Question

UNIT 33 | Embryonic Development and Heredity 671 s. What is the specific function of the two umbilical arteries? 2. Observe a fresh or preserved animal fetus and placenta, if available. Identify the following structures and then write a brief description of each a. Placenta b. Amnion (amniotic sac) c. Umbilical cord 蚰鷊 3. Observe a model of a pregnant human torso, if available Figre33-7 Human male karyotype with 23 pairs The placenta is located in which region of the uterus? of chromosomes. contributed one set of chromosomes (23 paternal chromo 4. Observe a prepared slide of a section of human placenta. Then sketch and label as many structures as possible somes), and 23 maternal chromosomes came from the in- dividual's mother. Twenty-two of the 23 pairs are called autosomes, and the members of each pair are similar in appearance; the other pair-the X and Y chromosomes, called the sex chromosomes-determine the sex of the indi- vidual Females have two X chromosomes (designated XX), whereas males have one X and one Y。 Collectively, an individual's entire set of DNA is termed his or her genome. Figure 33-7 shows a sample karyotype, a display of all 23 chromosome pairs of an individual arranged by size and structure. The only pair that has chromosomes different sizes is the pair of sex chromosomes in a male- he XY Homologous chromosomes have pairs of genes that code for the same trait at the same location, or locas, on those chro- mosomes. However, the pairs of genes may have different vari- ants, or alleles, that code for a particular trait. For example, one gene for eye color may have an allele that codes for brown eyes, whereas the other gene for eye color may have an allele that codes for blue eyes. If two alleles code for the same trait (such as brown eyes), they are said to be homozygous for that trait. If two alleles are different (such as one for brown eyes Total magnification:X The Language of Genetics and one for blue eyes), they are heterozygous Some alleles mask or suppress the expression of another All body traits, such as eye color and bone structure, are allele of the same gene. An allele that masks another allele is in segments of DNA called genes, each of which called dominant; an allele that is masked is called recessive. codes for a specific protein. Because most body structures Dominant alleles are usually represented by capital letters are proteins, genes effectively provide the blueprint for all of whereas recessive alleles are usually represented by lower- case letters. Freckles, for example, are at least partially the re- an individual's traits In a cell preparing to divide, the DNA is folded and coiled sult of a dominant trait whose allele is designated "F; lack into chromosomes. Recall from Unit 5 that in humans, all of freckles is at least partially the result of a recessive trait nucleated somatic (body) cells have 46 chromosomes ar whose allele is designated f ranged in 23 pairs of homologous chromosomes; these Individuals with the genetic makeup FF are homozygous cells are diploid (designated 2n). The individual's father dominant for freckles, individuals with the genetic makeup

Answer 1

g. What is the specific function of the two umbilical arteries? A pair of umbellical arteries carry deoxygenated and nutrient-depleted blood away from the fetus 2. Observe a fresh or preserved animal fetus and placenta. if available. Identify the following structures and thern write a brief description of each a. Placenta Placenta, is a tube like structure that is formed by about 8th formed from the conceptus (foetal portion), which is directly attached with the endometmum (matemal portion). It provides nounshment and oxygen supply from maternal blood to the foetus and removes waste products and carbon dioxide week of pregnancy. It is b. Amnion (amniotic sac) The amnion is an extraembryonic membrane that develops into a protective fhuid producing membrane. The amnion lines the amniotic cavity and serves as a diffusion membrane for amniotic flhuid. Amniotic fhuid provides protection to the developing embryo offers protection against dehydration and mechanical shock. It also maintains stable temperatures, facilitates proper lung development, and assists in urine excretion. c. Umbilical cord Umbilical Cord is a tube-like, flexible structure. The umbilical cord joins the embryo, which is present inside the amniotic sac (the fhuid-filled sac that contains and protects a fetus in the womb) to the mother's placenta.