Lecture 2 - Genetics

Question 1

Gene:

Answer 1

a sequence of nucleotides that represents a functional unit of inheritance; a region of DNA that codes for a product, either RNA or protein.

Question 2

Chromosome:

Answer 2

a highly ordered structure composed of DNA and proteins that carries the genetic information. In humans, there are 46 chromosomes ordered in pairs

Question 3

Chromatid:

Answer 3

one half of a replicated chromosome that contains all of the genetic material equivalent to a chromosome. This is usually seen at metaphase.

Question 4

Centromere:

Answer 4

the primary constriction of a chromosome; the point at which the chromatids are held together at metaphase. This region is comprised of repeat sequence DNA.

Question 5

Karyogram:

Answer 5

an image of the chromosome constitution of an individual. Also, a figure showing the paired chromosomes from a cell arrayed in a standard sequence.

Question 6

Autosome:

Answer 6

all chromosomes other than the X and Y chromosomes which are designated the sex chromosomes.

Question 7

Homologous chromosomes or homologs

Answer 7

sister chromosomes, the members of a pair of chromosomes in which one is inherited from the mother and the other from the father.

Question 8

Disomy:

Answer 8

the presence of 2 chromosomes.

Question 9

Isodisomy:

Answer 9

2 chromosomes from the same source, i.e., duplication of 1 chromosome.

Question 10

Heterodisomy:

Answer 10

2 different chromosomes

Question 11

Locus:

Answer 11

position of a gene on chromosome

Question 12

Allele:

Answer 12

an alternative form of a gene occupying the same locus. An allele may be the result of a mutation. There is a maximum of two alleles per diploid chromosome complement (one allele per chromosome), but multiple alleles may exist within a population.

Question 13

Mutation:

Answer 13

a permanent heritable change in the sequence of genomic DNA. This may manifest at both the molecular and cytogenetic levels. Not all mutations are negative events. Many are benign (i.e., blue eye color) and some have positive effects (i.e., sickle cell trait in countries with significant risk of malaria).

Question 14

Constitutional Mutation

Answer 14

a permanent heritable change in the sequence of genomic DNA. This may manifest at both the molecular and cytogenetic levels. Not all mutations are negative events. Many are benign (i.e., blue eye color) and some have positive effects (i.e., sickle cell trait in countries with significant risk of malaria).

Question 15

Acquired mutation

Answer 15

may arise in a single somatic cell which then divides mitotically giving rise to a new clone of cells. The mutation will be limited to this clone and will not be transmitted to progeny of the individual. ie - cancer

Question 16

Syndrome:

Answer 16

A disorder with a set of characteristics that occur together and are assumed to have a common basis. Not all characters occur in all affected individuals. There is a range of variability within a population.

Question 17

Diploid:

Answer 17

the presence of two copies of each unique chromosome per cell. In humans, the chromosomes occur in pairs and the diploid (2N) number is 46.

Question 18

Haploid:

Answer 18

one copy of each unique chromosome. In humans, the gametes are haploid (N = 23)

Question 19

Recombination:

Answer 19

the generation of new allelic combinations on chromosomes, usually by crossing over

Question 20

Mitosis

Answer 20

somatic cell division in which the DNA replicates and is even distributed to two equal daughter cells

Question 21

Meiosis

Answer 21

cell division in the gonads that produces the gametes. A single DNA replication is followed by two cell divisions which reduces the total DNA content of a cell from 2N to N. Recombination occurs to increase genetic diversity in a population.

Question 22

Cross-over

Answer 22

an exchange between homologous chromosomes resulting in a reassortment of the genes/alleles present on each chromosome

Question 23

Nondisjunction

Answer 23

failure of chromosomes or chromatids to separate to opposite poles in cell division. Usually results in one too many or one too few chromosomes in a cell.

Question 24

Biochemical genetics

Answer 24

subspecialty that deals with the diagnosis, treatment, and research of inborn errors of metabolism (mutations of biochemical pathways)

Question 25

Examples of a simple biochemical pathway?

Answer 25

Question 26

Describe PKU (phenylketonuria)…

Answer 26

Phenylalanine hydroxylase isn’t able to convert phenylalanine to tyrosine. Small amount of PHE converted to phenylpyruvic acid - can be detected in urine. Affects 1/10,000 births, autosomal recessive, treat by diet modification

Can lead to mental retardation

Question 27

What are the other types of hyperphenylalaniemias?

Answer 27

Question 28

Describe what occurs with the loss of function of tetrahydrobiopterin (BH4)…

Answer 28

BH4 is the cofactor that is in the signlaing pathway of phenylalanine hydroxylase. When knocked out, it causes the same clinical phenotype as PKU.

Question 29

Cytogenetics

Answer 29

The study of the structure and function of the cell, especially the chromosomes

Question 30

Describe the process of spermatogenesis

Answer 30

Question 31

Oogenesis

Answer 31

Question 32

Describe the timing of oogenesis

Answer 32

Oogenesis begins in the devloping fetues - by the 3rd month of gestation, primary oocytes are present. These cells reach prophase 1 by birth are remain so until ovulation. At ovulation, the oocyte completes meiosis 1, becoming a secondary oocyte. Meiosis will only be completed if fertilization occurs. Penetration of the sperm head stimulates the final division and release of second polar body.

Question 33

Describe the main differences between spermatogenesis and oogenesis.

Answer 33