HGEN: Chapters 2, 5 and 6 Study Guide
Test on TUESDAY, 10/15/2013!
Vocabulary to Know:
CHROMATIN: UNCOILED DNA; present when the cell isn’t dividing.
CHROMOSOMES: COILED DNA; present when the cell is performing mitosis.
SISTER CHROMATIDS: joined together by centromere; matching alleles at same place
HOMOLOGOUS CHROMOSOMES: Chromosomes that are of the same size, shape, information, and
centromere location
heteromorphic chromosomes: sex chromosomes that are different; XY
homomorphic chromosomes: sex chromosomes that are the same; XX
Primary sex differentiation: gonad development for production of gametes
Secondary sex differentiation: other characteristics of overall appearance; mammary glands, facial hair, etc.
Unisexual: “one sex”; organisms are either male or female
bisexual/hermaphroditic: “two sexes”; containing both male and female sex characteristics
intersex: between two sexes; neither fully male or female
heterogametic sex: gametes look different from one another; males produce an X and Y chromosome
homogametic sex: gametes look the same; females produce 2 X chromosomes
Bipotential gonads: gonadal ridges can become ovaries or testes
Mullerian ducts: become fallopian tubes and uterus of the female reproductive system
Wolffian ducts: become vas deferens, glands of male reproductive system
disjunction vs nondisjunction: disjunction is the NORMAL separation of tetrad – dyad – monad.
Nondisjunction is the abnormal condition of tetrads not separating or dyad centromeres not splitting that causes
chromosomal aberrations to occur during meiosis.
What is the purpose of MEIOSIS? Division of nucleus to segregate DNA into new gametes. DIPLOID to HAPLOID.
Reductional division and Equational division of centromeres that allow for separation of chromosomes to achieve a
haploid condition.
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What is the order of steps? Occurs in 2 phases, order of steps is the same as in Mitosis. Prophase 1 is the
most significant as CROSSING OVER occurs that allows for genetic variation.
What is the general description of chromosome action in meiosis? Beginning of Meiosis 1 begins with a
TETRAD; at the end of Meiosis 1, there is a DYAD in each cell produced; at the end of Meiosis 2, there is a
single MONAD in each cell produced.
How is meiosis different in human males and human females? Meiosis in males in a CONTINUOUS process,
beginning at puberty. Meiosis in females is a HALTING process. It begins during the 12 th week of fetal
development, arresting at Prophase 1 and not beginning again until puberty begins. Then, each month a
single immature ova completes Meiosis 1 prior to ovulation and will complete Meiosis 2 following fertilization
by a mature sperm.
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What are the specific steps of Prophase 1? What is significant about Prophase 1?
o Leptonema: chromatin condenses to form chromosomes
o Zygonema: rough pairing of homologs
o Pachynema: synapsis; formation of tetrads
o Diplonema: crossing over at chaisma
o Diakinesis: preparing for prometaphase1
Describe oogenesis and spermatogenesis in humans. How are they alike? How are they different?
Spermatogenesis produces 4 mature spermatozoa that are capable of fertilizing an egg. In humans, the sperm
SHOULD contain 23 single chromosomes = the haploid number.
Oogenesis produces 1 mature ova and 4 polar bodies. Only the ova is capable of sustaining fertilization due to the
presence of organelles and cytoplasm that will permit embryonic development until the placenta and amniotic sac are
formed later in gestation. The ova SHOULD also contain the human haploid number of 23.
Understand the process of sex differentiation/fetal development in humans (p. 99)
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Gonadal ridges are produced during the 5th week of gestation. The embryo is potentially bipotential at this
stage the gonads can become ovary or testis.
Cortex portion can develop into ovarian tissue; Mullerian ducts will become fallopian tubes and uterus.
Medulla portion can develop into testis; Wolffian ducts will become vas deferens, ejaculatory duct, and male
glands.
Presence or absence of the Y chromosome determines the transition of gonadal ridges into ovaries or testes.
In the absence or malformation of genetic information of Y chromosome, no male GONADAL development
occurs.
During the 12th week of fetal development, ovaries begin meiosis for the production of eggs.
Describe nondisjunction and the impact it CAN have on gamete chromosome numbers.
Nondisjunction is the abnormal condition of tetrads not separating or dyad centromeres not splitting that causes
chromosomal aberrations to occur during meiosis. SEE DIAGRAM from CHAPTER 5 QUIZ!
Be able to differentiate human chromosome numbers (karyotypes) in –somic conditions.
Be able to identify the critical areas AND describe the functions of the Y chromosome and its influence in sex
differentiation. SEE CHAPTER 5 QUIZ!!
What term is used to describe the relationship between the X and Y chromosomes? HETEROMORPHIC
Describe the genotype and phenotype – Be able to ID the karyotype - of the following -somic conditions:
Turner Syndrome
Klinefelter Syndrome
Down Syndrome
45, X
Patau Syndrome
47, 13+
47, XXY
Edward Syndrome
47, 18+
KNOW Down Syndrome! Cause, description, statistics, pre-natal diagnosis (p.115)
47, 21+