Inheritance - Ch. 27

What is gestation?

time a developing embryo and fetus spends in uterus

What is pregancy?

state of female during the time of gestation

What is development?

gradual anatomical and physiological changes

What is fertilization?

-fusion of 2 haploid (23 chromosomes) gametes

-forms a zygote with 46 chromosomes

Where does fertilization occur?

in the uterine tube, near the junction between the ampulla and the isthmus (within a day after ovulation)

What is embryonic development?

first 2 months after fertilization

What is embryology?

study of embryos and their development

What is fetal development?

-begins at the 9th week and continues until birth

-divided into three trimesters that are each three months long

What are the steps in fertilization?

1. ovulation

2. fertilization and activation

3. pronuclei develop

4. spindle formation

5. amphimixis

6. 2 blastomeres form

What occurs during the first step, ovulation, of fertilization?

-secondary oocyte is released with polar body

-suspended in metaphase II

What occurs during the second step, fertilization and activation, of fertilization?

-acrosomal enzymes

-meiosis II finishes = ovum

-membrane fusion and oocyte activation

-changes in oocyte lead to calcium release from smooth ER

What 3 effects does the rise of calcium (from the 2nd step of fertilization) have?

-1. release enzymes to harden zona pellucida to prevent fertilization by more than one sperm

-2. end meiosis II and formation of second polar body

-3. activation of enzymes that increase in ovum's metabolism

What occurs during the third step, pronuclei develop, of fertilization?

-sperm absorbed

-pronuclei form

What occurs during the fourth step, spindle formation, of fertilization?

-chromatin coils

-cleavage begins

What occurs during the fifth step, amphimixis, of fertilization?

-conception

-pronuclei fuse

What is cleavage?

-approx. 7 days

-division of the zygote into numerous, smaller blastomeres

-group of blastomeres creates a pre embryo

-the pre embryo travels the length of the uterine tube

-after 3 days, the pre embryo is a solid ball of cells called a morula

-over the next 2 days, blastomeres form a hollow ball of cells called a blastocyst with cavity called blastocoele

What is a morula?

solid ball of cells formed from a zygote during cleavage

What is a blastocyst?

hollow ball of cells formed from a morula

What is a blastocoele?

fluid filled cavity in blastocyst

What occurs during week 3 of early embryonic development?

• Central nervous system forming as deep groove develops in ectodermal band along posterior midline of embryo

• Neural plate (future brain) and neural folds located adjacent to neural groove

What occurs during week 4 of early embryonic development?

• Heart is beating

• Providing nutrients for addtnl growth & development

What occurs during week 6 of early embryonic development?

• Placenta has formed

• Embryo is floating in the amniotic cavity

• Limbs grow longer

• Skull bones forming

What has occurred by the end of the first trimester in relation to organ formation?

-human features are defined

-muscles are forming

-fetal movements begin soon

What occurs by the end of 4 months in relation to organ formation?

-face and palate have formed

-cerebral hemispheres are enlarging

-hair is growing

-peripheral nerves are formed

What occurs during the third trimester in relation to organ formation?

-organ systems become ready for normal function

-rate of growth slows a little

-largest weight gain (fetus gains approx. 5.7 lbs)

What is labor?

-spontaneous contractions of the smooth muscle in the uterine myometrium

-positive feedback system

-stretching of the uterus causes a gradual increase in the rate of those contractions

-during early pregnancy, progesterone from placenta inhibits contractions

What are braxton hicks contractions?

-false labor

-spasms in the uterine muscles that are neither regular nor persistant

What is true labor?

involves placental and fetal factors for initiation

What is premature delivery?

-birth at 28 to 36 weeks (birth weight over 2.2 lbs)

-newborn has a good chance of survival

What occurs during the first stage, dilation, of labor?

-begins with the onset of true labor

-cervix dilates, and fetus shifts towards the cervical canal, moved by gravity and uterine contractions

-lasts >8 hours

-frequency and duration of contractions increase

What occurs during the second stage, expulsion, of labor?

-amnion ruptures ("water breaks")

-begins as the cervix completes dilation and is open

-contractions reach maximum intensity and continues until delivery

-lasts <2 hours

What occurs during the third stage, placental stage, of labor?

-uterine contractions continue and decrease the size of the uterus

-contractions tear connections between endometrium and placenta (afterbirth) is ejected

-continued contractions compress uterine blood vessels to restrict blood loss

What is inheritance?

-heredity

-transfer of genetic characteristics to next generation

What is genetics?

study of mechanisms responsible for inheritance

What is a genotype?

chromosomes and their component genes

What is a phenotype?

anatomical and physiological characteristics displayed by the collective expression of your genes

What is the human genome?

-full set of genetic material (DNA) in our chromosomes

-contains estimated 20,000 to 25,000 genes

What is a karyotype?

-entire set of chromosomes

-normal human: 23 pairs of chromosomes

What are homologous chromosomes?

-same structure and carry genes for the same traits at same locus

-may carry the same or different form (allele) of the gene

What are autosomal chromsomes?

22 pairs (minus one pair because they are sex chromosomes)

What kind of chromosomes do we have?

-22 pairs of autosomal chromosomes

-1 pair of sex chromosomes

What does XY stand for?

male

What does XX stand for?

female

How do alleles interact?

-phenotype from a heterozygous genotype depends on how the corresponding alleles interact

-most common form of interaction is simple inheritance

What is strict dominance?

-any dominant allele present is expressed in the phenotype regardless of any other allele

-ex: freckles

-a recessive allele is only expressed if it is present on both chromosomes of the homologous pair

What are punnett squares?

-grid used to predict genetic probabilities

-dominant alleles indicated by capital letters

-recessive alleles indicated by lowercase letters

-homozygous dominant (TT)

-heterozygous (Tt)

-homozygous recessive (tt)

What are the 2 major patterns of inheritance?

-1. inheritance of autosomal chromosomes

-2. inheritance of sex chromosomes

What is incomplete dominance?

-heterozygous alleles produce intermediate phenotype

-ex: sickle cell disease

What is codominance?

-heterozygous individuals exhibit both phenotypes

-ex: AB blood type

What is sex-linked inheritance?

-involves genes on the sex chromosomes

-X linked

-Y linked

What is polygenic inheritance?

-interactions among several genes determine phenotypic characteristics

-cannot use simple punnett squares to predict phenotype