Chapter 5 Flashcards
Sexual Reproduction
- formation of offspring that are genetically distinct from parent
Sex is defined by:
- phenotype of the individual
Sex Determination Mechanisms
- Chromosomal Sex Determination
- Genetic Sex Determining
- Environmental Sex Determining
Chromosome theory of inheritance
- genes are located on chromosomes and chromosomes are substrate for gene segregation
_____ said male insects had a strange body in the nuclei= X body
- hunking
_____ said male grasshoppers have a heterochromosome and female grasshopper cells had one more chromosome than males
- McClung
_______ said female mealworms have 20 large chromosomes and males have 19 large and one smaller (Y)
- Stevens
____ said female butterflies have two X chromosomes and males have one X
- WIlson
All mammals chromosomes are:
- XX/XY
In simple systems what is the chromosomal sex determination
- XX for females
- XO for males
O=no chromosome
At _____ half sperm receive X and other half gets no chromosome
- meiosis
Heterogametic sex
- sex that produces two different gametes
Homogametic sex
- sex that produces identical gametes
What is a ZZ/ZW chromosome sex determination?
- male is homogametic (ZZ)
- female is heterogametic (ZW_
- female produces two diff gametes, half with Z other half with W
In haplodiploidy what is the result?
- males are haploid (1n) bc develop from unfertilized eggs
- females are diploid (2n)
- sex is determined by the number of chromosome sets
Are there any sex chromosomes in genetic sex determination?
- no, there is no obvious difference
In genetic sex determination what determines the sex of the individual?
- genes
In environmental sex determination what is it dependent on? Give example
- temperature dependent
- alligators in warm temperatures during embryonic development produces males and in cool weather will produce females
Nondisjunction
- When the X chromosome fails to separate in Anaphase 1 of meiosis
- some eggs get two copies of XX and others get more
Sex determination in Drosophilia
- Females XX, males XY, but Y does not determine maleness
- the ratio of autosomes to X determine the sex = genic balance system
- X has female producing genes, and autosomes have male producing genes
In drosophilia what is sex determined by?
- the X:A ratio (# of X chromosomes/ # of haploid sets of autosomes)
Turner Syndrome
- females don’t undergo puberty, immature secondary female characteristics
- low hairline and folds of skin on neck
- may have cognitive impairment or sterility
- XO
- also known as 45, X
Klinefelter Syndrome
- males
- small testes, breast enlargement, reduced facial/pubic hair
- one or more Y chromosome, multiple X chromosomes
- often sterile, may have mild cognitive impairment
- also known as 47, XXY
Poly-X Females
- Triplo-X syndrome (XXX)
- tall, thin, sometimes normal fertility, normal intelligence
- XXXX, XXXXX has normal female anatomy, but cognitive impairment
- severity increases in # of X chromosomes
How many X are required for each sex?
- X contains genetic info essential for both sexes
- one is required for each
Male determining gene is located on which chromosome?
- Y chromosome
What does the absence of Y indicate?
- a female
What chromosomes are the genes required for fertility on?
- the X and Y chromosomes
- females need at least 2 to be fertile
What happens with extra X chromosomes?
- it is detrimental, the more X chromosomes the more severe
What is the purpose of the SRY gene?
- this gene triggers men to develop both male phenotypes and genotypes
- if lacking this gene can have XY genotype, but will develop female phenotypes such as female reproductive systems
- ONLY found in males with XY
- no females (XX OR XY) have this gene
What hormones do the SRY gene secrete?
- anti-mullerian hormone to inhibit and block female reproductive systems from developing
- testosterone- triggers the male characteristic developments
Androgen-insensitivity syndrome
- have female sexual characters, but no uterus, ovaries or oviducts
- these women are XY
where is pseudoautosomal region 1?
- at the tip of the short arm
where is pseudoautosomal region 2?
- at the bottom of the long arm
What is the pseudoautosomal region?
- a region of homology between the mammalian X and Y chromosomes
- in between the PAR 1 and 2 there is a differential region of the X(Xlinked genes) and Y (Ylinked genes)
- on the Y gene there is also the maleness gene SRY on the short arm below PAR 1
How does androgen-insensitivity syndrome occur?
- SRY triggers teste development
- the testes secrete testosterone
- if there is no receptor for testosterone (or defective receptor), then no male characterisics
- defect ends up on X chromosome
Where are the genes for males and female secondary characteristics located?
- on the autosomes (control of expression is key)
What is dosage compensation?
- how to deal with multiple Xs
How does dosage compensation affect fruitflies, worms and placental mammals?
- fruitflies double the activity of genes on X in males
- worms (C. elegans) halves activity of genes on both Xs
- placetal mammals inactivate one X chromosome
______ observed darkly staining body in nuclei of cat cells
- Barr
- Barr body
_____ proposed that Barr body was inactivated X chromosome
- Lyon
- called Lyon hypothesis
X-inactivation
- females are heterozygous at X loci, will express one allele or the other in a given cell
What is a barr body?
- the inactivated X chromosome in females
Females are _____ for expression of X-linked genes
- mosaic
X inactive specific transcript (XIST) gene
- located on X chromosome and is required
- only the copy of XIST on inactivated X is expressed and is expressed during inactivation
What is an example of X inactivation? (hint cherokee)
- Two alleles for orange coat X+(black) X-(orange)
- Male X+Y (so black OR orange, not both)
- Female X+X+(black), X-X-(orange)
BUT when X+X- (BOTH are expressed)
-> tortoiseshell
What is a name for a mosaic cat?
- tortoiseshell
