Genetics Exam 4 Review Part 1 (Lessons 18-20A)

acrocentric

The Y chromosome is an _________ chromosome (NOT Y-shaped).

nonrecombining

95% of the Y gene = ___________ region of the Y (NRY) or male-specific region of the Y (MSY)

SRY gene

on the Y chromosome; determines the male sex and encodes a protein called the testis-determining factor (TDF)

female

What sex would an XY individual be considered if they were missing a functional SRY gene?

male

What sex would an XX individual be considered if they had an SRY gene?

Turner syndrome

absence of Y chromosome (XO) results in female phenotype

female

homogametic — XX; produce two of the same gametes in terms of sex chromosomes

male

heterogametic — XY; produce two different gametes in terms of sex chromosomes

equal

Inheritance of human sex results in _______ numbers of male and female offspring.

female (XX); male (XY)

If a locus controlling a trait is located on the X chromosome, the frequency at which the trait is observed will be different in males and females:

• In _________, a gene on the X will have two copies

• In _________, a gene on the X will have one copy

half; half

For an X-linked trait, the F2 generation will produce females that all show the dominant trait, while the ______ of the males will show the dominant phenotype and ______ of the males will show the recessive phenotype.

Barr bodies

inactivated X-chromosome areas (genes) on one of the X chromosomes visible in the nucleus of the cells in female mammals

Lyon hypothesis

X inactivation is random; happens early in development; in heterozygous females, 50% of cells express one allele and 50% of cells express the other allele; once an X is inactivated, it remains inactivated in all somatic cells that descend from the cell

lyonization

X inactivation yielding a Barr body

Xist gene (X-inactivation-specific-transcription)

the gene that controls lyonization

RNA; chromatin

On the X chromosome destined to become inactivated, the Xist gene produces an _____ molecule that coats the X chromosome and inactivates the genes on it by altering the __________ structure.

repressed

On the active X chromosome, the Xist gene is _________.

75%

About ______ pf X-linked human genes are inactivated.

pedigree

a pictorial representation of a family history, essentially a family tree that outlines the inheritance of one or more characteristics; can go back several generations; often follow detailed medical records

autosomal recessive traits

AA, Aa: normal

aa: abnormal

autosomal dominant traits

AA, Aa: abnormal

aa: normal

X-linked recessive traits

X+X+, X+Xa, X+Y: normal

XaXa, XaY: abnormal

X-linked dominant traits

XAXA, XAXa, XAY: abnormal

XaXa, XaY: normal

Y-linked traits

XY+: normal

XYa: abnormal

equally; skip

Autosomal recessive traits usually appear ________ in males and females and tend to _______ generations.

consanguinity

mating between closely related people

related

Autosomal recessive traits are more likely to appear among progeny of _________ parents.

equally; affected

Autosomal dominant traits appear ________ in males and females, and affected persons have at least one _________ parent.

false

True or false?

Unaffected persons can transmit an autosomal dominant trait.

sons; daughter

For X-linked recessive traits, an affected male does not pass the trait to his _______, but can pass the allele to a _________, who is unaffected and passes it to sons who are affected.

males

X-linked recessive traits appear more frequently in _______.

true

True or false?

An X-linked recessive trait does not pass from father to son.

X-linked dominant trait

does not skip generations; affected males pass the trait on to all their daughters and none of their sons; affected females (if heterozygous) pass the trait on to about half of their sons and about half of their daughter

Y-linked trait

only males are affected; trait passed from father to all sons; an affected father will produce affected sons; no skipping of generations

independent assortment

2 genes on different chromosomes assort independently, and we get four gametes in equal proportion

linked genes

genes located close together on the same chromosome; travel together in meiosis and go into the same gametes as long as crossing over does not occur; do not assort independently

linked

Completely ________ genes on the same chromosome (no crossing over) travel together during meiosis.

recombination

crossing-over between two genes occurs in meiosis I and results in recombinant genes

randomly

Normally, the crossing over between homologous chromosomes happens _________ at different locations across the whole chromosome.

recombinant frequency

the percentage of recombinant progeny produced in a cross; (number of recombinant progeny/total number of progeny) x 100

proportional

The amount of crossing over between any two loci on a chromosome is __________ to the distance between them.

false

True or false?

A recombinant frequency can be greater than 50%.

closer; farther

The ________ two loci are on a chromosome, the lower the probability of crossing over. The _________ two loci are, the higher the probability of crossing over.

recombinant frequency

Linkage phase doesn’t affect _____________, but affects the progeny number of each phenotype.

coupling (cis)

the recessive alleles of both genes are on one chromosome and the dominant alleles are on the other homologous chromosome

repulsion (trans)

a recessive allele of a gene and a dominant allele of another gene are on one chromosome and the corresponding dominant and recessive alleles are on the other homologous chromosome