Transcript 無投影片標題 - MADANIA

Inheritance
• The transfer or transmission of some
features from one generation to the next
is called inheritance.
• The characteristics are controlled by
genes which are like coded instruction.
• Genes from one generation are
transmitted to the next in the gametes.
Inheritance
• At fertilization, the gametes fuse to form
a zygote which contains the genetic
information from both parents.
• A new individual grows from the zygote –
half of its genetic information comes
from its male parent and half from its
female parent
What are chromosomes?
• Genetic materials found inside the nucleus
of a cell
• Made up of DNA & protein
• Appear as very thin & thread-like structures
called Chromatins
• Each cell in each type of organism has a
definite number of chromosomes ( human
has 46 chromosomes in their nucleus)
gene controlling
skin colour
• A gene is a short length of
DNA on a chromosome
gene controlling
which is a unit
tongue rolling
determining an inherited
character
chromosome
• It consists of a chemical
gene controlling
substance called
eye colour
deoxyribonucleic acid
gene controlling
(DNA)
blood group
gene controlling
skin colour
gene controlling
tongue rolling
chromosome
gene controlling
eye colour
gene controlling
blood group
• DNA is responsible for
telling the cell to make
the right type of protein
& control the metabolic
activities of the cells
• Chromosomes always exist in pairs in the
body (somatic) cells
• Each human somatic cell has 46
chromosomes (diploid number)
– 23 pairs of homologous chromosomes
• Alternative forms of genes on the same
position of the homologous
chromosomes which control the same
character but have different
expressions
allele for
white skin
colour
allele for
dark skin
•
colour
Members of homologous
chromosomes carry the
same genes (controlling
the same character) in
same loci
• But the genes on the
members of homologous
chromosomes may be of
different forms (effects)
 Alleles
Gregor Mendel: Father of Modern Genetics
• The first scientist develop a method for
predicting the outcome of inheritance
patterns.
• Performed his work with pea plants,
studying seven traits: plant height, pod
shape, pod color, seed shape, seed color,
flower color, and flower location.
• Pea plants develop individuals that are
homozygous for particular characteristics.
These populations are known as pure
lines.
ILLUSTRATION
Creating sentences
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DNA – nucleus
Inheritance – traits
Chromosome – chromatin
Haploid – gamete
Zygote – diploid chromosome
Diploid number– human cell
Gene – DNA
Genetic – inherited
Mendel - genetics
Mendelian crosses
• In his work, Mendel took pure-line pea plants and cross-pollinated
them with other pure-line pea plants.
• He called these plants the parent generation.
• When Mendel crossed pure-line tall plants with pure-line short
plants, he discovered that all the plants resulting from this cross
were tall. He called this generation the F1 generation (first filial
generation).
• Next, Mendel crossed the offspring of the F1 generation tall plants
among themselves to produce a new generation called the F2
generation (second filial generation).
Two Innovations of Mendel
1. Developed pure lines
2. Counted his results and kept statistical notes
•
Pure Line (galur murni) - a population that breeds true for a
particular trait
Mendelian crosses
•
To predict the possibility of an individual trait, several steps
are followed:
1. The dominant allele is represented by a capital letter while
the recessive allele by the corresponding lowercase letter.
Homozygous dominant individual (the genotype is EE);
heterozygous individual (the genotype is Ee); and for a
homozygous recessive person (the genotype is ee).
2. Performing a genetic cross is determining the genotypes of
the parents and the genotype of the gametes. A
heterozygous male and a heterozygous female to be crossed
have the genotypes of Ee and Ee. During meiosis, the allele
pairs separate. A sperm cell contains either an E or an e,
while the egg cell also contains either an E or an e.
Mendelian crosses
3. To continue the genetics problem, a
Punnett square is used. A Punnett square
is a boxed figure used to determine the
probability of genotypes and phenotypes
in the offspring of a genetic cross.
4. This is done by filling in each square with
the alleles above it and at its left.
5. Therefore, the ratio of phenotypes is 3
with curly hair to 1 with straight hair
(3:1). The ratio of genotypes is 1:2:1 (1
EE : 2 Ee : 1 ee).
Monohybrid cross
• Involves a study of inheritance patterns for organisms
differing in one traits.
• Using symbols we can predict the cross of tall (DD) and short
(dd) pea plants in the following manner:
Dihybrid Cross Problem Set
• A dihybrid cross involves a study of inheritance patterns for
organisms differing in two traits.
• Mendel invented the dihybrid cross to determine if different
traits of pea plants, such as flower color and seed shape,
were inherited independently.
Terms to know in Mendelian Genetics
1. Alleles: The different forms of a gene. Y and y
are different alleles of the gene that
determines seed color. Alleles occupy the same
locus, or position, on chromosomes.
2. F1 generation
Offspring of a cross between true breeding
plants, homozygous for the trait of interest
3. F2 generation
Offspring of a cross involving the F1
generation.
4. Homozygote - an individual which contains
only one allele at the allelic pair; for example
DD is homozygous dominant and dd is
homozygous recessive; pure lines are
homozygous for the gene of interest
Terms to know in Mendelian Genetics
5. Heterozygote - an individual which contains
one of each member of the gene pair; for
example the Dd heterozygote
6. Incomplete dominance
The flowers of the snapdragon plant can be
red, pink, or white. The genotype RR results
in red flowers and rr results in white flowers.
The heterozygote genotype of Rr results in
pink flowers.
7. Genotype - the specific allelic combination
for a certain gene or set of genes based on
trait.
8. Monohybrid cross.
Cross involving parents differing in only one
trait.
Terms to know in Mendelian Genetics
9. Phenotype
The physical appearance of an organism with
respect to a trait, i.e. yellow (Y) or green (y)
seeds in garden peas. The dominant trait is
normally represented with a capital letter,
and the recessive trait with the same lower
case letter.
10. Recessive trait.
The opposite of dominant. A trait that is
preferentially masked.
11. Dominance - the ability of one allele to
express its phenotype (trait)
Terms to know in Mendelian Genetics
12. Backcross - the cross of an F1 hybrid to one
of the homozygous parents; for pea plant
height the cross would be Dd x DD or Dd x
dd; most often, though a backcross is a cross
to a fully recessive parent
13. Testcross - the cross of any individual to a
homozygous recessive parent; used to
determine if the individual is homozygous
dominant or heterozygous
14. Monohybrid cross - a cross between
parents that differ at a single gene pair
(usually AA x aa)
15. Monohybrid - the offspring of two parents
that are homozygous for alternate alleles of a
gene pair
EXERCISES-1
1.Human blood type is determined by codominant alleles.
There are three different alleles, known as IA, IB, and i. The IA
and IB alleles are co-dominant, and the i allele is recessive.
The possible human phenotypes for blood group are type A,
type B, type AB, and type O. Type A and B individuals can be
either homozygous (IAIA or IBIB, respectively), or
heterozygous (IAi or IBi, respectively).
A woman with type A blood and a man with type B blood
could potentially have offspring with which of the following
blood types?
A. type A
B. type B
C. type AB
D. type O
E. all of the above
EXERCISES-2
• What are the possible blood types of the offspring of a cross
between individuals that are type AB and type O? (Hint: blood
type O is recessive)
A. AB or O
B. A, B, or O
C. A or B
D. A, B, AB, or O
E. A, B, or AB
Meiosis
 Producing cells with chromosome
number half of the parent cell
 Two nuclear divisions
– Meiosis I and meiosis II
 Four haploid cells are produced
First Meiotic Division
• Chromosomes
become visible
• Nuclear
membrane
disappears
• Homologous
chromosomes
pair up
(not in mitosis)
• Crossing-over
(not in mitosis)
may occur
between
homologous
chromosomes
genetic materials exchanged
Homologous
chromosomes line
up in the middle of
cell randomly
 The 2 members of
each homologous
chromosome
separate from each
other and move
towards the opposite
poles of the cell
 Nuclear membrane
reforms
 Followed by
cytoplasmic
cleavage
Second Meiotic Division
 Separation of
chromatids of each
chromosome
 4 daughter cells
with half of the
chromosome
number of the
parent cell are
formed
Occurrence of meiosis
 Plants: anthers and ovules
 Mammals: testes and ovaries
Comparison between
Mitosis & Meiosis
Mitosis
Meiosis
Number of division
1
2
No. of daughter cells
produced
2
4
Type of cells produced
Somatic (body) cells
Gametes (sex cells)
Chromosome number
of daughter cells
Same as parent cell
(diploid)
Half of parent cell
(haploid)
Comparison between
mitosis & meiosis
Mitosis
Pairing of homologous
chromosomes
Occurrence
Role
Meiosis
No
Yes
Growing tissues
Reproductive
tissues (gonads)
For Growth &
Replacement
For Gamete
Formation
Significance of meiosis
 Produce haploid gametes which, after
fertilization, can restore normal
diploid conditions
 Produce genetic variations
Sources of genetic variation
• Different combination of the genes of
each gamete
• Random fusion of gametes during
fertilization
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