Chromosomal Basis of Inheritance II

Question 1

What is the purpose of GWAS?

Answer 1

To identify which parts of the genome are responsible for certain diseases or conditions.

Question 2

How do GWAS work?

Answer 2

By comparing DNA from thousands of patients to DNA from thousands of control subjects genetic differences (such as allelic differences or differences in single nucleotide polymorphisms or SNPs) that partially account for the phenotypic differences between the two groups can be identified.

Question 3

When is recombination frequency best correlated with genetic distance?

Answer 3

This relationship is better established over short distances than over long distances.

Question 4

What happens in nondisjunction?

Answer 4

Pairs of homologous chromosomes do not separate normally during meiosis. As a result, one gamete receives two of the same type of chromosome, and another gamete receives no copy. The other chromosomes are usually distributed normally.

Question 5

What happens if nondisjunction occurs during meiosis I?

Answer 5

You get an abnormal number of chromosomes in all of the gametes.

Question 6

What happens if nondisjunction occurs during meiosis II?

Answer 6

Some gametes are affected and others are not.

Question 7

What causes aneuploidy?

Answer 7

It is a result of the fertilization of gametes in which nondisjunction occurred.

Question 8

What is the result of aneuploidy?

Answer 8

It results in monosomic (2n-1) and trisomic (2n+1) individuals.

Question 9

For most alterations of chromosome number, what is the result?

Answer 9

The organism is non-viable (trisomies and monosomies are the main reason for human pregnancy loss). Most of the viable ones are associated with some serious disorders.

Question 10

What is Down syndrome?

Answer 10

An aneuploid condition that results from three copies of chromosome 21. It affects about one out of every 830 children born in the United States.

Question 11

What causes Patau syndrome?

Answer 11

Trisomy of chromosome 13.

Question 12

What are the symptoms of Patau syndrome?

Answer 12

Serious eye, brain, circulatory defects as well as cleft palate. Children rarely live more than a few months.

Question 13

What causes Edward’s syndrome?

Answer 13

Trisomy of chromosome 18.

Question 14

What are the symptoms of Edward’s syndrome?

Answer 14

Almost every organ system affected, and children generally do not live more than a few months.

Question 15

What are the symptoms of trisomy of the X chromosome?

Answer 15

Healthy and fertile, usually cannot be distinguished from normal female except by karyotype. Slightly taller than average.

Question 16

What causes Klinefelter syndrome?

Answer 16

Having two X chromosomes and one Y chromosome (XXY)

Question 17

What are the symptoms of Klinefelter syndrome?

Answer 17

Unusually small testes, sterile, breast enlargement and other feminine body characteristics.

Question 18

What causes Turner syndrome?

Answer 18

Also known as monosomy X, this is the result of having only one X chromosome and no Y. (XO)

Question 19

What are the symptoms of Monosomy X (Turner syndrome)?

Answer 19

The only known viable monosomy in humans. Phenotypically female, but sterile due to lack of female organ maturation.

Question 20

What are the symptoms of having one X and two Y chromosomes (XYY)?

Answer 20

Healthy and fertile, tend to be taller than average. Phenotypically male.

Question 21

What is triploidy syndrome?

Answer 21

There are three chromosomes for every chromosome. This typically results in miscarriage or death within the first year of life.

Question 22

What are accessory, dispensable, supernumeray, or B chromosomes?

Answer 22

Some organisms (eg fungi, insects), aside from a core set of chromosomes, also contain chromosomes present in some but not all individuals. These accessory chromosomes are not essential for survival.

Question 23

What are core chromosomes?

Answer 23

These are chromosomes that carry essential genes that encode housekeeping functions such as cellular metabolism and reproduction; they evolve slowly.

Question 24

What do accessory chromosomes do?

Answer 24

They show high mutation rates, the acquisition of foreign genes, copy number polymorphisms, and frequent rearrangements; they evolve fast (“the 2-speed genome”)

Question 25

What causes polyploidy?

Answer 25

Complete nondisjunction.

Question 26

What is polyploidy?

Answer 26

A condition in which an organism has more than two complete sets of chromosomes. Ex. triploidy (3n), tetraploidy (4n), hexaploid (6n), etc.

Question 27

How does the effect of polyploidy compare to the effect of one extra or missing chromosome?

Answer 27

Generally, polyploidy causes smaller disruption of genetic balance.

Question 28

How does the rate of polyploidy compare between plants and animals?

Answer 28

In animals, it is rare, but it is common in plants.

Question 29

What is the only known polyploid mammal?

Answer 29

The plains viscacha rat.

Question 30

What is the purpose of polyploidy in the tissues of animals?

Answer 30

Polyploidy increases the metabolic capacity of a tissue.

Question 31

What is the purpose of polyploid hepatocytes and placental TGCs?

Answer 31

They provide nutrients and metabolites. TGCs can be 8n to 64n and hepatocytes can be 4n to 8n.

Question 32

What is the purpose of polyploid megakaryocytes?

Answer 32

These are large bone marrow cells responsible for producing platelets. They can be viewed as a stockpile of components needed to generate platelets. They can be 16n to 128n.

Question 33

What is a chromosomal deletion?

Answer 33

A deletion removes a chromosomal segment.

Question 34

What is a chromosomal duplication?

Answer 34

A duplication repeats a segment.

Question 35

What is a chromosomal inversion?

Answer 35

An inversion reverses a segment within a chromosome.

Question 36

What is a chromosomal translocation?

Answer 36

A translocation moves a segment from one chromosome to a nonhomologous chromosome.

Question 37

What are the four types of chromosome structure alterations?

Answer 37

1. Deletion
2. Duplication
3. Inversion
4. Translocation

Question 38

What causes cri du chat syndrome?

Answer 38

A specific deletion in chromosome 5.

Question 39

What is the result of cri du chat syndrome?

Answer 39

A child born with this syndrome is mentally impaired and has a catlike cry; individuals usually die in infancy or early childhood.

Question 40

What chromosomal alteration is associated with chronic myelogenous leukemia?

Answer 40

Translocation on chromosomes 9 and 22 (the translocated chromosome 22 is known as the Philadelphia chromosome). Cancer occurs by activating a gene that is involved in the cell cycle, leading to the loss of control of cell growth.

Question 41

What is genomic imprinting?

Answer 41

For a few mammalian traits, the phenotype depends on which parent passes along the alleles for those traits. This variation amongst phenotypes is known as genomic imprinting.

Question 42

How does genomic imprinting work?

Answer 42

It involves the silencing of certain genes depending on which parent passed them on.

Question 43

Which allele of the IGF2 gene is expressed?

Answer 43

Only the parental allele.

Question 44

What are extranuclear or cytoplasmic genes?

Answer 44

Mitochondria and plastids contain their own genomes. Collectively, genes in these genomes are known as extranuclear or cytoplasmic genes.

Question 45

How is the inheritance of traits by extranuclear genes controlled?

Answer 45

Inheritance is dependent on the maternal parent because the zygote’s cytoplasm comes from the egg.