Chapter 29 - Development And Inheritance

The correct statement is (b) "Occasionally an error in meiosis called nondisjunction results in an abnormal number of chromosomes." This statement is correct because nondisjunction is a type of error that can occur during meiosis, leading to an abnormal distribution of chromosomes in the resulting gametes. This can result in conditions such as Down syndrome, where there is an extra copy of chromosome 21. The other statements are incorrect: (a) normal traits do not always dominate over abnormal traits, (c) the sex of the child is determined by the father's contribution of either an X or Y chromosome, (d) most patterns of inheritance are not simple dominant-recessive, and (e) genes can be influenced by outside factors such as chemicals or radiation.

A blastocyst is a fluid-filled sphere of cells that enters the uterine cavity. This stage occurs during early embryonic development, after the morula stage. The blastocyst consists of an outer layer of cells called the trophoblast, which will eventually form the placenta, and an inner cell mass, which will develop into the embryo. The blastocyst is important for implantation into the uterine wall and the further development of the embryo.

The correct answer is "trophoblast". The trophoblast is the outer layer of cells in the blastocyst, which is the early stage of development after the zygote undergoes cleavage and forms a morula. The trophoblast plays a crucial role in implantation and the formation of the placenta.

The correct answer is 1. Cleavage refers to the early division of the zygote. During cleavage, the zygote undergoes rapid cell divisions, resulting in the formation of smaller cells called blastomeres. This process eventually leads to the formation of a solid ball of cells called a morula, which further develops into a blastocyst. Therefore, cleavage is the most appropriate choice to describe the early division of the zygote.

During gastrulation, the process of differentiation into the three primary germ layers occurs. This is when the zygote undergoes a series of cell movements and rearrangements, resulting in the formation of the ectoderm, mesoderm, and endoderm. These germ layers give rise to different tissues and organs in the developing embryo.

Neurulation is the process in embryonic development where the neural plate forms and eventually develops into the nervous system. This includes the formation of the neural tube, which will give rise to the brain and spinal cord. Therefore, choice 9, neurulation, is the correct answer as it directly relates to the embryonic development of structures that will become the nervous system.

Relaxin is the correct answer because it is a hormone that is responsible for increasing the flexibility of the pubic symphysis and helping to dilate the uterine cervix during labor. This hormone is released by the ovaries and the placenta during pregnancy, and its main function is to relax the ligaments and connective tissues in the pelvic area, allowing for easier passage of the baby through the birth canal.

Corticotropin-releasing hormone is secreted by the placenta and helps establish the timing of birth. It also increases the secretion of cortisol, which is important for fetal lung maturation.

Oxytocin is the correct answer because it stimulates uterine contractions and is responsible for the milk ejection reflex.

14) nondisjunction

Nondisjunction is the failure of homologous chromosomes or chromatids to separate during cell division, resulting in an abnormal number of chromosomes. This can lead to aneuploidy, which is an abnormal number of chromosomes in a cell. Therefore, choice 14, nondisjunction, is the correct answer that explains the given statement.

The correct answer is 9, umbilical cord. The umbilical cord is a flexible cord-like structure that connects the developing fetus to the placenta. It contains blood vessels that allow for the exchange of nutrients, oxygen, and waste products between the mother and the fetus.

Chorionic villi are finger-like projections of the chorion that bring maternal and fetal blood vessels into close proximity. These villi play a crucial role in facilitating the exchange of nutrients and waste products between the mother and fetus during pregnancy. They increase the surface area available for this exchange, allowing for efficient transfer of oxygen, nutrients, and hormones from the mother to the fetus, and removal of waste products from the fetus.

The correct answer is 11 because the developing individual from week nine of pregnancy until birth is referred to as a fetus.

The fusion of male and female pronuclei results in the formation of a zygote.

Human chorionic gonadotropin (HCG) stimulates the corpus luteum to continue production of progesterone and estrogen.

Prolactin is the correct answer because it promotes milk synthesis and secretion. During pregnancy, progesterone inhibits the action of prolactin to prevent milk production. However, after childbirth, progesterone levels decrease, allowing prolactin to stimulate milk production and secretion.

Phenotype refers to how the genetic makeup is expressed in the body, specifically the physical or outward expression of a gene.

Traits linked to the X chromosome are known as sex-linked inheritance. This means that the genes responsible for these traits are located on the X chromosome. In humans, males have one X and one Y chromosome, while females have two X chromosomes. Therefore, males are more likely to express X-linked traits because they only have one copy of the X chromosome. Females can be carriers of X-linked traits if they have one copy of the mutated gene on one of their X chromosomes. The presence of a Barr body, which is an inactivated X chromosome, is also related to sex-linked inheritance.

The given statement describes a situation where neither allele in an allelic pair is dominant over the other, and the heterozygote has a phenotype that is intermediate between the two homozygotes. This is a characteristic of incomplete dominance, where the heterozygous genotype results in a blending or mixing of the phenotypes of the two homozygous genotypes.

The given correct answer is "genotype." Genotype refers to the genetic makeup of an organism, which can be homozygous dominant (having two dominant alleles), homozygous recessive (having two recessive alleles), or heterozygous (having one dominant and one recessive allele). This term describes the actual gene arrangement in an individual.

The correct answer is "dominant trait". A dominant trait is an allele that masks the presence of another allele and is fully expressed. When an individual has one dominant allele and one recessive allele for a particular trait, the dominant allele will be expressed in the phenotype, while the recessive allele will be masked. This is why the presence of the dominant allele is fully expressed and can be observed in the individual's physical characteristics.

Polygenic inheritance refers to the control of inherited traits by the combined efforts of many genes. This means that multiple genes contribute to the expression of a particular trait, resulting in a wide range of phenotypic variations. Polygenic inheritance is responsible for traits such as height, skin color, and intelligence, where the phenotype is influenced by the interaction of multiple genes.

Cleavage is the process of cell division that occurs in the early stages of embryonic development. It results in the formation of blastomeres, which are the cells produced by cleavage. Therefore, choice 2, blastomeres, is the correct answer.

The correct answer is (3) morula. The morula is a stage in embryonic development where the zygote undergoes multiple rounds of cell division, resulting in a solid ball of cells. At this stage, the cells are still surrounded by the zona pellucida, a protective layer that helps the embryo implant into the uterus. The morula will eventually develop into a blastocyst, where a fluid-filled cavity forms in the center of the cell mass.

Angiogenesis is the process of forming new blood vessels from pre-existing ones. In the context of the developing embryo, angiogenesis is crucial for the formation of blood vessels to support the growing embryo. It allows for the delivery of oxygen and nutrients to the developing tissues and the removal of waste products. Therefore, choice 4, angiogenesis, is the correct answer as it directly relates to the formation of blood vessels to support the developing embryo.

An individual with different alleles on homologous chromosomes is referred to as heterozygous.

Homozygous refers to a person with the same alleles on homologous chromosomes.

The correct answer is (3) amnion. The amnion is a membranous sac that surrounds and protects the developing embryo. It is filled with amniotic fluid, which provides cushioning and support for the growing fetus. The amnion plays a crucial role in maintaining a stable environment for the embryo, regulating temperature, and preventing desiccation. It also allows for movement and growth of the developing fetus.

After implantation has occurred, the endometrium undergoes modifications and is referred to as decidua. The decidua is responsible for providing nourishment and support to the developing fetus. It separates from the endometrium after the fetus is delivered.

A permanent inheritable change in an allele that produces a different variant of the same trait is known as a mutation. Mutations can occur in various ways, such as changes in the DNA sequence or alterations in the structure of a gene. These changes can lead to the production of a different protein or the absence of a protein, resulting in a different phenotype or trait.

Heterozygous individuals who possess a recessive gene (but do not express it) and can pass the gene on to their offspring are called carriers. Carriers are individuals who carry a copy of a recessive gene but do not show any symptoms or traits associated with that gene. They can pass the gene on to their offspring, increasing the likelihood of the trait being expressed in future generations.

The correct answer is 5 - allantois. The allantois is a membrane that forms during embryonic development and serves as an early site of blood vessel formation. It plays a role in the exchange of gases and waste products between the embryo and the placenta.

The correct answer is 10. The chorion is a membrane derived from the trophoblast, which is the outer layer of cells in the blastocyst. The chorion plays a crucial role in the development of the placenta and is responsible for the exchange of nutrients and waste between the mother and the fetus.

The correct answer, 16, is referring to the Barr body. The Barr body is the inactivated X chromosome in females. In females, one of the two X chromosomes is randomly inactivated during embryonic development, forming a dense, inactive structure called the Barr body. This process ensures that females have the same dosage of X-linked genes as males, who only have one X chromosome. The Barr body can be visualized in the nucleus of cells and is used as a diagnostic tool in certain genetic disorders.

The correct answer is 6. The yolk sac functions as an early site of blood formation and contains cells that migrate into the gonads and differentiate into the primitive germ cells.

The notochord plays an important role in induction whereby an inducing tissue stimulates the development of an unspecialized responding tissue into a specialized tissue.

Translocation is the correct answer because it refers to the interchange of portions of nonhomologous chromosomes. This process can result in genetic disorders or abnormalities.

The correct answer is (4) chorion. The chorion is the outermost membrane of the embryo and becomes the principal part of the embryonic placenta. It is responsible for producing human chorionic gonadotropin (hCG), a hormone that is important for maintaining pregnancy.

The correct answer is 2 (placenta). The placenta is formed by the chorionic villi (fetal portion) and the decidua basalis of the endometrium (maternal portion). It serves as the site of exchange between the maternal and fetal blood, allowing oxygen and nutrients to diffuse from the maternal blood into the fetal blood.

In genetics, aneuploidy refers to the condition where there is an abnormal number of chromosomes in a cell. This can occur when one or more chromosomes of a set are either added or deleted. Therefore, choice 4, "aneuploid," is the correct answer for this question.

Human somatomammotrophin, also known as human placental lactogen, is a hormone that helps prepare mammary glands for lactation. It also regulates certain aspects of maternal and fetal metabolism.

The correct answer is 6 - multiple-allele. Inheritance based on genes that have more than two alternative forms is known as multiple-allele inheritance. An example of multiple-allele inheritance is the inheritance of blood type, where there are three possible alleles (A, B, and O) that determine the blood type of an individual.

The correct answer is "alleles". Alleles are the two alternative forms of a gene that code for the same trait and are at the same location on homologous chromosomes. They can be either the same (homozygous) or different (heterozygous).

Labor is an example of a positive feedback cycle, not a negative feedback cycle. In a positive feedback cycle, the initial stimulus is amplified, leading to a greater response. In the case of labor, contractions cause the release of oxytocin, which in turn stimulates more contractions, leading to the birth of the infant. Therefore, the statement that labor is an example of a negative feedback cycle is incorrect.

Muscle, bone, and peritoneum are derived from the mesoderm layer. The nervous system and epidermis are derived from the ectoderm layer. The epithelial linings of the respiratory and gastrointestinal tracts are derived from the endoderm layer.

During the first 3-4 months of pregnancy, the hormones produced by the corpus luteum are responsible for maintaining the pregnancy. The hormone produced by the trophoblast that prevents degeneration of the corpus luteum is human chorionic gonadotropin (hCG).

The correct answer is dilation, expulsion, placental. This is the correct order of occurrence during true labor. Dilation refers to the opening of the cervix, allowing the baby to move through the birth canal. After dilation, expulsion occurs when the baby is pushed out of the mother's body through contractions. Finally, the placental stage occurs when the placenta is delivered.

During the fourth week after fertilization, all of the structures mentioned in the answer options develop. Embryonic folding occurs as the embryo starts to fold in on itself. The neural tube forms, which is the precursor to the brain and spinal cord. The otic placode, which is the beginning of the ear, also develops. Additionally, the beginning of the eye and the upper and lower limb buds form during this time. Therefore, the correct answer is 1, 2, 3, 4, 5.

Amniotic fluid acts as a fetal shock absorber, helps regulate fetal body temperature, and prevents adhesions between the skin of the fetus and surrounding tissues. It is not derived entirely from a filtrate of maternal blood and does not provide nutrients to the fetus. Therefore, the correct answer is 2, 4, 5.