Introduction to Genetics

Question 1

___ are long linear DNA molecules. Humans have 23 pairs of them.

Answer 1

chromosomes

Question 2

____ are multiple repeats of the six-nucleotide sequence TTAGGG which are found at the ends of chromosomes

Answer 2

telomeres

Question 3

What are centromeres?

Answer 3

special regions of DNA where the kinetochore forms. This is the point where chromosomes become attached to the microtubules of the mitotic spindle

Question 4

Are gametes diploid or haploid?

Answer 4

haploid

note: diploidy arises from fusion of haploid gametes

Question 5

____ occurs when cells duplicate their DNA normally during S-phase of mitosis but fail to undergo cytokinesis causing the cell to contain more than two copies of certain chromosomes

Answer 5

polyploidy

Question 6

The first step in packaging DNA into chromatin involves formation of ____, which consist of 8 histone proteins

Answer 6

nucleosomes

Question 7

During S-phase of the cell cycle, each of the chromosomes is duplicated by DNA polymerase. As the DNA is synthesized, proteins bind the two copies of each chromosome together, and the two copies remain bound to each other as the chromosomes condense during prophase. While they are bound together, each copy of the chromosome is called a _____

Answer 7

chromatid

Question 8

The chromosome is divided by the centromere into a short arm, known as the ____ arm and the long arm, known as the ___ arm

Answer 8

p; q

Question 9

____ chromosomes have arms of more or less equal size

Answer 9

metacentric

Question 10

____ chromosomes have the centromere off-center so the p-arm is clearly shorter than the q-arm

Answer 10

submetacentric

Question 11

____ chromosomes have very short p-arms and centromeres near one end of the chromosomes

Answer 11

acrocentric

Question 12

____ chromosomes are not normally found in humans; in these chromosomes, the centromere is located at one end so there is a single arm

Answer 12

telocentric

Question 13

Give the length of time for each phase in the cell cycle

Answer 13

G1: 12-36 hours
S: 6-8 hours
G2: 4 hours
M: 1 hour

Question 14

Give the DNA content and amount of genetic information throughout meiosis

Answer 14

4d and 2n…. meiosis I….. 2d and 1n…..1d and 1n

Question 15

List the stages of prophase I in meiosis and describe what happens in each

Answer 15

leptotene: chromosomes begin to condense, homologs chromosomes begin to pair
zygotene: synaptonemal complex forms (keeps chromosomes aligned as they condense further)
pachytene: chromosomes condense further, becoming shorter and wider while the synaptonemal complex continues to keep the homologs chromosomes aligned
diplotene: synaptonemal complex breaks down and the homologs chromosomes remain attached to each other at the chiasmata
diakinesis: chromosomes complete condensation, nuclear envelope breaks down

Question 16

Cross overs are most frequent between genes that are close together on a chromosome. true or false?

Answer 16

false, far apart

Question 17

Of the 23 pairs of homologous chromosomes, how many are autosomes?

Answer 17

22; 1 pair of sex chromosomes

Question 18

Describe the series of events in spermatogenesis

Answer 18

before puberty, primordial sperms (spermatogonia) remain dormant in the seminiferous tubules of the testes. At puberty, they divide and become primary spermatocytes - the largest germ cells in the seminiferous tubules. Reduction division leads to formation of two haploid secondary spermatocytes. Second meiotic division forms four haploid spermatids which are gradually transformed into four mature sperms during a process called spermiogenesis

Question 19

Describe the series of events in oogenesis

Answer 19

oogonia (primordial oocytes) proliferate into primary oocytes - at birth, all primary oocytes have completed the prophase of the first meiotic division and remain here until puberty. Shortly before ovulation, a primary oocyte completes the first meiotic division forming a secondary oocyte and first polar body. At ovulation, the secondary oocyte begins the second meiotic division but progresses only to metaphase. If the secondary oocyte is fertilized by a sperm, the second meiotic division is completed and a second polar body is formed.

Question 20

The secondary oocyte released at ovulation is surrounded by a covering of amorphous material known as the ____ _____ and a layer of follicular cells called the ____ ____. The secondary oocyte is large, being just visible to the unaided eye.

Answer 20

zona pellucida; corona radiata

Question 21

___ occurs when there are multiple copies of the entire genome. ex: triploidy (3n = 69 chromosomes)

Answer 21

polyploidy

Question 22

Define aneuploidy

Answer 22

when cells or individuals gain or lose a chromosome. As a result, the chromosome in an aneuploid cell is not an even multiple of the normal haploid number. Occur because of non-disjunction of a chromosome which means the chromosomes fail to separate resulting in some gametes with two copies of the chromosome and other gametes which lack the chromosome. ex: trisomy or monosomy

Question 23

Name the following chromosomal abnormality:
due to an extra copy of chromosome 21. These children have characteristic facial and hand features, mental retardation, and frequently have congenital heart disease or other developmental malformation

Answer 23

trisomy 21

Question 24

Name the following chromosomal abnormality:
present only in males, due to having 47 chromosomes with sex chromosomes of XXY. Children with this are phenotypically males until puberty. Features include testicular atrophy, sterility and gynecomastia

Answer 24

klinefelter’s syndrome

Question 25

Name the following chromosomal abnormality:
results in a female appearance and is due to a chromosome set of 45X. Features include absence of ovaries, short stature, webbed neck, and a broad chest with widely spaced nipples

Answer 25

turner syndrome

Question 26

Name the following chromosomal abnormality:
due to a microdeletion on maternal chromosome 15. Features include inability to speak, prone to long periods of unprovoked laughter

Answer 26

angelman syndrome

Question 27

Name the following chromosomal abnormality:
due to micro deletion on paternal chromosome 15. Features include mental retardation, hypotonia, obesity, hypogonadism and cryptochidism

Answer 27

prader-willi syndrome

Question 28

Name the following chromosomal abnormality:
due to deletion of part of chromosome 5. Features include microcephaly, mental retardation and congenital heart disease. These children have a cry that sounds like a cat

Answer 28

cri-du-chat syndrome

Question 29

Name the following chromosomal abnormality:
individuals are phenotypically normal females, although they tend to be tall and have low IQ scores and learning disabilities. Increasing degrees of mental and physical impairment are associated with increasing number of X chromosomes

Answer 29

Trisomy X (47, XXX)