Genetics Exam 1

Question 1

Law of Independent Assortment

Answer 1

Gene pairs on different chromosome pairs assort independently at meiosis

Question 2

Gene Linkage

Answer 2

Genes that are typically inherited together. You can figure out the distance between genes by finding the recombination frequency (less than 50% = linked genes)

Question 3

Chiasmata

Answer 3

Sites of crossing over

Question 4

Crossing Over

Answer 4

At tetrad stage of meiosis, the crossing over of genetic material between non-sister chromatids at a chiasma. Multiple crossovers can include more than two chromatids. Recombinants are produced by crossing over

Question 5

Recombination Frequency

Answer 5

(Recombinants / Total Offspring)*(100). Units are in map units or centiMorgans

Question 6

Recombination v. Physical Maps

Answer 6

Recombination maps (map units) helpful when provided phenotypes; physical maps (kB) helpful when wanting to determine how physical distance affects function.

Question 7

Single Nucleotide Polymorphisms

Answer 7

A difference in sequence by a single nucleotide. Can determine via restriction digestion with restriction fragment length polymorphism. A restriction enzyme typically will excise out a region of DNA given a particular sequence. If the restriction enzyme does not recognize the sequence, it will not excise (i.e. sickle cell anemia).

Question 8

Simple Sequence Length Polymorphisms

Answer 8

Repeat sequences typically not in a coding region. Also known as variable number tandem repeats. These repeats are inherited. Micro satellite markers are 2+ nucleotides in length. Mini satellite markers are 15-100 nucleotides in length

Question 9

Y-linked inheritance

Answer 9

Only in males, passed down through the father such that 100% of male children are affected.

Question 10

Mitochondrial inheritance

Answer 10

Genetic info passed through mitochondria from the mother. There is not an even distribution of how much mitochondria will go in one cell or another during cell division, so if there is a mutation in some mitochondria, some cells may be more affected than others. If a mother is affected, all children will be affected with varying severity.

Question 11

Expression heterogeneity

Answer 11

Variability of how severe the expression of a gene is in a single family

Question 12

Codominance

Answer 12

More than one allele expressed in a phenotype (i.e. AB blood type)

Question 13

Propositus

Answer 13

Family member chosen as the starting point in genealogical research

Question 14

Autosomal Recessive Disorders

Answer 14

Mutation must be present in both copies of the gene. Typically rare unless inbreeding occurs.

1. affected child and unaffected parent
2. no difference in sex ratio
3. skips a generation

Question 15

Autosomal Dominant Disorders

Answer 15

One allele in the parent will cause phenotype in the children. If parent has two alleles, all children will have the trait.

1. One person affected in every generation
2. no difference in sex ratio

Question 16

Autosomal Polymorphisms

Answer 16

Mutations that are common in a population. Not disease conditions but present in every generation. Examples are brown v. blue eyes or pigmented v. blonde hair.

Question 17

X-linked recessive disorders

Answer 17

Mother is usually a carrier and passes X chromosome to male children. In female carriers, the Barr body is more likely to be the mutant X-chromosome

Question 18

X-linked dominant disorders

Answer 18

Only one copy of the gene needs to be affected for the offspring to be affected. Skew in sex ratio:

1. With an affected mother, 50% of all children will have the disorder
2. With an affected father, 0% of male children will have the disorder and 100% of female children will have the disorder

Question 19

Pleiotropy

Answer 19

One gene affects multiple traits

Question 20

Epistasis

Answer 20

Gene interaction where one gene hides the effects of another gene at a different locus. Usually this is for genes in the same pathway

Question 21

Locus heterogeneity

Answer 21

Opposite of pleiotropy; different genes lead to the same trait

Question 22

Complementation

Answer 22

A cross between two mutants for different loci and the resulting offspring is wild type

Question 23

Penetrance

Answer 23

% of individual organisms with a particular genotype that express an expected phenotype

Question 24

Expressivity

Answer 24

Degree to which a trait is expressed (i.e. wrinkled seeds may be more wrinkled than others). Often affected by environment

Question 25

Incomplete Dominance

Answer 25

Heterozygous individual leads to a third phenotype. Each wild type allele results in a protein product; the more product, the deeper the pigment/color.

Question 26

Haploinsufficiency

Answer 26

Heterozygous individual is not enough for proper function of the cell

Question 27

Dominant Negative

Answer 27

When 2+ polypeptides interact for protein to be functional, a mutation in one polypeptide is capable of distorting another polypeptide

Question 28

Recessive Lethal Alleles

Answer 28

Homozygous state of recessive alleles are lethal

Question 29

Sex Determination

Answer 29

1. Chromosomes
2. Genes
3. Environment

Question 30

SRY Gene

Answer 30

Sex-determining region Y (SRY) on Y chromosome determines “maleness” by encoding a transcription factor (testis determining factor). TDF upregulates genes that lead to testis development and leads to degeneration of female duct. Without the SRY gene, the body keeps the female duct and degenerates the male duct

Question 31

Androgen Insensitivity

Answer 31

Presence of testosterone leads to male characteristics. In androgen insensitivity, there is an issue with the androgen receptor so testosterone can’t bind. This leads to “default” female phenotype

Question 32

Sex-linked Characteristics

Answer 32

X-linked recessive disorders