Genetics Exam #1

What are discrete traits?

Also known as simple or either/or traits, these traits have 2 distinct phenotypes

Mendel’s Law of Segregation?

During meiosis, a pair of alleles will segregate such that a gamete will receive a random allele of the 2.

Mendel’s Law of Independent Assortment?

During meiosis, alleles assort independently into each gamete, means the inheritance of one gene does not influence the inheritance of another gene

What are the 3 rules for identifying dominant inheritance in pedigrees?

1. Equal ratio of males + females affected

2. Affected kids usually have only have 1 affected parent

   1. Matings in which 1 parent affected result in ~1/2 offspring affected

If a trait is rare, what must we assume about outsiders marrying into the family?

They are NOT carriers for the trait

e,g. if trait requires 1 dominant allele, married in people are rr
e.g. if trait requires 1 recessive allele, married in people are RR

When would a recessive trait appear to be dominant in a pedigree?

when the trait is common a certain population of people

e.g. red hair among Scottish people (40%)

Delayed Lethality

When homozygous recessive individuals survive past birth but die later on due to genetic defects

Epistasis

When the expression of 1 gene reduces the expression of another gene

Recessive Epistasis + its F2 progeny ratio

Occurs when an individual is homozygous recessive for 1 gene and it reduces the effects of the other gene

9:3:4 F2 Phenotypic Ratio

e.g. Bbee makes a yellow dog because E controls the expression of brown pigment

Dominant Epistasis + its F2 progeny ratio

Occurs when an individual has at least 1 dominant allele + it completely hides the expression of another gene

12:3:1 F2 Phenotypic Ratio

Reciprocal Dominant Epistasis

When the presence of 1 dominant allele from either gene produces the same phenotype (e.g. A_B_, A_bb, and aa_B_ produce the same dominant phenotype)

15:1 F2 Phenotypic Ratio

Locus Heterogeneity

When mutations in different genes produce the same disease/condition

What is complementation and non-complementation

complementation: when affected parents have mutations in different genes, so they produce an unaffected child

non-complementation: when affected parents have mutations in the same genes, so they produce an affected child

What are complex traits + its 2 subtypes

Traits that are controlled by multiple genes and the environment

Quantitative (measurable/gradient traits like height or eye color)
Discrete (clear and distinct traits)

Define penetrance and compare complete vs incomplete penetrance?

Penetrance: how potent a trait is among a population when individual’s have a specific phenotype

Complete Penetrance: when individual’s have the specific gene or genotype, they will always show the phenotype

Incomplete Penetrance: when individual’s have the specific gene orC genotype, they won’t always show the phenotype

Define expressivity

how strongly a genotype is expressed

e.g. some people with a specific genotype will only show a mild form while others will show an extreme form

Chemical phenocopy

when exposure to chemicals produces a phenotype similar to one caused by a disease

What gene codes for male features?

the SRY gene located on the Y chromosome

In which cell division process does non-disjunction occur?

It can occur in both meiosis and mitosis

What is the biological identity of an XXX or XYY individual?

nearly typical female and male respectively

What is the identity of an OY individual?

A dead individual because the X chromosome carries significantly more genes vital for survival than the y chromosome

What are PAR regions?

The terminal regions shared by sex chromosomes

What is the MSY region?

The region of the Y chromosome that isn’t the PAR regions. This is where many of the genes for male traits are located, including the SRY gene

Describe the function of the SRY gene on the Y chromosome?

SRY is a TF that binds to Sox9 on another chromosome, which initiates testes development

T/F XY individuals are always male?

True because the Y chromosome is the only chromosome that has the SRY gene that intimates the development of male traits

T/F XX individuals are always female?

True because neither of the X chromosomes have the SRY region to initiate the expression of male traits

T/F XY individuals can be intersex + why?

True because there could be mutations on genes downstream of the SRY gene that impair the development of male traits

Why are males considered hemizygous for X-linked genes instead of heterozygous?

Heterozygous individuals have 2 different alleles for 1 gene. Since males only have 1 X chromosome, they can only have 1 allele per X-linked gene. Thus they are considered hemizygous

T/F females are homozygous for X-linked genes?

False, they can be either homozygous or heterozygous for x linked genes because they get 1 x chromosome from each parent, which could carry a different allele

What proportion of a mother’s son’s would be affected if the mother was a carrier for an X linked recessive disorder

½ of the sons because they only need 1 recessive allele for them to develop the condition

What is Dosage Compensation

A process that equalizes the amount of X chromosome expression between males and females by randomly inactivating one of the X chromosomes iun somatic cells during embryonic development.

Through what type of measurement is linkage measured

Through RF, which reflects the probability that 2 genes will separate during crossing over + the map unit distance between 2 genes

Linkage Group

All the genes specific to 1 chromosome

T/F linkage is used to identify genes?

True because linkage can be used to identify unknown genes being inherited with known genes

Why can linkage analysis be used to identify genes responsible for diseases

If a disease is consistently inherited with a particular gene, researchers can use linkage analysis to identify disease causing genes

T/F linkage analysis can be used to track ancestry

True

What are the 3 advantages of Recombination?

1) mechanism for evolution
2) provide genetic diversity by making new allele combinations
3) ensure chromosome segregation