Meiosis I and II
A Visual Tour of the Stages of Meiosis
Animation: Meiosis step-by-step
Animation: Meiosis
Animation: Crossing over
Three sources of genetic variability in sexually
reproducing organisms:
1) independent orientation of chromosomes at
metaphase I (random alignment) (223 = 8 million)
2) random fertilization (64 trillion possibilities)
3) crossing over during prophase I of meiosis (1 to
3 crossover events occur per chromosome pair).
Animation: Random alignment
Animation: Comparing mitosis and meiosis (Mitosis
occurs in somatic cells, while meiosis takes place in
germ cells)
Mitosis Maintains the Chromosome Number of the
Parent Cell
Meiosis Reduces the Chromosome Number by Half
2n
germ cell
germ cell
each chromosome
duplicated during
interphase
n
MEIOSIS I
separation of
homologues
MEIOSIS II
separation of sister
chromatids
gametes
gametes
2n
zygote
diploid number
restored at
fertilization
Fig. 18-17, p. 371
Introduction to Genetics
Chapter 19
(page 374-378)
Objectives
1. Be able to distinguish between “genes” and
“alleles.”
2. Know Mendel’s principles of dominance and
segregation.
3. Understand how to solve genetics problems that
involve monohybrid and dihybrid crosses.
4. Understand the variations that can occur in
observable patterns of inheritance.
5. Explain how a given pair of genes on homologous
chromosomes can separate during meiosis.
Video: ABC News: All in the family:
Mixed race twins
Basic Concepts of Heredity
• Genes provide the instructions for
all human traits, including physical
features and how body parts
function
• Each person inherits a particular
mix of maternal and paternal
genes
• Genes
– Humans have ~21,500
– Chemical instructions for
building proteins
– Locus: specific location on a
chromosome
• Diploid cells contain two copies of
each gene on pairs of homologous
chromosomes
• Allele: each version of a gene
MENDEL’S LAWS
Gregor Mendel, Brunn, Austria ( now Brno, Czech Republic)
Experimental genetics began in an abbey
garden
 Gregor Mendel discovered principles of
genetics in experiments with the garden pea
• Mendel showed that parents pass heritable
factors to offspring (heritable factors are now
called genes)
• Advantages of using pea plants
–
–
–
–
Controlled matings
Self-fertilization or cross-fertilization
Observable characteristics with two distinct forms
True-breeding strains
Petal
Stamen
Carpel
White
1
Removed
stamens from
purple flower
Stamens
Carpel
Parents
(P)
2
Purple
Transferred
pollen from stamens of white
flower to carpel of purple flower
White
1
Removed
stamens from
purple flower
Stamens
Carpel
Parents
(P)
2
Purple
3
Transferred
pollen from stamens of white
flower to carpel of purple flower
Pollinated carpel
matured into pod
White
1
Removed
stamens from
purple flower
Stamens
Carpel
Parents
(P)
2
Purple
3
Transferred
pollen from stamens of white
flower to carpel of purple flower
Pollinated carpel
matured into pod
4
Offspring
(F1)
Planted seeds
from pod
Character – a
heritable feature
that varies
among
individuals
(flower color,
flower position,
seed color, seed
shape, etc.)
Trait –each
variant of a
character (purple
or white flowers,
axial or terminal
flower position,
yellow or green
seeds, round or
wrinkled seeds,
etc.)
Mendel’s law of segregation describes the inheritance
of a single character
Example of a
monohybrid
cross
Parental
generation:
purple
flowers 
white flowers
Monohybrid cross – when the parents differ in only one character
F1 generation:
all plants with
purple flowers
F2 generation:
3/4 of plants
with purple
flowers;
¼ of plants with
white flowers
Mendel needed to
explain
Why one trait
seemed to
disappear in the
F1 generation
Why that trait
reappeared in
one quarter of
the F2 offspring
Four Hypotheses
1. Genes are found in alternative
versions called alleles; a
genotype is the listing of
alleles an individual carries for
a specific gene
2. For each characteristic, an
organism inherits two alleles,
one from each parent; the
alleles can be the same or
different
– A homozygous
genotype has identical
alleles
– A heterozygous
genotype has two
different alleles
Four Hypotheses
3. If the alleles differ, the dominant allele
determines the organism’s
appearance, and the recessive allele
has no noticeable effect
- The phenotype is the appearance or
expression of a trait
- The same phenotype may be
determined by more than one
genotype
4. Law of segregation: Allele pairs
separate (segregate) from each other
during the production of gametes so
that a sperm or egg carries only one
allele for each gene
Each Pair of Gene Alleles Is Separated and Two Alleles
End Up in Different Gametes
Genetic makeup (alleles)
pp
PP
P plants
Genotype –
genetic
makeup
Gametes
All p
All P
F1 plants
(hybrids)
Phenotype –
All Pp
Gametes
1
–
2
expression, or
physical
appearance of
traits
1
–
2
P
p
Sperm
P
F2 plants
Phenotypic ratio
3 purple : 1 white
p
P
PP
Pp
p
Pp
pp
Eggs
Genotypic ratio
1 PP : 2 Pp : 1 pp
Punnett
square
Animation: Chromosome
segregation
Animation: Monohybrid cross
Homologous chromosomes bear the alleles for each character

For a pair of homologous chromosomes, alleles of a gene reside at the same
locus
 Homozygous individuals have the same allele on both homologues
 Heterozygous individuals have a different allele on each homologue
Copyright © 2009 Pearson Education, Inc.
Many Genetic Traits
Have Dominant and
Recessive Forms
• Allele: each version of a gene
• Homozygous condition: identical alleles
• Heterozygous condition: different alleles
• Dominant allele
– Effect masks recessive allele paired with it
• Genetic representations
– Homozygous dominant (PP)
– Homozygous recessive (pp)
– Heterozygous (Pp)
• Genotype
– Inherited alleles
• Phenotype
– Observable functional or physical traits
Animation: Genetic terms
Genetic Tools: Testcrosses and Probability
• When potential parents are concerned about passing a harmful
trait to a child, genetic counselors must try to predict the likely
outcome of the mating
PROBABILITY
• Measure of the chance that some particular outcome will occur
• Factor in the inheritance of single-gene traits
• Cross CC x cc
– All of the offspring will be heterozygous, Cc
• Cross Cc x Cc
– ¼ CC, ½ Cc, and ¼ cc
A Punnett Square Can Be Used to Predict the Result of a
Genetic Cross
• Punnett square
– Grid used to determine
possible outcomes of
genetic crosses
– Rules of probability apply
because fertilization is a
chance event
– Possibility can be expressed
mathematically, e.g.,
between 0% and 100%
• Most probable outcome does
not have to occur
• In a given situation, probability
does not change
Different Genetic Results Possible in Second Generation
after Monohybrid Mating
A Testcross Also Can Reveal Genotypes
• Testcross
– Learn the genotype of a (nonhuman) organism
– Cross organism with homozygous recessive
organism (aa)
• If all offspring are Aa, parent was probably AA
• If some of the offspring have the dominant trait and
some have the recessive trait, parent was Aa
Animation: Testcross
How Genes for Different Traits Are
Sorted into Gametes
• When we consider more than one trait, we see
that the gene for each trait is inherited
independently of the gene of other traits
How Genes for Different Traits Are Sorted into
Gametes
• Independent assortment
– Occurs during meiosis
– A given chromosome and its genes move randomly into
gametes
• Metaphase I
• Metaphase II
• Crosses between individuals heterozygous for two traits yields
sixteen different gamete unions
– Probability displayed using a Punnett square
Independent Assortment: Chromosomes Moved at
Random into Forming Gametes
Animation: Independent
assortment
Single Genes, Varying Effects
• Some traits have clearly dominant and
recessive forms
• For most traits, however, the story is not so
simple
Animation: Sickle-cell anemia
Animation: Symptoms of sickle-cell
anemia
In Codominance, More Than One
Allele of a Gene Is Expressed
• Codominance
– Heterozygous for a trait, but both alleles are
expressed
– Example: alleles for blood type determine presence
or absence of polysaccharides on surface of red
blood cells
• IA and IB; codominant when paired with each other
• Multiple allele system
– A gene that has three or more alleles
Animation: Codominance: ABO
blood types
Conclusion
1.
2.
3.
4.
5.
6.
Cell division.
Mitosis.
Meiosis.
Basic concepts of heredity: genes, alleles.
Monohybrid crosses.
Pleiotropy and codominance.
Homework (from Student Interactive Workbook)
Write the answers in your Student Interactive Workbook:
• Page 283-286; 289-291; 297-298
• Page 302-305;
• !!!Write on a piece of paper answers to the following questions:
• page 300-301 - 2, 5, 6, 10, 19; page 311- 1, 4, 6, 10, 11.
• Give to the instructor before the class!!!!