Download genetics and human development

GENETICS
AND HUMAN
DEVELOPMENT
Date
THE DEVELOPMENT OF THE EMBRYO-FETUS TAKES PLACE IN
THE UTERUS AND LASTS AN AVERAGE OF 40 WEEKS.
Fertilization of the egg by the sperm usually takes place in the
fallopian tube.
The acrosome of the sperm becomes more fragile
(capacitation); the enzymes released will digest the membrane
of the egg.
The diploid number is restored in the zygote.
Both men and women have 22 pairs of autosomes.
Sex chromosomes: XX –
XY –
GENDER DETERMINATION
A female fetus (XX) will develop when the ovum
unites with a spermatozoon with an X
chromosome
 A male fetus (XY) will develop when the ovum
unites with a spermatozoon with a Y
chromosome

 There
is approximately a 50/50 chance of either
occurrence
PROCESSES OF THE PRE-EMBRYONIC STAGE OF
DEVELOPMENT

Fertilization
 Occurs

when the sperm penetrates the ovum
Cellular reproduction
 The
zygote begins the process of mitotic division
known as cleavage

Implantation
 The
trophoblast develops fingerlike projections that
help the blastocyst to burrow itself into the nutrientrich endometrium
PRE-EMBRYONIC STAGE





1 sperm cell out of 250 million in
the typical ejaculation penetrates
egg
Once the sperm cell burrows
through the outer membrane and
penetrates the ovum, their genetic
material combines and forms a new,
rapidly dividing cell
Fertilization
Cellular Reproduction
Implantation
ZYGOTE TO BLASTOCYST – IMPLANTATION TAKES PLACE
5 TO
8 DAYS AFTER FERTILIZATION
Within the fallopian tube the zygote begins a series of mitotic
divisions called cleavage:  two-cell stage  four-cell stage 
eight-cell stage, and so on.
A morula is a solid sphere of cells.
Blastocyst – the trophoblast (outer cell layer) secretes enzymes
to form a crater in the endometrium –
Inner cell mass – embryonic stem cells.
EMBRYONIC STAGE







From the end of the 2nd week after
fertilization until the end of the 8th
week
About the size of a kidney bean
Webbed fingers and toes present
Eyelids almost cover eyes
Constant shifting and moving
Organogenesis
Average gestation: 40 weeks, of
which the 1st 8 are the period of
embryonic growth

Mesoderm: Muscles, circulatory
system, bones, reproductive
system, connective tissue, kidneys,
ureters

Ectoderm: Skin, nervous system,
nasal passages, crystalline lens,
pharynx, mammary and salivary
glands

Endoderm: alimentary and
respiratory tracts, bladder,
pancreas, liver
EMBRYONIC MEMBRANES
Yolk sac – forms the first blood cells and reproductive stem
cells.
Amnion – surrounds the fetus; contains amniotic fluid –
Chorion – develops chorionic villi that will contain blood vessels
and will become the fetal portion of the placenta.
PLACENTA AND UMBILICAL CORD
The placenta is formed by the chorion of the embryo and the
endometrium of the uterus.
Fetal blood does not mix with maternal blood in the placenta; fetal
capillaries are within maternal blood sinuses. This is the site of
exchanges between fetal blood and maternal blood.
The placenta is delivered after the baby and is called the
afterbirth.
Question: What are the mechanisms of placental exchange?
PLACENTAL HORMONES – THE PLACENTA IS A
TEMPORARY ENDOCRINE GLAND
Human chorionic gonadotropin
Estrogen
Progesterone
FETAL STAGE





Begins at 9 weeks
Grape size
Eyelids fused shut and won’t open
until 27 weeks
All major joints functioning
Earlobes formed
FETAL STAGE




12 weeks
Uterus above pelvic bone
Intestines that grew rapidly and
into umbilical cord, begin to move
back into abdomen
Fetus excretes urine
FETAL STAGE




20 weeks
Skin covered with vernix caseosa
Uterus at the level of the umbilicus
Eyebrows and scalp hair are present
PARTURITION AND LABOR
Parturition – birth.
Labor – the sequence of events during birth.
First stage – dilation of the cervix –
Second stage – delivery of the infant
Oxytocin –
Third stage – delivery of the placenta.
THE INFANT AT BIRTH
The umbilical cord is clamped and severed.
Increased CO2 stimulates breathing; the lungs are inflated; more
blood returns to the left side of the heart.
The foramen ovale closes.
The ductus arteriosus constricts.
The ductus venosus constricts.
GENETICS
Genetics - the study of inheritance
 Human characteristics regulated by genes
 Chromosomes and Genes - each cell of an
individual contains 46 chromosomes except
mature RBC’s, ovum and sperm cells
 Homologous pairs 
 chromosomes
in 23 pairs
 maternal - from egg
GENETICS

Chromosomes


Genes






23 from each
parent
Dominant
Recessive
Genotype
Phenotype
Homozygous
Heterozygous
GENETICS

Chromosomes made of DNA & proteins
 DNA
- hereditary material
 DNA code for one protein is a gene
 genetic make-up = 2 genes for each protein
GENETICS

Autosomes
 chromosome
pairs 1 to 22
 remaining pair are sex chromosomes
 women XX
 men XY
GENETICS

Genotype and Phenotypes
 each
gene of a pair, may be 2 or more possibilities =
alleles
 if 2 alleles are the same, they are homozygous
 if 2 alleles are different, they are heterozygous
GENETICS
Genotype - actual genetic make-up, alleles
present
 Phenotype - appearance, how alleles are
expressed
 Dominant - characteristic expressed if only one
gene present, does not mean “common” or
“frequent”, just that one gene is sufficient for a
characteristic to appear
 Recessive - characteristic expressed only if 2
genes present

Dominant-recessive inheritance
A dominant gene will appear in the phenotype of a
heterozygous individual.
A recessive gene will appear in the phenotype only if the
individual is homozygous.
Example: Rh blood type
Rh (+) is dominant; Rh (–) is recessive.
Questions: What are the possible genotypes for an Rh(+) person? For an Rh(–)
person?
ANSWERS
An Rh (+) person may have a genotype of ++ or +–.
An Rh(–) person will have the genotype – –.
GENETICS
Inheritance: Multiple alleles
 Blood types A, B, O
 O - is recessive
 A & B - are co-dominant alleles (over O, not
each other)
 4 possible type combinations: A, B, O, AB
 Blood Rh, either positive (dominant) or
negative (recessive), Rh inhereted
independent of ABO

GENETICS

Sex-linked traits
X
- linked traits, genes for these located only on X
chromosomes
 X - linked traits are recessive
 man only needs one gene to express one trait in his
phenotype
 women are carriers, may pass on to children, but
don’t express the trait
GENETICS

Red-green color blindness
 mom
carrier, dad w/ normal vision
 each daughter has a 50% chance of being a carrier,
100% normal vision
 each son has a 50% chance of red-green color
blindness, a 50% chance of normal vision
QUESTION

Mom is a carrier of red-green color blindness
and dad is re-green colorblind. What is the
chance that their daughter will be a carrier?
QUESTION

Mom is homozygous for type A blood and dad
is homozygous for type B blood. What are the
chances of their child having either A or B
blood?
QUESTION

Mom is homozygous for type A blood and dad
is homozygous for type B blood. What is the
chance that their child will have type AB blood?
PUNNETT SQAURE
H
e
t
e
r
o
z
y
g
o
u
s
Heterozygous
Parent

If both parents are carriers of
the recessive allele for a
disorder, all of their children
will face the following odds of
inheriting it:

25% chance of having the
recessive disorder
50% chance of being a
healthy carrier
25% chance of being healthy
and not have the recessive
allele at all


P
a
r
e
n
t
PRACTICE
1. B= Brown eyes b= blue eyes Mom= Bb Dad= BB What
are the eye color possibilities if they chose to have
children?
Genotypes
Phenotypes
2. Curly hair is recessive, and straight hair is dominant. A
woman with curly hair marries a man who is
homozygous dominant for straight hair. Predict the
outcomes for their children.
Genotypes
Phenotypes
PRACTICE
3. Black hair is homozygous dominant. Brown hair is
heterozygous. Blonde hair is homozygous recessive.
(This is an example of incomplete dominance.) A woman
with brown hair marries a man with brown hair. What are
the possible outcomes for their kids?
Genotypes
Phenotypes
4. Attached earlobes are dominant over free hanging
earlobes. Complete the Punnett Square for the following
individuals: Mom=BB and Dad=bb
Genotypes
Phenotypes
PRACTICE
5. Incomplete dominance problem: T=tall (5’11”-6’2”);
Tt=medium height (5’4”-5’10”) t=short (5’3” or smaller)
Mom= 5’5”
Dad= 6’0”
What are the possible height outcomes of their children?
Genotypes
Phenotypes
6. Freckles are recessive. No freckles are dominant.
Mom= heterozygous Dad=homozygous recessive
Possible outcomes for kids?
Genotypes
Phenotypes
WRAP-UP QUESTION
Name the part or aspect of development or genetics described.
1. The appearance or expression of a trait
2. Inheritance of hemophilia
3. Having two different alleles for a trait
4. Maternal and paternal chromosome pair
5. Embryo stage implanted in uterus
6. Embryonic part of the placenta
7. Carry blood from fetus to placenta
8. Hormone that facilitates labor

___ 1. Alleles

___ 2. Genotype

___ 3. Phenotype

___ 4. Heterozygous

___ 5. Dominant

___ 6. Recessive

___ 7. Homozygous

___ 8. Punnett square

___ 9. Genetics

___ 10. Traits
MATCHING
a. Characteristics
that can be passed only from one living
thing to its young
b. Alleles paired together for a specific trait are identical
c. When one allele masks the presence of another, the
allele is…
d. An allele that is masked by another is…
e. All the forms of a gene for any given trait are…
f. Grid system used to determine possible genotypes of
offspring
g. The study of heredity
h. The physical result of a gene combination
i. The genetic make-up, or combination, of an organism
j. Alleles paired together that are different from each other
1. Genetics is the study of _______________.
2. Traits are characteristic that can be passed only from a ___________ thing to
its _______________.
parents to offspring is ________
4. Each cell of a Punnett square represents one possible _______________
outcome for any offspring of two specific parents.
5. Genotype refers to the ______________ make-up of an organism.
6. _____________ is the physical trait that is expressed in an individual.
7. __________ are the different forms of a gene for any given trait.
8. For each trait, there are _____ allele possibilities.
9. When the expression of one allele is masked by the presence of another, it is said to be
___________________.
10. When an allele masks the presence of another allele, it is said to be ________________.
11. When both alleles of a parent or offspring are identical, one is said to be
_______________.
12. A heterozygous genotype is when the alleles present are ______________, such as Bb.
13. The female’s genes should usually be placed along the _________________ side of the
Punnett square.
14. It is proper to put the _____________ allele before a recessive allele when determining the
genotype of the offspring in a Punnett square.
15. For an offspring to ___________ a recessive trait, both parents must have at least one
______ allele in their genotype.