Ch 5 Part 1: Sex determination & chromosomes (SEPT 24th)

Define sex

sex: one of two or more mating classes

-syngamy possible between different classes

define gender

gender: cultural norms sometimes associated with sex

-vary across cultures and through time

-relationship to inheritance is complicated

sexual organisms are often divided into mating types, what is it

-binary: male and female (may be mono or dimorphic)

-way more mating classes than that

what did nettie stevens observe

male beetles produce two distinct gametes differing by one chromosome

define heterogametic and homogametic

what are males known as

heterogametic: producing two kinds of gametes (X or Y)

homogametic: producing one kind of gamete (X only) 

males produce two diff gametes, known as heterogametic

What did nettie stevens suspect

she suspected that the Y chromosome inhibited expression of the x chromosome resulting in male development.

Explain the Y-chromosome mechanism

(Sex determination in mammals)

-Y chromosome includes testis-determining factor

-initiates development of testes

-without TDF, gonads become ovaries

-XX: female

-XY: male

Define Aneuploidy

(Sex determination in mammals)

what is it lethal in

where is it not unusual to occur

what do dosage effects do

aneuploidy: Condition of having more or less than two homologous chromosomes for any chromosomes

-lethal for all autosomes except for Chr. 21

-not unusual at sex chromosomes

-dosage effects early in embryogenesis result in altered development

How does aneuploidy occur

an abnormal number of chromosomes, arises due to errors in cell division during meiosis or mitosis

Define non-disjunction 

failure of chromosomes to segregate properly during anaphase I or II

Draw nondisjunction in meiosis I and meiosis II

Define Primary non-disjunction

non-disjunction for an individual with a normal set of chromosomes (diploid)

Describe XO female, Turner syndrome

symptoms

how many die and when

how many in live births

-have 45 chromosomes
-Shorter than average, webbed neck, undeveloped breasts, immature sex organs, sterile
-reduced ability to interpret spatial relationships
-99% die before birth
-1 in 10,000 live births

Describe XXY male, Klinefelter Syndrome

symptoms

how many in live births

-have 47 chromosomes
-taller than average, breast development (gynecomastia), broad hips, small testes (hypogonadism), mostly infertile
-subnormal intelligence (rarely)
-often difficulty with verbal learning
-1 in 1,000 live births

Describe XYY male, Jacobs syndrome

symptoms

how many die and when

how many in live births

what did studies suggest about these XYY males

-have 47 chromosomes
-often unidentified due to very few phenotypic changes
-slightly taller on average than XY males
-Increased incidence of learning disorders
-Some evidence of delayed speech, decreased language skills
-~1 in 1,000 births

Some studies have suggested XYY males: are more likely to commit violent crimes

-focus on incarcerated XYY males
-most lack experimental controls
-confounded by higher likelihood of poverty

Describe XXX female, triple X syndrome

symptoms

how many die and when

how many in live births

-have 47 chromosomes
-often unidentified due to very limited phenotypic change
-slightly taller on average than XX females
-decreased fertility (slightly)
-delayed motor-skills and learning disorders (rarely)
-1 in 1,000 births