Lecture 1: Intro to Genetics

Question 1

When Mendel crossed two pure line traits what were his findings?

Answer 1

he found that only one trait was expressed in the offspring

Question 2

When is a dominant trait expressed?

Answer 2

can be expressed if only one copy of a gene is present

Question 3

When is a recessive trait expressed?

Answer 3

trait is only expressed when both copies of a gene are present

Question 4

What is the law of segregation?

Answer 4

dominant and recessive traits exist and are passed on from parent to offspring

Question 5

What is the law of independent assortment?

Answer 5

traits are passed independently of other traits from parent to offspring

Question 6

What is genotype?

Answer 6

an individuals collection of genes or can reference to two particular alleles that code for a gene -> genotype determines phenotype

Question 7

What is phenotype?

Answer 7

the observed trait or set of traits that is created from your genetic makeup

Question 8

What is penetrance?

Answer 8

disease is expressed in 100% of people with a particular genotype; incomplete or complete

Question 9

Briefly describe the structure of DNA.

Answer 9

a double stranded helix; hydrogen bonds connect the two strands; there are four base pairs or nucleotides present; adenine, thymine, guanine, and cytosine; adenine pairs with thymine and is connected by two hydrogen bonds; cytosine pairs with guanine and is connected by three hydrogen bonds; the 5’ end has a phosphate group and the 3’ end has a hydroxyl group

Question 10

What is the significance of the promoter region?

Answer 10

during transcription it is the region where RNA polymerase binds to a strand of DNA after unzipping the double helix

Question 11

How is a chromosome formed?

Answer 11

genes are arranged in a complex called a nucleosome which is composed of DNA and histone and then nucleosomes are linked together to form chromatin which Is then further condensed to form a chromosome

Question 12

What is the locus?

Answer 12

location of a particular gene on a chromosome

Question 13

What is an allele?

Answer 13

a homologous copy of a gene… humans have two sets of each gene and one copy on each chromosome

Question 14

What are the different kinds of mutations?

Answer 14

germinal which occurs during formation of an egg or sperm; somatic which occurs after conception; chromosomal aberration which is an alteration in the number or the physical structure of a chromosome

Question 15

What are the three types of mutations that lead to an abnormal number of chromosomes?

Answer 15

monosomy- only one member of chromosome pair is present
trisomy- three chromosomes are present
polysomy- one chromosome is present 4 or more times

Question 16

What is the most common trisomy?

Answer 16

down syndrome trisomy 21 which occurs 1 in 800 births

Question 17

What are the presentations of a baby with trisomy 21?

Answer 17

cardiac defects, intestinal malformations, vision abnormalities, hearing loss, recurrent respiratory infections, memory loss with an increased risk of Alzheimer’ at an early age

Question 18

What are the common characteristics of down syndrome?

Answer 18

decreased muscle tone. enlarged and protruding tongue, small nose, upward slant of eyes, abnormally shaped ears, deep palmer crease, hyperflexibility, extra space between first and second toe

Question 19

XXY genotype

Answer 19

Klinefelter Syndrome

Question 20

What is the most common genetic abnormality associated with primary hypergonadism?

Answer 20

Klinefelter Syndrome

Question 21

What are the consequences of Klinefelter Syndrome?

Answer 21

males have small external genitalia and testes, 50% will develop breasts, usually sterile and impaired spermatogenesis, elevated levels of FSH and LH, decreased serum testosterone, abnormal arm and leg length, increased risk for breast cancer and pulmonary disease, may have impaired social skills including ADHD and impaired judgment, impaired higher language skills, increased risk of Non Hodgkin’s Lymphoma, leg ulcers, diabetes, lupus

Question 22

XO genotype

Answer 22

turner syndrome

Question 23

What is the female appearance in Turner Syndrome?

Answer 23

short wide chest, usually sterile, low estrogen, small breasts, normal mental development, neck skin folds, webbing of the neck

Question 24

What are the consequences of Turner syndrome?

Answer 24

hearing loss, hypothyroidism, autoimmune thyroiditis, elevated liver enzymes, primary amenorrhea, osteoporosis, increased fractures, renal structure abnormalities, vision and ocular abnormalities, autoimmune disease, diabetes, hyperlipidemia, hypertension, cardiac structural abnormalities, aortic dissection, increased CV mortality

Question 25

When taking a family history who should be included?

Answer 25

all first degree relatives and should include parents, siblings, and offspring

Question 26

What is the pedigree pattern in autosomal dominant inheritance?

Answer 26

multiple generations are affected and in a vertical pattern

Question 27

What is autosomal dominant inheritance?

Answer 27

mutation in a SINGLE allele of autosome is enough to cause disease or abnormal phenotype… only one affected parent is necessary for child to be affected

Question 28

What is the chance of each child having an abnormal phenotype with autosomal dominant inheritance?

Answer 28

50%

Question 29

What are some examples of autosomal dominant diseases?

Answer 29

Huntington’s Disease, Hypercholesterolemia, Neurofibromatosis Type 1, Polycystic Kidney Disease

Question 30

What is autosomal recessive inheritance?

Answer 30

mutation in which two copies of the allele of autosome are required to manifest the abnormal phenotype; horizontal patter in the pedigree

Question 31

Who must be a carrier in order for offspring to manifest the trait in autosomal recessive inheritance?

Answer 31

both parents must be carriers in order for offspring to manifest the trait

Question 32

What is the chance for offspring to be affected or a carrier in autosomal recessive inheritance?

Answer 32

offspring have a 25% chance of being affected… 50% chance of being a carrier

Question 33

What are some examples of autosomal recessive diseases?

Answer 33

Phenylketonuria, Sickle cell anemia, cystic fibrosus, thalassemia

Question 34

Are males and females hemizygous, heterozygous or homozygous for the mutant alleles in x-linked inheritance?

Answer 34

males are hemizygous- XY

and females are either heterozygous or homozygous- Xx or xx or XX

Question 35

What are some examples of X-linked dominant disease?

Answer 35

Hypophosphatemic rickets

Rett’s syndrome

Question 36

How many copies of mutant allele are required to produce X-linked recessive disease in males and females?

Answer 36

two copies of mutant allele are required to produce the disease in females but only one copy is required in males to produce the disease

Question 37

What are some examples of x-linked recessive diseases?

Answer 37

hemophilia A, duchenne’s muscular dystrophy, red-green color blindness

Question 38

What is mitochondrial inheritance?

Answer 38

transmission of mitochondrial DNA is maternal; mother passes her mitochondrial DNA including mutant DNA to all of her children, male or female

Question 39

What are some examples of mitochondrial mutations?

Answer 39

cyclic vomitting syndrome, myoclonic epilepsy with red-ragged fibers, nonsyndromic deafness, Leigh syndrome