Transcript Trait

THE PASSING OF TRAITS
FROM PARENT TO OFFSPRING
“Looking at Your Traits”
• Number your paper 110
• Beside each number,
write the “Trait” we
are looking at.
• Tell whether you are
“dominant” or
“recessive” for this
trait.
•
Lastly, write your
“Genotype”—which
will be represented
by given letters
Ex.
1.
2.
PTC-Dominant-TT or Tt
Tongue RollingDominant-RR or Rr
“Looking at Your Traits”
1. PTC is a chemical called phenylthiocarbamide and is harmless. It is used in medical
genetics and as a diagnostic tool in medicine. The
ability to taste the chemical is a dominant trait.
People who cannot taste this chemical are
recessive for the trait.
“Looking at Your Traits”
2. Tongue Rolling
“Looking at Your Traits”
3. Earlobes
“Looking at Your Traits”
4. Earbump
“Looking at Your Traits”
5. Widow’s Peak
“Looking at Your Traits”
6. Hitchhiker’s Thumb
“Looking at Your Traits”
7. Polydactyly
“Looking at Your Traits”
8. Syndactyly
“Looking at Your Traits”
9. Cleft Chin
“Looking at Your Traits”
10. Hair Whorl
I.
•
•
•
•
Terms
Trait – characteristic of an organism
Gene – a heredity unit that codes for a trait.
Allele – different gene forms
Dominant – the gene that is expressed
whenever it is present
• Recessive – the gene that is “hidden”. It is
not expressed unless a homozygous
condition exists for the gene.
I.
Terms
• Homozygous – two identical (same) alleles
for a given trait (TT).
• Heterozygous – two different (opposite)
alleles for a given trait (Tt).
• Gamete – sexual reproductive cell.
• Fertilization – the fusion of two gametes.
• Phenotype – physical trait of an organism.
• Genotype – the genes present in the cell.
II. Gregor Mendel“The Father of Genetics”
A.*Mendel was the first to come up with
rules regarding heredity-which formed the
basis of genetics.
B. Mendel’s Hypotheses
1. For each inherited trait, an individual
has two factors that control heredity
(these “factors” are called genes) which
are inherited from each parent.
B. Mendel’s Hypotheses
2. There are alternative versions of
genes—(each version is called an allele).
Ex. Purple flowers or white flowers
Brown eyes or blue eyes
B. Mendel’s Hypotheses
3. When two different alleles occur together, one of
them may be completely expressed, while the other
may have no observable effect on the organism’s
appearance.
--Dominant or recessive Purple flowers are dominant to
white flowers
B. Mendel’s Hypotheses
4. When gametes are formed, the alleles for each
gene in an individual separate independently
of one another. Thus, gametes carry only one
allele for each inherited trait. When gametes
unite during fertilization, each gamete contributes
one allele.
C. Laws of Heredity
1. Law of Segregation—the two alleles for a
trait segregate (separate) during the formation
of gametes (meiosis).
2. Law of Independent Assortment—the alleles
of different genes separate independently of
one another during gamete formation.
*Ex. The alleles for height separate independently of
the alleles for flower color
III. Studying Heredity
A. Punnett Square
1.
2.
3.
4.
Determine the traits used.
Determine the dominant vs. recessive trait.
Determine the letters for each trait.
Express the cross and determine the
gametes formed.
5. Set up Punnett Square.
Punnett Square
• Place the two female gametes across the top
• Place the two male gametes down the side.
• Determine the offspring by filling in the squares.
Ex. Problem
b
b
• Trait-Eye Color
B
Bb
Bb
• Brown is dominant to
blue
B
Bb
Bb
• B = Brown
b = blue
* Cross a homozygous
0 4 0
brown eyed male with
Genotypic ratio: ___:___:___
a blue eyed female.
4
0
Phenotypic ratio:____:____
BB x
bb
Passing on of
Traits
IV. Sexual Reproductionreproduction where two gametes
unite.
Sexual Reproduction
--Two parents each form reproductive
cells that have one-half the number of
chromosomes—these cells are called
gametes and the process that they are
made is called meiosis.
A. MEIOSIS
--A form of cell division
that halves the number
of chromosomes when
forming specialized
reproductive cells, such
as gametes.
**Four cells are produced,
each with half as much
genetic material as the
original cell.
B. Chromosome Number in a Cell
1.Diploid number 2n—the number of
chromosomes in a body cell of an organism.
2.Haploid number n—half of the diploid
number.
– The diploid number for a human is 46 (humans
have 46 chromosomes in each body cell)
23 and is
– The haploid number for a human is ___
found only in the gamete cells (sperm/egg)
Determine the Diploid or Haploid
number of each organism:
Homo sapiens (human)
Mus musculus (house mouse)
Zea mays (corn or maize)
Drosophila melanogaster (fruit fly)
Xenopus laevis (South African clawed frog)
Caenorhabditis elegans (microscopic roundworm)
Saccharomyces cerevisiae (budding yeast)
Canis familiaris (domestic dog)
Arabidopsis thaliana (plant in the mustard family)
Muntiacus muntjac (its Indian cousin)
Myrmecia pilosula (an ant)
Parascaris equorum var. univalens (parasitic roundworm)
Cambarus clarkii (a crayfish)
Equisetum arvense (field horsetail, a plant)
2n
n
46
40
20
8
___
36
___
12
___
32
78
10
6
___
2
___
2
200
216
23
20
___
10
___
4
18
6
16
___
___
39
___
5
3
1
1
___
___
100
___
108
Meiosis and Sexual Reproduction
Question:
What is the difference in the
number of cell divisions and the
change in chromosome number
during mitosis and meiosis?
Meiosis and Sexual Reproduction
2n
Mitosis
Meiosis
2n
2n
2n
n
n
n
n
n
n
C. Mitosis VS. Meiosis
Mitosis
• Produce identical cells
• Produce diploid cells
• Occurs in:
– Plants—stems, leaves,
roots
– Animals—skin, bones,
digestive organs, etc.
Meiosis
• Produce gametes (sex
cells)
• Produce haploid cells
• Occurs in:
– Plants—ovules, spores
– Animals—ovules (eggs),
sperm
V. Genetic Problems
Genetic Diseases
• http://www.marchofdimes.com/pnhec/4439
_4136.asp
A. Pedigrees
• Pedigree help determine the inheritance and
probability of human genetic disorders.
Example Pedigree
Generation:
Generation:
Generation:
Generation:
B. Karyotype
--A picture of the paired chromosomes,
arranged in order from largest to smallest.
In humans, there are 23 pairs of chromosomes.
-22 autosomes (chromosomes that code for regular body traits)
-1 sex chromosome
Gender is determined by the combination of sex chromosomes
inherited in the zygote (the fertilized egg).
XX = Female
XY = Male
*it is the sex chromosome with in the sperm that is the determining factor for
gender.
Karyotypes
• Karyotypes can be obtained by blood
samples or by amniocentisis.
• Amniocentesis detects or rules out Down's syndrome.
Amniocentesis also detects neural tube defects such as spina
bifida. Babies born with spina bifida have a backbone that did
not close properly. Serious complications of spina bifida can
include leg paralysis, bladder and kidney defects, brain swelling
(hydrocephalus), and mental retardation. If a pregnancy is
complicated by a condition such as rh-incompatibility, your
doctor can use amniocentesis to find out if your baby's lungs are
developed enough to endure an early delivery.
Amniocentesis
C. Nondisjunction- the failure of
chromosomes to separate properly
during meiosis.
• Karyotypes can also detect other
chromosomal abnormalities such as:
– Down’s Syndrome—an extra #21 autosome.
– Klinefelter’s Syndrome—an extra sex
chromosome
– Turner’s Syndrome—a missing sex
chromosome